An Evalutation Of Repair Methods For Cantilever Bridge Piers

Cantilever bridge piers are occasionally used in place of standard symmetrical hammerhead bents in areas where limited right-of-way prevents placement of the bents directly under the roadway. This design produces extremely high moments in the joint region, where the caniliver overhang joins the vertical pier. Many bents of this type were used in the I-10/I-35 highway interchange in San Antonio. A design flaw was discovered in the joint of these bents, and field investigations revealed significant cracking in this region in several of the bents.

Earlier phases of Texas Department of Transportation Project 1364, “Design of Large Structural Members Utilizing Partial Prestressing,” examined the strength of the deficient joint regions and designs for future bents with increased strength, while this study examines various methods for repairing and retrofitting existing bents to bring them up to full design strength.

Three types of cantilever bridge piers were used in the San Antonio interchange. One type contained only mild reinforcement, another utilized post-tensioning in the overhang but not in the pier, while the third was post-tensioned throughout. The last type did not exhibit the joint design flaw, so the study concentrated on the other two. Scale models of each type of pier were constructed and tested. Several repair options, including various methods of internal and external post-tensioning, were designed, constructed, and tested. The different repair options were then evaluated and compared based on ultimate strength, serviceability, cost, constructibility, and aesthetics. The results of the tests, evaluations, and comparisons are presented in this report, along with recommendations for the Texas Department of Transportation on the most suitable repair method.