Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Language：Japanese   Publishing type：Research paper (scientific journal)  

A countermeasure method is proposed for fatigue cracks that initiate from the weld root of U-rib to deck welded joints of orthotropic steel decks, which does not require traffic restrictions and does not increase the dead load. On the other hand, fatigue durability of general parts except for cross rib sections and ranges of peening treatment are still unclear. This paper attempts to solve those problems and verifies the durability of the fatigue countermeasure method. First, fatigue test methods that can reproduce fatigue cracks in the general parts of U-rib to deck welded joints of existing orthotropic steel decks was investigated. Next, based on the investigation results of fatigue test methods, the fatigue durability of general parts of the countermeasure was clarified by wheel running test, and the data necessary for determining the peening treatment areas were obtained. Finally, a proposal for improved countermeasures is presented.

DOI： 10.2208/jscejj.24-00187

Language：English   Publishing type：Research paper (scientific journal)  

This study developed a tap bolt joint method with tap holes in both plates as a preventive maintenance method against weld root failure in fillet-welded cover plates. The method aims to reduce the relative displacement between two plates, which is the cause of weld root crack. To evaluate the fatigue strength of the joint and the relative displacement of the plates, fatigue tests and finite element analysis were conducted to examine the fundamental characteristics of tap bolt joints. The results showed that the fatigue strength of the tap bolt joint was distributed around the JSSC-E class under cyclic tensile axial loads and the JSSC-A class under cyclic compressive axial loads and was significantly higher than the JSSC-S class under cyclic shear loads. Furthermore, tap bolt joints were installed in fillet-welded sole plates in plate girders, and their effectiveness was examined through fatigue tests and finite element analysis. The results showed that the tap bolt joint method can extend the fatigue life of the weld root of a sole plate.

DOI： 10.1007/s40194-025-01986-8

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, the reinforcement with patch plates from the top of the deck plate against bead-through fatigue cracks at the intersection of transverse ribs was considered by FEM analysis. The analysis was performed for different bolt arrangements and thicknesses of the patch plate, and the stress reduction at the root were examined. The analysis results showed that adding bolts to the inside of the U-ribs reduces the stress at the root, and the greater stress reduction can be achieved when the thickness of the patch plate was increased. The effect of reinforcement was also evaluated by fatigue life, and it was found that the fatigue life was significantly improved by increasing the thickness of the patch plate.

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, to examine the possibility of detecting root cracks using acoustic emission (AE), fundamental characteristics of AE waveform were measured through fatigue test on load-carrying cruciform fillet welded joints. The transient waveform emitted from the root crack was observed in the initial stage of crack propagation. As the crack grows significantly, the amplitude of the AE decreases. While the number of AE hits originating from a root crack increases as the crack propagates in the initial stage of crack propagation, it decreases as the crack grows larger. In addition, dynamic finite element analysis was conducted to simulate the AE waveform.

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, fatigue tests and finite element analyses were conducted on T-joints using various new welding materials, in order to investigate the effect of enhancing fatigue strength through the application of unconventional welding materials, which are not commonly used in steel bridges. The results revealed that using low transformation temperature welding materials reduced the tensile residual stress around the weld, leading to the improvement of fatigue strength. Additionally, it was found that applying additional welding method with a newly developed material for Ar-shielded MIG welding decreased stress concentration at the weld toe, resulting the improvement of fatigue strength.

Language：English   Publishing type：Research paper (scientific journal)  

To systematically maintain a large number of overhead transmission towers, it is important to understand the mechanism of fatigue failure and its evaluation methods. In this study, we evaluate the fatigue damage ratios for a case involving fatigue cracks in the slotted tubular joints of a testing tower to discuss the application range of the evaluation method and factors affecting the fatigue damage ratio. The fatigue damage ratios are calculated using wind data observed near the tower, a response estimation method for vortex-induced vibration (VIV), and previous fatigue strength data for slotted tubular joints. The results show that the fatigue damage ratios of horizontal and web members on the north side of the tower, directly exposed to strong winds, exhibited good agreement with the actual failure state. However, the accuracy of the results for members in the cross-arm sections was diminished, primarily due to the stress range induced by VIV nearing the cut-off limit. Additionally, the wind acting on these members were disturbed by the other members located upwind of them. Furthermore, the slenderness ratio of a member with a high fatigue damage ratio was limited to a specific range.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue life in orthotropic steel bridge deck using a newly developed steel plate, which specially improved crack propagation rate da/dN in the low ΔK range, was examined by the structural model fatigue tests. A fatigue crack initiated at the weld root of the trough rib and deck plate was simulated. The stiffness changes during cyclic loading and the fracture surfaces suggested the fatigue life improvement in the specimen whose deck plate was replaced to the newly developed steel plate. The mechanism in which the fatigue crack resistance improvement of the deck plate reflected on the fatigue life of the structural model specimens was discussed from viewpoint of ΔK change along the fatigue crack path.

DOI： 10.11273/jssc.31.123_13

Language：Japanese   Publishing type：Research paper (scientific journal)  

To investigate the reduction of stress in drilled crack-arrest holes by applying patch plates with high-strength bolts under combined axial and shear loading, static loading tests with a plate girder and parametric finite element analyses were conducted. The stress concentration factor for drilled holes was found to be influenced by the combined action of stresses, and the effectiveness of the patch plate diminished as the ratio of the shear stress increased. This study proposed a method to accurately estimate the effect of combined stress actions on reducing stress concentration in drilled holes with patch plates.

DOI： 10.11273/jssc.31.123_57

Language：English   Publishing type：Research paper (scientific journal)  

High-frequency mechanical impact (HFMI) is a user-friendly and efficient mechanical post-weld treatment method, and the achieved fatigue life improvement is statistically proved and is attributed to HFMI-induced compressive residual stresses amongst other effects. Several studies have shown in the past that the process parameters (treatment time and working speed) have an influence on the stress state introduced by the HFMI treatment. Thus far, however, only device-specific quantitative recommendation for the HFMI treatment exists based on the instructions of each HFMI device manufacturer. It is not clear if a certain treatment time for a given intensity leads to optimum results regarding the enhanced fatigue life and the treatment parameters of the several HFMI devices cannot be directly compared with each other. For these reasons, a universal and simple definition of the HFMI treatment’s intensity based on the kinetic energy of the HFMI pin was used to quantitatively correlate the HFMI-induced compressive residual stress with the HFMI-process parameters for two different HFMI devices: pneumatical impact treatment (PIT) and high-frequency impact treatment (HiFIT). To this purpose, data from former studies of HFMI-treated base material and welded specimens are revaluated. It is shown, that the compressive residual stresses show only slight changes after reaching a threshold value of the applied kinetic energy (= 50 to 100 J/mm). This energy-based approach for the quantification of the treatment intensity was also used for a case study with PIT- and HiFIT-treated transverse stiffeners with different treatment intensities (2 J/mm and 7 J/mm). A high influence of the treatment intensity on the residual stress state was determined.

DOI： 10.1007/s40194-024-01812-7

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue cracks have been observed in the welded joints of end diaphragms at steel railway trough-girder bridges due to unexpected vertical movement at their supports, which was not anticipated during the design phase. Because this movement is complex and varies for each bridge depending on the damage around the support, effective retrofitting methods against these cracks have not yet been established. In this study, the influence of the vertical movement at the bridge supports on crack propagation at the end diaphragm was investigated through numerical simulation. The results indicated that the relative displacement at the bedplate affected the location of crack initiation and the direction of crack propagation, and that the stress intensity factor tended to gradually decrease after the crack reached a certain length. Furthermore, the repair effect of a hole drilled in the crack tip was numerically investigated. The results showed that the local stress around the hole edge decreases as the length of the repaired crack increases.

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

A survey of works in progress on the fatigue strength of welded joints in Japan was conducted on the basis of replies to a questionnaire distributed to the researchers majoring in fatigue of welded joints as well as the members of Commission XIII of the Japanese Institute of Welding and Fatigue Strength Committee of the Japan Welding Society. Three on fatigue behavior, two on fatigue crack propagation and three on fatigue strength improvement and repair are included in this report.

Language：English   Publishing type：Research paper (international conference proceedings)  

This study developed a tap bolt joint method with tap holes in both plates as a preventive maintenance method against weld root failure in fillet-welded cover plates. The method aims to reduce the relative displacement between two plates, which is the cause of weld root crack. To evaluate the fatigue strength of the joint and the relative displacement of the plates, fatigue tests and finite element analysis were conducted to examine the fundamental characteristics of tap bolt joints. The results showed that the fatigue strength of the tap bolt joint was distributed around the JSSC-E and F strength classes under cyclic tensile axial loads, the JSSC-A class under cyclic compressive axial loads, and was significantly higher than the JSSC-S class under cyclic shear loads. Furthermore, tap bolt joints were installed in fillet-welded sole plates in plate girders, and their effectiveness was examined through fatigue tests and finite element analysis. The results showed that the tap bolt method can extend the fatigue life of the weld root of a sole plate.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Many cases of fatigue cracks at welded joints of sole plates in steel bridges have been reported. And the causes of the cracks generation and countermeasures have been studied. However, the study has so far mainly focused on corrective maintenance, and practical preventive maintenance measures have not been established. In this study, focusing on the toe crack and root crack that generates at welded joint of sole plate, preventive maintenance measures by peening treatment and tap bolts were studied by FEA and fatigue tests. As a result, it was clarified that the peening treatment could improve the fatigue strength of the weld toe of sole plate under the conditions of compressive stress acting on the weld, and the method using tap bolts could extended the fatigue life of the weld root of sole plate.

DOI： 10.2208/jscejj.23-00234

Language：Japanese   Publishing type：Research paper (scientific journal)  

Many fatigue tests have been conducted to reproduce a root crack in deck-to-U rib welded joints and to investigate its fatigue durability. Nevertheless, no unified fatigue strength evaluation method for the root crack has been established. In this study, total of 154 fatigue test results were reproduced in the analysis to obtain artificial notch stress at weld root, and the test results were rearranged by the notch stress. Two million cycles fatigue strength and its standard deviation based on the notch stress are discussed in this paper. Two million cycles fatigue strength tends to be higher when the mean stress in cyclic loading is in compression. By correcting the test results with the stress ratio, all test results located around a unified fatigue strength curve.

DOI： 10.11273/jssc.31.121_72

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, as a preventive maintenance method against root cracks at welded joints of cover plates, the tap bolt joint method with tap holes in both plates was proposed based on the concept of reducing the relative displacement between plates which is the cause of root crack initiation. As a fundamental study on the tap bolt joint, the fatigue strength of the joint and relative displacement of plates were evaluated by fatigue tests and FEA. It was revealed that the fatigue strengths were distributed around JSSC-E to F classes under cyclic tensile axial loads, JSSC-A class under cyclic compressive axial loads and much higher than JSSC-S class under cyclic shear loads.

DOI： 10.11273/jssc.31.121_115

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue cracks were initiated at slotted tubular joints in a testing overhead transmission tower. It was estimated that the cracks were caused by vortex induced vibration (VIV). In this study, the fatigue evaluation for steel tubular members in the tower was conducted with observed wind data and a response estimation method for VIV. The fatigue damage ratios of horizontal members and web members on the north side of the tower were good agreement with the actual failure state. However, those of members in the cross arm section were low accuracy because stress ranges were similar to the cut-off limit and wind was disturbed by upwind members Moreover, it was clarified that slenderness ratio of a member with a high fatigue damage ratio was limited to a certain range.

DOI： 10.11532/structcivil.70A.521

Language：Japanese   Publishing type：Research paper (scientific journal)  

In orthotropic steel deck, many fatigue crack has been found at the weld joint between deck plate and vertical stiffeners. As a counter measure for the fatigue, semi-circular notch has been adopted to reduce the stress concentration around boxing weld. However, more effective notch geometry should be considered from viewpoint of ease of construction and fatigue improvement. In this study, reduction of stress and stress intensity factor were investigated for newly developed slit-like notch and sigma-shaped notch. In addition, fatigue tests were performed for the weld joints between deck plate and vertical stiffener with sigma-shaped notch. The crack initiation life and crack propagation can be extended by constructing sigma-shaped notch at the top of vertical stiffener.

DOI： 10.11532/structcivil.70A.458

Language：English   Publishing type：Research paper (scientific journal)  

Numerous studies have been conducted regarding the fatigue strength of longitudinal welded gusset joints. Most studies employed relatively small specimens. Thus, this study aims to evaluate the variation of fatigue life of longitudinal welded gusset joints by using the probabilistic fracture mechanics approach, particularly for larger specimens. Although some studies claimed that lower fatigue strength is found in the thicker main plate specimens, however only a limited number of fatigue test was conducted. A probabilistic approach was employed to conquer the shortfall. In this study, fatigue crack propagation analysis was performed on the main plate thicknesses of 12, 40, and 60 mm to evaluate the effect of main plate thickness on the fatigue life of the joints. Then, a probabilistic approach is given to investigate the variation of fatigue life of the joint. In addition, fatigue tests were carried out to investigate the crack propagation behavior on larger specimens. A significant decrease in fatigue life was observed by the increase of the main plate thickness from 12 to 40 mm, however, no further decrease thereafter. The fatigue strength of longitudinal welded gusset joints with the main plate thickness of 12 mm was appertained to category F in the JSSC design curve. Meanwhile, the fatigue strength of longitudinal welded gusset joints with the main plate thickness of 40 and 60 mm falls into category G in JSSC. This condition was also confirmed by the fatigue test results, where both specimens were classified as category G in JSSC.

DOI： 10.1007/s13296-024-00812-z

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

The structural hot-spot stress approach is an effective method for assessing welding details when nominal stress is hard to determine due to geometric or loading complexities. Hot spots can be classified into two types: type “a,” which refers to a weld toe located on a plate surface, and type “b,” denoting one located on a plate edge. Previous studies on type “b” hot spots have mainly focused on in-plane gusset welded joints, and the applicability of type “b” hot-spot S-N curves proposed for in-plane gusset joints in IIW to the other details is not well understood. In this study, fatigue tests were conducted with a load-carrying attachment welded on a plate surface, where a crack occurred from a weld toe on the plate edge. The tests were also numerically simulated using finite element analysis. Upon evaluating the test results through the nominal stress, structural hot-spot stress (4, 8, and 12 mm method), and notch stress approaches, it was found that all the data lie above FAT71 for nominal stress, FAT100 for hot-spot stress, and FAT225 for effective notch stress.

DOI： 10.1007/s40194-024-01724-6

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, the repair method of riveted joints by re-driving new rivets with an Induction Heating (IH) technique was considered. First, fatigue tests for riveted joints using IH technique were performed. As a result, the specimens have similar fatigue strength to those fabricated in the traditional way. In addition, finite element analysis to simulate the replacement of the rivets under static load, assuming a repair work under dead load, was performed. The analysis results clarified the load-displacement relationship and load re-distribution mechanism of the joint when replacing rivets under static load.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Some steel piers collapsed in past earthquake due to low-cycle fatigue from corner weld joints with unwelded part. In this study, low-cycle fatigue tests were performed on corner weld joints with un welded parts ot understand the failure pattern. when the penetration of the outer weld was less than half the thickness of the base metal, the brittle fracture was observed, in which the inner filler weld fractured first and then the outer partial penetration weld fractured. In addition, the crack initiation point and the crack propagation path can be estimated from the effective notch strain range and the equivalent plastic strain distribution obtained from the finite element analysis.

Language：English   Publishing type：Research paper (international conference proceedings)  

Root cracks in U-rib to deck welded joints of orthotropic steel decks (OSDs) have been reported, which are two types of fatigue cracks initiating at the weld root that propagate into either the deck plate or the weld bead. For early detection of these internal cracks which may cause road surface damage, screening methods for priority inspection area in areal extent OSDs is needed. Therefore, the authors proposed a method of fatigue damage evaluation by estimating stresses to evaluate root crack initiation and propagation behavior from measurable stresses near the joints, aiming to establish a screening method. This paper examines application of the developed evaluation method for these root cracks in the actual OSDs. Field measurements were conducted in two sections with different trends of crack initiation, and a procedure was proposed to obtain the cumulative fatigue damage ratio from the measurement results and regularly obtained data. In addition, the validity of the developed evaluation method for the crack initiation and propagation direction was verified by comparing with the actual crack situation, and a screening method to select out the priority inspection area was proposed.

Language：English   Publishing type：Research paper (international conference proceedings)  

Steel-concrete composite slab has rational structure consisting of bottom steel plate stiffened with ribs and concrete casted on them. In addition, the composite slab also has advantage in maintenance since there is no concern about concrete spalling. In recent years, replacement of aging slabs has been increasing, and the use of precast composite slabs is being promoted to shorten the construction period on site. When precasting concrete for composite slabs, rational joints thatachieve both strength and workability are required. Conventional bolted joints in bottom steel plate requires scaffolding to access the underside of the slab when fastening bolts and painting after fastening. Construction of scaffolding extends the whole construction period. In this study, two types of the joints that can be constructed from the top of the slab are proposed. Mechanical performance of the joints was investigated through the four-point bending tests. In addition,
evaluation method of yield resistance for each joint was discussed.

Language：English   Publishing type：Research paper (international conference proceedings)  

There have been many reports on fatigue cracks at fillet welded joints of sole plates of steel bridges. When preventive maintenance management of these cracks is conducted, the screening process to determine crack-prone fillet welded joints of sole plates and prioritize to apply the countermeasures to prevent the crack is necessary. In this study, in order to propose a screening method, a method for evaluating the local stress near the fillet welded joint of sole plate based on simple calculations was investigated by finite element analysis (FEA). The results revealed that the local stress at the front fillet welded joint of sole plate is well correlated with the local cross-sectional area of the lower flange and web. Moreover, it was revealed that the horizontal reaction force additionally caused by the movability loss of bearing can affect the local stress at the fillet welded joint of sole plate. Based on these results, a simple equation for evaluating the local stress at the fillet welded joint of sole plate using the local cross-sectional area and horizontal reaction force was proposed.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

There are three main connection types, such as welding, bolting, and riveting. Among them, riveted joints are hardly used in current bridge assembly. On the other hand, a large number of old bridges with riveted joints still exist and its proper maintenance are required. In this study, the repair method of riveted joints by re-driving new rivets with an Induction Heating (IH) technique was considered. First, fatigue tests for riveted joints using IH technique were performed. As a result, it has similar fatigue strength to those fabricated in the traditional way. In addition, finite element analysis to simulate the replacement of the rivets under statically applying load (dead load) was performed. The analysis clarified the load-displacement relationship and load re-distribution mechanism of the joint when replacing rivets under static load.

Language：English   Publishing type：Research paper (international conference proceedings)  

Anti-fatigue damage steel, in which the hard and soft phases in the microstructure of the steel are appropriately arranged by controlling the composition and manufacturing process to reduce the crack propagation rate, was developed in past studies. In this study, a steel newly developed with the concept of the existing anti-fatigue damage steel was applied to the main plate of out-of-plane gusset welded joints, and its crack propagation characteristics were clarified by plate bending fatigue tests. The results of the fatigue tests and the discussion using finite element analysis showed that the crack propagation rate of the out-of-plane gusset welded joints using the developed steel tended to be smaller than that using a structural steel conventionally used in steel bridges.

