Bridge Expansion Joint for Bridges with Fiber Reinforced Polymer Decks

Fiber reinforced polymer (FRP) bridge decks are increasingly used for bridge rehabilitation and new construction due to their light weight, high strength, and corrosion resistance. The expansion joint for an FRP deck bridge must be designed for the different thermal and mechanical properties of FRP compared to concrete or steel. Thermal expansion of FRP decks depends on the fiber orientation and the resin type. The coefficient of thermal expansion of glass fiber reinforced polymer (GFRP) is typically 10-20 x 10^-6 per degree C in the longitudinal direction, which is similar to or higher than concrete. The joint must be designed for the thermal movement calculated using the FRP coefficient of thermal expansion. Stiffness of FRP decks is lower than for concrete decks of the same thickness, resulting in larger deflections under traffic loading. These larger deflections create higher stress cycles in the joint components, requiring more careful fatigue design. The joint must be designed for the deflection-induced movements in addition to the thermal movements. Connection of the expansion joint to the FRP deck requires special attention because FRP cannot be welded and has different mechanical properties than steel or concrete. Mechanical connections using bolts and adhesive bonding are the standard approach. The connection must be designed to resist the traffic loads and thermal movements without damaging the FRP deck. Compatibility between the joint materials and the FRP deck must be verified. Some adhesives and coatings can attack the resin matrix of FRP, causing delamination or loss of strength. The joint manufacturer should confirm that all materials in contact with the FRP deck are compatible. Maintenance of FRP deck expansion joints requires inspection of the deck-joint interface for delamination, cracking, or debonding. Any damage to the FRP deck at the joint location must be repaired promptly to prevent water infiltration and further deterioration. FRP repair materials are available from the deck manufacturer for in-situ repairs.