Elastomeric Pad Expansion Joint for Integral Abutment Bridges

Integral abutment bridges eliminate the traditional expansion joint by making the deck-abutment connection monolithic. The thermal movement of the deck is accommodated by the flexibility of the abutment piles, which act as springs. Elastomeric pads play a supporting role in this system by distributing the bearing load and providing a degree of rotational flexibility. In an integral abutment bridge, the deck is cast monolithically with the abutment, creating a rigid connection. When the deck expands due to temperature increase, the abutment moves outward, bending the piles. The pile stiffness determines the force required to move the abutment, which in turn determines the stress in the deck. Elastomeric pads are used at the approach slab joint, which is the only movement joint in an integral abutment bridge. The approach slab is connected to the deck at one end and rests on the approach fill at the other end. As the deck moves, the approach slab slides on the elastomeric pads, accommodating the movement without damage to the approach fill. Pile design for integral abutment bridges must ensure that the piles are flexible enough to accommodate the thermal movement without exceeding the allowable pile stress. Steel H-piles oriented with their weak axis perpendicular to the bridge axis are the most common choice, as they provide the required flexibility while maintaining adequate vertical load capacity. Movement limits for integral abutment bridges depend on the pile flexibility and the allowable pile stress. Most design standards limit the total movement range to 25-50 mm for standard integral abutment bridges. For longer bridges with larger movements, semi-integral abutments with a sliding bearing between the deck and the abutment wall may be required. The approach slab joint at the end of the approach slab is a simple expansion joint that accommodates the full movement of the integral bridge. This joint is typically a simple elastomeric pad or a strip seal joint, depending on the movement range. The joint must be designed for the same movement range as the bridge thermal movement.