Diagnostic Load Tests of a Prestressed Concrete Bridge Damaged by Overheight Vehicle Impact

A series of diagnostic load tests performed on two prestressed concrete bridges located in western Iowa are discussed. The bridges are dual prestressed concrete I-beam structures. In June 1996, an overheight vehicle struck the westbound structure and caused significant loss of section and cracking. As a result of the severity of the damage and because of concerns about the remaining capacity and long-term durability of the damaged beams, the Iowa Department of Transportation decided to remove the two most severely damaged beams. The diagnostic load-testing portion of the research program consisted of positioning test vehicles of known weight at predetermined locations along the deck of the damaged westbound and undamaged eastbound bridge. Single-and dual-truck tests were conducted on each bridge. Following replacement of the damaged beams in the westbound structure, additional tests were conducted. The results of these three load tests are compared to determine the effect of the localized beam damage on the overall live load distribution pattern in the bridge. The objective of this research is to determine the effects of damage on the load distribution and the remaining strength of damaged prestressed concrete bridges. Noticeable differences in response were detected in the westbound and eastbound bridges before beam replacement, with the difference essentially disappearing after the repair of the westbound bridge. The research project also involved model bridge testing, along with the repair of the beams that were removed from service and those that were intentionally damaged in the laboratory. The project is now complete.