Seismic Response of Reinforced Concrete Frames

Analytical studies of the elastic and inelastic response of reinforced concrete frames subjected to earthquake motion are presented. The effect of stiffness degradation on the seismic response and in particular on ductility demand is examined. Several single-story frames are analyzed; stiffness degradation significantly increases ductility demand in short period systems. Studies of multistory frames are also presented; stiffness degradation again increases ductility demand but the effect is pronounced only in the upper stories. The bending moments and forces induced in an inelastic multistory frame are smaller than those in a purely elastic frame. However, if the columns are designed to remain elastic while the girders yield, the reduction in the column moments and axial forces is not as large as that in the girder moments.