Paper Number 30 A Probabilistic Seismic Loss Assessment of Advanced Post-Tensioned Precast Bridge Systems 2009 NZSEE Conference D.J. Marriott, S. Pampanin & D. Bull University of Canterbury, Christchurch, New Zealand. A. Palermo Technical University of Milan, Italy. ABSTRACT: Post-tensioned precast rocking systems have emerged as the next generation seismic resisting systems; however, they are not yet widely accepted and are seldom considered in practice, particularly for bridge systems, due to a combination of lack of understanding and the fallacy that such a system may not be cost effective when compared to traditional monolithic or emulation of cast-in-place construction. The results of a seismic loss assessment confirm that a traditional hybrid bridge system provides a significant financial benefit when compared to a monolithic precast system. Reasons for this relate to the reduced level of physical damage at each structural limit state and a greater displacement capacity for post-tensioned bridge piers. When combining viscous and hysteretic dampers within a post-tensioned bridge system (defining an advanced flag-shape system) a superior level of protection can be achieved for either far-field or near-field earthquake events. However, the initial cost of installing fluid viscous dampers (based on current market costs) can undermine the potential financial benefit of such a system. 1 INTRODUCTION This paper examines the performance of three post-tensioned (PT) reinforced concrete (RC) case study bridges and compares them to a conventional monolithic bridge. The four bridges are identical in terms of geometry and design objectives; however, they differ in terms of lateral capacity and mechanical damping. A seismic loss assessment is carried out for each bridge. The seismic loss assessment provides a means of directly comparing the performance of each system in terms of Expected Annual Loss (EAL) and the annual frequency of exceeding a specified level of loss (loss- hazard). This paper first introduces the prototype bridge systems and then provides a brief overview of seismic loss assessment, concluding with the results of the analysis. 2 PROTOTYPE BRIDGE A symmetric, six-span, reinforced concrete prototype bridge is illustrated in Figure 1. The bridge is symmetric about pier 3 with internal spans of 50m and end spans of 40m. A segmented, precast concrete box girder deck system is seated on bearings located on top of the cap beam and abutments. Each pier and abutment is founded on shallow soil (NZS1170.5 [2004] soil category C) with piled foundations to the bedrock. Dimensions of the box girder deck and pier assembly are illustrated in Figure 2. One ductile monolithic bridge and three post-tensioned hybrid equivalents are investigated. To aid in a direct comparison, each bridge is identical in geometry (pier heights and cross-section dimensions in Figure 2). Three variations of a post-tensioned, rocking bridge system are considered. Bridge 1. A precast (or an emulation of cast in-situ) bridge with monolithic ductile flexural hinging at the base of the piers, designed to satisfy the requirements of NZS3101 [2006]. This ductile system is termed benchmark monolithic.