Evaluation of a Noncomposite Steel Girder Bridge through Live-Load Field Testing

This paper presents the field evaluation of a damaged noncomposite steel girder bridge that is part of the interstate highway system in Vermont. This bridge is typical of late 1960s construction and spans over a two-lane state highway near the town of Weathersfield, Vermont. The superstructure contains three-span continuous girders supported on abutments at the ends and on RC multicolumn interior bents. Strains were measured during live-load testing that was conducted to better understand the bridge behavior. The field results were compared with results from finite-element models created using common engineering assumptions. In addition, the load-distribution characteristics of girders that were damaged by an overheight truck traveling on the state highway under the bridge were evaluated. The results indicate that alternate load paths were developed within the bridge superstructure as a result of damage from the truck impact. For the loading magnitude applied during the load tests, evidence of composite action was observed and participation of curbs on the response of the bridge was noticed. Bridge skew and partial restraint generated at the supports also contributed to differences in the observed and calculated responses. These nondestructive load testing results were used to provide confidence on the load-carrying capacity of the bridge and to avoid costly bridge closures and detours.