Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Piles

Bridge decks supported on piles have a different movement behavior than decks supported on continuous foundations. The pile stiffness affects the distribution of thermal movement between the expansion joints and the piles, requiring careful analysis. Pile stiffness calculation requires knowledge of the pile cross-section, the pile length, and the soil conditions. Long, slender piles in soft soil are more flexible than short, stocky piles in stiff soil. The pile stiffness is used in the structural analysis to determine the distribution of thermal movement between the piles and the expansion joints. Movement distribution between piles and expansion joints depends on the relative stiffness of the piles and the joints. For a bridge with flexible piles, most of the thermal movement is accommodated by the pile bending, and the expansion joints experience relatively small movements. For a bridge with stiff piles, most of the thermal movement is concentrated at the expansion joints. Pile design for thermal movement must consider the bending moments caused by the deck thermal movement. The piles must be designed to resist these bending moments without cracking or yielding. The pile reinforcement must be adequate for the combined effect of vertical load, thermal bending, and any other loads. Expansion joint design for pile-supported bridges must be based on the movement calculated from the structural analysis, not the free thermal movement of an unrestrained deck. The joint must be designed for the actual movement, which may be significantly less than the free thermal movement. Monitoring of pile-supported bridge expansion joints is recommended to verify that the movement distribution matches the design prediction. Displacement sensors at the joint and strain gauges on the piles can measure the actual movement distribution. Any significant deviation from the design prediction should be investigated.