Finite-Element Modeling of a Damaged Prestressed Concrete Bridge

Abstract

Spans 10 and 11 of the Interstate Highway 565 bridge structure in Huntsville, Alabama were noticed to be cracked shortly after their construction. Alabama Department of Transportation (ALDOT) employees investigated and concluded that the probable cause of the cracking was stress at the continuous support due to the temperature differential between the bridge deck and the bulb-tee girders. Further investigation to determine the cause of the cracking, the results of the cracking, and the possible repair methods was conducted by ALDOT in cooperation with Auburn University personnel. It was concluded that fiber-reinforced polymer (FRP) repair was feasible, and a repair procedure was devised. In order to measure the effect of the repair, load tests were planned to occur both before and after the repair. On June 1 and 2, 2005, the pre-repair load tests were conducted. A finite-element model (FEM) was created to provide a basis for an analytical comparison to measured data and observed bridge behavior. The model was designed to simulate the current behavior of the bridge and to predict the change in behavior due to the repair work. Modeling results supported the hypothesis that rather than behaving as a continuous two-span beam, the bridge displayed behavior consistent with a continuous beam including a hinge located in the cracked region. An additional goal of the analytical modeling was to determine which of the strain gauges used in the pre-repair bridge tests should be reassigned to other locations of the bridge for the post-repair tests. It was determined that eight gauges should be relocated from the face of the girder near the top pf the web to the base of the FRP reinforcement. Results of the analytical modeling warranted the prediction that the FRP repair would return the bridge to near fully continuous behavior. Further analysis will be necessary after the repair is complete and the post-repair test has been conducted to determine the results of the repair on the behavior of the bridge.