Faculty Profiles - SHIMIZU Masaru

FATIGUE STRENGTH IMPROVEMENT OF ROOT-DECK CRACK IN ORTHOTROPIC STEEL DECK BY MODIFYING U-RIB SHAPE

MAEDA Satoshi, TATEISHI Kazuo, HANJI Takeshi, SHIMIZU Masaru, TAKATA Koyo

Japanese Journal of JSCE Vol. 82 ( 2 ) page： n/a 2026

Language：Japanese Publisher：Japan Society of Civil Engineers

This paper investigates the fatigue strength improvement of root-deck crack in orthotropic steel decks with closed ribs by modifying the shape of the U-rib. First, the influence of U-rib width and spacing on stress at the crack initiation point was examined using finite element analysis, and structures expected to have improved fatigue strength compared to a conventional structure were proposed. Next, cyclic loading tests on cross-beam intersection and wheel running tests were conducted on the proposed structure to validate its fatigue strength. Finally, an analytical study on an actual bridge model was performed to quantitatively estimate the fatigue life under service conditions. The results of these studies demonstrate that modifying the U-rib shape is effective in improving the fatigue strength of deck propagation cracks.

DOI： 10.2208/jscejj.25-00223

Bending fatigue strength of slotted tubular joints in transmission steel tower members

SODA Naohiro, TATEISHI Kazuo, HANJI Takeshi, SHIMIZU Masaru

Kou kouzou rombunshuu Vol. 32 ( 128 ) page： 163 - 178 2025.12

Language：Japanese Publisher：Japanese Society of Steel Construction

Slotted tubular joints are commonly used in transmission steel tower members. In these joints, fatigue cracks have been initiated at plate-end welds, tube-end welds and bolted connections due to bending loads. In this study, bending fatigue tests on slotted tubular joints were conducted to investigate fatigue strength based on nominal stress. As a result, cracks at tube-end welds were caused by in-plane bending of the slotted plate, and their fatigue strength satisfied Class H in the Specifications for Highway Bridges. On the other hand, cracks at plate-end welds were caused by out-of-plane bending, and their fatigue strength was higher than that of tube-end welds, while it was lower than that of bolted connections.

DOI： 10.11273/jssc.32.128_163

Fatigue life evaluation of root failure in welded joints based on displacement around the weld root Open Access

Pradana, EW; Tateishi, K; Hanji, T; Shimizu, M

WELDING IN THE WORLD 2025.12

Publisher：Welding in the World

Unanticipated load transfer in load-carrying cruciform and butt-welded joints with incomplete penetration can initiate fatigue cracks from the weld root. Conventionally, the fatigue life of such joints is assessed using the nominal stress approach. However, this method is often inadequate for geometrically complex joints, particularly when the weld throat nominal stress cannot be clearly defined due to non-uniform stress distribution. Although the effective notch stress (ENS) method provides an alternative, it is computationally demanding and relies on an assumed notch radius which lacks a well-defined physical basis. This study proposes an alternative fatigue evaluation method based on displacement around the weld root, offering a physically meaningful and mesh-insensitive fatigue damage parameter. A linear-elastic finite element model with a 1 mm mesh around the unfused zone was employed to evaluate the displacement at a reference point 1 mm from the weld root. A dataset comprising 398 fatigue test results from specimens with incomplete penetration exhibiting root failure was extracted from the literature to validate the proposed method. A correction factor was introduced to normalize the fatigue damage parameter into a dimensionless form, allowing direct comparisons across specimens of varying sizes and geometries. The relationship between the normalized fatigue damage parameter and fatigue life was presented on logarithmic scales, resulting in the normalized Δd–N curve. This curve not only demonstrates improved predictive accuracy and reliability compared to the conventional S–N curve but also offers a physically interpretable approach applicable to complex welded joint geometries.

DOI： 10.1007/s40194-025-02293-y

Hot-spot stress fatigue strength curves for weld toe on plate edges Open Access

Hanji, T; Tateishi, K; Takeshi, M; Shimizu, M

WELDING IN THE WORLD 2025.11

Publisher：Welding in the World

Hot-spots are classified into two types: Type “a”, which refers to weld toes located on the plate surface, and Type “b”, which refers to weld toes located at the plate edge. In this study, fatigue test data on joint details in which Type “b” cracks occur were collected from 25 published papers, comprising a total of 264 data points across several different joint details. Finite element analysis was performed to compute hot-spot stress, with variations in element type and element size near the reference points used for hot-spot stress calculation. When the data were organized according to the nominal stress range, significant scatter was observed in the S–N diagram due to variations in fatigue strength among different joint details. In contrast, when analyzed based on the 4–8–12 mm method, as recommended in the IIW Designer’s Guide, the scatter was significantly reduced. Taking into account data scatter, the lower limit, which is defined as the mean minus two standard deviations, was 95.4 N/mm2. These findings indicate that fatigue test results for in-plane gusset welded joints, as well as other joint details, can collectively be assessed using the fatigue design curve of FAT90. Additionally, it was confirmed that variations in element size within the range of 1 mm to 4 mm near the reference points, as well as changes in element type, had negligible effects on the hot-spot stress assessment.

