Elastomeric Pad Expansion Joint for Concrete Slab Bridges

Concrete slab bridges are the most common bridge type for short spans of 5-20 meters, and elastomeric pad expansion joints are the most appropriate joint type for these bridges. The simple design and low cost of elastomeric pads make them ideal for the large number of short-span bridges on rural road networks. Design of elastomeric pads for concrete slab bridges begins with calculating the thermal movement of the bridge deck. For a 15-meter concrete slab bridge with a temperature range of 50 degrees C, the thermal movement is approximately 9 mm. Adding 30% for construction tolerances gives a design movement of 12 mm, which is within the range of standard elastomeric pads. Pad dimensions are selected based on the design movement and the bearing pressure. The pad must be wide enough to distribute the bearing load without exceeding the allowable bearing pressure on the concrete abutment. For a typical rural bridge with a design load of 100 kN per meter width, a pad width of 300 mm provides a bearing pressure of 0.33 MPa, which is within the allowable range. Pad thickness is determined by the required movement range and the allowable shear strain. The shear strain in the pad is equal to the movement divided by the pad thickness. For a design movement of 12 mm and a maximum allowable shear strain of 0.5, the minimum pad thickness is 24 mm. A standard 30 mm thick pad is typically specified. Installation on concrete slab bridges is straightforward due to the simple geometry. The pad is placed on the abutment bearing shelf, the gap is set for the installation temperature, and the deck is cast. No adhesive is required if the pad is adequately restrained by the deck concrete. The pad must be positioned to allow free movement in the longitudinal direction while preventing lateral displacement. Maintenance of elastomeric pads on concrete slab bridges is minimal. Annual inspection should check for displacement, cracking, and compression set. Replacement is typically required every 20-30 years, depending on the traffic loading and environmental conditions.