Modular Expansion Joint Seismic Performance and Design

Modular expansion joints in seismic regions must accommodate large seismic displacements while maintaining structural integrity. The multiple center beams and support bars of a modular joint create a complex structural system that must be analyzed carefully for seismic loading. Seismic displacement capacity of modular joints is determined by the maximum gap opening between center beams and between the outermost center beam and the edge beam. The total seismic displacement capacity is the sum of the individual gap openings across all gaps in the joint. For a modular joint with 5 gaps of 80 mm each, the total displacement capacity is 400 mm. Seismic gap setting requires the joint to be installed with a gap that allows the full seismic displacement to occur without the joint closing completely or opening beyond its capacity. The gap must be set to accommodate both the thermal movement and the seismic displacement in the worst-case direction. Restraint systems for modular joints in seismic regions must prevent the joint from opening beyond its capacity during the earthquake. Cable restrainers connecting the two edge beams limit the maximum gap opening. The restrainer must be designed to resist the seismic force without failure while allowing the required seismic gap to open. Support bar design for seismic loading must consider the horizontal forces from the seismic displacement. The support bars must resist the horizontal force from the center beam weight and the inertia of the center beams during the earthquake. The support bar connections to the edge beams must also be designed for these horizontal forces. Post-earthquake inspection of modular joints must verify that the joint has returned to its pre-earthquake position and that no components have been damaged. The gap width must be measured and compared with the pre-earthquake value. Any permanent displacement or damage must be repaired before the bridge is reopened to traffic.