Bridge Expansion Joint for Extradosed and Hybrid Bridge Systems

Extradosed bridges and hybrid structural systems combine features of different bridge types, creating unique expansion joint requirements. Understanding the structural behavior of these systems is essential for correct joint design. Extradosed bridges combine the structural principles of prestressed concrete box girder bridges and cable-stayed bridges. The cables are anchored at a low tower height, creating a system that is stiffer than a cable-stayed bridge but more efficient than a conventional prestressed concrete bridge. The expansion joints at the ends of an extradosed bridge are similar to those of a prestressed concrete bridge, with movements driven by thermal effects, creep, and shrinkage. The cable forces in an extradosed bridge create a hogging moment in the deck that partially offsets the sagging moment from traffic loading. This changes the stress distribution in the deck compared to a conventional prestressed concrete bridge, which may affect the expansion joint design. The joint must be designed for the stress state at the joint location in the completed structure. Hybrid bridge systems that combine different structural types (for example, a cable-stayed main span with approach viaducts) have expansion joints at the transitions between the different structural types. These joints must accommodate the different movement characteristics of the adjacent structures. The movement at the transition joint may be larger than at the end joints due to the differential movement between the two structural types. Temperature gradients in hybrid bridge systems can be complex due to the different thermal properties of the adjacent structures. A steel cable-stayed main span has a higher coefficient of thermal expansion than a concrete approach viaduct, creating differential thermal movements at the transition joint. The joint must be designed for the worst-case combination of thermal movements. Monitoring of expansion joints at transitions in hybrid bridge systems is particularly important due to the complex movement patterns. Displacement sensors at the joint can verify that the movements are within the design range and can detect any unexpected behavior. This monitoring data is valuable for validating the structural analysis and for planning maintenance interventions.