Graduation Year

2006

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Civil Engineering

Major Professor

Rajan Sen, Ph.D.

Co-Major Professor

Ashraf Ayoub, Ph.D.

Keywords

Seismic, Degradation, Fragility, Displacement estimates, Collapse

Abstract

Seismic code provisions are now adopting performance-based methodologies, where structures are designed to satisfy multiple performance objectives. Most codes rely on approximate methods to predict the desired seismic demand parameters. Most of these methods are based on simple SDOF models, and do not take into account neither MDOF nor degradation effects, which are major factors influencing structural behavior under earthquake excitations. More importantly, most of these models can not predict collapse explicitly under severe seismic loads. This research presents a newly developed model that incorporates degradation effects into seismic analysis of structures. A new energy-based approach is used to define several types of degradation effects. The research presents also an evaluation of the collapse potential of degrading SDOF and MDOF structures. Collapse under severe seismic excitations, which is typically due to the formation of structures mechanisms amplified by P-Delt

a effects, was modeled in this work through the degrading hysteretic structural behavior along with P-Delta effects due to gravity loads. The model was used to conduct extensive statistical dynamic analysis of different structural systems subjected to a large set of recent earthquake records. To perform this task, finite element models of a series of generic SDOF and MDOF structures were developed. The degrading hysteretic structural behavior along with P-Delta effects due to gravity loads proved to successfully replicate explicit collapse. For each structure, collapse was investigated and inelastic displacement ratios curves were developed in case collapse doesn't occur. Furthermore, seismic fragility curves for a collapse criterion were also developed. In general, seismic fragility of a system describes the probability of the system to reach or exceed different degrees of damage. Earlier work focused on developing seismic fragility curves of systems for several values of a calibrated

damage index. This research work focuses on developing seismic fragility curves for a collapse criterion, in an explicit form. The newly developed fragility curves represent a major advancement over damage index-based fragility curves in assessing the collapse potential of structures subject to severe seismic excitations. The research findings provide necessary information for the design evaluation phase of a performance-based earthquake design process.

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