Influence of imperfections on ultimate strength of girders

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In this study, regarding stiffener-end-gaps and fatigue cracks as imperfections against the state that these do not exist, the following researches are completed in order to clarify how much these influence the ultimate strength of girders1. Effects of stiffener-end-gaps on ultimate strength of girdersPlacing a large gap at horizontal-stiffener-ends and vertical-stiffener-ends is desirable to improve the movability of welding robots., The relation between the decrease of the ultimate strength of girders and the gap size at the vertical-stiffener-ends are investigated by the statically loading tests and the elasto-plastic large-deflection analysis with FEM for shear loading and combined loading of bending and shear. From this, the mechanism that the rigidity and gap size of vertical stiffeners as well as the shapes of the initial deflection of webs decrease the ultimate strength of girders is given clear2. Influence of cracks on the ultimate strength of girders under bendingThere are many instances of fatigue cracks occurring in steel bridges. Now it is not clear how much the fatigue cracks decrease the ultimate strength of girders. The effects of cracks on the deflection and the ultimate strength of girders under bending are investigated by the static loading tests of four plate girders with different cracks induced. The web cracks on the tension side of bending decrease a little the ultimate strength, but the drop of the load after the maximum load is smaller than that of the girders without such cracks. The cracks between a web and a top flange suddenly drop the load under the yield moment