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

When large cyclic deformations due to excessive external forces, such as those caused by an earthquake, are induced in steel bridge members, Low-cycle fatigue cracks sometimes occur in welded joints due to high strain concentration around the weld. Such cracks can lead to brittle fracture of the member. The low-cycle fatigue strength of steel members, particularly that of welded joints, should be evaluated as efficiently as possible to prevent low-cycle fatigue failure during earthquakes. In this study, as a first step to establish a simple and versatile low-cycle fatigue verification method, finite element analyses were conducted on cruciform joints of various dimensions to investigate a method to determine the local strain amplitude at the weld toe from the nominal strain amplitude by elastic analysis, and an estimation formula was developed.

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

High-Frequency Mechanical Impact (HFMI) treatment is a technique to improve the fatigue strength of welded joints by inducing compressive residual stress. In this study, fatigue tests under variable amplitude loading were conducted on HFMI-treated welded joints to clarify its fatigue strength improvement effect. As a fundamental investigation, multi-stage amplitude block loading, which is a relatively simple waveform among variable amplitude loading, was employed. In addition, the residual stress state due to the HFMI treatment was reproduced by finite element analysis, and the change in the residual stress state around the treated area was confirmed by applying several loading patterns.

Language：English   Publishing type：Research paper (international conference proceedings)  

Around the bridge bearing in steel plate girder bridge, various fatigue cracks have been found at the front fillet welded joint between lower flange and sole plate, such as toe cracks on lower flange or sole plate and root cracks. Therefore, various countermeasures are required for each of these cracks. The purpose of this study is to propose simple fatigue strength improvement methods for weld joints of sole plate. In order to verify the effect of the methods on fatigue strength, fatigue tests were conducted on a girder specimen simulating loss of movability in bearing support. As a result, it was clarified that the peening treatment had a significant improvement on the fatigue strength of the toe cracks, and the tap bolting and resin injection had a large effect on the fatigue strength of the root cracks.

Language：English   Publishing type：Research paper (international conference proceedings)  

In this study, as a simple repair method for fatigue cracks, injecting a corrosion accelerator to retard crack growth was investigated. When the inner surface of a fatigue crack is corroded, corrosion products arrest crack closure. Due to this wedge effect, the crack opening displacement and crack growth rate are reduced. In this study, Nitric acid (HNO3), which has highly corrosive property and low viscosity, was adopted as the corrosion accelerator. Fatigue tests were carried out on compact tension (CT) specimens with various load range, minimum to maximum load ratio, and initial crack length at injection. The corrosion accelerator is injected to the initial crack by the dropper. After the injection, the corrosion reaction inside the crack completed approximately after 24 hours. By producing corrosion products, the strain at crack tip and crack growth rate were significantly reduced. From the test results, the crack growth retardation effect was affected by the crack length at injection and load condition.

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

The structural hot-spot stress approach is an effective method for assessing welding details when nominal stress is hard to determine due to geometric or loading complexities. Hot spots can be classified into two types: Type “a”, which refers to a weld toe located on a plate surface, and Type “b”, denoting one located on a plate edge. Previous studies on Type “b” hot-spots have mainly focused on in-plane gusset welded joints, and the applicability of Type “b” hot-spot S-N curves proposed for in-plane gusset joints in IIW to the other details is not well understood. In this study, fatigue tests were conducted with a load-carrying attachment welded on a plate surface, where a crack occurred from a weld toe on the plate edge. The tests were also numerically simulated using finite element analysis. Upon evaluating the test results through the nominal stress, structural hot-spot stress (4, 8, and 12 mm method) and notch stress approaches, it was found that all the data lie above FAT71 for nominal stress, FAT100 for hot-spot stress, and FAT225 for notch stress.

Language：English   Publishing type：Research paper (scientific journal)  

Root cracks initiating from U-rib to deck welded joints of orthotropic steel deck bridges have become a problem for maintenance. Some fatigue strength evaluation methods for root cracks based on local stress criteria have been proposed, such as the effective notch stress method, but these methods cannot evaluate fatigue strength directly from the measurable response values of the structure. In this study, the evaluation method of crack initiation by measurable stresses was investigated by fatigue tests and FE analysis for both deck and bead propagation-type cracks, which are root cracks in U-rib to deck welded joints of orthotropic steel decks. As a result of the study, the relationship between the stress of weld root and the fatigue life was obtained by using the fillet shaped notch stress as the evaluation stress, and the S-N curve for the evaluation stress was proposed. And a method to estimate the evaluation stress of the root from the measurable stresses at four points was proposed. It was confirmed that the error of the proposed estimation method was generally within 10%. As a validation of the estimation method, it was confirmed that the fatigue test results could be properly evaluated.

DOI： 10.1007/s40194-023-01568-6

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Fatigue cracks have been observed from welded joints of end diaphragms at steel railway trough-girder bridges due to vertical movement behavior at their supports that is not expected during the design phase. Since this movement behavior is complicated and varies on each bridge depending on the damage around the support, effective retrofitting methods against the crack have not been established yet. In this study, the influence of the vertical movement tendency at the bridge supports on the crack initiation location and crack propagation behavior at the end diaphragm was investigated through numerical simulation. The result indicated that the relative displacement at the bedplate affected the crack initiation location and crack propagation path, and that the stress intensity factor tended to gradually decrease after propagating a certain length.

DOI： 10.11532/structcivil.69A.558

Language：Japanese   Publishing type：Research paper (scientific journal)  

There are many historical steel bridges with riveted joints, but damaged riveted joints is often repaired by replacing rivet with high-strength bolt. The reason is that the number of rivet casting engineers has decreased and application technique has not been passed on. The method of replacing damaged rivets with new rivets is effective in terms of workability and structural mechanics, and the rivet casting unit using high-frequency induction heating that can be used on site has been developed. In particular, the technical information necessary for riveting, which has not been recorded in conventional construction methods, was extracted through experiments, and the developed rivet casting technique was evaluated and verified.

DOI： 10.11532/structcivil.69A.537

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, a screening method for the fatigue cracks around the sole plate welds in preventive maintenance was studied based on measurements of the actual bridge and finite element analysis. First, the results of the actual bridge measurements show that the compressive stress at the lower surface of the lower flange increases as closer to the sole plate welds. Next, by parametric study with plate thickness, it was shown that the hot-spot stress range at the front fillet weld toe between the lower flange and sole plate can be estimated by the local cross-sectional area and the horizontal reaction force. Based on the results, a formula for the hot-spot stress range at the front fillet weld toe between the lower flange and sole plate was proposed to screen locations at high risk against fatigue.

DOI： 10.11532/structcivil.69A.568

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Because low-cycle fatigue is one of the failure modes in steel structures during earthquakes, crack growth prediction in the low-cycle fatigue region has become an important factor in the evaluation of the seismic performance of steel structures. This study conducted fatigue crack growth tests with several kinds of structural steels to clarify their crack growth behaviour in the low-cycle fatigue region. These tests employed an elastic compliance technique usually used in the high-cycle fatigue region to determine crack size. Before applying the elastic compliance method to a low-cycle fatigue crack growth test, a correlation between specimen load-line crack-opening elastic compliance and crack size was analytically derived. The test results indicated that crack sizes obtained by the elastic compliance method agree relatively well with those actually measured from images. Moreover, it was revealed that the crack growth rate can be correlated with the cyclic J-integral range calculated by finite element analysis, and that the relationships between the crack growth rate and the cyclic J-integral range are similar regardless of the steel type.

DOI： 10.1007/s13296-022-00677-0

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper proposes a countermeasure for fatigue cracks that propagate from the weld root of U-rib to deck welded joints to the deck plate or weld bead of orthotropic steel deck. Specifically, the lower flange of the U-rib is removed and the U-rib and deck plate welds are welded from the inside of the U-rib as a countermeasure method. First, to confirm the feasibility of this countermeasure with structural changes, the load-bearing capacity, workability of welding, and effects on asphalt pavement were verified. Next, changes in the local stress properties of the focused welds and other areas due to the countermeasures were confirmed by finite element analysis. Finally, the fatigue durability of the countermeasure was determined by fatigue tests.

DOI： 10.2208/jscejj.22-00231

Language：Japanese   Publishing type：Research paper (scientific journal)  

The adding splice plate with high strength bolts are often used in combination with the drilled crack-arrest hole as a permanent countermeasure against fatigue cracks. On the other hand, the fatigue design method for such splice plate has not been established, and the fatigue durability of the crack-arrest hole after adding splices has not been clarified.
In this study, we conducted several fatigue tests focusing on the geometric parameters of the splice plate to investigate the fatigue fracture mode and fatigue life of the crack-arrest hole after adding splices. Two types of cracks were observed in the fatigue tests. One was a crack re-occurring from the crack-arrest hole and the other was a fretting fatigue crack at the contact surface between the main plate and splices. It was found that by obtaining the local stress at the crack-arrest hole after adding splices, the fatigue life can be estimated using the fatigue design curve proposed for the hole without splices. The fretting fatigue life of splices against the crack was as same as the fatigue life of the high strength bolted frictional joints. From these results, the method of rationally designing the splice plates was proposed by evaluating the durability for the two fatigue fracture modes.

DOI： 10.2208/jscejseee.78.3_417

Language：Japanese   Publishing type：Research paper (scientific journal)  

Many fatigue cracks occur in the welded joint between deck plate and U-rib. So far, fatigue tests on small-scaled welded joints simulating deck-to-U-rib joint have been conducted. However, the relationship between the stress caused in the actual orthotropic steel deck system and small-scaled specimen have not been cleared. In this study, stress at the root of a small-scaled welded joint specimen and a full-scale steel deck system was investigated. In addition, estimation method for fatigue life of deck-to-U-rib welded joint in a full-scale steel deck system from small-scaled specimen was proposed.

Language：English  

Over the last decade, fatigue cracks have been observed at welded joints between U-ribs and deck plates in many orthotropic steel deck bridges in Japan. This paper focuses on fatigue cracks that initiate from a weld root of rib-to-deck welded joints and propagate to a deck plate. This study examines the effect of a countermeasure that uses overlaying Ultra-High Performance Fiber Reinforced cement-based Composites (UHPFRCs) on steel decks with cracks from U-rib welds, and confirms the fatigue durability of this method. Specifically, the retardation of crack propagation and the fatigue durability of the UHPFRC itself as well as the interface between the UHPFRC and the deck plate were confirmed by a wheel running test and finite element analysis. Based on the results, it was clarified that this countermeasure has a positive effect on retarding further crack propagation compared with the method of overlaying steel fiber reinforced concrete, which is generally adopted. In addition, it was revealed that the studied countermeasure has sufficient fatigue durability.

DOI： 10.1007/s13296-022-00660-9

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper examines application of a fatigue evaluation method for the cracks in the weld joints between a U-rib and a deck plate in orthotropic steel bridge decks. Field measurements were conducted in two sections with different crack initiation trends, and a method was proposed to obtain the cumulative fatigue damage ratio from the measurement results and routinely obtained data such as temperature and traffic volume. In addition, the validity of the evaluation of crack initiation and propagation direction by the developed evaluation method is verified by comparing with the actual crack situation, and a method to screen out the priority inspection and investigation area is proposed.

DOI： 10.2208/jscejseee.78.2_287

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

In this study, the effect of the stress state of a welded joint during application of high-frequency mechanical impact (HFMI) treatment on the resulting fatigue strength was investigated through fatigue tests and finite element analysis. A high-frequency impact treatment tool was used as the HFMI device. Longitudinal attachment welded joints were treated under a state in which a static load was applied and subsequently tested under a constant stress amplitude with stress ratios of 0 or 0.5. In addition, residual stress measurements and finite element analysis simulating welding and treatment processes were performed. The results indicate that the HFMI treatment is beneficial even when applied under a static tensile load, as the resulting compressive residual stresses are similar regardless of the stress state in the joint during treatment, meaning that the HFMI is applicable to existing structures.

DOI： 10.1201/9781003322641-262

Language：English   Publishing type：Research paper (international conference proceedings)  

This paper examines a fatigue evaluation method for the cracks in the weld joints between a U-rib and a deck plate in orthotropic steel bridge decks. The crack initiates from the weld root and propagates into the deck plate or the weld bead. Fatigue tests and FE analyses were conducted in order to examine the local stresses available for fatigue assessment, and to propose a method to estimate them from some reference stresses around the weld joint. In addition, based on fatigue crack propagation analyses, a method to predict the crack propagation path was proposed.

DOI： 10.1201/9781003322641-263

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

There are usually two methods to evaluate the low cycle fatigue strength of a welded joint, namely the local approach and the nominal approach. Previous research has revealed the applicability of the local approach for low cycle fatigue assessment of welded joints, where fatigue cracks were initiated from a weld toe. When calculating the local strain at the weld toe, elasto-plastic finite element analysis using a fine mesh with a resolution of about 0.01 mm is usually employed, but this is not practical because of the tremendous calculation and working costs involved. In this study, finite element analyses were performed for three types of welded joints (cruciform joint, T-joint, and longitudinal attachment joint) with different dimensions, and a simple estimation method for the local elasto-plastic strain amplitude at the weld toe was developed. A feature of this method is that it correlates the local strain amplitude at the weld toe with the elastic strain distribution around the toe obtained by a simple analysis using a relatively coarse mesh. Moreover, the proposed method was verified by low cycle fatigue tests of welded joins.

Language：English   Publishing type：Research paper (scientific journal)  

Root cracks initiating from U-rib to deck welded joints of orthotropic steel deck bridge have become a road surface travel safety problem. Some fatigue strength evaluation methods for root cracks have been proposed based on local stress criteria, such as effective notch stress method, but these methods cannot be evaluated directly from the measurable response values of the structure. In order to improve the efficiency of maintenance and to predict crack initiation, it is desirable to be able to accurately evaluate fatigue strength based on information obtained from the structure for root crack initiation. This study examines a fatigue strength evaluation method for the cracks in the weld joints between a U-rib and a deck plate in orthotropic steel bridge decks. The crack initiates from the weld root and propagates into the deck plate or the weld bead. Fatigue tests and FE analyses were conducted in order to examine the local stresses available for fatigue strength assessment, and to propose a method to estimate them from some reference stresses around the weld joint.

Language：English   Publishing type：Research paper (scientific journal)  

High-Frequency Mechanical Impact (HFMI) is an user-friendly and efficient mechanical post-weld treatment method and the achieved fatigue life improvement is statistically proved. The achieved fatigue life improvement is attributed to HFMI-induced compressive residual stresses amongst other effects. Several studies have shown in the past that the process parameters (treatment intensity and working speed) have an influence on the stress state introduced by the HFMI treatment. Thus far however, only device-specific quantitative recommendation for the HFMI-treatment exists based on the instructions of each HFMI device’s manufacturer. It is not clear, if a certain treatment time for a given intensity leads to optimum results regarding the enhanced fatigue life. Moreover, the treatment parameters of the several HFMI devices cannot be directly compared with each other. For these reasons, a universal and simple definition of the HFMI-treatment’s intensity based on the kinetic energy of the HFMI pin was used to quantitatively correlate the HFMI-induced compressive residual stress with the HFMI-process parameters for two different HFMI devices: Pneumatical Impact Treatment (PIT) and High Frequency Impact Treatment (HiFIT). To this purpose, data from former studies of HFMI-treated base material and welded specimens are revaluated. It is shown, that the compressive residual stresses after reaching a threshold value of the applied kinetic energy show only slight changes. This energy-based approach for the quantification of the treatment intensity was also used for a case study with PIT and HiFIT treated transverse stiffeners with different treatment intensities. A high influence of the treatment intensity on the residual stress state was determined. However, only a slight influence on hardness increase and fatigue strength was shown.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Corner plates are often welded at the intersection between web and flange in steel box girders. As a measure against fatigue in the weld joint between corner plate and lateral rib, the end of corner plate was cut-out in U-shape. Nevertheless, fatigue cracks have been generated from exposed root on the cut-out surface. In this study, fatigue strength and fatigue life improvement by ICR treatment were investigated. The fatigue strength of the weld joint was JSSC-G class. Application of ICR treatment improves the fatigue strength by 1 grade or more, and the fatigue limit was improved as 59 N/mm2 or more. Furthermore, stress concentration factor around exposed root was investigated by finite element analysis.

DOI： 10.11532/structcivil.68A.580

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, the effect of the stress state of a welded joint during application of high-frequency mechanical impact (HFMI) treatment on the resulting fatigue strength was investigated. Longitudinal attachment joints were treated under a state in which a static load was applied and subsequently tested under a constant stress amplitude with stress ratios of 0 or 0.5. The test results indicated that enhanced fatigue strength can be achieved even under a high stress ratio when the joint is treated under the minimum stress of fatigue loading. In addition, residual stress measurements and finite element analysis simulating a treatment process indicated that the magnitude of compressive residual stress introduced to a weld toe is similar regardless of the stress state in the joint during treatment.

DOI： 10.11532/structcivil.68A.591

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, a method for predicting residual stress introduced by high-frequency mechanical impact (HFMI) was investigated using kinetic energy of an accelerated indenter. Steel plates of different grades were treated by a high-frequency impact treatment device under different treatment conditions (such as intensity of impact, number of passes, and treatment length). In addition, the motion of the HFMI indenter was recorded using a high-speed camera during the treatment, and a simple calculation method for the kinetic energy applied to steel plates was proposed. The results confirmed that the compressive residual stress introduced to the steel plates correlated closely with the calculated kinetic energy. In addition, experiments demonstrated that the energy-based residual stress prediction is applicable to a longitudinal attachment welded joint with sufficient accuracy.

DOI： 10.1007/s40194-021-01230-z

Language：English   Publishing type：Research paper (scientific journal)  

In this study, fatigue crack growth was retarded by injecting corrosion accelerator, Nitric acid (HNO3), into the crack to induce corrosion. The presence of the corrosion products is expected to reduce the crack opening width and act as a wedge to control the crack closure. Fatigue tests were carried out on the compact tension (CT) specimens. The test revealed that the corrosion process due to HNO3 injection ends after 24 hours. Then, the reduction in crack opening displacement range can be observed. Retardation in the crack growth was observed regardless of the load range and the effective stress intensity factor range (delta_Keff) at injection. Meanwhile, the retardation level tends to be affected by the ΔKeff and crack length at injection.

DOI： 10.11273/jssc.28.112_111

Language：English   Publishing type：Research paper (scientific journal)  

Out-of-plane gusset joints are commonly used in welded assembly structures such as bridges. The studies regarding out-of-plane gusset joint often define fatigue life of this joint as the condition when the crack has fully penetrated through the web plate. However, the time frame from crack initiation until reaching complete structural failure is unclear. In this study, extended fatigue crack propagation analysis of out-of-plane gusset joint is performed. The variation of influential parameters such as flank angle, weld toe radius, material constant, and the threshold value of stress intensity factor range was considered. The crack propagation analysis was done until the crack reaches 80% of the lower flange plate of the bridge girder. Since the crack propagation life is highly influenced by traffic conditions, the probability distribution of the number of cycles and the crack width (2b) is presented in regards to the fatigue life ratio. In estimating the failure probability of the joint, the influence of human error to detect cracks during the inspection is considered. Five cases of the probability of crack detection are assumed to represent the capability of the inspector. It was found that bridge inspection and reparation of cracks are important in controlling the failure probability.

