Inelastic Beams for Seismic Analyses of Structures

The post-yield flexural characteristics of prismatic members with bilinear moment-curvature properties are investigated. The objective is to improve point hinge modeling of such members for inelastic dynamic analyses of large structures subjected to seismic excitations. By comparing incremental secant stiffness ratios derived under different loading patterns, an antisymmetric end loading can be used to derive improved average post-yield properties that approximately account for the spread of yielding. Subsequently, two sets of curves are presented for use in practical applications; the first gives equivalent post-yield stiffness ratios and the second the corresponding idealized yield moments. Ductility factors frequently used in practice are also examined, and some clarifications are made that are aimed at eliminating certain ambiguities associated with such factors.