Faculty Profiles - HANJI Takeshi

Papers - HANJI Takeshi

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Evaluation of through-thickness residual stress at T-joint weld toes using slitting method Reviewed

Yao Wu, Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu

Proceedings of the IABSE Symposium Tokyo 2025 page： CD-ROM 2025.5

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

Residual stress in welds is a critical factor influencing the fatigue strength of welded joints. Understanding the residual stress distribution, both on the surface and within the interior of the plates, is essential for improving the accuracy of fatigue strength evaluations in welded joints. This study aims to numerically evaluate the through-thickness residual stress at the weld toe of T-joints using the slitting method. This approach involves welding simulation, slitting simulation, and fracture mechanics to investigate the relationship between the internal residual stress and the strain changes on the plate surface near the weld toe, which occur due to stress relief during the slitting process. The results indicate that the through-thickness residual stress distributions estimated through the slitting method are consistent with those initially present in the welded joint, even under varying conditions such as different initial residual stress distributions, geometrical parameters of the joint (e.g., plate thickness, weld size), and slitting conditions (e.g., slit width and location, cutting depth ratio). Furthermore, this study identifies an optimal slitting strategy, which enhances the accuracy of residual stress evaluation.

Structural improvement of orthotropic steel decks focusing on fatigue durability and manufacturing costs Reviewed

Satoshi Maeda, Takayuki Kawakami, Hironori Ishii, Takeshi Hanji, Kazuo Tateishi

Proceedings of the IABSE Symposium Tokyo 2025 page： CD-ROM 2025.5

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

Orthotropic steel decks (OSDs) are widely used for long-span bridges or urban expressways because they are lightweight and allow rapid construction. However, an OSD designed according to Japanese specifications for highway bridges has several issues. For example, an OSD with closed ribs (CRD) requires a minimum deck plate thickness of 16 mm, but it has been revealed that this does not completely prevent fatigue crack initiation from the weld root in the rib to deck plate welded joints under heavy traffic loads. In contrast, an OSD with open ribs (ORD) has fewer fatigue problems, but the dead load (steel weight) and manufacturing cost tend to be higher due to the smaller spacing between transverse ribs compared to CRDs. This study investigated improved OSD structures that ensure fatigue durability while reducing the dead load and manufacturing cost.
For a conventional CRD, two improved structures were designed that reduce stress at both the cross-beam intersection and general section by reducing the width and spacing of U-ribs, even with a thinner deck plate. The improved CRDs reduced the steel weight compared to a conventional CRD, and had a similar manufacturing cost.
For a conventional ORD, an improved structure was designed that expands the cross-beam spacing to 4.0 m by using L-shaped steel for longitudinal ribs. The improved ORD reduced both the steel weight and manufacturing cost compared to those for a conventional ORD.

Investigation on the rational cut-out shape for fatigue countermeasure in vertical stiffeners of orthotropic steel decks Reviewed

Masaru Shimizu, Kazuo Tateishi, Takeshi Hanji, Hideya Hasegawa, Hiroki Suetsugu

Proceedings of the IABSE Symposium Tokyo 2025 page： CD-ROM 2025.5

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

In orthotropic steel bridge decks, many fatigue cracks have been found at the weld joint between deck plate and vertical stiffeners. As a countermeasure for the fatigue crack, semi-circular cut-out is introduced in the top of vertical stiffener to reduce the stress concentration around boxing weld. However, more effective cut-out geometry should be considered from viewpoint of fatigue improvement and constructability. In this study, stress reductions were investigated for newly developed slit-like cut-out and sigma-shaped cut-out.
For various cut-out shapes, the stress reductions were investigated from finite element analysis. Significant reduction in stress was found when the cut-out length was long and the distance from the upper edge of the cut-out to the bottom surface of the deck plate was short. Fatigue life extension was verified through fatigue tests on a welded joint specimen consisting of deck plate and vertical stiffeners. A cut-out dimensions were adopted as 20mm from the upper edge of the cut-out to the bottom surface of the deck plate, a length of 118.5 mm, and a hole diameter of 100 mm. As a result, the fatigue life extension for welded joint between deck plate and vertical stiffener at the crack initiation stage was more than 12 times that of a specimen without a cut-out. In addition, crack propagation was also retarded after introducing the cut-out in the vertical stiffener.

Fatigue strength of fillet welded T-joints using new welding materials Reviewed

Keita Asano, Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu, Yuki Kotani, Toshio Takebuchi

Proceedings of the IABSE Symposium Tokyo 2025 page： CD-ROM 2025.5

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

In this study, fatigue tests and finite element analyses were conducted on T joints using various new welding materials 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 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.

