With America’s aging bridges in desperate need of repair and replacement, careful safety monitoring procedures exist to distinguish between those in need of rehabilitation and those with remaining useable service life. The primary methods engineers use to monitor the condition of bridges is through bridge inspections and load ratings. Load rating is the analysis of the ability for structural components of a bridge to support the passage of live loads. Typical load ratings are calculated using the codified approximate analysis methods defined by AASHTO. It is the goal of this study to demonstrate that the load ratings calculated using AASHTO equations are overly conservative.
This report identifies the shortfalls of traditional load ratings for bridges and discusses the benefits of inplace load testing. It demonstrates that code provisions are conservative and do not accurately reflect bridge behavior. This is shown using case studies of two (2) different bridges by comparing calculated distribution factors through traditional load rating techniques and distribution factors obtained using a calibrated model generated from in-place load tests.
The results of this study show that performing in-place load tests and creating calibrated bridge models provide valuable information about the true system behavior of a bridge. This information, mainly in the form of updated live load distribution factors, can be used to calculate a more realistic load rating, which in turn can extend the service life of a bridge and allow the allocation of funds to a different project in need.