Seismic performance of skewed and curved RC bridges
Date
2013
Authors
Wilson, Thomas, author
Chen, Suren, advisor
Mahmoud, Hussam, advisor
Strong, Kelly, committee member
Johnson, Joshua, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Explicit knowledge of the behavioral response of complex reinforced concrete (RC) highway bridges to seismic events is essential to designing safe transportation systems. In the past, a number of skewed and curved highway bridges have experienced damage or suffered collapse due to earthquakes; and have most recently been observed during the Chile earthquake in 2010. Yet, there is very limited information on the combined effects of skew and curvature on the seismic response of RC bridges, and in particular identifying critical vulnerabilities to localized failures or system collapse. Recent research has also shown that the vertical component of earthquake ground motion, previously not considered, may have significant bearing on the response of highway bridges, particularly in near-fault regions. This study is comprised of two parts, including an examination of skewed and curved RC bridges of various configurations representative of a low seismic region, and an evaluation of the effect of vertical ground motion on complex geometry bridges in a moderate, near-fault, seismic region. Detailed numerical models are developed for various configurations of skew and curvature, and subjected to earthquake ground motion using nonlinear time-history analysis. In part one, detailed finite element models are developed and analyzed for eight bridge configurations of various degrees of skew and curvature, with consistent structural and geometric components. The bridge designs and earthquake hazard level are characteristic of the Mountain West region where the seismic risk is typically classified as low to moderate. Nonlinear time-history analysis is conducted on each bridge configuration for seven sets of earthquake records scaled to a site location in Denver, Colorado. The effects of earthquake input loading direction and abutment support condition, including integral and bearing supports, are also considered. The results show significant impacts on the seismic performance due to the effects of skew and curvature with stacking effects observed in the combined geometries. Insights on the complexities of curvature, skew, loading direction and support condition are made, which may lend themselves to more informed design decisions in the future. Part two of this study presents an assessment of the effect of vertical ground motion on horizontally skewed and curved highway bridges in moderate-to-high seismic regions. A numerical model of a skewed and curved, three-span bridge located in Tacoma, Washington is subjected to a suite of ground motions using non-linear time-history analysis. The ground motions selected represent a range of near-fault records with varying characteristics such as site condition, fault distance, and vertical-to-horizontal acceleration component ratios. The scenario developed characterizes the behavior of a bridge with a short fundamental period of vibration in a moderate seismic zone, where vertical ground motion effects may be applicable yet not considered by structural code. The results of the numerical simulations depict a significant impact from vertical ground motion in the substructure and superstructure, including responses typically not documented in existing studies. The implications of the results for structural designers may be to reconsider the current design approach involving vertical ground motion, particularly with shorter period bridges involving configurations of skew and curvature.