NEESR: Seismic Resilience of Pre-Tensioned Bridge Bents

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This research investigates a system to simultaneously achieve three major advances in the design and construction of bridge bents: improved seismic performance, faster on-site construction, and better long-term durability. First, the seismic performance will be addressed through the use of unbonded pre-tensioned columns, with the goal of re-centering the bridge after an earthquake. Second, the faster on-site construction is to be achieved through the use of pre-fabrication, which typically goes hand-in-hand with pre-tensioning. Connection details are critical, but basic configurations for them have already been developed. Third, the long-term durability is to be addressed by the use of high performance materials (hybrid fiber-reinforced concrete (HyFRC), stainless steel bars, and epoxy-coated strands) in key areas. Pilot studies have already been conducted and have shown that the system possesses the desired fundamental characteristics and has the potential to deliver the anticipated benefits. However, key aspects of the system need to be investigated, and numerical models need to be developed to investigate its dynamic performance under a wide variety of conditions. This research is a collaboration among the University of Washington, University of California at Berkeley, and University of Nevada, Reno. The testing of a two-span bridge designed with this new system will be conducted using the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) shake table facility at the University of Nevada, Reno. Data from this project will be archived and made available to the public through the NEES Project Warehouse data repository at http://www.nees.org.This project aims to break the limitation of achieving two out of the three long-standing "better, faster, cheaper" paradigm by providing three simultaneous improvements to the way that bridges are designed and built in seismic areas. The "better" aspect is provided by building upon basic technology that has been proven for buildings and was used to resist the seismic loads in a 40-story concrete building in San Francisco, among others. Pre-tensioning is being adapted for use in bridges, where it is being supplemented and optimized by the strategic inclusion in key regions of high performance materials, such as stainless steel and fiber-reinforced concrete, which are both selected for their toughness. Those materials will provide a quantum improvement in the response to earthquake motions by ensuring that bridges re-align properly and are open to traffic, including emergency response vehicles, immediately after an earthquake, and also by providing better long-term durability than is possible with conventional materials. The "faster" is achieved by the use of carefully designed pre-fabrication, which means that many components can be made off site and connected together rapidly on site. The connections must be easy to assemble but highly resistant to earthquake forces. Achieving those two goals together is challenging, but is possible due to the innovative configuration of the system. The "cheaper" is expected to follow from the significant reduction in construction time. Preliminary studies on individual aspects of the system have already shown their viability. This study focuses on the whole system, to optimize the arrangement and details of its components, and to create the mathematical models needed by engineers to design it in practice to reduce the cost of rebuilding the nation's aging bridge infrastructure. This award is part of the National Earthquake Hazards Reduction Program (NEHRP).