Seismic behavior of reinforced concrete bridges with skew-angled seat-type abutments Peyman Kaviani a , Farzin Zareian a,⇑ , Ertugrul Taciroglu b a Department of Civil and Environmental Engineering, University of California, Irvine, CA 92697, USA b Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095, USA article info Article history: Received 30 July 2011 Revised 10 April 2012 Accepted 5 June 2012 Available online 20 July 2012 Keywords: Skewed bridges Performance-based earthquake engineering Shear key Seat-type abutment abstract This study focuses on identifying trends in seismic behavior of reinforced concrete bridges with seat-type abutments under earthquake loading, especially with respect to abutment skew angle. To that end, a detailed approach for modeling skew-angled seat-type abutments is proposed; and a comprehensive vari- ety of bridge configurations are considered. Specifically, three short bridges located in California are selected as seed bridges, from which different models are spawned by varying key bridge structural parameters such as column-bent height, symmetry of span arrangement, and abutment skew angle. Through extensive nonlinear time-history analyses conducted using three suites of ground motions, it is demonstrated that demand parameters for skew-abutment bridges, such as deck rotation and column drift ratio, are higher than those for straight bridges. By investigating the sensitivity of various response parameters to variations in bridge geometry and ground motion characteristics, it is shown that bridges with larger abutment skew angles bear a higher probability of collapse due to excessive rotations, and that the shear keys can play a major role in reducing deck rotations and thus the probability of collapse. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Bridges with skew-angled abutments, also denoted henceforth as ‘‘skewed bridges,’’ are constructed to accommodate geometry constraints resulting from alignment of a waterway or roadway crossing that occurs at an angle that is different from 90°. In the present study, the focus is on the seismic response of short skewed bridges with ‘‘seat-type’’ abutments, which are very common in construction practice in California. Observations from past earth- quakes [1–3] suggest that there are significant differences between the response of straight and skewed bridges. A manifestation of this difference is the inherent tendency of the decks of skewed bridges to rotate about their vertical axes under seismic excitation, which can lead to unseating from abutments, and ultimately, to collapse. The primary cause of this excessive rotation is the eccen- tric passive resistance of the abutment backfill. Excessive deck rotations can lead to loss of bridge functionality and significant downtime for repairs, or loss of stability and casu- alties. Site investigation of the Foothill Boulevard Undercrossing lo- cated in California, 34.25N and 118.5W, (which has a skew angle of approximately 60°) showed that it rotated in its horizontal plane, resulting in a permanent offset of approximately 7.5 cm (i.e., 0.9  10 3 radians of deck rotation) in the direction of increasing skew angle during the 1971 San Fernando Earthquake [1]. Recon- naissance report of the 2010 Chile Earthquake [2,3] states that skewed bridges in affected regions rotated, mainly about their cen- ter of stiffness, and that those with weak exterior shear keys suf- fered higher levels of damage due to transverse unseating. Development of analytical/numerical models that can capture the peculiar collapse mechanisms of skewed bridges under seismic excitation, and can accurately quantify their damages have been a subject of research for quite some time. Ghobarah and Tso [4] used a spine-line model to represent bridge deck, and columns; they concluded that the bridge collapse was caused by coupled flex- ural-torsional motions of the bridge deck or by the excessive com- pression demands that resulted in column failures. Using simplified beam models, Maragakis and Jennings [5] concluded that the angle of the skew and the impact between the deck and abutment govern the response of skewed bridges. Wakefield et al. [6] conjectured that if the deck is not rigidly connected to the abutments, dynamic response of the bridge will be dominated by planar rigid body rota- tions of the deck rather than coupled flexural and torsional deformations. A more recent study by Meng and Lui [7] proposed that the seis- mic response of a bridge is strongly influenced by the column boundary conditions and skew angle. In a subsequent study [8], they used a dual-beam stick model to represent the bridge deck, and showed that in-plane deck rotations are mostly due to abut- ment reactions. Using nonlinear static and dynamic analyses, Abdel-Mohti and Pekcan [9] investigated the seismic performance 0141-0296/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.engstruct.2012.06.013 ⇑ Corresponding author. Tel.: +1 949 824 9866; fax: +1 949 824 2117. E-mail address: zareian@uci.edu (F. Zareian). Engineering Structures 45 (2012) 137–150 Contents lists available at SciVerse ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct