Study of the I-35 Bridge in Dallas

The bridge under study is an elevated section of I-345 near the interchange of I-45 and I-30 in downtown Dallas, Texas. The bridge is a twin steel plate girder bridge with transverse floor beams framing over the two main girders and supporting the concrete slab which is post-tensioned in both the longitudinal and transverse directions. Cracking has occurred in the connections of the floor beams to the girders in many places along the bridge. A retrofit was performed on the bridge in 2004 to try to mitigate this cracking, however new cracks later formed. The purpose of this study is to determine the reasons for continued cracking in this bridge. Field tests were performed on two sections of the bridge. The test consisted of running several controlled live load tests using trucks of known weights and monitoring the strain in the areas where cracking was most prevalent through the use of strain gages. These gages were then left on the bridge for one week after the live load tests to collect data which would be used to determine the fatigue performance of the bridge.

Once the field test data had been collected, a finite element model of one of the tested sections was created. The finite element model was used to better understand the behavior of the bridge and to provide a comparison to the field data. This model was also used to test the effectiveness of a possible retrofit plan for the bridge.