Fatigue, Ultimate, and Rail Capacity Comparison of Two Fiber Reinforced Polymer Bridge Decks

The use of glass fiber reinforced polymer (GFRP) bridge decks is appealing for applications where minimizing dead load is critical. The retrofit of the Granite Falls Bridge in Snohomish County, Washington is one example of a seismic retrofit project where a GFRP bridge deck is being designed to replace a heavier concrete deck. This replacement will reduce the active seismic weight of the structure, thereby reducing the seismic forces and providing savings in the retrofit of the steel truss arch superstructure. In support of this retrofit project, research has been performed to determine the response of two independently manufactured GFRP decks to multiple loading conditions.

Three tests are conducted to: (i) examine each deck’s ability to reach a specified fatigue life with minimal degradation in stiffness, (ii) determine whether each deck provides a minimum ultimate strength, and (iii) investigate the strength and failure mode of a novel guard rail connection. Each test uses a setup designed to be as close as practicable to what will be the in situ conditions for the deck. This includes the use of a 2% drainage cross-slope and previously untested deck to girder connections.  

Fatigue and ultimate strength tests will use 12 ft by 8 ft GFRP deck panels supported by three steel girders. The fatigue tests consist of a single 26 kip load applied for 2 million cycles, which corresponds to an AASHTO HS-20 truck with a 30% impact factor, and the ultimate strength tests consist of a monotonically applied 78 kip load at two loading points. For one deck specimen, two different connection mechanisms will be compared during fatigue and ultimate loading and their effect on load distribution is examined. Following the fatigue and ultimate strength tests, a barrier rail with an innovative connection through the GFRP deck to the flange of the outer steel girder will be constructed. The rail will then pushed to failure in a manner simulating the response of a vehicle impact and the resulting capacity and failure mode of the connection is determined. Results from the three phases of testing for each deck type will be compared, including degradation from fatigue, load distribution between girders, deflection under maximum loads, and barrier rail connection behavior.