Collapse Analysis and Displacement Estimates of Degrading MDOF Structures for Performance-Based Seismic Design

University Of South Florida, Tampa FL

Investigators

Abstract

Collapse Analysis and Displacement Estimates of Degrading MDOF Structures for Performance-Based Seismic Design, CMS proposal 0324442 PI: Ayoub, USF Seismic design methodologies have recently adopted the new general concept of performance-based procedures. The new concept has been reflected in several codes of practice. New analysis procedures have been developed to estimate seismic demands for performance evaluation. Most of these procedures are based on simple models, and do not take into account degradation effects, a major factor influencing structural behavior under earthquake excitations. More importantly, most of these models do not predict collapse of structures under seismic loads. The main objective of this research project is to develop a procedure for incorporating degradation effects for seismic demand evaluation of MDOF systems. A new numerical platform that permits analysis of degrading structural systems was already developed by the P.I. Energy-based approaches were used to define several types of degradation effects. The newly developed models were added to the material library of a widely used commercial software for seismic analysis of MDOF structural systems. The models also permit collapse prediction of MDOF structures under seismic excitations. The proposed work consists of several tasks. First, a numerical study on collapse prediction and displacement estimates of degrading SDOF systems will be conducted. Second, a statistical parameter study is performed in order to study the effectiveness of scaling earthquake records for MDOF analysis of degrading systems. Third, an extensive numerical study is conducted on degrading MDOF systems to estimate maximum inelastic displacements for use in performance-based seismic code provisions, and to determine strength levels that subject the structures to collapse for collapse-prevention limit state design purposes. Finally, seismic fragility analysis will be performed, where fragility curves for a collapse criterion for a large spectrum of structural systems will be generated numerically. The intellectual merit of the research project is to include degradation effects in performance based seismic design methodologies. To perform this task, accurate constitutive models of degrading materials have to be developed. Currently, few if any deterioration models exist in a general three-dimensional frame analysis program. The research project employs newly defined energy-based degrading models that have been incorporated into a commercial nonlinear seismic analysis program. The broader impact of the proposed research project is to provide an opportunity to expose students and structural engineers in the Tampa Bay area to new design techniques. This will be performed through the development of new courses on inelastic analysis of structures, and performance-based procedures, that will be available on the interactive web-based teaching tool Blackboard5. The project also represents an opportunity to involve students at USF, especially of underrepresented groups, in a research work of national interest on seismic hazard mitigation, as currently one such minority student is already involved in a similar work. Finally, the statistical outcomes of the proposed research will be documented in a database format to be available on the internet, which will provide important information to the whole structural community.