Kazuo Tateishi

Fatigue strength of cope hole details in steel bridges

Cope holes found at the intersections of steel structural members to access crossing welds may cause high stress concentration and decrease the fatigue strength of the detail. In this study, fatigue strength and local stresses for cope hole details existing in I-section beams bent in-planes were investigated by fatigue tests, stress measurements and stress analyses. The experimental results showed the fatigue strength of cope hole details was extremely low due to the local stress around the cope holes. In particular, when shear deformation was induced in a gap of flange plate inside a cope hole, the local stress was greatly increased. Using an analytical approach, the relationship between the magnitude of local stress and some influential parameters was investigated and a simple method to estimate the local stress for cope hole details is proposed.

Fatigue strengths of fillet-welded joints containing root discontinuities

Abstract In order to examine the fatigue performance of fillet-welded joints containing root crack or root-gap defects, fatigue tests are carried out. The specimens consist of two series: the first series are non-load-carrying cruciform, load-carrying cruciform and longitudinally welded joints. The second series are all load-carrying cruciform joints and have four kinds of details with various root-gap sizes and leg length. The test results indicate that the fatigue strength of joints which contain defects is equal to or higher than that of joints with no defects.

Improvement of Extremely Low Cycle Fatigue Strength of Welded Joints by Toe Finishing

The improvement of extremely low cycle fatigue strength of welded joints by TIG dressing and burr grinding was investigated. The weld toes of T-shape welded joints were improved by TIG dressing or burr grinding and tested under displacement control conditions. The crack initiation life of finished specimens was at least threefold longer than that of as-welded specimens. There was no clear difference in improvement between TIG dressing and burr grinding. We also analysed the local strain around the cracking point by finite element analysis and performed local strain-based fatigue assessment. The results indicated that extremely low cycle fatigue strength of the joints improved by TIG dressing and burr grinding can be assessed by evaluating the local strain and referring to the extremely low cycle fatigue strength curve.

Fatigue Crack Behavior at Rib-to-Deck Weld Bead in Orthotropic Steel Deck

One of the typical fatigue cracks observed in orthotropic steel deck is a through-thickness crack which penetrates and propagates along the weld bead. Moreover, according to some reports of the fatigue crack observed in some bridges, the fatigue crack sometimes changes its direction suddenly, and propagates to the rib wall and the deck plate. Such fatigue damage can cause the sudden decrease of stiffness of longitudinal rib. However, the propagation mechanism of the crack has not been investigated clearly. In this study, numerical studies on the through-thickness crack at rib-to-deck weld bead in the orthotropic steel deck were carried out. Finite element model (FEM) of an orthotropic deck with different through-thickness crack at rib-to-deck weld bead was created. In order to identify the propagation behavior of the fatigue crack, stress intensity factors for three deformation modes were estimated by the FE analysis (FEA) and the displacement extrapolation method. Based on the maximum energy release rate (MERR) criterion, the equivalent stress intensity factor and the crack direction were evaluated. From the numerical results, the crack direction change was found to be originated by the Mode II and Mode III deformation near the crack tip due to the out-of-plane bending of the rib wall along the crack.

APPLICATION OF IMAGE ANALYSIS TO STEEL STRUCTURAL ENGINEERING

We introduce three applications of the image analysis technique into steel structural engineering. The first is the surface shape measurement of corroded steel plates using digital stereography. The second and third are strain measurements by digital image analysis. In all cases, the image analysis technique works well and provides us with innovative information on mechanical behaviors of steel structures.

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

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.

Static and vibration characteristics of thin-walled box beams: An experimental investigation:

Static and vibration characteristics of thin-walled straight and curved box beams were investigated experimentally. Three different beam configurations were considered for the tests: one straight and two curved box beams. The load was applied at the centroid of the box section for the straight and one curved beam specimens. However, for the other curved specimen, the load was applied eccentrically to investigate its behavior under the additional torsion induced by the eccentricity. Displacements and strains were obtained using linear variable displacement transducer, one-directional and rosette strain gages. The specimens were excited using an impact at their free ends. The time history of strains was obtained to calculate natural frequencies and damping ratios. The experiment results were compared with those obtained from three-dimensional finite element analysis for all cases. The results obtained from implementing tests on the straight specimen were also used to validate an efficient numerical method recently developed by the authors.

FATIGUE STRENGTH OF THE JOINT BETWEEN DIAPHRAGMS AND LONGITUDINAL RIBS IN BOX SECTION GIRDERS

吊橋箱断面補剛桁のダイアフラム・下フランジ縦リブ交差部の局部応力の発生性状と疲労強度について, 疲労試験およびFEM解析により検討した. 試験体は箱桁の橋軸直角方向断面をモデル化した大型試験体であり, 交差部に様々な大きさのスカラップを有している. 結果として, スカラップを小さくすることにより局部応力が低下し, 疲労強度が高くなること, および, スカラップを省略するとUリブ内側に高い応力集中が生じ, 疲労強度が低下することが明らかとなった.

A STUDY ON DYNAMIC RESPONSE OF BRIDGE CAUSED BY LOADS IN LINE AT HIGH SPEED BY BOUNDARY ELEMENT METHOD

高速列車が橋梁を通過する際に生じる問題の1つに衝撃荷重がある. 今後さらに列車を高速にする計画があるが, 従来のモード法をベースにした解析法によれば, 高速域で, 衝撃率が極めて高くなることもある. 本研究では従来あまり試みられたことのない移動荷重による橋梁の動的応答を弾性波動から検討する目的で, 境界要素法を用いた解析を試みたものである.

Probabilistic Study on Influence of Blowholes on Fatigue Strength of Longitudinal Welded Joint.

The influence of blowholes on the fatigue strength of members with longitudinal welded joints was investigated by probabilistic approach. Random variables and parameters used were blowhole size, member length, probability of fatigue crack occurrence from blowholes, distribution of stress range and parameter C in Pariss law. Probabilistic functions of these variables were given from the results of previous fatigue tests or field measurements. By parametrical analysis, the influences of the above random valiables on the fatigue strength of longitudinal welded joints were evaluated quantitatively.