Experimental Behavior of a Steel Girder–Stringer–Floorbeam Bridge

Abstract

The presented case study summarizes a quick-response project for the Tennessee Department of Transportation (TDOT), which focused on the steel-stringer behavior for a girder–stringer–floorbeam bridge. TDOT was confronted with relatively low stringer load ratings for many of their 31 similar structures. As a result, TDOT initiated this field study to ultimately produce refined load ratings. This information was then to be utilized for deciding whether an intervention (e.g., retrofit) was necessary. Diagnostic load testing was the approach selected and a representative bridge was chosen. Then load testing was comprehensively designed and executed. This included the installation of 42 strain gauges, data-acquisition quality-control testing, weighing and measuring test trucks, load testing of the structure, and then removal of the system. The load-test data provided insight into the true behavior of the bridge. The stringers were subjected to a combined interaction of the global and local response. Overall, the local demands were the largest component, but the magnitudes were well below the predicted values. This was partly because of the lateral distribution of the load. Additionally, partial composite action was identified between the steel stringers and concrete slab. Refined load ratings were calculated using the field-measured data and following the AASHTO Manual for Bridge Evaluation. The comparison of predicted to measured responses clearly indicated the conservative nature of the prior analytical calculations. The stringer load ratings were increased by 68% based on the field testing. In the end, the steel-stringer load ratings were sufficient, with no intervention necessary.