Determination of Load Ratings for Non-Composite Steel Girder Bridges Through Load Testing

In this study, a family of single-span non-composite steel girder bridges with cast-in-place concrete decks was chosen to determine if predictable superstructures characteristics could be identified. These bridges lack a shear connection between the concrete deck and steel girders and were commonly built prior to 1950. Past testing has shown that these bridges will often produce a live load response lower than analytical models due to various factors, including partial composite action between the deck and girders, edge stiffening of the exterior girders due to the presence of curbs and railings, bearing restraint due to connection details partially restraining the end rotation of the girders, and more precise live load distribution factors. The study results were based on the testing and evaluation of six bridges using diagnostic load testing. Conventional load ratings of the six bridges were performed by three different rating agencies, and the results were compared to performance-based load ratings determined through diagnostic load testing. The test results showed that the diagnostic load test ratings were larger for all six bridges compared to the conventional ratings. There were some behavior characteristics that were predictable, and thus extrapolation of these performance characteristics could possibly be extrapolated to other bridges in the fleet. It is recommended that a more statistically significant sample group of fleet bridges be tested and evaluated before widespread application of fleet results can be reliably extrapolated.