Rubber Expansion Joint for Arch Bridge Crown and Springing Points

Arch bridges have a distinctive structural behavior that creates unique expansion joint requirements. The thermal movement of an arch bridge is primarily a change in the arch rise (the vertical distance between the crown and the springing points), rather than a horizontal elongation as in beam bridges. As the temperature increases, the arch elongates, causing the crown to rise and the springing points to move outward. As the temperature decreases, the arch shortens, causing the crown to drop and the springing points to move inward. The magnitude of these movements depends on the arch span, rise, and temperature range. For a concrete arch bridge with a span of 100 meters and a rise of 20 meters, the vertical movement at the crown due to a temperature change of 50 degrees C is approximately 15-20 mm. The horizontal movement at the springing points is approximately 25-30 mm. These movements must be accommodated by the expansion joints at the deck level. The deck of an arch bridge may be supported on the arch rib at multiple points, creating a series of short deck spans between the arch supports. Each deck span has its own thermal movement, and the expansion joints must be located to accommodate this movement. The joint at the crown of the arch accommodates the movement of the two deck spans on either side of the crown. Rubber expansion joints are suitable for arch bridge deck joints where the movement range is within the capacity of the rubber joint. For most arch bridges with spans up to 150 meters, the deck joint movement range is 20-40 mm, which can be accommodated by a standard rubber strip seal or compression seal joint. Installation of expansion joints on arch bridge decks requires attention to the curved deck geometry. The joint must follow the curve of the deck, which may require custom-fabricated edge beams or nosing strips. The joint gap must be set correctly for the installation temperature, accounting for the arch's thermal behavior.