Field Testing and Load Rating of a Steel-Girder Highway Bridge

The load rating of a highway bridge is often underestimated by engineering analysis. A method is presented for improving the load rating of a continuous-span concrete-slab-on-steel-girder highway bridge through field testing. Bonded foil-type strain gages and an electronic data acquisition system were used to evaluate the neutral axis locations, composite behavior, moment distribution behavior, and noncomposite deck flexure in the bridge. Data was recorded at thirty gage locations during a series of crawl-speed dynamic tests. As a result, the bridge’s AASHTO LFD operating and inventory load ratings were both improved by a factor of 1.25.