FEMA P-440A: Effects of Strength and Stiffness Degradation on the Seismic Response of Structural Systems

The FEMA 440 report, Improvement of Nonlinear Static Seismic Analysis Procedures (FEMA 2005), was commissioned to evaluate and develop improvements to nonlinear static analysis procedures used in prevailing practice. Recommendations contained within FEMA 440 resulted in immediate improvement in nonlinear static analysis procedures at the time, but many difficult technical issues remained unresolved. The FEMA-funded ATC-62 Project was commissioned, in part, to further investigate the issue of component and global nonlinear degrading response, including cyclic and in-cycle degradation of strength and stiffness. The result was the publication of a supplemental report, FEMA P-440A, Effects of Strength and Stiffness Degradation on the Seismic Response of Structural Systems (FEMA 2009a). The FEMA P-440A report includes an extensive summary of available research on modeling of degradation, a database of analytical results documenting the effects of a variety of parameters on the response of structures with degrading components, and recommendations for improving nonlinear analysis techniques in current practice.