DOI： 10.1007/s13296-021-00559-x

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In riveted bridges, generally, rivets deteriorated with loosening and corrosion are replaced with high-strength friction-type bolts. In this case, both riveted and bolted connections which have different load transfer mechanism coexist in the same joint, however, the mechanical behavior and limit states of the rivet-and-bolt combination joints have not been well investigated yet. In this study, in order to investigate the mechanical behavior and limit states of the combination joints using rivets and bolts, static tensile tests were performed on specimens with different arrangement of rivets and bolts. Moreover, finite element analysis was performed to investigate load transfer mechanism in the combination joints. Based on the experiment and analysis, the evaluation method for the strength of the combination joints was indicated.

DOI： 10.2208/jscejseee.77.3_489

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, the effect of the stress state of a welded joint during application of high-frequency mechanical impact (HFMI) treatment on the resulting fatigue strength was investigated through fatigue tests and finite element analysis. A high-frequency impact treatment tool was used as the HFMI device. Longitudinal attachment welded joints were treated under a state in which a static load was applied and subsequently tested under a constant stress amplitude with stress ratios of 0 or 0.5. In addition, residual stress measurements and finite element analysis simulating welding and treatment processes were performed. The results indicate that the HFMI treatment is beneficial even when applied under a static tensile load, as the resulting compressive residual stresses are similar regardless of the stress state in the joint during treatment, meaning that the HFMI is applicable to existing structures.

DOI： 10.1007/s40194-021-01208-x

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, the fatigue strength of welded joints in steel-concrete composite slabs was investigated by fatigue testing. In the test, fatigue cracks occurred at the toes of boxing welds of L-shaped shear connectors as a result of stress concentration due to the local out-of-plane bending deformation of the steel plates around the boxing weld. This local deformation can be produced by the steel and concrete behaving independent of one another locally near welds. The test results demonstrated that the fatigue assessment of welded joints in a composite slab can be performed using the hot-spot stress approach.

Language：English  

Damping devices such as shear panel damper (SPD) are used to ensure the soundness of the principal elements of a bridge in an earthquake. The SPD is made of low yield point steel, which absorbs seismic energy by its plastic shear deformation. Since SPD is assembled by welding, low cycle fatigue is a concern due to strain concentration at the shear panel-to-flange connection. In this study, the relationship between the weld toe radius of SPD and the low-cycle fatigue life was investigated. To examine the low cycle fatigue life and strain distribution, cyclic loading test was performed. In addition, finite element analysis was performed to investigate the influence of weld toe radius on the local strain range at the weld toe. Low cycle fatigue life was estimated from the local strain range for each weld toe radius. From the results, the effect of toe radius on the low-cycle fatigue life of SPD welded joints was quantified.

Language：English  

Corner plates are often welded to cover web-to-flange joints in box girders which can hold appropriate angle between webs and flanges during construction, and enhance the buckling resistance of the web plate. The corner plates are installed by single-sided welding because circumference of corner plates can only be approached from one side. Since weld root remains in the welded joints of corner plates, many fatigue cracks found out in the weld joints of corner plates. Although the end of corner plates was cut-out and ground smoothly as a countermeasure, fatigue cracks have again occurred from weld root exposed on the cut-out surface. In this study, the fatigue durability of cut-out at corner plate ends was investigated. Fatigue tests on small-scaled specimens were performed. Two types of specimens with different angles at the corner plate ends were tested. As the results, low fatigue durability can be seen regardless of the angle at the corner plate end. In addition, fatigue strength improvement due to peening application at the weld root was investigated. Peening application increased the fatigue strength grade and fatigue limit of the joint.

Authorship：Corresponding author   Language：English  

In this study, low cycle fatigue crack growth tests with several structural steels were performed, in which compliance method was newly introduced to determine crack size that is a technique usually used in high cycle fatigue region. The test results indicated that the crack size from the compliance method relatively agrees with that from image measurements, and the proposed relationship between the compliance and the crack size was verified. Moreover, it was revealed that the crack growth rate can correlated with the cyclic J-integral range calculated by finite element analysis regardless of the steel types.

Language：English  

Over the last decade, fatigue cracks have been observed at welded joints between U-ribs and deck plates in many orthotropic steel deck bridges in Japan. Among the cracks, this paper focuses on fatigue cracks that initiate from a weld root of rib-to-deck welded joints and propagate to a deck plate. This study examines the effect of countermeasure with overlaying Ultra-High Performance Fiber Reinforced cement-based Composites (UHPFRC) on steel decks with cracks from U-rib welds, and confirms the fatigue durability of this countermeasure method. Specifically, the suppressing effect on crack propagation and the fatigue durability of UHPFRC itself and the interface between UHPFRC and the deck plate were confirmed by a wheel running test and finite element analysis. As a result, it was clarified that this countermeasure has a positive effect to retard further crack propagation compared with a countermeasure with overlaying steel fiber reinforced concrete which is generally adopted. In addition, it was revealed that this countermeasure has enough fatigue durability.

Language：English  

Since orthotropic steel deck is lighter than concrete slab, it has been used for long span bridge and bridge in urban areas. Wheel loads induces the local stress reputation at weld joints between deck plate and vertical stiffener, and large number of fatigue cracks have been generated in their weld joints. In order to reduce the stress concentration, construction of semicircular notch at the top of the vertical stiffener has been suggested. In this study, construction of slit-shaped notch is suggested as enhancement of the stress reduction and retaining crack propagation.
The stress reduction at the weld joint by slit-shaped notch was investigated from finite element (FE) analysis. In addition, the crack with various size was introduced to the weld joint, and reduction in stress intensity factor (SIF) by slit-shaped notch was examined. To confirm the fatigue propagation life extension due to slit-shaped notch, fatigue tests were performed for small-scaled specimens. Fatigue life extension can be seen in most specimen while another crack was developed from the notch in a specimen.

Authorship：Corresponding author   Language：English  

In riveted bridges, generally, rivets deteriorated with loosening and corrosion are replaced with high-strength friction-type bolts. In this case, both riveted and bolted connections which have different load transfer mechanism coexist in the same joint, however, the mechanical behavior and limit states of the rivet-and-bolt combination joints have not been well investigated yet. In this study, in order to clarify the mechanical behavior and limit states of the combination joints using rivets and bolts, static tensile tests were performed on specimens with different arrangement of rivets and bolts. Moreover, finite element analysis was performed to investigate load transfer mechanism in the combination joints. Based on the experiment and analysis, the evaluation method for the strength of the combination joints was indicated.

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study investigated opening and closing behavior of root gap and weld crack occurrence in slit-welding under cyclic loading through welding tests and thermal elasto-plastic finite element analysis. Sectional observations after the welding test revealed that the crack occurrence highly depends on the magnitude of root gap opening displacement and loading frequency in welding process, and also restraint intensity of slits. Then, through the simulation of welding under cyclic loading, it was clarified that root gap opening behavior during welding changes due to the restraint intensity of the slit, which correlates the tendency of the crack occurrence under different restraint conditions. Based on the test and analysis results, a conditional expression for the weld crack occurrence consist of the initial root gap opening displacement, loading frequency and restraint intensity of slits was obtained, and its validity was verified by the experiments.

DOI： 10.2208/jscejseee.77.2_287

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper examines a fatigue evaluation method for the cracks in the weld joints between a U-rib and a deck plate in orthotropic steel bridge decks. The crack initiates from the weld root and propagates into the deck plate or the weld bead. Fatigue tests and FE analyses were conducted in order to examine the local stresses available for fatigue assessment, and to propose a method to estimate them from some reference stresses around the weld joint. In addition, based on fatigue crack propagation analyses, a method to predict the crack propagation path was proposed.

DOI： 10.2208/jscejseee.77.2_255

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, a method for predicting residual stress introduced by high-frequency mechanical impact (HFMI) was investigated using energetics. Steel plates of different grades were treated by a high-frequency impact treatment device under different treatment conditions (such as intensity of impact, number of passes, and treatment length). In addition, the motion of the HFMI indenter was recorded using a high-speed camera during the treatment, and a simple calculation method for the energy applied to steel plates was proposed. The results confirmed that the compressive residual stress introduced to the steel plates correlated closely with the calculated energy. In addition, experiments demonstrated that the energy-based residual stress prediction is applicable to a longitudinal attachment welded joint with sufficient accuracy.

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, the effect of the stress state of a welded joint during application of high-frequency mechanical impact (HFMI) treatment on the resulting fatigue strength was investigated through fatigue tests and finite element analysis. A high-frequency impact treatment tool was used as the HFMI device. Longitudinal attachment welded joints were treated under a state in which a static load was applied and subsequently tested under a constant stress amplitude with stress ratios of 0 or 0.5. The test results indicate that improved fatigue strength can be achieved even under a high stress ratio when the joint is treated under the minimum stress of fatigue loading. In addition, residual stress measurements and finite element analysis simulating welding and treatment processes indicated that the magnitude of compressive residual stress introduced to a weld toe is almost the same regardless of the stress state in the joint during treatment.

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

This study investigated the fatigue strength of welded joints in steel-concrete composite slabs by fatigue testing. In addition, the local stress around the welded joint was evaluated through finite element analysis. In the test, fatigue cracks occurred at the toes of boxing welds of angle-shape shear connectors as a result of stress concentration due to the local out-of-plane bending deformation of the steel plates around the boxing weld. This local deformation can be produced by the steel and concrete behaving independent of one another locally near welds when the bond at their interface is lost. The test results demonstrated that the fatigue assessment of welded joints in a composite slab can be performed using the hot-spot stress approach. Then, actual composite slabs with different structural characteristics were analyzed to investigate the local stress behavior around welded joints, and their fatigue performance was assessed based on the hot-spot stress approach.

DOI： 10.1201/9780429279119-365

Language：English   Publishing type：Research paper (international conference proceedings)  

A typical repair method for fatigue cracks in steel bridge members is the splice plate method. The crack tip is drilled out and splice plates are added over the crack. For evaluating the remaining fatigue life of the repaired members, the stress at a drilled crack-arrest hole after the addition of the splice plates with high-strength bolts is required. In this study, the effect of the geometric parameters of the splice plate on stress reduction at a drilled crack-arrest hole is investigated using static loading tests and parametric finite element analyses. Based on the results, a method for predicting the stress at the drilled hole that considers the load-carrying mechanism through the bolted splice plate is proposed. It is demonstrated that the proposed method can predict stress with an error of within 10%.

DOI： 10.1201/9780429279119-478

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue cracks have been observed at welded joints between U-ribs and deck plates in many orthotropic steel decks. Considering a fatigue crack at rib-to-deck welded joints can compromise transportation safety, it is necessary to detect and repair the crack at the early development stage.
This paper presents the accuracy of crack sizing with a Phased Array Ultrasonic Testing (PAUT) scanner developed for inspection. Firstly, an internal crack propagating from a weld root was induced at rib-to-deck welded joints by using a plate bending fatigue testing machine. Subsequently, the joints were inspected with the PAUT scanner. Appropriate sizing methods were determined for the deck and weld bead propagation type cracks, respectively, and the accuracy of crack sizing was evaluated. In addition, the influence of coating on the accuracy in crack sizing was examined. As a result, it is demonstrated that the PAUT scanner had enough crack sizing performance.

DOI： 10.1201/9780429279119-540

Language：English   Publishing type：Research paper (international conference proceedings)  

Carbon Fiber Reinforced Polymer (CFRP) composites, consisting of carbon fiber and matrix resin, has high stiffness and tensile strength. Recently, pultrusion method is developed for manufacturing CFRP composites. The bearing type bolted joint is typically adopted for permanent joint of CFRP composites. Due to bearing pressure around bolt hole, fatigue damage can be introduced around bolt hole in a bearing type bolted joint. In this study, fatigue performance of bearing type bolted joint with the pultruded CFRP composite was examined. To observe fatigue crack generation and propagation around bolt hole, tensile fatigue test on pultruded CFRP composites with a circular hole was performed. While fatigue crack was generated from the edge of the hole and propagates in longitudinal direction, the CFRP composites was not ruptured during the test. The fatigue test on a bearing type bolted joint for pultruded CFRP composites was also performed, and its fatigue strength was clarified. Finite element analysis (FEA) simulating multiple layer was constructed. The stress distribution around bolt hole was examined from FEA. The fatigue strength was arranged by maximum principal stress range.

DOI： 10.1201/9780429279119-496

Language：English   Publishing type：Research paper (scientific journal)  

Low cycle fatigue is a failure mode which is possibly caused by random large strains such as seismic motion. To examine the effects, this study elaborated crack propagation behavior in steel under random amplitude loading. Firstly, study on crack growth rate under constant amplitude conditions was conducted to obtain basic characteristics. Next, several patterns of random amplitude loading were applied. It is discovered that crack growth accelerated when amplitude decreased from high to low levels at tensile portions, compared to that in constant amplitude conditions. Prediction model was constructed with establishing relationship between cyclic J-integral range and crack growth rate and confirmed to give good estimation.

DOI： 10.11532/structcivil.67A.174

Language：Japanese   Publishing type：Research paper (scientific journal)  

Low-yield point steel has been used in seismic control dampers due to its high energy absorption ability. Meanwhile, thermal cycle during welding can change mechanical properties and microstructure of low-yield point steel. In addition, large plastic strains caused by seismic motion can induce defects in microstructure. They can cause the reduction in toughness of the low-yield point steel. In this study, Charpy impact tests were performed for low-yield point steel with thermal cycle simulating heat affected zone and preliminary plastic strain. Significant reduction in Charpy absorbed energy was observed when applying simulated thermal cycle, while the preliminary strain gives insignificant reduction.

DOI： 10.11273/jssc.28.109_183

Language：Japanese   Publishing type：Research paper (scientific journal)  

The drilled crack-arrest hole and the attaching splices by high strength bolts are often used in combination as retrofit for fatigue cracks in steel structures. In this case, in order to evaluate the remaining fatigue life, it is important to accurately estimate the strain at the crack-arrest hole. Non-linear FE analysis considered the friction contact was often applied for the strain estimation in previous researches. In this study, a linear analysis model with simplified meshing was newly introduced. Through static loading tests and parametric FE analyses, it was verified that the model can estimate the strain at the hole with practically sufficient accuracy.

DOI： 10.11273/jssc.28.109_155

Language：English   Publishing type：Research paper (scientific journal)  

Low cycle fatigue in steel caused by earthquakes can result in large cyclic strain failures. In the studies conducted to date, low cycle fatigue crack propagation has primarily been investigated under constant amplitude loading. However, actual seismic motions are characterized by amplitude changeability from high to low or from low to high levels, and the effect of these alterations on crack growth in steel has not yet been clarified. Accordingly, this study examines crack propagation patterns under two-steps variable amplitude loading, which has two different uniform amplitude steps. The first part of this paper examines crack growth rates under constant amplitude conditions to obtain basic characteristic. Then, several patterns of two-steps variable amplitude loading are investigated. Research results show that, when compared to constant amplitude conditions, crack growth rates in steel increase when the amplitude decreases from high to low levels. Finally, a formula containing finite element analysis parameters was constructed and verified, thus providing a new method for obtaining good estimations of the crack growth rate.

DOI： 10.11273/jssc.27.108_93

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Over the last decade, fatigue cracks have been observed at welded joints between U-ribs and deck plates in many orthotropic steel deck bridges in Japan. Among the cracks, this paper focuses on fatigue cracks that initiate from a weld root of rib-to-deck welded joints and propagate to a deck plate. This study examines the effect of countermeasure with overlaying Ultra-High Performance Fibre Reinforced cement-based Composites (UHPFRC) on steel decks with cracks from U-rib welds, and confirms the fatigue durability of this countermeasure method. Specifically, the suppressing effect on crack propagation and the fatigue durability of UHPFRC itself and the interface between UHPFRC and the deck plate were confirmed by a wheel running test and finite element analysis. As a result, it was clarified that this countermeasure has a positive effect to retard further crack propagation compared with a countermeasure with overlaying steel fiber reinforced concrete which is generally adopted. In addition, it was revealed that this countermeasure has enough fatigue durability.

DOI： 10.2208/jscejseee.76.3_542

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

During the 2011 Tohoku Earthquake, a truss bridge joint structure was cracked due to large cyclic deformation, making us recognize the importance of assessing the seismic performance of joint structures in truss bridges from the viewpoint of low-cycle fatigue. In this study, seismic response analysis of an actual deck truss bridge was performed under different seismic waves, and local strain behavior generated at welded joints around a joint structure was clarified using a zooming analysis technique. The results revealed the possibility that welded joints for a lateral gusset-plate in a joint structure can be cracking sites during earthquakes. In addition, it was indicated that seismic isolation bearings can significantly reduce the local strain at the joint structure and improve its low-cycle fatigue performance. Moreover, as a simple countermeasure, weld toe treatment by grinding is also effective to decrease the possibility of low-cycle fatigue cracking at the joint structure.

DOI： 10.1007/s13296-020-00399-1

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Low cycle fatigue is a failure mode exhibiting a small number of loading repetitions to failure. Former work conducting research on constant displacement amplitude presented crack growth rate was related to cyclic J-integral range, but the data were limited. This research aimed to provide additional information to cover study done at the past so that a formula for obtaining crack growth rate can be precisely proposed. Research work was conducted with applying two different cyclic displacement means of loading histories to CT specimen. Cumulative plots in crack growth rate addressed to past and current research work were found enforcing formula used for obtaining crack growth rate under larger cyclic strains proposed at the past.

DOI： 10.11273/jssc.27.106_75

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigated the applicability of low transformation temperature (LTT) arc welding consumables to improve fatigue strength against weld root failure. Transverse attachment joints formed by single-sided welding, similar to rib-to-deck connections in orthotropic steel bridge decks, were fabricated using an LTT welding consumable and conventional welding consumable. Fatigue tests were performed with out-of-plane bending loads using a vibration-type fatigue testing machine. The test results indicated that higher fatigue strength can be achieved in the joint with an LTT consumable compared with a conventional one. In addition, residual stresses around the weld bead were clarified by X-ray diffraction measurements and finite element analyses. The results revealed that the LTT consumable weld metal can reduce residual stress around the weld and also introduce compressive residual stress to the weld root, which can contribute to improved fatigue strength.

