CRITERIA FOR SUPPRESSION OF DEFORMATION CONCENTRATION OF BUILDING FRAMES UNDER SEVERE EARTHQUAKES

It has been revealed by symmetry limit theory that an unknown type of collapse behavior, characterized by cyclic growth of a bow-shaped mode overall deflection, could occur in a multistory multi-bay weak-beam p lanar frame subjected to a static cyclic program of top horizontal dis placement. Dynamic response analysis of the multistory frame, performe d later, has shown that the bow-shaped mode deflection is possible to appear in a restricted lower part of the frame and, thereby, deformati on concentration occurs in that part in the process of dynamic collaps e. In this paper, criteria for suppression of growth of the bow-shaped mode deflection and the deformation concentration will be proposed. E ven if a frame is designed so that the criteria are satisfied, a gradu al one-way drift of the sway-mode vibration center may still be observ ed under a cyclic ground motion. Criteria for suppression of the sway drift will also be proposed to meet higher-level safety requirements. (C) 1997 Elsevier Science Ltd.