Buckling of structural members under cyclic loading.

摘要

In many practical situations, structural members must be designed to withstand cyclic loading. This research project focuses on the investigation of the degradation, buckling and collapse of structural members under cyclic loading. The investigation concentrates on two related problems. The first one considers pure cyclic bending of I-beams of S and W sections. A combined experimental and analytical/numerical approach is used. A special four-point bending device and associated instrumentation have been constructed specifically for this project. Experimental results on A36 steel and 6061-T6 aluminum S3 x 5.7, and A36 steel W4 x 13 sections indicate that persistent cyclic bending can lead to structural degradation, buckling and collapse. Detailed measurements of this failure process have been conducted. They indicate that global (lateral-torsional) and local (wrinkling of the flanges) modes can interact to induce collapse. These experimental findings are confirmed and simulated by numerical finite element results. An initial imperfection sensitivity study has been conducted on the response of I-beams under monotonic and cyclic bending. The numerical results indicate that initial imperfections play an important role on the final collapse mode.; The second problem is an analytical study of the response of a column on an elastic-plastic foundation. The motivation for studying this problem stems from experimental observations that, under displacement controlled loading, the development of global buckling modes generally slows down with cycling, while most importantly, that of local buckling modes accelerates and causes collapse of the structure. The model can display either type of buckling mode depending on parameters of column and foundation. The mechanism that causes the development of local buckling has been carefully investigated by monitoring the length change of columns when loaded by symmetric cyclic displacement control.