Shaking Table Performance of a New Bridge System with Pretensioned Rocking Columns

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. Accelerated construction is achieved through the use of precast columns and cap beams that can be assembled quickly. Postearthquake residual displacements are reduced by pretensioning the columns with partially unbonded tendons. Damage in the columns is nearly eliminated by concentrating flexural deformations to specially detailed regions at the top and bottom of the columns. In this study, the seismic performance of the new system was evaluated with a multi-shaking table test of a quarter scale, two-span bridge at the Network for Earthquake Engineering Simulation (NEES) Earthquake Engineering Laboratory at the University of Nevada, Reno. The maximum displacements of the bents were similar to those expected for a conventional bridge through the 100% design-level event [peak ground acceleration (PGA) = 0.75 g]. Residual drift ratios never exceeded 0.2% up to the 221% design-level motion (PGA = 1.66 g). Damage to the column concrete was negligible; the columns would not need any repair after being subjected to the 100% design-level motion. The only structural damage to the bridge was the eventual fracture of the column’s longitudinal reinforcement and bulging of the column’s confining tube, both of which occurred at drift ratios of approximately 6%. These damage states could be delayed by increasing the debonded length of the deformed bar reinforcement at the ends of the columns and by using a thicker steel tube for the confining detail.