DOI： 10.1007/s40194-020-00915-1

Authorship：Lead author   Language：English  

The accuracy of Miner's rule has not been verified in an extremely large strain field, corresponding to the fatigue life of less than tens cycles. In this study, low cycle fatigue tests under variable strain amplitude in the extremely large strain field were conducted with a newly developed testing system. The result revealed that the Miner's rule always predicted a longer fatigue life than the observed life. Therefore, this study proposed a simple fatigue assessment model introducing the damage mechanics concept and examined its validity as another method for predicting low cycle fatigue life.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, the fatigue strength of welded joints in steel-concrete composite slabs was investigated by fatigue testing. In addition, the local stress around the welded joint was evaluated through finite element analysis. In the test, fatigue cracks occurred at the toes of boxing welds of L-shaped shear connectors as a result of stress concentration due to the local out-of-plane bending deformation of the steel plates around the boxing weld. This local deformation can be produced by the steel and concrete behaving in-dependent of one another locally near welds when the bond at their interface is lost. The test results demonstrated that the fatigue assessment of welded joints in a composite slab can be performed using the hot-spot stress approach. Then, actual composite slabs with different structural characteristics were analyzed to investigate the local stress behavior around welded joints, and their fatigue performance was assessed based on the hot-spot stress approach.

DOI： 10.2208/jscejseee.76.5_II_50

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Damaged steel bridge members are often repaired by patching steel plates with high strength bolts. Sometimes, due to spatial restriction, there is a need to be shorten bolt spacing or edge distance than those specified in a design specification. However, knowledge on fatigue performance of the joints with the compact bolt arrangement is little.
In this study, fatigue strength of friction type bolted joints with compact bolt arrangement was investigated through fatigue tests and finite element analyses. The test result indicated that the compact bolt arrangement, especially a smaller end distance, decrease the fatigue strength of the joints. The analysis results demonstrated that stress concentration occured at the surface around a bolt hole where the fatigue crack initiated in the test. Since the stress concentration was strongly correlated to the fatigue strength in the test, the effects of compact bolt arrangement with a variety of material strengths and joint dimensions were discussed based on the stress concentration.

DOI： 10.2208/jscejseee.76.2_212

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study examined low cycle fatigue behavior of cruciform welded joints containing incomplete penetration. Six types of specimens with different sizes of weld penetrations and weld leg lengths were tested under cyclic plastic strains. The test results revealed that the fatigue strength and cracking patterns depend on the ratio of the weld penetration to the main plate thickness and the ratio of the weld leg length to the main plate thickness, respectively. Then, elasto-plastic finite element analyses including the effective notch concept were performed. The results indicate that the fatigue strength and cracking pattern of the specimens can be correlated with the local strain distribution around the effective notch.

DOI： 10.11532/structcivil.66A.253

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study investigated the applicability of low transformation temperature (LTT) welding consumables to improve fatigue strength against weld root failure. Transverse attachment joints formed by single-sided welding were fabricated using an LTT welding consumable and conventional welding consumable. Fatigue tests with out-of-plane bending loads revealed that higher fatigue strength and fatigue limit can be achieved in the joint with an LTT consumable compared with a conventional one. In addition, residual stresses around the weld bead were clarified by X-ray diffraction measurements and finite element analyses. The results indicated that the LTT consumable can reduce tensile residual stress around the weld and also introduce compressive residual stress to the weld root.

DOI： 10.11532/structcivil.66A.607

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study examined the low-cycle fatigue behavior of load-carrying cruciform-welded joints containing incomplete penetration. Five types of specimens with different sizes of weld penetrations and weld leg lengths were tested under cyclic plastic strains. During testing, cracking behavior was observed on the side surface of the specimen. The test results revealed that the fatigue strength and cracking patterns depend on the ratio of the weld penetration to the main plate thickness and the ratio of the weld leg length to the 5main plate thickness, respectively. Elasto-plastic finite element analyses including the effective notch concept were then performed. The results indicate that the fatigue strength and cracking pattern of the specimens can be correlated with the local strain distribution around the effective notch.

DOI： 10.1007/s40194-019-00834-w

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

A shear panel damper can absorb seismic energy by its hysteresis damping. On the other hand, repetition of high strain around its welded joints could lead to low cycle fatigue failure. To avoid the low cycle fatigue, a simple assessment method was investigated in this study. The relationship between mean shear strain range and local strain range at a crack initiation point was examined for various shear panel dampers. From the relation, estimation equations for the local strain range at crack initiation point were established. In addition, low cycle fatigue strength curves based on the mean shear strain range were developed. Based on the fatigue strength curve, fatigue crack initiation life was discussed among the several shear panel dampers.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In recent years, the pultrusion method for manufacturing CFRP member has been established. The environment to stably supply large-scaled CFRP members is being developed. On the other hand, mechanical behavior and fatigue behavior of the bearing type bolted joint used for connection of FRP members is not clearly understood. In this study, tensile fatigue tests on perforated plate and double shear bearing type bolted joint of pultruded CFRP were performed. The perforated plate specimen represents sperior fatigue durability over 10million cycle even under nominal stress range of 260 N/mm2. However, the fatigue crack occurs from the edge of the hole, and propagates to longitudinal direction. As for bearing type bolted joint specimen, local bearing failure was observed around the contact part between bolt and CFRP member. The shear-out failure was also observed when the nominal stress is over 70 N/mm2. Moreover, finite element analysis was performed to examine the stress around the bolt hole. Fatigue durability of pulutruded CFRP member was discussed by arranging fatigue test results with maximum principal strain obtained from the analysis.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, fatigue strength of welded joints in steel-concrete composite slabs was investigated by a fatigue test and finite element analysis. In the test, fatigue cracks occurred at toes of boxing welds of angle-shape shear connectors and propagated into a bottom plate, which were caused by stress concentration due to local out-of-plane bending deformation of steel plates around the boxing weld. This local deformation can be caused because concrete and steel plates locally behave separately near welds when bond between them is lost. The test result demonstrated that fatigue assessment of welded joints in the steel-concrete composite slab can be performed using the structural hot spot stress approach. Then, actual composite slabs with different structural dimensions were analyzed to investigate local stress behavior around welded joints, and their fatigue performance was assessed based on the hot spot stress approach.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The present study examined a prediction method for the strain at drilled fatigue crack-arrest holes covered by splice plates to evaluate fatigue enhancement of the hole accompanied by the splices. Finite element analyses were performed in order to establish a method to predict the strain at a drilled hole from the strain that can be measured on a splice plate. In the present study, axially loaded center-cracked steel plates repaired by adding splice plates were analyzed for various plate thicknesses of both cracked and splice plates, bolt-hole arrangements and diameters, and crack lengths. The strain on the splice around the drilled hole was correlated with the strain at the hole. Based on the results, a prediction formula for the strain at the hole, which is a function of the pitch and diameter of bolt holes near the drilled hole, was proposed. Static tensile loading tests were conducted for several center-cracked plates repaired by adding splice plates in order to verify the proposed strain-prediction method. The test results demonstrated that the strain at the drilled hole can be predicted with enough accuracy based on the strain on the splice.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The presence of tensile residual stress caused by the welding process, at weld root of rib-to-deck joint in Orthotropic Steel Deck (OSD), believed can trigger fatigue crack occurrence although the applied cycle stresses are compression. In this study, a new method to reduce tensile residual stress at the weld root of rib-to-deck joint in OSD is proposed. It was started with simulating the welding process by using Finite Element (FE) analysis. Various structural parameters are considered to examine its sensitivity in the tensile residual stress distribution at the weld root through the deck plate. It was found that high tensile residual stress is generated at the weld root and tend to be increased with the increase of deck plate thickness and welding penetration. The proposed method is simulated after welding analysis. In this method, the plastic deformation is applied around the weld root by external opening force after cutting the bottom part of the through-rib. The tensile residual stress at the weld root was dispersed when expanding the web plate of through-rib. Significant reduction of tensile residual stress can be obtained when the weld bead size is relatively small.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Low cycle fatigue, is one of the main failure modes in steel structures due to the earthquake. Earthquake acceleration leads to contribute irregular and high plastic deformation to the affected structures. However, the low cycle fatigue durability under irregular loading has not been clarified. The objective of this research is to obtain crack propagation pattern and low cycle fatigue life prediction under various loading histories. Two types of controlled displacement sequences with mixed amplitude were applied to the CT specimen. One was the series with uniform value at constant high and constant low displacement. The remain was the series with changing amplitude from high to low displacement and from low to high displacement. Experimental work and Finite Element (FE) analysis conducted gave ΔJ-integral following applied cyclic loading histories trends and predicted fatigue life curve resulted showed non linear relationship for the crack growth rate during additional value of ΔJ-Integral.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study examined low cycle fatigue behavior of load-carrying cruciform welded joints containing incomplete penetration. Six types of specimens with different sizes of weld penetrations and weld leg lengths were tested under cyclic plastic strains. During testing, cracking behavior was observed on the side surface of the specimen. The test results revealed that the fatigue strength and cracking patterns depend on the ratio of the weld penetration to the main plate thickness and the ratio of the weld leg length to the main plate thickness, respectively. Then, elasto-plastic finite element analyses including the effective notch concept were performed. The results indicate that the fatigue strength and cracking pattern of the specimens can be correlated with the local strain distribution around the effective notch.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigated the applicability of low transformation temperature (LTT) consumables to improve fatigue strength against weld root failure. Transverse attachment joints formed by single-sided welding, similar to rib-to-deck connections in orthotropic steel bridge decks, were fabricated using an LTT welding consumable and conventional welding consumable. Fatigue tests were performed with out-of-plane bending loads using a vibration-type fatigue testing machine. The test results indicated that higher fatigue strength can be achieved in the joint with an LTT consumable compared with a conventional one. In addition, residual stresses around the weld bead were clarified by X-ray diffraction measurements and finite element analyses. The results revealed that the LTT consumable can reduce residual stress around the weld and also introduce compressive residual stress to the weld root, which can contribute to improved fatigue strength.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Under out-of-plane bending and shearing force, a crack develops in the thickness direction with an inclination toward the axial direction. Typically, three types of crack propagation behaviors can be observed; the crack develops in thickness direction up to the opposite surface, the crack is arrested after inclining toward an axial direction, and a counter crack comes from the opposite surface. In this study, the occurrence condition of each crack propagation behavior was investigated. Cyclic bending fatigue tests were conducted for notched steel plates. Furthermore, the crack propagation and counter crack occurrence were evaluated from finite element analysis. The crack propagation pass tends to be affected by the ratio between bending stress and shear stress near the crack. Also, in the case that the counter crack was generated, the strain on the opposite surface yielded.

Language：English  

Fatigue strength of longitudinal welded joints is used to be less focused since the other joints are considered more critical. However, the presence of blowholes in the fillet welds can be a weak point and cause unpredicted fatigue crack. For determining the appropriate period of inspection, it is important to understand the crack growth behavior in longitudinal welded joint of the primary member. In this study, fatigue strength of longitudinal welded joints with the presence of blowholes is studied. To obtain the crack propagation life, crack propagation analysis for large-scaled girder containing blowhole in its welded joint between web and flange is performed. In the end, the analysis results associated with the traffic volume data is employed to predict how long will it takes from the moment crack initiates from blowholes until reach member failure.

Authorship：Corresponding author   Language：English  

This study examined low cycle fatigue behavior of load-carrying cruciform welded joints containing incomplete penetration. Six types of specimens with different sizes of weld penetrations and weld leg lengths were tested under cyclic plastic strains. During testing, cracking behavior was observed on the side surface of the specimen. The test results revealed that the fatigue strength and cracking patterns depend on the ratio of the weld penetration to the main plate thickness and the ratio of the weld leg length to the main plate thickness, respectively. Then, elasto-plastic finite element analyses including the effective notch concept were performed. The results indicate that the fatigue strength and cracking pattern of the specimens can be correlated with the local strain distribution around the effective notch.

Authorship：Corresponding author   Language：English  

Steel truss bridges are widely used for intermediate spans because of its light weight and high load-carrying capacity. Failure accidents of truss bridge have shown that fracture of some members can lead to collapse of the whole bridge, called fracture critical member (FCM). In this study, from the viewpoint of low cycle fatigue, dynamic behavior of FCM under great earthquake was discussed. The results of finite element analysis indicated that large strains were locally occurred at the end of fillets of a gusset plate and around the boundary between the gusset and main chords, which have the possibility to become cracking sites due to low cycle fatigue.

Language：English  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding. Load-carrying and non-load-carrying cruciform welded joints with plate thicknesses of 8, 16, and 25 mm were tested under tensile cyclic loads and out-of-plane bending cyclic loads. In longitudinal joints, four-point bending fatigue tests were performed on plate girders with flanges and a web connected by laser-arc hybrid welding. When assembling the plate girder, tack welds were installed at the flange-to-web connection to clarify their effect on the fatigue strength of the longitudinal joints. Measurements of weld toe profiles and residual stress were also conducted. The residual stress was measured using X-ray diffraction. The test results revealed that the fatigue strengths of hybrid welded joints are equivalent to those of arc welded joints and satisfy the fatigue design curves specified by the Japanese Society of Steel Construction. In addition, the effect of plate thickness on the fatigue strength was observed in hybrid welded joints as well as in arc welded joints.

DOI： 10.1007/s40194-019-00745-w

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In current design codes, the minimum bolt spacing and edge distance for high-strength bolted friction joints are specified based on the bolt diameter, regardless of the plate thickness or steel strength. However, the mechanical performance of joints with a more compact bolt spacing than that given in the current design specifications has been little examined. In this study, the slip and ultimate strength of high-strength bolted joints with a compact bolt spacing and edge distance were investigated. Tensile tests were conducted on friction-type joints with various bolt arrangements. The use of a compact bolt arrangement was not observed to have a negative influence on the slip strength in these tests. The estimated strengths corresponding to the experimentally observed failure modes were found to agree fairly well with the experimental results within a 10% error. A parametric finite element analysis was also conducted to investigate the influence of the bolt arrangement on the slip coefficient. It was concluded that the bolt spacing and edge distance have little influence on the slip coefficient.

DOI： 10.1007/s13296-018-0199-3

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding, in which tack welds were installed at the connection. The cruciform joints were tested under tensile cyclic loads and out-of-plane bending cyclic loads. In the longitudinal joints, four-point bending fatigue tests were performed on plate girders fabricated with the hybrid welding. In addition, finite element analysis was performed on the cruciform joint to investigate the effect of tack welds on stress concentration at weld toes. The test results revealed that the fatigue strengths of the hybrid welded joints are equivalent to those of arc welded joints with or without tack welds and satisfy the fatigue design curves specified in JSSC recommendation. Moreover, the analysis results indicated that tack welds have little influence on stress concentration at weld toes in cruciform joints fabricated with laser-arc hybrid welding.

DOI： 10.2207/qjjws.37.99

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigated the applicability of low transformation temperature (LTT) consumables to improve fatigue strength against weld root failure. Transverse attachment joints formed by single-sided welding, similar to rib-to-deck connections in orthotropic steel bridge decks, were fabricated using an LTT welding consumable and conventional welding consumable. Fatigue tests were performed with out-of-plane bending loads using a vibration-type fatigue testing machine. The test results indicated that higher fatigue strength can be achieved in the joint with an LTT consumable compared with a conventional one. In addition, residual stresses around the weld bead were clarified by X-ray diffraction measurements and finite element analyses. The results revealed that the LTT consumable can reduce residual stress around the weld and also introduce compressive residual stress to the weld root, which can contribute to improved fatigue strength.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Over the last decade, fatigue cracks have been observed at welded joints between trapezoidal ribs and deck plates in many orthotropic steel deck bridges in Japan. Considering a fatigue crack at rib-to-deck welded joints can cause pavement damage and thus compromise transportation safety, it is necessary to detect and repair it at the early stage of its development.
This paper presents the accuracy of crack sizing with an electrically driven phased array ultrasonic scanner (PAUT scanner) developed for inspection of rib-to-deck welded joints in orthotropic steel decks. The PAUT scanner simultaneously examines a deck plate and a weld bead into either of which cracks propagate from a weld root. Moreover, it can detect the cracks as remained in the steel members.
In this research, firstly an internal crack is induced at rib-to-deck welded joints by using a plate bending fatigue testing machine where crack sizes are controlled by monitoring stresses at regions closed to weld beads. Subsequently, the joints are inspected with the PAUT scanner. Appropriate sizing methods are de-termined for the crack going through a deck plate and a weld bead, respectively, and the accuracy of crack sizing is evaluated by comparing with real cracks on the joints. In addition, the influence of paint coatings on the accuracy in crack sizing is examined. As a result of these investigation, it is demonstrated that the PAUT scanner has enough crack sizing performance.

DOI： 10.2208/jscejseee.74.516

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Service lives of steel bridges are limited by corrosion. Coating is commonly applied to steel structures in order to prevent corrosion. In recent years, a laser cleaning treatment is introduced as a new technique for surface preparation of steel structures. However, the influence of laser cleaning on fatigue life of welded joint is unknown. In this study, fatigue tests were conducted on as-welded and laser-treated out-of-plane gusset joints. The test results showed that the laser cleaning treatment only had little influence on fatigue strength of out-of-plane gusset welded joints.

DOI： 10.11273/jssc.25.100_73

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigated the fatigue strength of corroded reinforcing steel bars. Several types of rebars consisting of different yield stress and rib shapes were used. The rebar was galvanically corroded to three levels, which are considered as a percentage of mass reduction of 5, 10 and 15% respectively. Fatigue test results revealed that the fatigue life of the corroded rebar decreases as the corrosion level increases. Then, the fatigue life of the corroded rebar was predicted by crack propagation calculations based on fracture mechanics. There are relatively good agreements between the prediction and the test results.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

As for retrofitting cracked bridge members, it is often used to attach doubler plates by highstrength bolts after drilling holes at crack tips. In many cases, the doubler plate is designed as frictional connections, but the slip action at the doubler plate and its slip strength have not been well known yet. In this study, tensile tests and FE analyses were conducted as a fundamental study to investigate the slip strength at the doubler plate. The result revealed that the load-sharing ratio between a main plate and doubler plates have linear correlation with the ratio of cross sectional areas of both plates. Therefore, the slip strength at the doubler plates can be designed by using the load-sharing ratio estimated by structural dimensions of the main plate and doubler plates.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study examined fatigue strength of cruciform joints fabricated with laser-arc hybrid welding. Load-carrying and non-load-carrying cruciform welded joints with a plate thickness from 8mm to 25mm were tested under tensile cyclic loads and out-of-plane bending cyclic loads. Measurements of weld toe profile, residual stress and hardness around a welded portion were also conducted. The test results revealed that the fatigue strength of the hybrid welded joints is equivalent to that of arc welded joints and satisfies the fatigue design curves for arc welded joints in JSSC recommendation. Besides, the thickness effect on fatigue strength was observed in the hybrid welded joints as well as in arc welded joints.

