Stiffness and Strength Demands for Pin-Supported Walls in Reinforced-Concrete Moment Frames

Abstract

Criteria are proposed for determining the stiffness and strength demands for the seismic design of pin-supported walls in low- and medium-rise reinforced-concrete moment frames. A plasticity ratio and a global stiffness ratio are introduced to evaluate the effect of pin-supported walls (PS walls) in mobilizing the seismic capacity of the moment frame. Incremental dynamic analyses of 4-, 8-, and 12-story prototype PS wall-moment frames of various global stiffness ratios show that a constant stiffness ratio of two can generally ensure the formation of a global plastic mechanism no matter if the moment frame is a strong column-weak beam one or not. By mobilizing more structural elements to resist the earthquake action, the PS walls also increase the earthquake-resisting strength of the structure. Higher mode vibrations have a major effect on the strength demand for PS walls. Simple criteria are also developed for estimating the strength demands for the purpose of preliminary design of PS walls. The same methods for determining the stiffness and strength demands for PS walls are also applicable to other strong spine systems.