Plastic Collapse, Shakedown, and Hysteresis of Multistory Steel Structures

Abstract

The entire spectrum of incremental collapse behavior, including alternating plasticity, shakedown, and plastic (limit state) collapse, of multibay, multistory structures composed of elastic‐perfectly plastic materials can be determined from a consideration of the irrecoverable energy (hysteresis energy) dissipated by the plastic hinges that occur in such structures. An extensive study utilizing computer models of the relevant structural behavior has revealed that much of this hysteresis energy dissipation is concentrated in a relatively few dominant plastic hinges. Strengthening or weakening structural components at those locations where dominant plastic hinges form can significantly alter the incremental collapse behavior of the entire structure. The rate of energy dissipation, as well as the rate of approach to failure, can vary in a complex manner in multibay, multistory structures subjected to many cycles of repetitive loads. It is demonstrated that this complex structural behavior may be unraveled by performing a detailed investigation of the evolution of hysteresis energy at each of the plastic hinges that forms in the structure. A series of such investigations has revealed the roles that prominent and latent plastic hinges play in the overall response of the structure to repetitive loads. New directions for research aimed at improving the analysis and design of earthquake‐resistant buildings are indicated by the results, which show that the global resistance of the entire structure to incremental collapse depends upon the details of the applied loading program, as well as upon the local plastic moment resistance of the individual structural components. Illustrative results from the application of the new method are given for a two‐bay, two‐story rigid frame structure.