DOI： 10.2207/qjjws.36.219

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2208/jscejseee.74.290

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study examined the low cycle fatigue behavior of load-carrying cruciform welded joints containing incomplete penetration. Five types of specimens with different sizes of weld penetrations and weld leg lengths were tested under cyclic plastic strains. During testing, cracking behavior was observed on the side surface of the specimen. The test results revealed that the fatigue strength and cracking patterns depend on the ratio of the weld penetration to the main plate thickness and the ratio of the weld leg length to the main plate thickness, respectively. Elasto-plastic finite element analyses including the effective notch concept were then performed. The results indicate that the fatigue strength and cracking pattern of the specimens can be correlated with the local strain distribution around the effective notch.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Welded joints in steel structures are subjected to high strain amplitude during earthquake, which could cause a low cycle fatigue crack. To assess low cycle fatigue strength of welded joints, an estimation method based on local strain range at a crack initiation point has been established. In this method, an FE model with extremely-fine mesh is needed to obtain the local strain range accurately. In this paper, a prediction method of the local strain range from a model with relatively coarse mesh was proposed. Strain ranges obtained from coarse-mesh models were related to the local strain ranges from fine-mesh models. A prediction formula of the local strain range which is applicable to T-shaped joints, cruciform joints and out-of-plane gusset joints was established.

DOI： 10.11273/jssc.25.97_61

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Adding splice plates is a commonly used technique to repair fatigue cracks. The crack tip is drilled out before the splice plates are add. In some cases, however, a new fatigue crack initiates from the drilled hole. Because the drilled hole is entirely covered by the splice plates, it is impossible to measure its strain that can be used to assess the crack generation from the drilled hole. The purpose of this study is to propose a method to estimate the strain of the drilled hole by using a reference strain on the splice plate. By conducting parametric FE analyses and loading tests, the location for the reference strain which is strongly correlated with the strain in the drilled hole was proposed.

DOI： 10.11532/structcivil.64A.445

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

A typical repair method for fatigue cracks in steel bridge members is the splice plate method. The crack tip is drilled out, and splice plates are added over the crack. For evaluating the remaining fatigue life of the repaired members, it is needed to know the stress of the drilled hole after adding splice plates. In this study, the effect of the splice plates geometric parameters on the stress reduction of a drilled hole was investigated by tensile tests and parametric FE analyses. As a result, a new method to estimate the stress of the drilled hole was proposed, considering stress carrying mechanism of the splice plate. This method could estimate the stress within 10% error.

DOI： 10.11532/structcivil.64A.435

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Multiple Steel Columns is an earthquake-resistance bridge pier which has shear panel dampers between four steel columns. In the previous study, although the shear panel damper absorbs the seismic energy, low-cycle fatigue crack has been observed around welding of shear panel. In this study, evaluation method of low-cycle fatigue based on local strain range at crack initiation point was applied to crack in shear panel. To simplify calculation of local strain range, relationship between mean shear strain range of shear panel and local strain range at crack initiation point was developed. For quasi-static and dynamic loading condition, crack initiation life was evaluated by simplified estimation method.

DOI： 10.11273/jssc.24.96_17

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue cracks have been reported in I-beam ends of railway steel bridges, which occur at a lower end of an I-beam web. Its growth may lead to failure of the I-beam, but effective repair methods for the crack have not been established yet. This research investigated countermeasures against the crack at the I-beam end. From the result of the stress measurement, the differential settlement causes out-of-plane bending deformation of the I-beam web, which leads to a fatigue crack at the lower end of the web. The effect of several countermeasures was confirmed by analytical examinations and field trial experiments.

Authorship：Lead author   Language：English  

As for bolt spacing and edge distance of high strength bolted joints, minimum values are specified as a function of bolt diameter D, regardless of plate thickness and steel strength. That is, the minimum value is not clearly defined by mechanical performance of the joint. Moreover, there is little knowledge on the performance of the joint with the bolt spacing more compact than given in the current design specifications. This study investigates slip and fracture strength of high strength bolted joints with compact bolt spacing and edge distance. Tensile coupon tests on frictional joints with various bolt arrangement were conducted. It was not clearly observed the negative influence of compact bolt arrangement on the slip strength. The fracture strengths estimated from the cross
sectional area where the fracture occurred and steel strength of the plate agreed with the experimental results within 10% error in all fracture modes. Parametric analyses were also conducted to investigate the influence of the bolt arrangement to the slip coefficient. It was concluded that the bolt spacing and edge distance have small influence on the slip
coefficient.

Authorship：Lead author   Language：English  

This study newly proposed a low cycle fatigue assessment method for steel members which can predict their low cycle fatigue life from nominal strain history calculated with a beam analysis. After establishing a fatigue strength curve for base joints in steel bridge piers, seismic response analyses with beam elements were conducted to assess their low cycle fatigue performance against earthquakes. The analysis results revealed that some of the piers, even though they satisfy with the current seismic design code, have possibility to fail due to low cycle fatigue under earthquake.

Authorship：Lead author   Language：English  

Fatigue cracks have been reported in I-beam ends of railway steel bridges, which occur at a lower end of an I-beam web. As a temporary measure, the crack is typically repaired with drilling holes at its tips, called a stop-hole method. In the cracked I-beam ends, however, the effect of life extension due to a stop-hole has not been clearly evaluated yet. In this study, fatigue tests of I-beams repaired with a stop-hole were conducted. And also, in order to make sure local stress distribution around the stop-hole in the test, a finite element analysis was performed. As a result, it was proven that the fatigue life of the repaired I-beam can be predicted from the local stress range at the stop-hole edge. Furthermore, several case studies on life extension of an I-beam due to the stop-hole method were performed.

Authorship：Lead author   Language：English  

Shear panel damper possess high energy absorption capacity by its hysteresis damping. However, repetition of high strain concentration around welding joint could lead to low cycle fatigue. To avoid the low cycle fatigue, estimation method should be established. So far, a prediction method of low cycle fatigue initiation life based on the local strain range has been proposed. However, the calculation of local strain usually needs much time and effort to build finite element model. In this study, the relationship between mean shear strain range and local strain range at crack initiation point was examined for various shear panel damper. From the relation, prediction equation of local strain range was established. In addition, low cycle fatigue strength curve based on mean shear strain range was developed. Comparing fatigue strength curve for several shear panel damper, fatigue crack initiation life was discussed.

Authorship：Lead author   Language：English  

In this study, fatigue lives of corroded reinforcing steel bars were investigated. Several kinds of rebars consisting of different yield stress and rib shapes were used. The rebar was galvanically corroded to three levels, which are considered as a percentage of mass reduction of 5%, 10% and 15% respectively. Fatigue tests were carried out under constant stress amplitude. The test results revealed that the fatigue life of the corroded rebar decreases as the corrosion level increases. Then, 3D elasto-plastic finite element analyses were conducted with models reflecting surface profiles of the corroded rebar. The analysis results indicated that a cross section where the maximum local strain occurs corresponds to a cracking site observed in the test. Finally, the fatigue life of the corroded rebar was predicted by crack propagation calculations based on linear fracture mechanics. There are relatively good agreements between the prediction and the test results.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Low-cycle fatigue is one of the failure modes in steel structures during earthquakes. With a focus on crack growth in the low-cycle fatigue region, this study developed a fatigue crack growth curve and verified its applicability to crack growth prediction in welded joints. Fatigue crack growth tests under highly plastic conditions were performed using compact tension specimens with side grooves. The results indicate that the crack growth rate in the low-cycle fatigue region correlates with the cyclic J-integral range, which can be calculated using finite element analysis. Additionally, the results for both plain steel and weld metal were distributed in the same region within a narrow band. Based on the results, a formula for the fatigue crack growth rate under large cyclic strains was proposed. Low-cycle fatigue tests were then performed on welded joints to clarify their crack growth behavior, and the crack growth observed in these tests was compared with the crack growth calculated using the proposed formula. The calculation results were found to be in relatively good agreement with the experimental results, verifying the applicability of the formula.

DOI： 10.1007/s40194-017-0504-3

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

High strength bolted joints are often used in retrofitting steel bridges members, but sometimes bolts cannot be arranged by following current specification because of narrow spacing. There is no knowledge about the performance of the joints that spaced narrower than current specification. In this paper, we investigated the slip coefficient and the fracture strength of joints that bolts are spaced narrowly by tensile tests and parametric FE analysis. As the result, the slip coefficient is not influenced by the bolt spacing. The fracture strength of compact spacing bolted joints is less than standard spacing, but it can be improved by increasing the plate thickness. The fracture strength was estimated by the conventional method within 10% error.

DOI： 10.11273/jssc.24.95_25

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding. Load-carrying and non-load-carrying cruciform welded joints with plate thicknesses of 8, 16 and 25 mm were tested under tensile cyclic loads and out-of-plane bending cyclic loads. In longitudinal joints, four-point bending fatigue tests were performed with plate girders to which flanges and a web were connected with laser-arc hybrid welding. When assembling the plate girder, tack welds were installed at the flange-to-web connection to clarify their effect on the fatigue strength of longitudinal joints. Measurements on weld toe profiles and residual stress were also conducted. The test results revealed that the fatigue strengths of hybrid welded joints are equivalent to those of arc welded joints and satisfy the fatigue design curves specified in Japanese Society of Steel Construction. In addition, the effect of plate thickness on fatigue strength was observed in hybrid welded joints as well as in arc welded joints.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study investigated the effect of the static strength of steels on fatigue strength improvement of welded joints by toe treatments. Out-of-plane gusset welded joints made of four kinds of steels, which are SM490, SBHS400, SBHS500 and SBHS700, were treated by toe grinding or peening (ultrasonic impact treatment and hammer peening) techniques and tested with a plate-bending type fatigue testing system. The test results indicated the tendency that higher improvement of fatigue strength can be achieved by the grinding and peening techniques as the static strength of steels increases.

DOI： 10.11532/structcivil.63A.646

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

With a focus on a crack generated from a weld toe on a U-rib web around a cutout in orthotropic steel decks, this study performed fatigue tests with out-of-plane gusset welded joints under plate bending loads which simulates deformation in a U-rib web. The test result indicated that the conventional improvement methods, such as improving weld toe configuration and introducing compressive residual stress techniques, can increase the fatigue strength of the joint with the thin main plate as well.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Low cycle fatigue is one of the failure modes in steel structures during earthquakes. With a focus on crack growth in the low cycle fatigue region, the authors have developed a fatigue crack growth curve for steels. In this study, low cycle fatigue tests were performed on welded joints of a rectangular steel tube to clarify their crack growth behavior, and the crack growth observed in these tests was compared with the crack growth calculated using the proposed formula. The calculation results were found to be in relatively good agreement with the experimental results, verifying the applicability of the formula.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, focusing on crack growth in low cycle fatigue region, a fatigue life prediction method was proposed and its applicability to a crack in welded joints was verified through fatigue tests. First, a fatigue crack growth curve under large cyclic strains, which is a relationship between crack growth rate, da/dN, and cyclic J-integral range, ΔJ, was proposed for plain steel materials and weld metal. Then, crack growths in welded joints obtained in experiments were predicted by crack growth calculation with the proposed curve. Finally, the validity of the fatigue life prediction method proposed in this study was confirmed by comparing the test results and the predictions.

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Fatigue cracks have been reported in I-beam ends of railway steel bridges. The crack occurs around a rounded part between a web and a lower flange. Previous studies have revealed that out-of-plane bending deformation of a web plate due to non-uniform settlement of a support is a main trigger of the crack. On the other hand, its propagation characteristics which becomes useful information to decide a repair method have not been clarified yet. In this study, fatigue tests were performed with specimens which were cut out from I-beams in an actual railway bridge to investigate occurrence and propagation behavior of the crack. As a result, it was revealed that a crack occurs along the rounded part between the web and the lower flange and grows straight along the rounded part when cyclic load was applied just above the support. Furthermore, the result demonstrated that the crack tends to change its propagation from horizontally to downward as it approaches the sole plate end, and also that there is a possibility that this tendency was independent on loading positions.

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Multiple steel columns consist of four steel pipes and connection beams between them. A shear panel in a connection beam is expected to absorb and disperse seismic energy by its plastic deformation. Some experiments on a shear panel have revealed that there is a possibility that low cycle fatigue crack could occur at welded joints in the panel. Therefore, it is needed to make clear conditions when low cycle fatigue cracks occur. Previous study has indicated that low cycle fatigue life of a shear panel can be assessed based on local strain amplitude at a crack initiation point. In this study, influential factors on low cycle fatigue of a shear panel were investigated through finite element analyses, and then, a simple assessment method for low cycle fatigue at a boxing weld of a scallop in a shear panel was proposed. By using the method, low cycle fatigue assessments under seismic motions were conducted. The results indicated that the method can estimate fatigue life in more conservative than the local strain based method.

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In orthotropic steel deck systems, traffic loads lead to local deformation around welded joints repeatedly, which causes fatigue cracks. Specifically, a large number of fatigue cracks have been found around a cutout between a longitudinal closed rib (U-rib) and a transverse rib web. This study focuses on a crack generated from a weld toe on a U-rib web in a cutout. This crack is mainly caused by local out-of-plane bending deformation of a U-rib, so the connection can be regarded as an out-of-plane gusset welded joint under bending loads. However, thickness of a U-rib, which is regarded as a main plate of the gusset joint, is thinner than that used in conventional joints. Therefore, there may be difference in fatigue strength improved by conventional techniques. In this study, fatigue tests were conducted with out-of-plane gusset welded joints under bending load which simulates deformation in a U-rib web. The test result indicated that conventional improvement methods, such as improving weld toe configuration and introducing compressive residual stress techniques, can increase the fatigue strength of the joint with the thin main plate as well.

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Tensile residual stress existing near a weld reduces fatigue strength of welded joints. A peening technique is one of the methods to reduce tensile residual stress and introduce compressive residual stress at a cracking point, which can improve fatigue strength. In a peening method, the improvement on fatigue strength is considered to be related to the magnitude of introduced compressive residual stress. And also, it is considered that the magnitude of compressive residual stress by peening depends on the static strength of base material. Therefore, the fatigue strength of welded joints improved by peening may depend on the static strength of steel used in the joint.
This study focuses on UIT (Ultrasonic Impact Treatment), which is one of the peening methods, and investigated the effect of static strength of steel on the fatigue strength improvement of welded joints. First of all, introduced compressive residual stress due to UIT was measured by X-ray diffraction method, and the measurements were correlated with the static strength of materials. The results indicated a tendency that higher compressive residual stress can be induced by UIT as the static strength increases. In addition, fatigue tests on out-of-plane gusset welded joints made with different grades of steels were performed to reveal the effect of the static strength on fatigue strength improvement. As a result, it was confirmed that the fatigue strength of welded joints can be improved by UIT and its effect slightly varies depending on the static strength of steel.

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In this study, the improvement effect by Carbon-Fiber Reinforced Polymer (CFRP) repair to a crack was quantified. In order to make clear opening behavior of a crack under CFRP, tensile tests for butted steel plates which were bonded with CFRP plates were performed. The test results indicated that local peel-off around a crack needs to be introduced in a finite element model when analyzing the opening behavior of a crack under CFRP. Secondary, in order to estimate the effect of CFRP repair, stress intensity factor of a crack covered with various sizes and numbers of lamination of CFRP sheet was calculated through finite element analyses. As a result, it was indicated that length of CF sheet can affect reduction of stress intensity factor and even shorter sheet can achieve adequate improvement. In addition, fatigue tests of out-of-plane gusset welded joints repaired with CF sheets were carried out under bending load. The test results demonstrated that fatigue life of the joint is considerably improved by using CFRP.

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Laser-arc hybrid welding, which is combined with laser welding and arc welding, has been recently developed. Laser welding commonly requires less heat-input than ordinary arc welding, additionally it achieves deep penetration even in fast welding operation. On the other hand, an allowable root gap of a joint by the laser welding is smaller than that by arc welding due to thick weld bead. The laser-arc hybrid welding has the advantage of the laser welding and also improves the allowance of the gap, meaning that it can provide deep weld penetration, high processing speeds and wider allowance of the gap. Meanwhile, fatigue strength of the laser-arc hybrid welding has not been clarified. In addition, stress concentration and residual stress after the welding have not been deeply investigated yet. In this study, tensile and plate bending fatigue tests were carried out to examine the fatigue strength of load-carrying cruciform welded joints with the laser-arc hybrid welding. Furthermore, their residual stresses and weld toe configurations affecting the stress concentration were measured.

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Low cycle fatigue is one of the main failure modes in steel structures during earthquake. In this study, focusing on crack growth in low cycle fatigue region, a fatigue crack growth curve was proposed and its applicability to a crack growth prediction in welded joints was verified. Fatigue crack growth tests under large plastic condition were performed by using compact tension specimens with side grooves. The results indicated that crack growth rate in low cycle fatigue region correlates with cyclic J-integral range which is calculated by finite element analysis. Besides, the results in both plain steel material and weld metal distribute in the same region with narrow band. Based on the result, a formula of fatigue crack growth rate under large cyclic strains was proposed. Then, low cycle fatigue tests for welded joints were performed to clarify their crack growth behavior, and the crack growth obtained in the experiments were compared with the prediction based on crack growth calculation with the proposed curve. The prediction was in relatively good agreement with the experiments, which can verify the applicability of the curve.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue damage due to large cyclic strains is one of the main failure modes of steel structures during earthquake. This study investigated fatigue crack propagation behavior of structural steels under large cyclic strains. Crack propagation tests for plain material and deposited metal were performed with a compact tension type specimen. Besides, as an index for crack propagation, cyclic J-integral range was defined based on fracture mechanics concept and calculated by finite element analysis. Based on the results, a fatigue crack growth curve under large cyclic strains was proposed by using the cyclic J-integral range. Then, the applicability of the proposed curve was verified through fatigue tests of corner welded joints.

DOI： 10.11273/jssc.23.89_85

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There are some cases when weld-lines exist close to each other, for example in steel bridges, an end of a horizontal stiffener is located close to a vertical stiffener. This study performed fatigue tests and finite element analyses with plate girders where vertical and horizontal stiffeners were attached with a small distance between them. The test result revealed that fatigue cracks occurred from the end of the horizontal stiffeners and their fatigue strength slightly varied with the distance between the stiffeners. And then, the fatigue cracks were repaired by ICR treatment, and its applicability to a crack in a plate girder was investigated.

DOI： 10.11532/structcivil.62A.667

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Weld toe grinding is known to have relatively large variations in the improvement effects of fatigue strength. On the other hand, the residual stress distribution near the ground groove has not been revealed although it has a significant influence on the fatigue strength. In this research, X-ray stress measurements and finite element analyses were conducted in order to reveal the redistribution behavior of welding residual stress resulting from weld toe grinding. Based on the results, it was confirmed that the redistribution occurs near the ground surface and high tensile stress which can be higher than that at the original weld toe remains at the bottom of the ground groove as a result of the redistribution.

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This paper presents a new fatigue strength evaluation method for root failure in fillet weld joints, based on the displacement at unfused root gap. The displacement at the spot 1mm away from the weld root on unfused gap surfaces, obtained by FEA with 1mm size elements, was used as a parameter for fatigue strength evaluation. The accuracy of the method was verified with fatigue test results. A unique relationship was found between the displacements and the fatigue lives regardless of joint type and joint size and loading modes.

