Modular Expansion Joint for Long-Span Suspension Bridges

Long-span suspension bridges experience the largest thermal and live load movements of any bridge type, requiring modular expansion joints with very large movement capacities. The design of these joints is a specialized engineering challenge that requires close collaboration between the bridge engineer and the joint manufacturer. Thermal movement of long-span suspension bridges is proportional to the bridge length and the temperature range. A 2000-meter suspension bridge with a temperature range of 60 degrees C has a thermal movement of approximately 1440 mm at each end joint. This requires a modular joint with a movement capacity of at least 1500 mm. Live load movement at the ends of a suspension bridge is caused by the deflection of the main cables under traffic loading. When traffic loads the central span, the cable deflects downward, causing the deck to move longitudinally at the towers and abutments. This live load movement adds to the thermal movement and must be included in the joint design. Wind-induced movement at the ends of a suspension bridge is caused by the lateral deflection of the deck under wind loading. The lateral movement at the joint location depends on the wind speed, the deck width, and the stiffness of the deck. For very long-span bridges, the lateral movement can be significant and must be accommodated by the joint. Center beam design for very large movement joints requires careful attention to the center beam cross-section and the support bar spacing. As the number of center beams increases, the structural complexity and the maintenance requirements increase. The joint manufacturer must balance the movement capacity with the structural efficiency and maintainability. Installation of large modular joints on long-span suspension bridges requires careful planning and coordination. The joint is typically installed in sections that are assembled on the bridge deck. The gap setting must account for the temperature at the time of installation and the expected movements from creep, shrinkage, and live load.