Faculty Profiles - HANJI Takeshi

Papers - HANJI Takeshi

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Low cycle fatigue characteristics of steel deformed bars Reviewed

Takeshi Hanji, Kazuo Tateishi, Kenyuu Ushida, Naoki Nagamatsu, Sung-Min Choi

Proceedings of the 10th Pacific Structural Steel Conference page： 505-510 2013.10

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

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.

Fatigue life extension of cracked welded joints by ICR treatment under tensile loading Reviewed

Kazuo Tateishi, Takeshi Hanji, Yoshitaka Tsuruta, Sho Sasada, Sung-Min Choi

Proceedings of the 10th Pacific Structural Steel Conference page： 493-498 2013.10

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

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.

Low cycle fatigue assessment of steel bridge piers subjected to long duration ground motions Reviewed

Takeshi Hanji, Kazuo Tateishi, Shun Ukai, Sung-Min Choi

Proceedings of the 10th Pacific Structural Steel Conference page： 499-504 2013.10

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

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.

Fatigue strength of welded joints using steels for bridge high performance structures (SBHS) Reviewed

Takeshi Hanji, Kazuo Tateishi, Shuichi Ono, Yoshinori Danshita, Sung-Min Choi

Proceedings of the 13th East Asia-Pacific Conference on Structural Engineering and Construction page： CD-ROM 2013.9

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.

Local stress behavior at closed rib to crossbeam connections in orthotropic steel bridge decks Reviewed

Keito Kato, Takeshi Hanji, Kazuo Tateishi, Sung-Min Choi, Shigeyuki Hirayama

Proceedings of the 13th East Asia-Pacific Conference on Structural Engineering and Construction page： CD-ROM 2013.9

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

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.

Fatigue strength evaluation of out-of-plane gusset weld joint

Kengo Anami, Yusuke Goda, Daisuke Uchida, Takeshi Hanji, Shigeyuki Hirayama

Proceedings of the 12th Japan-Korea Joint Symposium on Steel Bridges page： CD-ROM 2013.8

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.

A study on weld repair of steel members under cyclic loading

Yoshio Hasegawa, Takeshi Hanji, Kazuo Tateishi, Sung-Min Choi

Proceedings of the 12th Japan-Korea Joint Symposium on Steel Bridges page： CD-ROM 2013.8

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.

Residual stress distribution in welded joints by applying low-temperature transformation welding material

Naohiro Souda, Kazuo Tateishi, Takeshi Hanji

Proceedings of the 12th Japan-Korea Joint Symposium on Steel Bridges page： CD-ROM 2013.8

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.

Local stress characteristics at cross-beam web cutout in closed rib orthotropic deck Reviewed

Takeshi Hanji, Keito Kato, Kazuo Tateishi, Sung-Min Choi, Shigeyuki Hirayama

Proceedings of the 3rd Orthotropic Bridge Conference page： CD-ROM 2013.6

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.

Local stress characteristics at cross-beam web cutout in closed rib orthotropic deck Reviewed

Takeshi Hanji, Keito Kato, Kazuo Tateishi, Sung-Min Choi, Shigeyuki Hirayama

Journal of Structural Engineering, JSCE Vol. 59A page： 781-789 2013.3

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

Fatigue strength of base joint with partial penetration weld in steel bridge brackets Reviewed

Kazuo Tateishi, Takeshi Hanji, Sung-Min Choi, Kenshi Yoshimine, Tatsuya Takase

Steel Construction Engineering, JSSC Vol. 20 ( 77 ) page： 15-24 2013.3

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

Experimental study on low cycle fatigue behavior of concrete-filled steel bridge piers Reviewed

Jin-Eun Park, Takeshi Hanji, Kazuo Tateishi, Sung-Min Choi

Proceedings of the 9th German-Japanese Bridge Symposium page： CD-ROM 2012.9

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

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.

Local strain estimation method for low- and high-cycle fatigue strength evaluation Reviewed

Kawin Saiprasertkit, Takeshi Hanji, Chitoshi Miki

International Journal of Fatigue Vol. 40 page： 1-6 2012.7

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

Fatigue strength assessment of load-carrying cruciform joints with material mismatching in low- and high-cycle fatigue regions based on the effective notch concept Reviewed

Kawin Saiprasertkit, Takeshi Hanji, Chitoshi Miki

International Journal of Fatigue Vol. 40 page： 120-128 2012.7

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

Low and high cycle fatigue behaviour of load-carrying cruciform joints containing incomplete penetration and strength mismatch Reviewed

Takeshi Hanji, Chitoshi Miki, Kawin Saiprasertkit

Welding in the World Vol. 56 ( 5/6 ) page： 133-146 2012.5

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

Low cycle fatigue design curves for base joints of steel bridge piers Reviewed

Takeshi Hanji, Kazuo Tateishi

Proceedings of the International Workshop on Advances in Seismic Experiments and Computations page： 223-228 2012.3

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.

Weld repair for fatigue cracked joints in steel bridges by low temperature transformation welding material Reviewed

Chitoshi Miki, Takeshi Hanji, Kohei Tokunaga

Welding in the World Vol. 56 ( 3/4 ) page： 40-50 2012.3

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

Fatigue strength evaluation for welded joints by newly developed local stress estimation method Reviewed

Kazuo Tateishi, Takeshi Hanji, Wataru Naruse, Isao Ito, Sung-Min Choi

Journal of Structural Engineering, JSCE Vol. 58A page： 647-654 2012.3

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

Low- and high-cycle fatigue behavior of load-carrying cruciform joints with incomplete penetration and strength under-match Reviewed

Takeshi Hanji, Kawin Saiprasertkit, Chitoshi Miki

International Journal of Steel Structures Vol. 11 ( 4 ) page： 409-425 2011.12

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

Evaluation of scatter in fatigue life of welded joints by fracture mechanics Reviewed

Kazuo Tateishi, Moritaka Yoshida, Takeshi Hanji

Journal of Constructional Steel Vol. 19 page： 351-354 2011.11

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.

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Papers - HANJI Takeshi