Date of Award

5-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Civil Engineering

Advisor

Nielson, Bryant G

Committee Member

Atamturktur , Sezer

Committee Member

Pang , Wei C

Abstract

Most of the past seismic fragility studies on typical highway bridges in the Central and Southeastern United States (CSUS) have focused on regular multi-span bridges with little to no skew. However, past earthquakes and studies have shown that skewed multi-span simply supported bridges may also be susceptible to earthquake damage, specifically causing coupled responses (longitudinal and transverse) that place more demand on individual components. With over 27 percent of simply supported steel girder highway bridges in the CSUS having a skew angle over 15 degrees, there is a specific need to further quantify the vulnerability of such bridges exposed to seismic hazard.
This study seeks to add to the current knowledge base of the seismic fragility of multi-span steel girder bridges in the CSUS by specifically addressing the issue of skew in the assessment. A sensitivity study of a three span bridge for each of the column, abutment, and bearing components along with the system as a function of skew angle is presented. This comparison indicates that bridge vulnerability appears to be largely unaffected by skew angles under 30 degrees, but larger skew angles do indeed result in more fragile bridge systems. Within this system the longitudinal components of the bridge become less fragile with increasing skew, but to a lesser degree than the transverse components becoming more fragile. Understanding the impact skew plays on seismic bridge fragilities will facilitate more robust regional risk analyses of highway systems.
Another aspect of this study is a presentation of seismic fragility curves developed for skewed multi-span simply supported steel girder bridges. The fragility curves indicate that for skew angles les than thirty degrees bridge fragility is not significantly affected. Larger skew angles result in a more fragile system in relation to increasing skew values. A comparison between the number of spans and system fragility results in a significant decrease in system fragility with an increase in the number of spans. The implications of the effects of skew angle and the number of spans will greatly contribute to regional risk assessment procedures such as those presented by HAZUS-MH.

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