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This study proposed a method for estimating weld crack initiation in weld repair under cyclic loading through welding tests and thermal elasto-plastic finite element analyses. Sectional observations after the welding test revealed that the initiation of a weld crack highly depends on the magnitude of root gap opening displacement, especially in welding process. Then, through the simulation of welding under cyclic loading, this study proposed a prediction equation for the root gap opening displacement during welding. As a result of the experimental and analytical investigations, an estimation method for the crack initiation in weld repair under cyclic loading was established.

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Extremely low cycle fatigue, which is caused by large cyclic deformation with small number of loading repetition, is one of the main failure modes in steel structures during earthquake. In this study, crack propagation behavior of structural steels for welded structures (not only plain material but also weld deposit) under large cyclic deformation was investigated. As a result, a prediction equation for crack propagation under large deformation was proposed based on cyclic J-integral range. Besides, the proposed equation was verified through low cycle fatigue tests of corner welded joints.

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Weld toe grinding is known to have relatively large variations in its improvement effects of fatigue strength. On the other hand, the residual stress distribution near the ground groove has not been revealed although it has a significant influence on the fatigue strength. In this research, X-ray stress measurements and finite element analyses were conducted in order to reveal the redistribution behavior of welding residual stress resulting from weld toe grinding.

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As a new repair method, Carbon-Fiber Reinforced Polymer (CFRP) adhesive repair has been getting attention. In this study, the effect of CFRP adhesive repair for a fatigue crack in a steel plate was investigated experimentally and analytically. The fatigue tests revealed that the propagation rate of a crack repaired with CFRP was reduced comparing with that without repair. Based on the results, a fatigue life prediction method for a crack with CFRP was proposed.

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Multiple Steel Columns can absorb seismic energy by shear deformation of shear panel. Due to large shear deformation in the shear panel, however, the low cycle fatigue crack could occur at the welding joint of shear panel. In this study, a cyclic loading test of Multiple Steel Columns was simulated by finite element analysis. Further, prediction method for crack initiation and propagation of low cycle fatigue in a welding joint of shear panel was developed.

Authorship：Lead author   Language：English  

In welded steel structures, there are some cases when weld-lines exist close to each other. As an example in steel highway bridges in Japan, a vertical stiffener is connected to a web plate close to an end of a horizontal stiffener. In this case, stress concentrations due to each joint may be superposed, and consequently, fatigue strength of the stiffeners may become lower compared with typical welded joints. In this study, fatigue tests and finite element analyses were performed on plate girders where vertical and horizontal stiffeners attached with a small gap between them. The result revealed that the stress concentration at the end of the horizontal stiffener slightly varied with the distance between the stiffeners, resulting in small difference of the fatigue strength.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2208/jscejseee.71.315

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This study investigated fatigue strength evaluation methods based on the structural hot spot stress concept, focusing on a crack at a crossing between a longitudinal closed rib and a cross-beam (transverse rib) web cutout in an orthotropic steel bridge deck. The results indicated the possibility that the fatigue strength of the connection can be evaluated with the hot spot stress range. And also, it was revealed that the hot spot stress range hardly decreases with increasing of deck plate thickness and decreasing of transverse rib distance.

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Extremely low cycle fatigue, which is caused by large cyclic deformation with small number of loading repetition, is one of the main failure modes in steel structures during earthquake. In this study, crack propagation behaviour of structural steel in extremely low cycle fatigue region was evaluated based on a non-linear fracture mechanics parameter calculated by analyses. The results demonstrated that crack propagation rate in extremely low cycle fatigue region can be estimated by using cyclic J-integral.

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As a simple repair method for fatigue cracks in steel bridges, the resin injection method has been proposed. The method can decrease fatigue crack growth rate by injecting resin into a crack. In this study, the applicability of the method for cracks occurred by cyclic compressive loading was investigated by experiments and finite element analyses. The results revealed that the crack growth retardation can be expected even under the compressive loading when enough elastic modulus and infiltration of resin are achieved.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study proposed a local strain based fatigue strength evaluation method for deformed bars in low cycle fatigue region. Fatigue tests were conducted with the bars which have different yield strength and transverse rib shapes. The results indicated that low cycle fatigue strength of the deformed bars is almost the same regardless of the yield strength but it depends on the rib shapes. This is because strain concentration at the rib changes due to its shape. Finally, this study demonstrated that the fatigue strength of the bars with different rib shapes can be uniquely evaluated by considering local strain at the rib.

DOI： 10.11532/structcivil.61A.767

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This paper presents an assessment method for extremely low cycle fatigue cracks from corner joints in concrete-filled steel piers. Low cycle fatigue tests indicated that one of the main failure modes of concrete-filled steel piers are a fatigue crack from corner joints, which is caused by out-of-plane bending deformation of flange and web plates. In the previous study, authors had proposed extremely low cycle fatigue strength curves for the corner joints based on the effective notch strain approach. In this study, the proposed method was applied to the experiment of the concrete-filled piers and it is demonstrated that extremely low cycle fatigue life of the pier can be predicted by using the method.

DOI： 10.11532/structcivil.61A.662

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

The impact crack closure retrofit treatment (called ICR treatment) is a technique to delay or arrest fatigue crack growth and enhance residual fatigue life of weld joints including a crack. The treatment is carried out with an air tool to peen plate near the crack and to produce plastic deformation of the steel surface in order to close crack opening. In this study, several fatigue tests on weld joints were conducted under tensile or bending loads in order to verify the life extension effect by ICR treatment. Besides, the effect of the loading types to the life extension was analytically investigated.

DOI： 10.11532/structcivil.61A.627

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Reducing welding residual stress can improve fatigue strength of weld joints. Several techniques to reduce the welding residual stress have been developed and their benefits on fatigue strength have been confirmed by many fatigue tests. The test results also demonstrate that the benefit is influenced by mean stress and stress amplitude. In this study, with considering cyclic stress behavior at the cracking point, the influence of residual stress, the mean stress and the stress amplitude on fatigue strength improvement is discussed.

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Low cycle fatigue strengths of corner welded joints with single bevel groove welding were studied. Low cycle fatigue tests were performed with three types of specimens which have different sizes of weld root face. The test results indicated that the low cycle fatigue strength of the corner welded joints strongly depends on the weld root size. Then, the fatigue strength of the corner joints was evaluated based on the effective notch strain at the weld root tip which was calculated by elasto-plastic finite element analyses. A unique relationship between the effective notch strain and the fatigue life of the joint was observed regardless of the weld root size. Therefore, it was revealed that the effective notch strain approach is applicable to evaluate the low cycle fatigue strength of the corner welded joints.

DOI： 10.1007/s13296-014-3015-8

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One of the main failure modes of steel bridge piers is low cycle fatigue. In a concrete-filled steel pier with a box section, it has been reported that low cycle fatigue cracks are often initiated from longitudinal welds connecting flange and web plates (called corner joint) when it is subjected to large cyclic deformation. In this study, low cycle fatigue strengths of the corner joints were investigated. Low cycle fatigue tests were performed with corner joint specimens with different weld root sizes. Then, the fatigue strength of the corner joints was evaluated based on the effective notch strain at the root tip which was calculated by elasto-plastic finite element analyses. The results indicated a unique relationship between the effective notch strain range and the fatigue life of the joint regardless of the weld root size. Besides, the test results of the corner joints located in the same region as those of load-carrying cruciform joints. Therefore, it was demonstrated that the effective notch strain approach is applicable to evaluate the low cycle fatigue strength of welded joints regardless of the joint types.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue strength of overlap welded joints in which transverse fillet welds were provided was investigated under an out-of-plane bending condition. Fatigue test results demonstrated the joints were failed by weld toe cracks, and the fatigue strength was equal to that of non-load carrying cruciform joints. When intermittent fillet welds were provided, the fatigue strength was reduced, but it was properly evaluated by using the hot spot stress approach.

DOI： 10.11273/jssc.21.81_47

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, fatigue strength of welded joints using a newly developed steel called Steels for Bridge High Performance Structures (SBHS) was investigated.
Fatigue crack propagation tests with compact tension specimens were performed to clarify fatigue crack growth characteristic of materials. Then, fatigue strengths of welded joints using SBHS were investigated. These test results revealed that the fatigue performances of welded joints using SBHS are almost the same as those of conventional structural steels.

DOI： 10.11532/structcivil.60A.587

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue strength category of out-of-plane gusset welded joint was determined based on large number of previous fatigue tests and is categorized with gusset length. However, the variety of the joint size of specimens used in previous researches is very limited and the size is much smaller than the joints in large structures like steel bridges. In this study, stress analyses with out-of-plane gusset welded joint models having large variety of joint size like from small joint specimen to joint in steel bridges were conducted and size effect on fatigue strength was discussed. In addition, the fatigue strength of joint having large out-of-plane gusset is analytically evaluated.

DOI： 10.11532/structcivil.60A.651

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Weld joint with a cope hole has relatively low fatigue strength, since high stress concentration is generated due to local shear deformation inside the cope hole. In this study, fatigue strength improvement for the cope hole joint by burr grinding is investigated. I-section beams with cope holes, of which boxing weld toes were smoothly finished by burr grinding, were tested and analyzed in order to know the fatigue strength and the local stress behavior of the joint. Test and analysis results demonstrated that the benefit of grinding on fatigue strength improvement is relatively small when shear stress is largely applied to the cope hole detail.

DOI： 10.1007/s13296-013-4009-7

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Under seismic loadings, the main failure modes of steel bridge piers are local buckling and brittle fracture triggered by low cycle fatigue. In this study, the low cycle fatigue behavior of the steel pier in which concrete is filled for retrofitting against the local buckling was investigated experimentally and analytically. The low cycle fatigue tests on concrete filled steel pier specimens revealed that fatigue cracks occurring from corner welds caused final failure of the pier. Besides, strain behaviors around the cracking sites were revealed by elasto-plastic finite element analyses.

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This study revealed low cycle fatigue strength of deformed bars and proposed a strain based fatigue strength evaluation method based on fatigue tests and FE analyses. The low cycle fatigue strength of the material of deformed bars is equivalent to that of structural steels. The low cycle fatigue strength of a deformed bar depends on the shape of ribs, but can be evaluated by using the strain amplitude at the cracking site and fatigue strength curve for the material.

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Recently, a lot of fatigue cracks have been found in steel bridges in Japan. It is therefore urgent to develop a simple repairing and retrofitting method for such fatigue cracks. A new repair method named Impact Crack Closure Retrofit treatment (ICR treatment) was developed, which induces compressive residual stress and closes a crack by hammering around the crack. In this study, improvement of the method was investigated by finite element analyses and fatigue tests. As the result of the analysis, stress intensity factor of the crack treated by the ICR decreased. The test results also showed that fatigue life was extended by the ICR treatment under cyclic tensile load.

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For low cycle fatigue assessment of steel members, strain behavior in the member should be accurately estimated. In this study, the strain behaviors of steel bridge piers subjected to several types of long duration ground motions were investigated, and low cycle fatigue performances of the pier were assessed by a proposed strain based method. Parametric analyses with various geometry configurations of the pier were conducted. Nominal strain amplitudes in effective failure length of the pier were obtained by nonlinear dynamic analyses, and then fatigue damage index was calculated from the strain by using nominal strain based fatigue strength curves proposed for the piers.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, the fatigue performance on the welded joints of the newly developed steel called Steels for Bridge High Performance Structures (simply called SBHS) was investigated. In order to clarify the fatigue crack growth characteristic of the SBHS, the crack propagation tests were performed with compact tension type specimens. Then, the fatigue strengths of out-of-plane gusset welded joints and non-load-carrying cruciform welded joints of the SBHS were investigated. Plate girder specimens, in which gusset plates were attached on their webs, were also fabricated with the SBHS and tested. The fatigue test results revealed that the fatigue performances of the welded joints of the SBHS are almost the same as those of the conventional steel.

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A large number of fatigue cracks have been reported at the connection between longitudinal closed ribs and cross-beam webs in orthotropic steel decks because of high stress concentrations due to complicated local deformations of the rib and the web. In this study, the local stress behaviors around the weld end adjacent to the cross-beam cutout were analytically investigated. Finite element analyses were conducted by using a full scale model of an actual bridge, where plenty of cracks were detected around the cross-beam cutout, to investigate the deformation modes causing the cracks. Then, the effective cutout configurations to reduce the crack-inducing local stresses were investigated by comparing the local stress in different cutout types.

Language：English   Publishing type：Research paper (scientific journal)  

Fatigue strength category of out-of-plane gusset welded joint was determined based on large number of previous fatigue tests and is categorized with gusset length. However, the variety of the joint size of specimens used in previous researches is very limited and the size is much smaller than the joints in bridge structures. In this study, stress analyses with out-of-plane gusset welded joint models having large variety of joint size like from small joint specimen to joint in steel bridges were conducted, and existing fatigue test results of joint specimen and girder specimen with out-of-plane gusset weld joint were analyzed. From these analysis and survey, the following points are discussed.
(1) Change in stress (toe stress, hot spot stress and stress at the area adjacent to the boxing weld toe) with change in joint geometry not only of base plate thickness and gusset length but also base plate width and gusset height of out-of-plane gusset weld joint; In this part, size effect in fatigue strength and in toe stress concentration factor, relationship between toe stress and hot spot stress, and nominal stress evaluation were mainly discussed.
(2) Fatigue strength of out-of-plane gusset weld joint in bridge structures; In this part, using hot spot stress approach and existing fatigue test data, fatigue strength of large scale out-of-plane gusset weld joint was analytically evaluated.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Since a large number of fatigue cracks have been detected in steel bridges and its number is expected to increase more and more in the future, simple repair methods are strongly required. Repair by welding will be more cost efficient and shorten work period comparing with a conventional bolted splice method, because the weld repair requires no additional members. On the other hand, the weld repair has a possibility to induce weld defects, especially when applied in service condition. Vehicle loads generate cyclic deformation of members and opening and closing behaviour of cracks. In order to employ the weld repair in actual bridges, therefore, it is necessary to make clear appropriate weld repair conditions to achieve sound weld quality under cyclic loading.
In this study, experiments were performed to investigate weld repair quality in service condition. Specimens with a fictitious crack in their mid-width were repaired by arc-welding under cyclic loading. Several series of the tests were carried out with changing magnitude of root gap opening displacement, load frequency, welding position and groove geometry etc. After the repair welding, sections of the specimen were observed to detect weld cracks. From the observations in some specimens, the weld crack was detected in weld deposit. The experiments demonstrated that occurrence of the weld crack under the cyclic loading strongly depends on the magnitude of the root gap opening displacement and the load frequency.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

It is well known that reduction of tensile residual stress around cracking sites is effective to improve fatigue strength of welded joints. Several methods to improve the fatigue strength, such as burr grinding, peening, and TIG-dressing techniques, have been proposed and applied to actual steel structures. Recently, a new welding material called low-temperature transformation welding material (LTT), which can induce compressive residual stress has been developed and examined about its applicability.
In this study, thermo-elasto-plastic analyses were carried out to clarify fatigue strength improvement mechanism when applying LTT from the view point of introduction of compressive residual stress. Residual stress distribution in an out-of-plane gusset welded joint when applying LTT or a conventional welding wire was identified. In the analyses, in order to simulate actual welding procedures, heat was applied with moving its location. The analysis results indicated that compressive residual stress was introduced around a weld toe in case that LTT was used for welding. As for a weld root, it was revealed that tensile residual stress is deceased by LTT in case that LTT was used for first layer and a conventional material was the second layer.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

A large number of fatigue cracks have been reported in orthotropic steel decks, especially at the connection between longitudinal closed ribs and cross-beam webs, because of high stress concentration due to complicated local deformations of the rib and the web. In this study, the local stress characteristics around the weld end adjacent to the cross-beam cutout were analytically investigated. Finite element analyses were conducted by using a full scale model of an actual bridge, where plenty of cracks were detected around the cross-beam cutout, to figure out the deformation modes causing the cracks. Then, the effective cutout configurations to mitigate the crack-inducing deformations were investigated by comparing the local stress behaviors in different cutout types.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Connections between a bracket flange and a main girder are fabricated by full penetration welds. Generally, the joints at the lower flange of the bracket are subjected to cyclic compressive stresses. It means that there is a possibility to change the welding method between the lower flange of the bracket and the main girder into partial joint penetration in terms of fatigue strength under compression. In this study, the fatigue strength of the base joints of the brackets was examined. The test results revealed that the joints have enough fatigue strength under the compressive stress even though partial joint penetration is applied there.

DOI： 10.11273/jssc.20.77_15

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

A large number of fatigue cracks have been found in orthotropic steel decks, especially at the connection between longitudinal closed ribs and cross-beam webs. In this study, local stress characteristics around the weld end adjacent to the cross-beam cutout, which lead to fatigue damage, were analytically evaluated. Finite element analyses were first conducted by using a full scale model of the actual bridge, where plenty of cracks were detected around the cross-beam cutout, to figure out the deformation modes causing the cracks. Then, the cutout shapes which have influence on reducing the crack-inducing deformations were investigated by comparing the local stresses in different cutout types.

DOI： 10.11532/structcivil.59A.781

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During the Hyogo-ken Nanbu Earthquake in 1995, two types of failure modes were observed in steel bridge piers; one is a local buckling and the other is a brittle fracture triggered by a low cycle fatigue. A large number of researches on the local buckling have conducted after the earthquake and proposed several methods to prevent the local buckling of the pier, such as filling concrete in the steel pier. The concrete-filled steel pier has high deformation capacity since the internal concrete can constrain local deformation of flange and web plates, and even with an origination of the buckling, the concrete can restrain its growth. When the pier endures large cyclic plastic deformations, the low cycle fatigue will be an issue. There are, however, few researches which investigating the concrete-filled steel pier in terms of the low cycle fatigue. In this study, the low cycle fatigue behavior of the concrete-filled steel pier was experimentally investigated. The concrete-filled pier specimens were fabricated and tested under large cyclic displacement. The test results revealed the crack initiation and propagation behavior in the concrete-filled pier and the effect of the axial loading on the low cycle fatigue strength of the pier.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The authors previously proposed a fatigue strength evaluation method based on the effective notch strain concept and reported that the fatigue strength of load-carrying cruciform joints can be assessed by the effective notch strain regardless of the mismatching and the incomplete penetration ratio from the low- to the high-cycle fatigue region. However, in applications to actual structures, this method has difficulty in modeling and analysis because it requires extremely fine meshing around the welds. Therefore, in this paper, an estimation method of the effective notch strain from nominal strain is proposed.

DOI： 10.1016/j.ijfatigue.2012.01.021

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study examined the applicability of the effective notch concept to the low- and high-cycle fatigue regions for load-carrying cruciform joints. Low- and high-cycle fatigue tests were performed on specimens with various strength matching conditions and incomplete penetration ratio. Fatigue test results revealed that the effect of strength matching becomes obvious in low cycle fatigue region, while, it was negligible in high cycle fatigue region. Different failure patterns can be observed for specimen with different strength mismatching condition in the low cycle fatigue tests. Elasto-plastic finite element analyses were performed under the same conditions as the experiments. The effective notch strains were determined at the crack initiation points. A unique relationship between effective notch strain and fatigue life was obtained regardless of matching condition and incomplete penetration ratio.