DOI： 10.1007/s40194-025-02244-7

ENHANCEMENT OF FATIGUE STRENGTH AT THE ROOT OF OUT-OF-PLANE GUSSET WELDED JOINT BY HIGH FREQUENCY INDUCTION HEATING TREATMENT Open Access

SHIMIZU Masaru, MURAI Kouhei, KANO Suguru, TATEISHI Kazuo, HANJI Takeshi

Kou kouzou rombunshuu Vol. 32 ( 127 ) page： 72 - 82 2025.9

Language：Japanese Publisher：Japanese Society of Steel Construction

In this study, the enhancement of fatigue strength at the weld root in out-of-plane gusset welded joint by high frequency induction heating (IH) treatment was investigated. Fatigue tests were conducted to examine the fatigue strength enhancement by IH treatment. IH treatment was applied to both sides of a boxing weld in the specimens. Test results show 1-grade or more fatigue strength enhancement while the fatigue cracks were generated both from weld root and weld toe in a longitudinal attachment. Additionally, finite element analysis was performed to investigate the fatigue strength enhancement based on effective notch stress. Two million cycle fatigue strength was improved 2.25 times than the welded joint without IH treatment.

DOI： 10.11273/jssc.32.127_72

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

Niwa, Y; Tateishi, K; Hanji, T; Shimizu, M

WELDING IN THE WORLD Vol. 69 ( 8 ) page： 2239 - 2251 2025.8

Publisher：Welding in the World

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

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

Shimizu M., Tateishi K., Hanji T., Hasegawa H., Suetsugu H.

IABSE Symposium Tokyo 2025 Environmentally Friendly Technologies and Structures Focusing on Sustainable Approaches Report page： 2909 - 2916 2025

Publisher：IABSE Symposium Tokyo 2025 Environmentally Friendly Technologies and Structures Focusing on Sustainable Approaches Report

In orthotropic steel deck, many fatigue cracks have been found at the weld joint between deck plate and vertical stiffeners. As a countermeasure for fatigue, semicircular cut-out has been adopted to reduce the stress concentration around the welded joint between the deck plate and the vertical stiffeners. However, more effective cut-out geometry should be considered in terms of ease of design and fatigue improvement. In this study, the stress reductions were investigated for newly developed slit-like cut-out and sigma-shaped cut-out. In addition, fatigue tests were conducted on the welded joints between the deck plate and the vertical stiffener with sigma-shaped cut-out. The crack initiation life and crack propagation can be prolonged by constructing a sigma-shaped cut-out at the top of the vertical stiffener.

DOI： 10.2749/tokyo.2025.2909

Fatigue Strength of Fillet Welded T-Joints using New Welding Materials

Asano K., Hanji T., Tateishi K., Shimizu M., Kotani Y., Takebuchi T.

IABSE Symposium Tokyo 2025 Environmentally Friendly Technologies and Structures Focusing on Sustainable Approaches Report page： 2474 - 2482 2025

Publisher：IABSE Symposium Tokyo 2025 Environmentally Friendly Technologies and Structures Focusing on Sustainable Approaches Report

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.

DOI： 10.2749/tokyo.2025.2474

Fatigue Strength Improvement by Induction Heating against Weld Root Failure in Out-of-Plane Gusset Welded Joints

Kano S., Maeda S., Tateishi K., Hanji T., Shimizu M.

IABSE Symposium Tokyo 2025 Environmentally Friendly Technologies and Structures Focusing on Sustainable Approaches Report page： 1159 - 1166 2025

Publisher：IABSE Symposium Tokyo 2025 Environmentally Friendly Technologies and Structures Focusing on Sustainable Approaches Report

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. 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. Further numerical investigation based on finite element analysis to reproduce the welding and IH clarified the residual stress distributions around the weld.

DOI： 10.2749/tokyo.2025.1159

Evaluation of Through-Thickness Residual Stress at T-Joint Weld Toes Using Slitting Method

Wu Y., Hanji T., Tateishi K., Shimizu M.

