幅厚比の大きいH形断面曲げ材の荷重-変形挙動に関する実験的研究

Abstract

In the design of large-span prefabricated building frames under gravity loads, members are required to have strength and stiffness just large enough to resist bending moments working on each member. Such frames are economically designed by using thin-walled H-section steels as their members. Under the influence of strong earthquake motions, however, deformation capacity of members is a ruling factor in controlling the maximum responses of the structures. For the seismic design of these structures, the evaluation of rotation capacity of members after local and/or lateral buckling is a key subject that remains to be solved. This paper presents the results of series of tests on moment-rotation behavior of thin-walled welded H-section beams and beam-columns, and discusses effects of local and lateral buckling on moment and rotation capacities. The variables in the specimens are the width-thickness ratios of flanges and webs, laterally unbraced length, moment gradient and intensity of axial load. The results are summarized as follows: 1) The moment capacity of laterally buckled members immediately decays after the maximum load. The energy absorption capacity of such members is inferior to that of locally buckled members. 2) The ultimate strength of members is predicted by a formula that incorporates strength deteriorations due to local and lateral buckling, and also due to interactions with axial load.