Influence of Traffic Loading on the Seismic Reliability Assessment of Highway Bridge Structures

Traditionally, the impacts of traffic and earthquake loading have been considered independently when assessing bridge reliability. This paper presents a framework for joint seismic and live-load fragility assessment of highway bridges. Full probabilistic analyses accounting for variation in bridge parameters, ground motion, and truck load and position are proposed to develop bridge system fragility curves and to identify the critical truck position that renders the bridge most vulnerable to earthquakes. A fragility surface is derived for the critical truck position at which the failure probability is conditioned on the governing vehicle weight in addition to ground motion intensity, thus depicting the impact of truck load on bridge seismic fragility. This fragility surface is convolved with the governing vehicle weight distribution (obtained from weigh-in-motion data) and probability of truck occurrence (function of truck flow rate) to determine traffic-informed conditional seismic reliability estimates. The proposed methodology is demonstrated on a case study of a multispan continuous steel girder bridge in the central and southeastern United States. The framework can find ready extensions to assess the joint impact of earthquake and live loads for other bridges and hazard conditions and can offer a basis for deriving reliability-based load combinations consistent with emerging trends in bridge design. © 2013 American Society of Civil Engineers.