A Pre-Tensioned, Rocking Bridge System for Accelerated Construction and Enhanced Seismic Performance

Abstract

A new bridge bent system has been developed to reduce on-site construction time, minimize residual displacements even after a large earthquake, and reduce seismic damage in comparison with conventional cast-in-place construction. Precast connections used in the system have been tested successfully under quasi-static conditions and found to perform exceptionally well, re-centering with essentially no concrete damage or residual drift after being loaded cyclically to drift ratios of up to 10%. The seismic performance of the new system was evaluated with shaking table tests of a quarter-scale, two-span bridge. The maximum displacements of the bents were similar to those expected for a conventional bridge through the Design Level event (PGA=0.75g). Damage to the column concrete was negligible; the columns would not need any repair after being subjected to the Design Level motion. Residual drift ratios never exceeded 0.2% up to the 221% Design Level motion (PGA = 1.66g). The only structural damage to the bridge was the eventual fracture of the column’s longitudinal reinforcement and bulging of the column’s confining tubes placed at the ends of the columns, both of which occurred at drift ratios of approximately 6%. Results from the subassembly and shaking table tests were used to develop a design methodology for the new system that aligns with the displacement-based procedure outlined in the AASHTO Guide Specifications for LRFD Seismic Bridge Design (2015). The modifications to this procedure necessary to align with the objectives of the new system are straightforward and could be implemented within current design practice. A modeling strategy for the pre-tensioned bent system is also proposed and specific aspects of this approach are validated against the subassembly and shaking table test results.