Experimental Load Rating of a Posted Bridge

Abstract

Results of an experimental load test of a posted, three-span, steel-girder-and-slab bridge are presented. The bridge was designed to have three simple supported spans, each consisting of a cross section with nine noncomposite steel girders. Through diagnostic load testing, it was determined that the girders were acting compositely with the concrete deck and that significant restraint was being developed at the bearing supports. A finite-element model of the main span was generated using the measured response of the bridge. Results of analyses conducted using the numerical model were compared to the measured response and found to be quite similar. Using this model, along with models that account for the loss of composite action and/or support restraint, a variety of load ratings for the bridge was determined. By comparing the various load ratings, and by considering the nature of the unintended composite action and support restraint, decisions regarding the determination of a safe bridge rating are discussed. Final conclusions suggest that the current posting levels may be unnecessary.