ICHINOSE Luiza Hiroko Osaka City University, Department of Civil Engineering, Research Associate, 工学部, 助手 (60220810)
KITADA Toshiyuki Osaka City University, Department of Civil Engineering, Associate Professor, 工学部, 助教授 (30029334)
明橋 克良 大阪市立大学, 工学部, 助手 (30202568)
酒造 敏廣 大阪市立大学, 工学部, 助手 (90137175)
|Budget Amount *help
¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1989: ¥1,000,000 (Direct Cost: ¥1,000,000)
This study was focused on the fatigue behaviors of curved girder bridges and attempted to find a method for developing a limit state design method, based on fatigue strength, for curved girder bridges during two years, from 1988 until 1989, since this subject has not yet been researched extensively. In evaluating the fatigue strength of curved girder bridges, there are a lot of difficult problems, caused by the curvature of the bridge axis, to estimate the stress in floor beams, lateral bracings and so on. Thus, the induced stress is somewhat different from that of ordinary straight girder bridges and there are no distinctions between primary and secondary stress in the curved girder bridges, which yields complicated 3-dimensional state of stress.
Among these problems, the fatigue strength due to out-of-plane bending of curved web plate,the so-called "web breathing", was examined by fabricating five isolated curved I-girder specimens in the first year, 1988. From the analytical results,
an approximate formula to estimate the out-of-plane bending stress in curved web plate was proposed and its validity was checked by means of the test results. Moreover, it was shown from the fatigue tests that the cracks were not found at the welded portion of flange and web plates even af ter the number of cycles exceeded N=2xlO^6 with the stress range almost nearly equal to the allowable unit stress of their base metal. Therefore, it was concluded that the fatigue check is not necessary in case where the web plate is designed safely against buckling.
In the second year, 1989, a curved multiple I-girder with two main girders connected by floor beams and lateral bracings were fabricated to investigate the static behaviors, as well as stress concentrations of the rib and gusset plates at the junctions between main girders and secondary members. The test results were examined from various points of view and compared with the results of the FEM analysis, which was derived as a part of this series of study. After these static loading tests, the model girder was tested up to the fatigue failure. The locations, the number of loading cycles and the propagation of fatigue cracks in the rib and gusset plates were carefully observed. Finally, the fatigue strength of curbed girder bridges was discussed and compared with the S-N curve proposed by JSSC. These experimental results offered valuable data for designing the curved girder bridges safely against fatigue in future. Less