Assessment of bridge vulnerability due to seismic excitations considering wave passage effects S.S.F. Mehanny a,b,⇑ , O.M.O. Ramadan a , H.A. El Howary b a Structural Engineering Department, Faculty of Engineering, Cairo University, Egypt b Dar Al-Handasah, Giza, Egypt article info Article history: Received 22 November 2013 Revised 3 April 2014 Accepted 4 April 2014 Available online 8 May 2014 Keywords: Out-of-phase ground motions Incremental dynamic analyses Seismic fragility Continuous bridges abstract Uniform ground motion excitation at different supports is typically assumed in practice while performing seismic response analysis of structures with somehow limited footprints. In essence, design of bridges is customarily performed assuming identical signal at all bridge supports. In fact, ground motions may vary at the different supports, especially, for long extended structures, such as long bridges, dams and pipe- lines. This paper illustrates the impact of the difference in the arrival time of the ground motions on the seismic performance of continuous box girder bridges in both bridge orthogonal directions (longitu- dinal and transverse). For illustration purposes, a nine-span case-study bridge with a total length of 430 m is considered. Non-linear time history analyses are carried out using opensees software and the ‘‘out-of-phase ground motions at different supports’’ phenomenon is examined using a set of 20 real records originally extracted from the peer (Pacific Earthquake Engineering Center) Strong Motion Data- base. The analyses are repeated for different apparent wave propagation velocities (namely, 100, 200, 400 m/s, and 1 designating synchronized arrival time of the signal at all supports) along the bridge lon- gitudinal direction. Results of the non-linear time history analyses performed in an incremental dynamic analysis context are hence manipulated through a probabilistic analysis framework to generate fragility curves associated with various performance levels for the case study bridge. Fragility curves giving the conditional probability of exceeding various performance levels are then integrated with generated hazard curves defining the expected seismic hazard in a specific zone. The outcome of this integration process results in values of mean annual frequency of exceeding pre-defined performance levels. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Since the 1960s, the effects of seismic ground motion spatial variation on the response of lifeline structures including continu- ous multi-span or long span bridges have been studied extensively. The results indicate that the type of response (conservative or not) induced by the spatially variable motions compared to that of identical ones depends strongly on the spatial variation models used in the analyses, and a realistic characterization of seismic ground motions in addition to the bridge structural system. A com- prehensive overview of this previous research is not within the scope of the present paper; however, a briefing of some researches pertinent to the investigation established in the current study that inspects nonlinear response of bridges under asynchronous seismic excitations within a probabilistic performance-based seismic engi- neering framework is presented below. Due to space limitations the reader is referred to [1] for a more inclusive literature review. There are wealth of data for the various effects of non-uniform seismic excitation on bridge structural response including wave passage, coherency, attenuation and local site/soil effects (e.g., 2–5). General findings of these investigations are scattered depending on the case study bridge considered in each and on the spatial variation model adopted. For instance, Sextos et al. [3] studied the effect of soil–structure interaction and spatial variabil- ity of ground motion on an existing curved irregular bridge hosting twelve spans. They concluded that in light of asynchronous motion, the angle of incidence of the incoming spatially variable waves seems to play a secondary role in the overall dynamic response of the studied bridge. Li and Yang [4] studied the seismic responses of an existing long span pre-stressed concrete continu- ous rigid-framed bridge subjected to multi-support excitations. Their final conclusion was that long-span structure response under multiple excitations may be more intensive than that under http://dx.doi.org/10.1016/j.engstruct.2014.04.010 0141-0296/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: sameh.mehanny@stanfordalumni.org, ssfmehanny@eng.cu. edu.eg (S.S.F. Mehanny), omoramadan@yahoo.ca (O.M.O. Ramadan), hesham. ayman@dargroup.com (H.A. El Howary). Engineering Structures 70 (2014) 197–207 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct