Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Spread Footings

Bridge decks on spread footings are susceptible to differential settlement and footing rotation that can affect the performance of expansion joints. The joint design must accommodate these foundation movements in addition to the thermal and live load movements. Spread footing settlement depends on the soil conditions, the footing size, and the applied load. For bridges on compressible soils, differential settlement of 10-50 mm between adjacent footings is not uncommon over the design life. The expansion joint must be designed to accommodate this differential settlement. Footing rotation occurs when the footing tilts due to eccentric loading or differential soil conditions. The rotation creates a vertical movement at the joint location that adds to the thermal movement. The joint must be designed for the combined effect of thermal movement and footing rotation. Foundation investigation for bridges with expansion joints must include geotechnical borings and laboratory testing to characterize the soil conditions. The investigation must extend to the depth of the founding stratum to determine the settlement potential. The geotechnical report must provide settlement predictions that can be used in the joint design. Joint gap setting for bridges on spread footings must account for the expected settlement and rotation. The gap must be set to accommodate the remaining settlement and rotation after installation, plus the full thermal movement range. The calculation must consider the age of the structure at the time of joint installation and the expected future movements. Monitoring of spread footing bridge expansion joints is recommended to verify that the settlement and rotation match the design predictions. Settlement monitoring points on the bridge deck near the joint allow the settlement to be tracked over time. Any unexpected settlement should be investigated to determine the cause.