Stability Analysis of Softening Frames

Abstract

As the design process is refined, second‐order (stability) analysis becomes more important for both steel and concrete structures. Softening in concrete members, defined as the loss of moment capacity at advanced curvatures, is a material instability. The presence of significant axial force in a softening member raises the possibility of double or interactive instability, i.e., instability from large axial forces and instability from softening. Stability functions for members with finite softening lengths are derived. Computer program SOAPS (Second‐Order Analysis with Plasticity and Softening), developed for the stability analysis of plane frames with elastic‐plastic‐softening characteristics, incorporating stability functions and the