Faculty Profiles - HANJI Takeshi

Papers - HANJI Takeshi

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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.

Improvement methods in extremely low cycle fatigue strength of base joints in steel bridge bents by weld toe treatment Reviewed

Takeshi Hanji, Naoki Nagamatsu, Kazuo Tateishi

Journal of Constructional Steel Vol. 19 page： 355-360 2011.11

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

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

Retardation of fatigue crack propagation in welded joints under plate bending by hardening material injection Reviewed

Kazuo Tateishi, Ryuichi Tsuboi, Takeshi Hanji

Proceedings of the 6th International Symposium on Steel Structures page： 352-357 2011.11

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

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

Fatigue strength evaluation method for welded joints by new local stress concept Reviewed

Kazuo Tateishi, Wataru Naruse, Takeshi Hanji, Isao Itoh

Proceedings of the International Conference on Advanced Technology in Experimental Mechanics' 11 page： CD-ROM 2011.9

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

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

Low cycle fatigue strength of under-matched welded joint with incomplete penetration Reviewed

Takeshi Hanji, Kawin Saiprasertkit, Chitoshi Miki

Quarterly Journal of the Japan Welding Society Vol. 29 ( 3 ) page： 162-173 2011.8

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

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

DOI： 10.2207/qjjws.29.162

Improvement in extremely low cycle fatigue strength of steel bridge piers by weld toe grinding

Naoki Nagamatsu, Takeshi Hanji, Kazuo Tateishi

Proceedings of the 11th Japan-Korea Joint Symposium on Steel Bridges page： CD-ROM 2011.8

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

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

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

Kazuo Tateishi, Moritaka Yoshida, Takeshi Hanji

Proceedings of the 11th Japan-Korea Joint Symposium on Steel Bridges page： CD-ROM 2011.8

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

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

Local stress based fatigue assessment for out-of-plane gusset welded joints

Sho Sasada, Kazuo Tateishi, Takeshi Hanji

Proceedings of the 11th Japan-Korea Joint Symposium on Steel Bridges page： CD-ROM 2011.8

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

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

Fatigue strength of base joints of outrigger bracket in steel bridges

Shun Ukai, Kazuo Tateishi, Takeshi Hanji, Kenshi Yoshimine

Proceedings of the 11th Japan-Korea Joint Symposium on Steel Bridges page： CD-ROM 2011.8

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

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

Fatigue crack propagation at attachment welded joint

Kengo Anami, Takayuki Arai, Akira Tanikaga, Yusuke Kobayashi, Daisuke Uchida, Takeshi Hanji, Shigeyuki Hirayama

Proceedings of the 11th Japan-Korea Joint Symposium on Steel Bridges page： CD-ROM 2011.8

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

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

Fatigue crack initiation point of load carrying cruciform joints in low cycle fatigue region Reviewed

Takeshi Hanji, Kawin Saiprasertkit, Chitoshi Miki

The 64th Annual Assembly of International Institute of Welding page： XIII-2385-11 2011.7

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

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

Fatigue strength assessment of load carrying cruciform joints in low and high cycle fatigue region based on effective notch concept Reviewed

Kawin Saiprasertkit, Takeshi Hanji, Chitoshi Miki

The 64th Annual Assembly of International Institute of Welding page： XIII-2384-11 2011.7

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

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

Experimental study of load-carrying cruciform joints containing incomplete penetration and strength under-matching in low and high cycle fatigue regions Reviewed

Kawin Saiprasertkit, Takeshi Hanji, Chitoshi Miki

Proceedings of the 12th East Asia-Pacific Conference on Structural Engineering and Construction page： CD-ROM 2011.1

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

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

Seismic retrofit of existing highway steel bridges using devices considering driving safety of vehicles Reviewed

Khac Thanh Nguyen, Takeshi Hanji, Chitoshi Miki

Proceedings of the 3rd ASIA Conference on Earthquake Engineering page： CD-ROM 2010.12

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

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

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

Chitoshi Miki, Kohei Tokunaga, Takeshi Hanji

Doboku Gakkai Ronbunshuu A Vol. 66 ( 4 ) page： 836-849 2010.12

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

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

DOI： 10.2208/jsceja.66.836

Seismic resistance evaluation of load carrying cruciform welded joints with material matching and incomplete penetration Reviewed

Kawin Saiprasertkit, Takeshi Hanji, Chitoshi Miki

Proceedings of the 3rd ASIA Conference on Earthquake Engineering page： CD-ROM 2010.12

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

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

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

Takeshi Hanji, Chitoshi Miki, Kawin Saiprasertkit

The 63rd Annual Assembly of International Institute of Welding page： XIII-2330-10 2010.7

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

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

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Papers - HANJI Takeshi