Design and experimental verification of seismic mitigation and energy-dissipated equipment for immersion tunnel joint

In order to investigate the earthquake reduction performance of immersion joint subjected to seismic loading, based on metal buckling dampers, a novel method for enhancing the seismic performance of the immersion joint was proposed. An energy-dissipated equipment for the tube joint in immersed tube tunnel was designed. By the method of optimizing key parameters, taking the area encircled in moment-rotation curve as the optimal objective function, the elastic stiffness of the proposed energy dissipation equipment was selected. Finally, two large-scale structural comparison experiments for joints with and without energy-dissipated equipment were conducted by applying horizontal bending moment to the joints. The moment-rotation curves were obtained as well as the mechanical parameters (e. g. flexural stiffness and area of hysteretic loop) of the joint under the two test cases. These parameters were compared and analyzed and technical feasibility of the equipment for enhancing the seismic performance of the tunnel was verified. The results show that the hysteretic loops with similar shape are found obviously in both moment-rotation curves for joints with and without energy-dissipated equipment. Compared to that without such equipment, the maximum bending moment of joint with the equipment increases from 730 to 1 000 kN·m, around 37%; the flexural stiffness of the joint increases from 6.19×10⁵ to 8.97×10⁵ kN·m·rad^-1, around 45% under same rotation; the hysteretic area of the immersion joint encircled by the moment-rotation curves which fully reflect the energy dissipation of joint increases about 69%. These results show that the hysteretic performance of the joint is remarkably enhanced.