Faculty Profiles - HANJI Takeshi

Papers - HANJI Takeshi

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Influence of shear panel shape in multiple steel columns on low cycle fatigue Reviewed

Masaru Shimizu, Kazuo Tateishi, Takeshi Hanji, Hiroshi Noda, Hiroki Sugiyama, Yasumasa Soga

Proceedings of the ISSS 2017 page： 466-469 2017.11

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.

Fatigue crack growth prediction of welded joints in low-cycle fatigue region Reviewed

Takeshi Hanji, Kazuo Tateishi, Nao Terao, Masaru Shimizu

Welding in the World Vol. 61 ( 6 ) page： 1189-1197 2017.10

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

Slip coefficient and strength after slip of high strength bolted friction joints with compact bolt spacing and edge distance Reviewed

Shogo Kiyokawa, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu

Steel Construction Engineering, JSSC Vol. 24 ( 95 ) page： 25-40 2017.9

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

Fatigue strength of cruciform joints and longitudinal joints with laser-arc hybrid welding Reviewed

Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu, Daisuke Uchida, Koichi Asano, Ryosuke Kimura

The 70th Annual Assembly of International Institute of Welding page： XIII-2698-17 2017.6

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.

Influence of static strength of steels on fatigue strength improvement of welded joints by toe treatment Reviewed

Takeshi Hanji, Kengo Anami

Journal of Structural Engineering, JSCE Vol. 63A page： 646-658 2017.3

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

Fatigue strength improvement on welded joints in cutout of transverse ribs in orthotropic steel bridge decks Reviewed

Takeshi Hanji, Ayumi Itoh, Kazuo Tateishi, Masaru Shimizu

Journal of Constructional Steel Vol. 24 page： 657-662 2016.11

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.

Fatigue crack growth prediction of welded joints of rectangular steel tube in low cycle fatigue region Reviewed

Takeshi Hanji, Nao Terao, Kazuo Tateishi, Masaru Shimizu

Journal of Constructional Steel Vol. 24 page： 628-632 2016.11

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.

Crack propagation life prediction for welded joints in low cycle fatigue region Reviewed

Takeshi Hanji, Nao Terao, Kazuo Tateishi, Masaru Shimizu

Proceedings of the 11th Pacific Structural Steel Conference page： 625-632 2016.10

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.

Characteristics of fatigue crack propagation in I-beam end of railway steel bridges

Masaki Iwai, Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu, Shunsuke Kase, Yuichiro Niwa, Ken Ikegashira

Proceedings of the 11th German-Japanese Bridge Symposium page： CD-ROM 2016.8

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

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.

Low cycle fatigue verification of connection part in the shear panel in multiple steel columns

Hiroshi Noda, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu, Riku Adachi, Hiroki Sugiyama

Proceedings of the 11th German-Japanese Bridge Symposium page： CD-ROM 2016.8

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

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.

Fatigue strength improvement for welded joints simulating longitudinal-to-transverse rib connection in orthotropic steel deck

Ayumi Ito, Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu

Proceedings of the 11th German-Japanese Bridge Symposium page： CD-ROM 2016.8

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

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.

Effect of static strength of steel on fatigue strength improvement by introducing compressive residual stress

Hiroki Takamatsu, Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu

Proceedings of the 11th German-Japanese Bridge Symposium page： CD-ROM 2016.8

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

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.

Fatigue life extension for a crack in welded joints by CFRP repair

Yuko Kanayama, Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu, Mamiko Hattori, Kenyu Ushida

Proceedings of the 11th German-Japanese Bridge Symposium page： CD-ROM 2016.8

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

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.

Fatigue strength of load-carrying cruciform welded joints with Laser-arc hybrid welding

Naoya Honda, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu, Daisuke Uchida, Koichi Asano

Proceedings of the 11th German-Japanese Bridge Symposium page： CD-ROM 2016.8

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

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.

Fatigue crack growth prediction of welded joints in low cycle fatigue region Reviewed

Takeshi Hanji, Kazuo Tateishi, Nao Terao, Masaru Shimizu

The 69th Annual Assembly of International Institute of Welding page： XIII-2651-16 2016.7

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

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.

Fatigue strength of welded joints with adjacent attachments and its life extension by ICR treatment Reviewed

Takeshi Hanji, Kazuo Tateishi, Masaru Shimizu, Shunsuke Kase, Masaki Iwai

Journal of Structural Engineering, JSCE Vol. 62A page： 667-674 2016.3

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

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

Fatigue crack growth rate of steels under large cyclic strain and its application to crack growth prediction in welded joints Reviewed

Takeshi Hanji, Nao Terao, Kazuo Tateishi, Masaru Shimizu

Steel Construction Engineering, JSSC Vol. 23 ( 89 ) page： 85-95 2016.3

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

Redistribution of welding residual stress due to weld toe grinding Reviewed

Satoshi Maeda, Kazuo Tateishi, Takeshi Hanji, Masaru Shimizu

Journal of Constructional Steel Vol. 23 page： 630-636 2015.11

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.

Displacement based fatigue strength evaluation for root failure in fillet weld joints Reviewed

Kazuo Tateishi, Naohiro Soda, Takeshi Hanji, Masaru Shimizu

Proceedings of the ISSS 2015 page： 169-170 2015.11

Authorship：Lead author Language：English

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.

An estimation method for weld crack initiation in weld repair under cyclic loading Reviewed

Takeshi Hanji, Yoshio Hasegawa, Kazuo Tateishi, Masaru Shimizu

Proceedings of the ISSS 2015 page： 397-398 2015.11

Authorship：Lead author Language：English

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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Papers - HANJI Takeshi