DOI： 10.1016/j.ijfatigue.2011.12.016

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigated the low- and high-cycle fatigue strength of load-carrying cruciform joints containing incomplete penetration and strength mismatch between base metal and weld deposit, and proposed an assessment method based on the local approach. Low- and high-cycle fatigue tests were performed on specimens with varying mismatch and sizes of incomplete penetration. The test results revealed that the crack initiation life was extremely small for this type of joint. In fractographs, dimples observed around the crack initiation site provided evidence of ductile crack propagation. Also, it was found that strength mismatch had a negligible effect on the high-cycle fatigue strength but that under-matching reduced the low-cycle fatigue region. However, a unique relationship was found between local strain around a weld root tip calculated by elasto-plastic finite element analysis and both the low- and high-cycle fatigue life of the specimen.

DOI： 10.1007/BF03321357

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In Japan, more than 5000 steel piers exist in elevated bridges in urban area, which play an important part in transportation. The Kobe Earthquake in 1995 caused enormous damage to steel bridge piers, such as collapse, buckling and brittle fracture. It has been revealed two types of main failure modes in the pier, which are local buckling and low cycle fatigue. Therefore, both local buckling and low cycle fatigue are key issues to prevent the piers from damaging and also to secure the public safety.
In this study, we focused on the low cycle fatigue failure occurring from base joints of the pier. The low cycle fatigue assessment method based on the nominal strain approach was proposed for the base joints of the pier. The nominal strain can be simply calculated by finite element analysis with a beam element. Fatigue tests with steel pier specimens demonstrated that the proposed fatigue assessment method could provide fatigue life estimation with enough accuracy.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

When repairing fatigue damage by welding, the fatigue strength of cracked joints needs to be restored and also improved to prevent the reoccurrence of cracks. In this study, a new welding wire called low temperature transformation (LTT) welding wire, which enables the introduction of compressive residual stresses around a weld bead and the reduction of weld deformation, was applied to the weld repair. Its applicability was investigated by fatigue tests with compact tension specimens and a plate girder specimen. The compact tension specimens revealed that compressive residual stresses introduced by LTT welding wire have positive effects on crack initiation and propagation behaviour. The plate girder specimen indicated that the fatigue lives of cracked joints are restored and also improved by weld repair with LTT welding wire. Therefore, weld repair with LTT welding wire makes it possible to improve the fatigue strength of cracked joints.

DOI： 10.1007/BF03321334

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study proposed a simple method for estimating local stresses in as-welded joints and established a fatigue assessment method by using the estimated local stress. In this method, the local stress at the as-welded toe is estimated from the stress at the weld toe finished by grinding, where the stress can be measured by strain gauges. Fatigue tests and finite element analyses were conducted with out-of-plane gusset welded joints in as-welded and finished conditions. Based on the results, the local stress at the as-welded toe was correlated with the stress at the finished groove. It was concluded that the fatigue strength of the as-welded joints can be evaluated by using the local stress estimated by the proposed method.

DOI： 10.11532/structcivil.58A.647

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The fatigue strengths of load-carrying cruciform joints with incomplete penetration and a strength mismatch between the base metal and the deposit metal were studied. Low- and high-cycle fatigue tests were performed on specimens with five matching conditions and two sizes of incomplete penetration. The test results revealed that the failure life was governed by crack propagation in both the low-cycle and high-cycle fatigue regions, and the crack propagation paths differed according to the matching and loading conditions. In addition, the fatigue strengths of the joints were compared for the degree of strength matching and the size of incomplete penetration in the low- and high-cycle fatigue regions. It was found that the effect of strength matching on the fatigue strength is negligible in the high-cycle fatigue region, but it becomes large in the low-cycle fatigue region and significantly reduces the fatigue life of the specimen in the under-matched joints.

DOI： 10.1007/s13296-011-4002-y

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, an evaluation method for the scatter in fatigue life of welded joints was developed by applying linear elastic fracture mechanics and Monte-Carlo simulation technique. Fatigue crack propagation analysis, of which initial conditions were determined by the Monte-Carlo simulation, was performed on non-load-carrying cruciform welded joints and out-of-plane gusset welded joints. It is demonstrated that the estimated fatigue life by the proposed method distributes around the similar region as the fatigue test data. Consequently, the results indicate the possibility that the fatigue strength curves of welded joints can be established by incorporating a small number of fatigue test data with the proposed method.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

This study investigated the effect of extremely low cycle fatigue strength improvements on steel bridge piers by weld toe grinding. Low cycle fatigue tests on steel pier specimen of which base joints were finished by grinding were performed. Test results revealed that the fatigue strength of the pier was improved by the toe grinding in comparison to those in as-welded condition. Local strains around finished weld toe were analyzed by finite element analysis. It was confirmed that it is possible to estimate the extremely low cycle fatigue life by using local strain and suggested fatigue strength curves.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The number of fatigue cracks at in steel bridges is increasing, while it is difficult to repair all cracks just after detecting them. In this study, a simple repair method for cracks in steel bridges was proposed. This method can retard or arrest the crack growth by injecting hardening material into the crack to restrain its closure. To verify the applicability of the proposed method, fatigue tests under plate bending were conducted on out-of-plane gusset welded joints repaired by the hardening material injection. It was indicated that the effect of the crack growth retardation depends on when injecting the hardening material into the crack, and that the proposed method can extend the fatigue life regardless of the stress ratio.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Local stress approach has been proposed as the fatigue strength evaluation method of welded joints without any classifications by the joint types and verified in the past studies. Generally, since it is difficult to directly measure the local stresses at the crack initiation point, ex. weld toe, the stress analysis helps us to estimate them, which requires establishing a model with weld toe geometry in fine mesh and great amounts of time. Thus, this study proposed the simple method for estimating the local stress in as-welded joints. In this method, the local stress at the as-welded toe is estimated from the stress at the toe finished by the grinding technique, where the strain gauge measurement is applicable. Fatigue tests and finite element analyses were conducted with out-of-plane gusset welded joints of as-welded and finished condition, respectively. Based on the results, the correlation of the local stress in the as-welded and finished joints was established. Consequently, it was demonstrated that the fatigue strength of the as-welded joints can be evaluated by using the local stress estimated by the proposed method.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Low cycle fatigue strengths of load-carrying cruciform joints with incomplete penetration and strength under-match between base metal and deposit metal were studied. Fatigue tests were performed on specimens with five matching conditions and two sizes of incomplete penetration. Test results revealed that failure life was governed by crack propagation, and that crack propagation paths differed by matching and loading conditions. Also, fatigue strength of the joints was compared regarding the degree of strength matching and size of incomplete penetration. It was found that the effect of the strength matching on the fatigue strength becomes large in low cycle fatigue region by significantly reducing fatigue life of the specimen in the case of under-match joints.

DOI： 10.2207/qjjws.29.162

Language：English   Publishing type：Research paper (scientific journal)  

In this study, the validity of the assumption made for the crack propagation analysis, that fatigue crack propagates in the plane perpendicular to the loading direction, was discussed. The comparison of stress intensity factor obtained by the conventional method and analytical codes were made. In addition, fatigue tests with out-of-plane gusset welded joints were carried out and the front profile of fatigue crack originated in out-of-plane gusset welded joint was closely observed.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigated the effect of the extremely low cycle fatigue strength improvement on steel pier by weld toe grinding. Low cycle fatigue tests on the steel pier specimens, of which base joints were ground smoothly, were performed, and their results were compared with those of the specimens under as-welded condition. It was revealed that the burr grinding is applicable to increase the fatigue strength in extremely low cycle fatigue region. Local strain around finished weld toe was analyzed by finite element analysis. It was confirmed that it is possible to estimate the extremely low cycle fatigue life by using local strain at a crack initiation point and proposed fatigue strength curves. Moreover appropriate grinding areas were considered by the analysis.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, an evaluation method for the scatter in the fatigue life of the welded joints was developed with employing LEFM and Monte-Carlo simulation technique. Fatigue crack propagation analysis, of which initial conditions were determined by the Monte-Carlo simulation, was performed on non-load-carrying cruciform welded joints and out-of-plane gusset welded joints. It was demonstrated that the estimated fatigue life by the proposed method distributes around the similar region as the fatigue test data. Consequently, the results indicate the possibility that the fatigue strength curves of welded joints can be established by incorporating a small number of fatigue test data with the proposed method.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Local stress approach has been proposed and verified in past studies as the fatigue strength evaluation method of welded joints without any classifications by the joint types. Even though the local stress approach is valid for assessing the fatigue life of the joints, it is difficult to measure the local stresses at the as-welded toe directly. The stress analysis makes it possible to estimate the local stresses, which requires establishing a model with weld toe geometry in fine mesh. This study proposed the simple estimation method for the local stress in as-welded joints. In this method, the local stress at as-welded toe is estimated from the stress measured at the toe finished by the grinding technique. Fatigue tests and finite element analyses were conducted with out-of-plane gusset welded joints in as-welded and finished condition, respectively. Based on the analysis results, a correlation between the stress at the finished groove and the local stress at the as-welded toe was established. Then, fatigue test results verified that the fatigue strength of out-of-plane welded joints can be uniformly evaluated by using proposed local stress based fatigue assessment method.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In present, the upper and lower flanges of outrigger bracket are attached to main girder by using full penetration welding. However, the full penetration weld of lower flange might be mainly subjected compressive stress by live load, and also the generated stress level is relatively low. This study investigated the possibility to change the full penetration weld joint of lower flange to partial penetration weld joint considering fatigue strength. In this study, fatigue test was carried out on partial penetration welded cruciform joint under compressive cyclic load which simulates new welding joint of the lower flange. Moreover, finite element analysis was performed to identify the stress distribution around the welded joint outrigger bracket. The results revealed the possibility to change the full penetration welds of lower flange to partial penetration welds.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Load carrying cruciform joints with incomplete penetration have two fatigue cracking points which are the weld root and toe. The crack initiation point in high cycle fatigue region depends on only weld leg size and incomplete penetration ratio, while the strength mis-matching between the base and deposit metal becomes important when considering it in low cycle fatigue region. Elasto-plastic analysis was performed on load carrying cruciform joints regarding the size of weld leg and incomplete penetration, and strength matching. The effective notch was assigned at the weld root and toe, and the strains around both notches were compared. It was demonstrated that the cracking points estimated from the analysis agreed with the experimental results.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study newly defined effective notch strain and examined its applicability in elastic and elasto-plastic condition for load carrying cruciform welded joints. Low and high cycle fatigue tests were performed on specimens with different strength matching conditions and incomplete penetration sizes. To calculate the effective notch strain of the specimen, elasto-plastic finite element analyses were performed under the same condition as experiments. The unique relation between the effective notch strain and fatigue life can be obtained regardless of the matching condition and incomplete penetration size. Furthermore, the simple method for estimating effective notch strain was proposed and verified by the experiments.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Fatigue behaviors of load-carrying cruciform joints containing incomplete penetration and strength under-matching between base metal and weld deposit were studied. Low and high cycle fatigue tests were performed on specimens with five matching conditions and two sizes of incomplete penetration. Observation of the specimens revealed that crack propagation paths differ by low and high cycle loading conditions and that failure life was dominated by crack propagation. Besides, it was found that the effect of the strength under matching on the fatigue strength becomes large in low cycle fatigue region by significantly reducing fatigue life of the specimen. Moreover, local strain obtained from analysis model can be governing parameter to fatigue life of specimens.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Previous research suggested that driver's reaction during earthquake, which is responsible for driving safety, is related to velocity response of bridge deck. To reduce the velocity response of the deck, conventional devices like rubber bearings, base isolators and dampers system are employed. Analytical results reveals that rubber bearings, while more commonly used than dampers, cannot not reduce velocity response even though they can be effective in controlling strain response of steel bents.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

The weld repair requires no additional member such as splice plates, therefore it will be more cost efficient and shorten the work period comparing with the conventional bolted repair method. However, the weld repair has possibility to introduce weld defects or residual deformation which may reduce the fatigue strength of the repaired joints. Besides, even though fatigue cracked joints are restored to the initial condition with sound weld repairs, the fatigue crack will reoccur in the repaired joint, because the fatigue strength of cracked joints is low in most of the cases.
In this study, a new welding material named low temperature transformation (LTT) welding material, which enables to introduce compressive residual stress in the vicinity of the weld bead and reduce weld deformation, was applied to the weld repair. The applicability of the LTT welding material to the weld repair was investigated by the fatigue tests with compact tension specimens and a steel girder specimen.

DOI： 10.2208/jsceja.66.836

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigates the applicability of local approach to assess the fatigue strength of load carrying cruciform joints containing incomplete penetration and strength mismatching. Low and high cycle fatigue tests were conducted. Test results indicate that the effect of the strength mismatch on the fatigue strength is negligibly small in high cycle fatigue region but becomes large in low cycle fatigue region. Elasto-plastic FE analysis was performed, where the concept of effective notch was assigned at weld root tip. Different types of notch shapes were investigated. It is clear that local strain obtained from FE model can be used to arrange fatigue strength of load carrying cruciform joints. A unique curve can be established from low to high cycle fatigue regions.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study investigated effects of incomplete penetration and strength mismatch between base metal and weld deposit on fatigue strength of load-carrying cruciform welded joints. Low and high cycle fatigue tests were performed on specimens with changing matching conditions and sizes of in-complete penetration. Test results revealed that fatigue life was dominated by crack propagation, and that crack propagation directions vary according to strength matching and loading conditions. In fractographs, dimples were observed around the crack initiation point which produces an evidence of ductile crack propagation. Also, it was found that the effect of the strength under matching, in which yield strength of weld deposit is lower than that of base metal, on the fatigue strength is negligibly small in high cycle fatigue region but becomes large in low cycle fatigue region by significantly reducing fatigue life of the joints.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The weld repair requires no additional member such as splice plates, therefore it will be more cost efficient and shorten the work period comparing with the conventional bolted splice method. However, the weld repair has possibility to induce weld defects or residual deformation which may reduce the fatigue strength of the repaired joints. Besides, even though fatigue cracked joints are restored to the initial condition with sound weld repairs, cracks will reoccur in the repaired part, because the fatigue strength of cracked joints is originally low in most of the cases. In this study, a new welding wire named low temperature transformation (LTT) welding wire, which enables to introduce compressive residual stress in the vicinity of the weld bead and reduce weld deformation, was applied to the weld repair. The applicability of LTT welding wire to the weld repair was investigated by the fatigue tests with compact tension specimens and a plate girder specimen.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This study presents a newly developed web database for fatigue damage and repairing cases. Authors use a new platform “PukiWiki" for the web data base instead of html documents. The new platform includes two advantages. One is the editing language, the simple structure of which enhances easy updating; hence, it is possible for the researchers and engineers who are unfamiliar with editing a web page to use it. Another advantage is multi-editor system. Authorized researchers and engineers can edit and update the web at any time from anywhere; that is, we can skip the process of collecting, editing and updating information by a web administrator. It means the platform enables to less laborious editing and quick updating. We expect to enlarge new information on the web; also, expand professional judgment and outlooks to the world from the new database.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Ultrasonic tip echo is scattered wave which radiates all direction from the sharp tip of reflection source such as fatigue cracks. Tip echo has been utilized for sizing defects as so-called “tip echo method" and also may apply to identify fatigue cracks from other defects. In this study, radiation characteristics of the tip echo were experimentally examined. A linear phased array ultrasonic testing system was applied to send and receive ultrasonic waves in various directions. The experimental results demonstrated the relationship between incident wave directions and directivity of the tip echo. Besides, the tip echo method was applied to a fatigue crack in a welded steel plate, and damping of echoes due to fatigue crack closure was indicated.

DOI： 10.2208/jsceja.66.219

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to guess the behavior of member causing fatigue damage at joint part in a railway truss bridge, experimental measurements in actual bridge was conducted by using wireless acceleration sensor devices and strain gauge. The grobal behavior of member, causing the fatigue damage when train passed through the target panel point, was verified based on the local strain data from strain gauges and acceleration data from wireless sensors. Finally, from the measurements, a countermeasure for the prospective fatigue crack was suggested.

DOI： 10.11532/structcivil.56A.671

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, fatigue behavior of load-carrying cruciform joints with incomplete penetrations under cyclic plastic strains, corresponding to the fatigue life is less than hundreds cycles, was experimentally investigated. In all specimens, fatigue cracks initiated from the weld root and propagated into the weld deposit. Crack initiation life was rather small compared with crack propagation life. This means that the propagation life is dominant in the fatigue life of the joints. Fracture surfaces under cyclic plastic strains contained dimples, which can produce an evidence of ductile crack propagation.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Steel bridge piers are often used for elevated highway bridges. The Hanshin-Awaji earthquake in 1995 revealed two types of failure mode in the pier, which are local buckling and low cycle fatigue. However, researches on low cycle fatigue of civil structures are limited, and design methods have not been established yet.
In this study, low cycle fatigue strength curves for base joints of the steel pier based on nominal strain, which can be calculated by finite element analysis with a beam element, were proposed. Fatigue tests with steel pier specimens demonstrated that the proposed fatigue strength curves could provide fatigue life estimation with enough accuracy.

DOI： 10.11273/jssc.16.64_21

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The improvement of extremely low cycle fatigue strength of welded joints by TIG dressing and burr grinding was investigated. The weld toes of T-shape welded joints were improved by TIG dressing or burr grinding and tested under displacement control conditions. The crack initiation life of finished specimens was at least threefold longer than that of as-welded specimens. There was no clear difference in improvement between TIG dressing and burr grinding. We also analysed the local strain around the cracking point by finite element analysis, and performed local strain-based fatigue assessment. The results indicated that extremely low cycle fatigue strength of the joints improved by TIG dressing and burr grinding can be assessed by evaluating the local strain and referring to the extremely low cycle fatigue strength curve.

DOI： 10.1007/BF03321135

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Fatigue crack propagation simulations on T-shape welded joints were carried out. Main plate of the joint was supported at ends and tensile and bending loads were applied to an attached rib. An initial crack of 0.5 mm in length was given at weld toe on the main plate. Five kinds of stresses, i.e. nominal bending stress, membrane stress and average shear stress in the main plate, nominal bending stress and membrane stress in the attached rib, were picked up as parameters. With changing these parameters, the crack propagation simulation was performed. Simulation results demonstrated that the crack direction at the beginning was influenced by the parameters, particularly the average shear stress in the main plate. These results were supported by fatigue test results conducted under the same conditions as the simulation. Finally, the relationship of the average shear stress and the crack direction at the beginning were presented.

Language：English   Publishing type：Research paper (scientific journal)  

The purpose of this study is to evaluate the fatigue strength of load carrying cruciform welded joints which contain incomplete penetration in both high and low cycle fatigue regions. Cyclic loading experiment was carried out in this study, and failure surfaces were investigated in order to verify the crack propagation and initiation point.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In this paper, fatigue strength of welded joints with incomplete penetrations was experimentally investigated overall from low-cycle to high-cycle fatigue regions, corresponding to the fatigue life is from tens cycles to millions cycles. Fatigue tests on load-carrying cruciform joints containing root discontinuities were carried out. In all specimens, fatigue cracks initiated from the weld root and propagated into the weld metal. Fracture surfaces of the specimen were observed in order to verify the crack initiation point and propagation behavior.

