Static Load Testing of a Damaged, Continuous Prestressed Concrete Bridge

Abstract

Shortly after the completion of interstate highway I-565 in Huntsville, Alabama, cracks were discovered in the continuous end of many of the prestressed concrete bulb-tee girders. Alabama Department of Transportation (ALDOT) employees determined that differential temperature gradients across the depth of the members were the likely cause. ALDOT personnel, along with Auburn University personnel, performed additional research to verify the causes of the cracking and to investigate possible repair methods. It was concluded that the temperature gradients were the cause of the cracking, and a fiber-reinforced polymer (FRP) repair was designed. Load tests before and after the FRP repair were recommended to determine the effectiveness of the repair. A finite-element model (FEM) analysis was conducted as well to verify the behavior of the bridge and to determine the possible effects of the repair. The current state of the bridge was observed and recorded, and a pre-repair load test was conducted in order to provide a baseline to which the post repair load test results could be compared. A comparison between the two will provide a method of determining the effectiveness of the repair. The load test was focused on two girders that exhibited typical cracking behavior. The girders were tested with concrete surface strain gages, deflectometers, and crack opening devices. The pre-repair load test results showed that the bridge is acting in either a partially continuous or fully continuous manner. An additional goal of the test was to determine the effectiveness of superpositioning in bridge girders. It was determined that superpositioning was effective for large scale bridge behavior measurements such as deflections, but was not applicable for more localized measurements like strains and crack openings. A follow-up load test will be required to determine the effectiveness of the FRP repair. The results can be compared to the FEM results in order to verify the FEM predictions.