Abstract
Pre-fabricated large-span building frames with rigid conections are economically designed by using thin-walled H-sections as their members. Under gravity load conditions, the strength of members forms a ruling factor in the design of these frames. Under the influence of strong earthquake motions, however, the deformation capacity of members is another decisive factor in controlling the maximum responses of these structures. For members that are braced against lateral deflection, the evaluation of the rotation capacity of the members after local buckling is a subject that remains to be solved for the seismic design of these structures. This paper discusses effects of local buckling on moment-rotation hysteretic behavior of thin-walled welded H-section beams that are simply supported and under a concentrated load on the center. Specimens are fully braced against lateral deflection and are tested in either monotonic or cyclic loading. The variables in the specimens are width-thickness ratios of flanges and webs, whose values are varied as follows; b/f=9-15 H/ω=60-180 in which b denotes the half width of the flange ; f, the thickness of the flange ; H, the depth of the cross section ; and ω, the thickness of the web. The following are observations from monotonic loading tests. The moment capacity of sections immediately decreases to 95-85 % of its maximum value as a result of local buckling of the flanges. After the load decay, moment-rotation curves show a gradual decrease in moment capacity as a further rotation is imposed until the beams sustain large deflection. The hysteretic behavior as follows was observed from cyclic loading tests. Hysteresis loops show a remarkable decrease in capacity during early stages of cyclic loading. However, the capacity degradation turns out insignificant after applying 4-5 cycles of loading. In conclusion simple empirical formulas for predicting moment-rotation relationships of these sections are proposed based on the existing test results.
