Sensitivity Analysis of Seismic Fragility Curves for Skewed Multi-Span Simply Supported Steel Girder Bridges

Most of the past seismic fragility studies on typical highway bridges in the Central and Southeastern United States (CSUS) have focused on regular three-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 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 fifteen 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 become more fragile. Understanding the impact skew plays on seismic bridge fragilities will facilitate more robust regional risk analyses of highway systems.