Bridge Expansion Joint for Bridges with Integral Deck Slabs

Bridges with integral deck slabs have a continuous concrete deck that spans between girders without separate deck joints. The expansion joints are located at the abutments and at intermediate pier locations where the deck is separated. The joint design must accommodate the movement of the continuous deck. Continuous deck bridges have fewer expansion joints than simply supported bridges, reducing the maintenance requirements. A continuous deck bridge with three spans typically has only two expansion joints (at the abutments), compared to four joints for three simply supported spans. This reduction in joint count reduces the maintenance cost and the risk of joint failure. Movement range at the abutment joints of a continuous deck bridge is larger than for simply supported spans of the same length. The thermal movement of the entire continuous deck is concentrated at the two abutment joints. For a three-span continuous bridge with a total length of 150 meters, the thermal movement at each abutment joint is approximately 75 mm, compared to 25 mm for each of three simply supported 50-meter spans. Creep and shrinkage of continuous deck bridges cause long-term shortening of the deck, reducing the joint gap at the abutments. The creep and shrinkage movements must be included in the joint gap calculation to ensure that the joint does not close completely over the design life. Pier design for continuous deck bridges must accommodate the thermal movement of the deck. Fixed piers resist the thermal movement, generating horizontal forces in the deck and the piers. Sliding piers allow free movement, concentrating the movement at the abutment joints. The distribution of movement between fixed and sliding piers depends on the pier stiffness and the joint design. Monitoring of continuous deck bridge expansion joints is recommended to verify that the movement distribution matches the design prediction. Displacement sensors at the abutment joints and strain gauges on the piers can measure the actual movement distribution. Any significant deviation from the design prediction should be investigated.