Investigation of Design and Repair Methods for Cantilever Bridge Bents

Large cantilevered substructures were constructed in San Antonio to support a massive concrete box-girder superstructure. AASHTO Standard Specifications do not integrate design criteria for reinforced concrete, prestressed concrete, corbels, and deep members. Because designers integrated all or most of these criteria in the design of cantilevered substructures, the resulting designs contained highly-congested joint regions.

An experimental program was developed to examine the contributions of reinforcement corresponding with the different design criteria, and to examine the behavior of cantilever-bent specimens designed using an “integrated” approach that incorporated strut-and-tie models to aid in detailing reinforcement. The testing program included a series of large-scale (1:2.75) cantilever-bent specimens with various details. Behavior at service as well as ultimate load levels was evaluated. The experimental program involved construction and testing of five specimens: two San Antonio ‘Y’ prototype models and three integrated design models. The prototype specimens included a reinforced concrete design and a fully-prestressed overhang design. The three integrated design models included a reinforced concrete design with headed reinforcement, a 54 percent prestressed ultimate design, and a 74% prestressed design, where the percentage of prestress indicates the percent of the flexural capacity provided by the prestressed reinforcement.

The design method, service-load performance, and response of specimens to ultimate loads are presented. Results of these tests were used to establish an integrated design method for the design of partially prestressed members.

A strength model that considers details of reinforcement was developed and verified by the experimental study. The strength model was used to evaluate existing cantilever bents. Eight full-scale cantilever substructures with deficient joint details were identified. Reinforcement details and analysis of two of the eight substructures are presented.

One external and two internal post-tensioned repairs were developed to strengthen the (1:2.75) prototype model reinforced concrete and fully-prestressed overhang specimens. The analysis model, design of the repairs, and experimental results are presented.