P-Δ and Axial Column Deformation in Aseismic Frames

Abstract

A study of the influence of P-Δ and axial deformation of columns on the response of unbraced multistory building frames subjected to strong earthquake motion is presented. The columns are assumed to behave elastically while the girders follow a nonlinear moment-curvature behavior defined by a Ramberg-Osgood function. The method of analysis is a step-by-step numerical procedure developed for use on a high-speed digital computer. The lateral response of the structure to a horizontal component of ground motion parallel to the plane of the frame is computed. Two 10- and 25-story frame models are analyzed for the El Centro, 1940, and the Taft, July, 1952, earthquakes. The results indicate that, for the type of structures considered, the P-Δ effect does not appear to have a significant influence on their inelastic response to strong earthquakes. But the axial deformation of columns may affect the response by as much as 10% to 20%.