Seismic mitigation for immersion joints: Design and validation

Immersion joint, generally considered as the critical part for seismic design of immersed tunnels, could damage first under strong earthquakes due to its smaller stiffness compared to adjacent tunnel elements. Until now, however, solutions or measures for mitigating seismic damage to immersion joints are still missing in literature. In this paper, a seismic mitigation measure for enhancing the performance of immersion joints is proposed, i.e. the Buckling Restrained Brace (BRB). The optimized design of the device is obtained from a parametric analysis to ensure it works in coordination with the immersion joint in such a way that the maximum energy dissipation is reached. Validation tests of an immersion joint, i.e. with and without the optimized BRB device, are presented with a large geometric scale of 1/10. Test results indicate that the hysteretic performance of the immersion joint working with the optimized BRB device reaches a 69% increase, compared to that without such device.