Seismic Performance of Precast, Pretensioned, and Cast-in-Place Bridges: Shake Table Test Comparison

Abstract

A new bridge system has been developed to (1) reduce on-site construction time by using precast components, (2) eliminate major earthquake damage by utilizing column rocking and confinement of the column ends with a steel tube, and (3) maintain the system functionality after a strong earthquake by minimizing residual drift through the use of pretensioned strands in the columns. Furthermore, it uses only conventional materials. This paper compares the shaking table performance of a quarter-scale, two-span bridge constructed through the use of the new system with that of a conventional cast-in-place bridge with similar geometry tested in 2005. The new bridge system was constructed in approximately 20% of the time needed for the conventional cast-in-place system. In tests, the conventional bridge suffered major concrete cracking and spalling, whereas in the new system, damage to the concrete was only cosmetic. In the conventional bridge, the longitudinal bars buckled, and both the longitudinal and spiral reinforcement fractured, whereas in the new system, the damage to the reinforcement was limited to longitudinal bar fracture, and that occurred only under excitations much larger than the design-level motion. Furthermore, bar fracture in the new system could be delayed by increasing the unbonded length of the bars. The residual drift of the new system was essentially zero for all motions, whereas one of the exterior bents of the conventional bridge was so badly damaged and out of plumb that some of the supplemental mass on the bridge had to be removed, and testing was stopped shortly thereafter.