Report No.: CCEER-02-1

Seismic Performance and Retrofitting of
Reinforced Concrete Bridge Bents

Authors: C. Pulido, M. Saiidi, D. Sanders, and A. Itani

Date: January 2002

Sponsoring Agency: California Department of Transportation (Caltrans)
Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557
Abstract:
With the objective of studying the seismic behavior of two-column bents with drop cap beams built prior to the 70’s, four ¼ scale models were built and tested using shake tables. The bents incorporated typical pre-70’s reinforcement and the construction details used at the time. Two bents represented as-built piers and the other two were retrofitted to address the seismic deficiencies of the as-built bents. All the bents were subjected to the 1994 Northridge-Sylmar record and tested in an identical manner.
The failure of the as-built piers was due to severe shear damage of the cap beam at a displacement ductility of approximately 2 and lap splice failure at the bottom of the columns. The two remaining specimens were retrofitted using carbon fiber reinforced plastic (CFRP) fabrics on one, and an infill wall in the other. The CFRP retrofit was designed using Caltrans guidelines to enhance the confinement of the column, flexural capacity of beam, and the shear capacity of columns, beam, and joints. The infill wall was designed following the current Caltrans practice. Testing of the retrofitted bents showed that the retrofit enhanced the performance and increased the displacement ductility to 7. The study also revealed that the actual CFRP fabric strains are considerably lower than the values assumed in design. The gap left at the top of the infill wall had a significant, unexpected effect on the load path. Analytical studies were developed to determine the performance of the as-built and retrofitted bents subjected to lateral loads. The models focused on overall lateral loading response. It was found that the current pushover analysis method should be modified to include shear and bond slip deformations. In the course of analyzing the CFRP-retrofitted bent, a new simple model was developed to determine the properties of concrete confined by CFRP fabrics.