Strip Seal Expansion Joint for Highway Bridge Widening Projects

Highway bridge widening projects require careful consideration of expansion joint design to ensure that the widened bridge performs correctly over its full design life. The new deck section added alongside the existing bridge may have different movement characteristics, requiring special joint design provisions. The primary challenge in bridge widening is differential movement between the existing and new deck sections. The existing deck has already undergone most of its long-term creep and shrinkage, while the new section will continue to shorten for several years after construction. This differential movement can cause the joint to be misaligned across its width, with different gap widths on the existing and new sides. For small differential movements (less than 10 mm), a standard strip seal joint can be used across the full width of the widened bridge. The joint is designed for the maximum movement on either side, and the seal accommodates the differential movement through its flexibility. The edge beams are designed to resist the bending moment caused by the differential movement. For larger differential movements, a longitudinal joint between the existing and new deck sections may be required. This joint allows the two sections to move independently, with separate transverse expansion joints at each end. The longitudinal joint must be waterproofed and designed to accommodate the differential vertical movement between the two sections. The movement range of the widened bridge must be recalculated accounting for the combined thermal properties of the existing and new sections. If the new section uses a different material, the thermal expansion coefficients may differ, creating additional differential movement. The joint must be designed for the worst-case combination of movements. Installation of the new joint on the widened bridge must be coordinated with the widening construction sequence. The joint should be installed after the new deck section has been completed and the temporary supports removed, so that the final deck geometry is established before the joint gap is set.