Stability of the yield displacement

This chapter examines the kinematics of the yield displacement, clarifying the mechanical basis for using an assumed yield displacement in seismic design. The relative stability of the yield displacement as longitudinal reinforcement content is refined in design iterations makes yield point spectra and yield frequency spectra especially useful in seismic design. The relative stability of the yield displacement can be seen most easily from a kinematic perspective, first for individual members and then for entire lateral force resisting systems. Yield displacements determined in pushover analysis depend on the sources of flexibility that are represented in the structural models employed. At one extreme are software packages that require the user to specify the percentage of gross section stiffness to use for a linear beam-column element, but which readily model shear deformations and flexibility of beam-column joints.