On Assessing Near Collapse in Seismic Performance-Based Design

Among the more challenging aspects of performance-based seismic design is the development of techniques to reliably establish the so-called "collapse prevention" performance objective. Possible approaches include one from FEMA 273 Guidelines for the Seismic Rehabilitation of Buildings that employs linear or nonlinear seismic analyses together with acceptance criteria in the form of element-based limits on forces and deformations. Another method, proposed in the recently published SAC Seismic Design Criteria for New Moment-Resisting Steel Frame Construction, defines acceptance criteria in terms of probabilistically determined interstory drift limits. While both of these methods are major steps towards achieving comprehensive performance-based design, neither fully accounts for aspects of inelastic system stability as influenced by nonlinear strength and stiffness degradation under cyclic loads. An new approach is proposed herein that utilizes cumulative damage indices and a second-order analyses to evaluate the remaining stability of structures that have been subjected to strong ground motions. Application of the technique is demonstrated through a series of incremented time-history analyses of a composite steel-concrete moment frame.