Language：English   Publishing type：Research paper (scientific journal)  

The purpose of this research is to guess the behavior of member causing fatigue damage at joint part in Railway Truss Bridge using wireless acceleration sensor devices and local strain measurement, and to suggest the countermeasure for the prospective fatigue crack. In this paper, the experimental measurement in actual bridge was conducted, then the behavior of member causing the fatigue damage when train passed through the target panel point was verified by the local strain data from strain gauge and acceleration data from wireless sensor. Finally, from the measurement results, the countermeasure is suggested.

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, fatigue crack propagation analysis on T-shape welded joints under out-of-plane plate bending was carried out. Main plate of the joint was supported at the ends, and tensile and bending loads were applied to an attached rib. We picked up five kinds of stresses as parameters, i.e. nominal bending stress, membrane stress and average shear stress in the main plate and nominal bending stress and membrane stress in the attached rib. We performed the analysis with changing these parameters and investigated the crack propagation path. The analysis results indicated that the crack angle at the beginning was influenced by these parameters, particularly the average shear stress in the main plate. These results were verified by fatigue tests conducted in the same conditions as the analysis. Finally, we presented the correlation between the average shear stress in the main plate and the crack angle at the beginning.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Tip echo is scattered wave which radiates all direction from the sharp tip of reflection source such as fatigue cracks. Tip echo has been utilized for sizing defects as tip echo method and also may apply to identify fatigue cracks from other defects. The radiation characteristics of tip echo were examined experimentally and the relationship between incident wave directions and directivity of echo and dumping of echo due to fatigue crack closure were shown. The steering and focusing functions of linear phased array ultrasonic testing system was applied to send waves to the tip of crack with various angles and to receive echo waves from various directions. Then, the tip echo method was applied to a crack to grasp crack tip opening and closing behaviour in the residual stress field.

Language：English   Publishing type：Research paper (scientific journal)  

In this study, we analyzed the local strain around the cracking point of the finished joint and the as-welded joint by FEA, and demonstrated that the local strain could be affected by the toe geometry parameters, such as radius, depth of the groove, and the main plate thickness. Then, we presented an example way to determine the desirable shape of the finished zone for satisfying the fatigue performance requirement of the welded joint.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this study, fatigue crack propagation simulations in steel girder bridges were conducted by ZENCRACK, which is a commercial software for three dimensional crack propagation analysis based on fracture mechanics. A steel bridge with three I-girders was employed and modeled in detail. It was confirmed that the crack propagation simulation can be a beneficial method to investigate the changes on structural behavior of the bridge due to crack propagation and identify the serious cracks for the bridge.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In the Great Hanshin Awaji Earthquake (1995), steel bridge piers were damaged by extremely low cycle fatigue, which has raised concerns about the seismic performance of the piers. However, researches on extremely low cycle fatigue strength of structural steel members have been limited and no design guidelines have been established for bridge structures. The authors have already conducted a series of researches on extremely low cycle fatigue strength of structural steel members and proposed a simple assessment method for extremely low cycle fatigue strength of the steel bridge piers. In this study, steel pier specimens were fabricated and tested under large cyclic deformation, and the proposed assessment method was verified by the test results.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, the improvement of extremely low cycle fatigue strength by toe finishing was investigated. T-shape welded joints, which are in as-welded, TIG dressed or burr ground condition, were tested under displacement control conditions. The test results indicated that crack initiation lives of finished specimens were much longer than those of as-welded specimens. Between TIG dressing and burr grinding, no clear difference on improvement was observed. We also performed elasto-plastic finite element analyses to calculate local strain around the cracking point, and assessed the fatigue strength of the finished specimen based on the local strain. The results demonstrated that the fatigue strength of TIG dressed and burr ground joints can be reasonably assessed using the local strain at the cracking point and the extremely low cycle fatigue strength curves.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, fatigue crack propagation analyses on T-shape welded joints subjected to plate bending were carried out. We picked up five kinds of stresses as parameters, i.e. nominal bending stress, membrane stress and average shear stress in the main plate, nominal bending stress and membrane stress in the attached rib. We analyzed the crack propagation path with changing these parameters. Analysis results indicated that the crack angle at the beginning was influenced by these parameters, especially the average shear stress in the main plate. These results were supported by fatigue test results conducted on T-shape welded joints with the same conditions used in the analysis. Finally, we presented the relationship of the average shear stress and the crack angle at the beginning.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The improvement of extremely low cycle fatigue strength of welded joints by TIG dressing and burr grinding was investigated. The weld toes of T-shape welded joints were improved by TIG dressing or burr grinding and tested under displacement control conditions. The crack initiation life of finished specimens was at least threefold longer than that of as-welded specimens. There was no clear difference in improvement between TIG dressing and burr grinding. We also analysed the local strain around the cracking point by finite element analysis, and performed local strain-based fatigue assessment. The results indicated that extremely low cycle fatigue strength of the joints improved by TIG dressing and burr grinding can be assessed by evaluating the local strain and referring to the extremely low cycle fatigue strength curve.

Language：English   Publishing type：Research paper (scientific journal)  

This paper presents the results of un-stiffened cantilever column subjected to incremental or constant amplitude cyclic loading. The objectives of this study are to investigate the extremely low cycle fatigue life of the column and verify the proposed strain based approach. During the test, fatigue cracks initiated from the weld toe at the corner and propagated along the weld toe. Finally, the column ruptured without a local buckling. The failure of low cycle fatigue induced by large cyclic deformation has been elucidated. In a further step, the crack initiation life was estimated based on the local strain by proposed simple approach. It is indicated that correlation between the test result and the estimated life was good enough.

DOI： 10.2208/jsceja.64.288

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Recently, a lot of fatigue cracks have occurred at some members in steel bridges. Besides, steel bridge have a possibility that the cracks would be initiated in future resulting the increase of their ages. In order to repair and retrofit the cracks properly, it is important to predict how they will propagate and to specify why they were initiated. In this paper, fatigue crack propagation analysis of welded joint was carried out with ZENCRACK software, and some factors which can be influence on the crack propagation process were investigated.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

A number of transportation agencies throughout the world have adopted and implemented the bridge management system with advanced asset management decision-making capabilities. However, there are still significant room for improvement in the information and data upon which the bridge management systems are based, and on the results and decision-making that occurs based on the output of these systems. In order to address some of gaps in knowledge, the Federal Highway Administration (FHWA) of the U.S. Department of Transportation is initiating a Long-Term Bridge Performance (LTBP) program in 2006. In this paper, we will introduce the recent bridge management systems and the LTBP program in the States.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Several steel piers suffered low cycle fatigue damage in the Great Hanshin Earthquake (1995), which raises concerns about their performance in future earthquakes. However, researches on the low cycle fatigue of civil structures in extremely large strain region, corresponding to a strain magnitude of more than 10% and a fatigue life of less than ten cycles, are limited and design guidelines have not been established. In order to provide the benchmark data for extremely low cycle fatigue assessment, thick-walled steel piers with box section were fabricated and subjected to incremental or constant amplitude cyclic loading. During the test, fatigue cracks were initiated from weld toe at the corner. With the loading repetition, the cracks propagated along the weld toe. Finally, oblique cracks formed both in flange and web plate, and the pier was ruptured without local buckling. Although the cracks occurred at relatively early stage of the test, the loading capacity hardly decreased before failure. In other words, the crack propagation occupied the most part of life of the specimen. After the test, the low cycle fatigue strength of steel pier specimens was assessed based on the strain near the crack initiation point.

Language：English   Publishing type：Research paper (scientific journal)  

In a seismic event, steel piers may undergo large strain fluctuations of typically one to tens of cycles. That will possibly result in fracture of base end joints or beam-column joints, namely extremely low cycle fatigue. In this paper, thick walled un-stiffened box section steel piers subjected to incremental cyclic loading are analyzed by a three-dimensional elastic-plastic finite element analysis with shell and solid elements to investigate the behavior of local strain at weld toe. Several parameters, such as width thickness ratio, slenderness ratio, weld toe radius and axial loading, are taken into account. From engineering point of view, it is preferable to employ a simple parameter reflecting the local strain behavior. Here, the local strain is correlated to nominal strain, which is average strain along effective failure length by fiber model. Finally, a simple approach to extremely low cycle fatigue assessment is proposed and applied to test results.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

As a method to predict fatigue strength of welded joints in extremely low cycle fatigue region, local strain based approach was discussed in this paper. Low cycle fatigue tests were conducted on T-shaped welded joints in order to find the crack initiation point and to obtain the fatigue life. On the other hand, local strain field around welded toe, where fatigue cracks were formed in fatigue tests, was analyzed by elasto-plastic finite element analysis, and the local strain amplitude at the cracking point was quantified. Based on the fatigue life obtained by fatigue test and the local strain amplitude by FEA, fatigue test results were compared with the low cycle fatigue strength curve, i.e., strain versus fatigue-life diagram. Test data were consistent with the strength curve. Consequently, it was demonstrated the fatigue assessment method based on local strain approach is available to predict the fatigue strength of welded joints even in extremely large strain region.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Miner's rule has been accepted as a simple and effective method for predicting the low cycle fatigue life under variable strain amplitude. However, in an extremely large strain field, corresponding to the fatigue life of less than 10 cycles, the accuracy of Miner's rule has not been verified. In this study, low cycle fatigue tests under variable strain amplitude in an extremely large strain field were conducted with a newly developed testing system. Miner's rule always predicted a longer fatigue life than the observed life. A simple model introducing the damage mechanics concept was proposed and its validity was examined as another method for predicting low cycle fatigue
life.

DOI： 10.1016/j.ijfatigue.2006.08.001

Language：English   Publishing type：Research paper (scientific journal)  

Several T-shaped welded joint models are analyzed by finite element method for low cycle fatigue assessment in this paper. Joint is subjected to random loading blocks and strain history is counted by range pair-range counting method. Endeavor is exerted to correlate local strain range of coarse FE model that ignores the weld toe profile with strain range obtained by fine material properties and loading pattern are also taken into account. After that, strain range factor while others' effects are insignificant. At last, proposed approach is introduced to the analysis of T shaped welded joint test. It turns out simple and convenient in low cycle fatigue assessment since cumbersome modeling of weld local profile becomes not necessary.

DOI： 10.11273/jssc1994.13.52_73

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Miner's rule has been accepted as a simple and effective idea for predicting the low cycle fatigue life under variable strain amplitude. However, in an extremely large strain field, corresponding to the fatigue life of less than ten cycles, the accuracy of Miner's rule has not been verified. In this study, low cycle fatigue tests under variable strain amplitude in an extremely large strain field were conducted with a newly developed testing system. Since test results indicated that Miner's rule always predicted a longer fatigue life than the observed life, we proposed a modified life prediction model introducing the damage mechanics concept and investigated its validity.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to prevent the low cycle fatigue damage in existing steel bridge members as observed in the Hanshin-Awaji Great Earthquake in 1995, improving the fatigue strength of welded joints can be a realistic option. In this study, the effect of TIG dressing, which is one of the ways to finish the weld toe, was investigated. As a specimen, T-shape welded joint specimens were employed. Some specimens were finished with TIG dressing, and the others were left as-welded. The low cycle fatigue tests were conducted for these specimens in the same conditions. The test results indicated that TIG dressing made the low cycle fatigue life of welded joints much longer.

DOI： 10.11273/jssc1994.13.50_27

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

As an estimation method of low cycle fatigue strength of welded joint in extremely large strain field, fatigue assessment method based on peak strain approach was verified. T-shape welded joints were employed for the low cycle fatigue test. The local strain field around welded portion and the peak strain at the cracked point was analyzed by elasto-plastic finite element method. The relationship between the peak strain and the fatigue life was consistent with the fatigue strength curve proposed by the authors. Consequently, it was demonstrated the fatigue assessment method based on peak strain approach was available even in extremely large strain region.

DOI： 10.2208/jsceja.62.101

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

As an estimation method of fatigue strength of welded joint in extremely low cycle fatigue region, peak strain based fatigue assessment method was verified. T-shape welded joints were employed for the verification test. The specimen was analyzed by elasto-plastic finite element method in order to quantify the local strain field around welded portion and the peak strain at the cracked point. On the other hand, fatigue life of the specimen was experimentally obtained by low cycle fatigue tests. The relationship between the peak strain and the fatigue life was consistent with the fatigue strength curve proposed by the authors. Consequently, it was demonstrated that the fatigue assessment method by peak strain approach was available even in extremely low cycle fatigue region.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Extensive experiments on low cycle fatigue for plain steel material have been conducted and obtained some important results. However there are few studies for extremely low cycle fatigue, corresponding to the strain more than 0.10.
In this study, a new low cycle fatigue testing system, in which a steel plate specimen was subjected to bending deformation and the image technique was introduced to measure the strains in the specimen, was developed. The testing system has enabled the low cycle fatigue test with introducing extremely large strains into the specimen. Low cycle fatigue tests on plain steel plates under constant and variable strain amplitude were conducted by using the system. Based on the test results, an estimation method for low cycle fatigue strength in extremely low cycle fatigue region was proposed.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The improvement of extremely low cycle fatigue strength of welded joints by TIG dressing was investigated. T-shape welded joint specimens of which weld toes were finished by TIG dressing were tested. The fatigue test results were compared with that of as-weld specimens tested in the same conditions. The test results indicated that TIG dressing could substantially increase the extremely low cycle fatigue strength of welded joints.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

A new low cycle fatigue testing system has been developed, in which a steel plate specimen is subjected to bending deformation, and strains of the specimen are measured by image technique. In this study, the low cycle fatigue tests of steel welded joints under constant and variable strain amplitude, particularly the fatigue life less than ten cycles in extremely large strain field, was conducted by using the newly developed testing system. On the basis of the test results, the applicability of low cycle fatigue life prediction model was confirmed, which has been developed for plain steel material, to welded portion, such as deposit metal and heat affected zone (HAZ).

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Surface profile of structural members sometimes gives valuable information to estimate mechanical behavior of existing structures. In this study, based on stereography technique, a simple method to measure the surface profile was developed, and apllied to a corroded steel plate surface. The method gave good results even for corroded steel plate surface which has few image patters and characteristics. The accuracy of the method was also discussed on the results for a variety of system conditions, such as camera position and camera resolution.

DOI： 10.11273/jssc1994.12.46_27

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

We investigated the low cycle fatigue strength of welded materials under constant and variable strain amplitude in extremely large strain region. The test results indicated that fatigue strength of welded materials, particularly heat-affected zone (HAZ), was much lower than that of plain material. We then developed a model to predict the extremely low cycle fatigue strength of welded materials. Fatigue life estimated by this model was well agreed with test results.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In this study, we investigated the low cycle fatigue strength of welded joints using a new fatigue testing system in which the image analysis technique was used to measure the strains in specimens. After checking the validity of the testing system, we used this new system to conduct fatigue tests on welded joint specimens. The test results indicate that the fatigue strength of welded material (weld deposit and heat affected zone) is much lower than that of the plain material.

DOI： 10.1016/j.ijfatigue.2004.03.016

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authors have developed a new low cycle fatigue testing method, in which a specimen is subjected to bending deformation and strain of the specimen is measured by image analysis. The advantage of this method is to be able to induce extreme large strain in steel plate even if it includes welding. In this study, the fatigue strength of welded joints in extreme large strain field was investigated by a newly developed testing system. The test results indicated that the fatigue strength of welded joints was much lower than that of plain material, and heat affected zone (HAZ) was the weakest spot.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

For predicting the low cycle fatigue life under variable strain amplitude, Miner's rule has been accepted as a simple and effective idea. In extreme large strain field corresponding to the fatigue life of less than ten cycles, however, the accuracy of Miner's rule has not been verified yet. In this study, by means of a newly developed testing system, low cycle fatigue tests under variable strain amplitude in extreme large strain field was conducted. The test results showed Miner's rule always predicted longer fatigue life than actual life. As another idea for predicting low cycle fatigue life, we proposed a simple model introducing the damage mechanics concept and examined its validity.

DOI： 10.2208/jscej.2004.773_149

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Extensive experiments on the low cycle fatigue for plain steel material have been conducted and obtained some important results. There are few studies, however, on the low cycle fatigue in the extreme large strain field, corresponding to the fatigue life less than ten cycles.
In this study, we developed a new low cycle fatigue testing system, in which a specimen was subjected to bending deformation and the strain in the specimen was measured by image analysis technique. Low cycle fatigue tests on plain steel plates under constant and variable strain amplitude were conducted by using the testing system. Based on the test results, an estimation method for low cycle fatigue strength in the extreme large strain field was proposed.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Low cycle fatigue strength of welded joints was investigated by means of newly developed fatigue testing system in which image analysis technique was applied to measure the strain of specimens. It was validated that the strain measured by the image analysis was almost equal to measured value by strain gauge, and the low cycle fatigue strength of steel plate without welding was in good agreement with the results reported in former researches. After verifying the testing system, fatigue tests were carried out on welded joint specimens. The test results indicated that the low cycle fatigue strength of welded joints was much lower than that of plain material, and fatigue life was reduced by half.

DOI： 10.2208/jscej.2004.752_277

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Since Great Hanshin-Awaji Earthquake caused low cycle fatigue failures at base joints and beam-to-column connections in steel piers, it is important to investigate the low cycle fatigue strength of welded joints in civil structures. In this study, low cycle fatigue strength of welded joints was investigated by means of a new fatigue testing system in which image analysis technique was introduced to measure the strain of specimens. It was validated that the strains measured by the image analysis were almost equal to those by strain gauges, and the low cycle fatigue strength of plain steel plate was in good agreement with the result reported in the former studies. The low cycle fatigue tests carried out on welded joint specimens indicated that the fatigue strength of the welded joints was much lower than that of plain material.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Almost all the low cycle fatigue cracks observed in Hanshin-Awaji Earthquake were initiated from welded joints. In this study, a new testing system was developed, which enables the investigation on the low cycle fatigue strength of welded joints. In this testing system, a specimen was subjected to bending deformation, and the strain in the specimen was measured by means of image analysis technique. It was shown that the strains measured by the image analysis were almost equal to those measured by strain gauges, and the low cycle fatigue strength of plain steel material obtained by this testing system was in good agreement with the results reported in former studies.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Recently, a lot of fatigue cracks have been found in steel bridges to the increase of the large-scale vehicles in number as well as weight. In order to consider a repairing this study, a method to estimate the fatigue crack propagation rate is proposed, which is based on the crack opening width measured by image analysis on a digital image recorded with a portable digital microscope. The accuracy and limitation of the method were investigated through a fatigue test carried out on a fatigue crack in welded joint specimen.

DOI： 10.11273/jssc1994.8.31_11

Language：English   Publishing type：Research paper (scientific journal)  

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