Fatigue strength improvement by induction heating against weld root failure in out-of-plane gusset welded joints Reviewed

Suguru Kano, Satoshi Maeda, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu

Proceedings of the IABSE Symposium Tokyo 2025 page： CD-ROM 2025.5

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

This study investigated the improvement of fatigue strength at the weld root in out-of-plane gusset welded joints by induction heating (IH). IH works by locally heating the object with coils energized by high-frequency AC power, which can alter the residual stress distribution.
This study specifically focused on introducing tensile residual stress by locally heating the area around the boxing weld, thereby redistributing the residual stresses to introduce compressive residual stresses at the weld. This process helps transform the tensile residual stresses introduced during welding into compressive residual stresses, thus improving the fatigue strength of welded joints. Unlike other methods such as weld toe treatment, IH does not need to treat the potential crack initiation site directly, making it a promising approach for improving fatigue strength at the weld root.
The improvement in fatigue strength by IH was verified using fatigue tests under out-of-plane bending loads with a vibration-type fatigue testing machine. The results showed that the fatigue strength of the IH-treated specimens was higher than that of the specimens in the as-welded state.
Further numerical investigation based on finite element analysis to reproduce the welding and IH treatment clarified the residual stress distributions around the weld. Additionally, residual stress measurements were carried out using the X-ray diffraction method. These results confirmed that IH can reduce residual stress at the weld and introduce compressive residual stress to the weld root, which is consistent with the fatigue strength improvement against weld root failure obtained in the fatigue tests.

Fatigue durability of countermeasures for u-rib to deck welded joints from underside of existing orthotropic steel decks Reviewed

Masafumi Hattori, Kazuo Tateishi, Takeshi Hanji, Takuya Terazawa

Japanese Journal of JSCE Vol. 81 ( 2 ) page： 24-00187 2025.2

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

Extending fatigue life of weld roots in fillet-welded cover plates by installing tap bolt joints Reviewed International journal

Yuichiro Niwa, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu

Welding in the World Vol. ?? ( ?? ) page： ???-??? 2025.2

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

An analytical study on retrofitting by patch plates from the top of deck plate against bead-through fatigue cracks at intersections in orthotropic steel deck Reviewed

Takuya Terazawa, Masaru Shimizu, Kazuo Tateishi, Takeshi Hanji, Hideya Hasegawa, Hiroki Suetsugu

Journal of Constructional Steel Vol. 32 page： 1-9 2024.11

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.

Fundamental investigation on the detection of root crack by measuring acoustic emission Reviewed

Masaru Shimizu, Kazuo Tateishi, Takeshi Hanji

Journal of Constructional Steel Vol. 32 page： 39-46 2024.11

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.

Fatigue strength of fillet welded T-joints using new welding materials Reviewed

Keita Asano, Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu, Yuki Kotani, Toshio Takebuchi

Journal of Constructional Steel Vol. 32 page： 77-88 2024.11

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.

Evaluation of fatigue damage ratio for slotted tubular joints of overhead transmission tower with fatigue cracks Reviewed

Naohiro Soda, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu

Proceedings of the 18th East Asia-Pacific Conference on Structural Engineering and Construction page： E0054 2024.11

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.

Improvement of fatigue life in orthotropic steel bridge deck by using developed steel plate Reviewed

T.Huyen Doan, Yasuyuki Kurihara, Yoshihiro Hyodo, Takahiro Sakimoto, Takeshi Hanji, Tetsuya Tagawa

Steel Construction Engineering, JSSC Vol. 31 ( 123 ) page： 13-22 2024.9

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

Stress concentration reduction for drilled crack-arrest holes using patch plates with high-strength bolts under axial and shear loads Reviewed

Shogo Kiyokawa, Kazuo Tateishi, Takeshi Hanji, Maoling Zhao, Takayuki Kawakami

Steel Construction Engineering, JSSC Vol. 31 ( 123 ) page： 57-68 2024.9

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

Quantifying the intensity of high frequency mechanical impact treatment Reviewed International coauthorship International journal

Jan Schubnell, Takeshi Hanji, Kazuo Tateishi, Stefanos Gkatzogiannis, Thomas Ummenhofer, Majid Farajian

Welding in the World Vol. 69 ( 1 ) page： 125-137 2024.7

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

2024 Report of work in progress (WIP) on fatigue strength of welded joints in Japan Reviewed

Takeshi Hanji, Eiichi Sasaki

The 77th Annual Assembly of International Institute of Welding page： XIII-3088-2024 2024.7

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.

Extending fatigue life of weld roots in fillet-welded cover plates by installing tap bolt joints Reviewed

Yuichiro Niwa, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu

The 77th Annual Assembly of International Institute of Welding page： XIII-3084-2024 2024.7

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.

Numerical simulation of fatigue crack propagation and repair with drilled hole in trough-girder bridges Reviewed

Takeshi Hanji, Kazuo Tateishi, Miki Shibata, Masaru Shimizu, Makoto Yamaguchi, Yuichiro Niwa

The 77th Annual Assembly of International Institute of Welding page： XIII-3083-2024 2024.7

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.

Preventive maintenance measures against fatigue cracks at welded joints of sole plates of steel bridges Reviewed

Yuichiro Niwa, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu

Japanese Journal of JSCE Vol. 80 ( 5 ) page： 23-00234 2024.5

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

Fatigue evaluation of U-rib to deck weld joint in orthotropic steel deck based on local stress at weld root Reviewed

Masaru Shimizu, Takeshi Hanji, Daisuke Uchida, Masafumi Hattori, Rei Yoshida

Steel Construction Engineering, JSSC Vol. 31 ( 121 ) page： 72-87 2024.3

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

Evaluation of fatigue strength of tap bolt joint and relative displacement of plates Reviewed

Yuichiro Niwa, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu

Steel Construction Engineering, JSSC Vol. 31 ( 121 ) page： 115-126 2024.3

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

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Papers - HANJI Takeshi