IABSE Symposium Tokyo 2025 Environmentally Friendly Technologies and Structures Focusing on Sustainable Approaches Report page： 2459 - 2465 2025

Publisher：IABSE Symposium Tokyo 2025 Environmentally Friendly Technologies and Structures Focusing on Sustainable Approaches Report

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.

DOI： 10.2749/tokyo.2025.2459

Evaluation of Fatigue Damage Ratio for Slotted Tubular Joints of Overhead Transmission Tower with Fatigue Cracks

Stress Measurement for Vortex-induced Vibration of Steel Tubular Tower Member Open Access

SODA Naohiro, TATEISHI Kazuo, HANJI Takeshi, SHIMIZU Masaru

Summaries to Technical Papers of Annual Meeting, Japan Association for Wind Engineering Vol. 2025 ( 0 ) page： 217 2025

Soda, N; Tateishi, K; Hanji, T; Shimizu, M

PROCEEDINGS OF THE 18TH EAST ASIA-PACIFIC CONFERENCE ON STRUCTURAL ENGINEERING AND CONSTRUCTION, VOL 2, EASEC 2024 Vol. 725 page： 502 - 509 2025

Publisher：Lecture Notes in Civil Engineering

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 transmission tower to discuss the applicability of the evaluation method and relevant factors for the fatigue damage ratio. The fatigue damage ratios are calculated using wind data observed near the tower, estimated 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 fatigue progression. 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.

DOI： 10.1007/978-981-96-9917-9_65

Study on the Seismic Capabilities of Various Diameters Oil Storage Tanks Located in an Earthquake Hazard Area Open Access

Hafidz M., Panjaitan A., Afifuddin M., Hasibuan P., Putra R., Bermansyah S., Fauzi M., Haiqal M., Shimizu M.

Iop Conference Series Earth and Environmental Science Vol. 1578 ( 1 ) 2025

Publisher：Iop Conference Series Earth and Environmental Science

Oil storage tanks are essential structures that may be located in an earthquake hazard area. However, the tank's seismic capabilities due to random amplitude (earthquake loading) have not been clarified. This research work elaborates on the seismic capabilities of several different diameter storage tanks, F-6020, F-6021, and F-6022, which are located at PT. Arun in Lhokseumawe City. The research began with a site visit that revealed rusted areas on most surfaces of the roof and tank walls. Next, some FE models of tanks were subjected to Random Variable Amplitude Loading (RVAL). Results showed that the largest diameter tank (F-6022) demonstrated the best dissipated energy ratio (general seismic capability) due to the widest support at the bottom plate to withstand earthquake load. Additionally, the dissipated energy ratio followed a power function trend as displacement increased, regardless of the distinction of tank diameter. Observing the strength-dissipated energy relationships showed that the F-6022 performs the longest plots of strength at the sustenance of dissipated energy due to the largest and most stable hysteretic curve. Furthermore, the smallest diameter tank (F-6020) performed the von Mises stress exceeded the allowable limit, suggesting that seismic reinforcements are necessary for F-6020.

DOI： 10.1088/1755-1315/1578/1/012004

Seismic Performance of the High-Speed Diesel Storage Tank Wall under Several Different Random Variable Amplitude Loadings Open Access

Ayyasi R., Panjaitan A., Afifuddin M., Hasibuan P., Putra R., Bermansyah S., Fauzi M., Haiqal M., Shimizu M.

Iop Conference Series Earth and Environmental Science Vol. 1578 ( 1 ) 2025

Publisher：Iop Conference Series Earth and Environmental Science

A High-Speed Diesel (HSD) oil storage tank is composed of steel and prone to rusting on its walls and roof. This study aims to evaluate the seismic performance of an HSD storage tank in the PT. Arun Gas Lhokseumawe, named F-6018, with a focus on its wall components. The study was initially conducted through a site investigation, which revealed that corrosion was predominantly exposed on the roof and wall surfaces. The seismic analysis was carried out by applying Random Variable Amplitude Loadings (RAs) to the FE models. The results showed that the dissipated energy (general seismic performance) exhibited an escalation trend in the power function at the sustenance of the displacement, regardless of the difference in RA displacement ranges. Additionally, observing the alteration in displacement amplitude of RAs revealed a distinct pattern in the dissipated energy ratio. Increasing amplitudes in RAs revealed that the dissipated energy ratio linearly escalates, and the decreasing amplitude showed a constant function of dissipated energy ratio, together with the additional value of displacement ratio. Furthermore, the analysis also discovered that the equivalent stresses were higher than the allowable values, indicating that the tank requires seismic strengthening.

DOI： 10.1088/1755-1315/1578/1/012001