Live-Load Testing of a Steel Cantilevered Deck Arched Pratt Truss Bridge

The Kettle River Bridge is an arched, steel cantilevered deck, Pratt Truss Bridge. In order to quantify the live-load performance of the bridge superstructure and provide a baseline for future comparisons, it was instrumented with 151 strain gauges on various beam, stringer and truss members. In addition, eight vertical displacement gauges were attached along the truss. All gauges were simultaneously monitored as the bridge was subjected to a non-destructive, live-load test. The recorded bridge response was analyzed to quantify in-situ behavior. The measured behavior was then used to validate a finite-element model using solid and frame elements, which was subsequently used to obtain an inventory and operating load rating of 2.03, and 2.64, respectively. Based on the results of the test, it was concluded that the large gusset plates added partial fixity to the truss members demonstrated by the significant measured in-plane bending strains. However, the beam-and-stringer deck support system behaved nearly simply supported between consecutive panels. The actual bridge distribution factors were found to be conservative, in comparison to those calculated according the AASHTO (American Association of State Highway and Transportation Officials) LRFD (Load and Resistance Factor Design) Specifications, by 17 to 44%.