An innovative shape memory alloy flexible circumferential joint for tunnel seismic mitigation

Seismic mitigation performance of shape memory alloy flexible circumferential joint in shield tunnel

“…An SMA ring spring is composed of an SMA ring and two steel rings, which is an efficient shock-absorbing functional element (Figure 1). 12,32 The SMA ring spring has excellent energy dissipation capacity due to the superelasticity of SMA (Figure 2). The deformation of SMA ring springs is mainly concentrated in the SMA ring, while the steel ring remains elastic.…”

“…SMA joints can weaken the joint stiffness and improve the ability of the tunnel to adapt to soil deformation, thus reducing tunnel damage. 12 SMA joints can also dissipate energy due to cyclic deformation under earthquakes and reduce the internal force of joints, hence reducing earthquake damage. According to the function of the SMA joint, it can be arranged near the location with a large seismic response in the tunnel to conduct longitudinal seismic mitigation and improve the seismic safety of the tunnel.…”

“…From the working principle of the SMA ring spring, the analytical solution of the performance during loading and unloading can be derived. 12 During loading, the SMA ring spring is subjected to axial force (F). Pressure (N) and relative sliding friction (f μ ) are applied to the contact surfaces of the SMA and steel rings (Figure 3).…”

“…They can enhance the deformation capacity of the tunnel structure and have energy dissipation and self-recovery effects, potentially improving the seismic safety of the structure. 12 SMA is a smart material with a unique shape memory effect and superelasticity, which has a large recoverable strain (up to 8% compared with 0.2% for ordinary materials) and good corrosion resistance. [13][14][15][16][17] The shape memory effect is a phenomenon in which SMA has residual strain after loading and unloading at a certain temperature and can return to the original shape by heating.…”

“…It can provide loads through the expansion of the SMA ring, and the friction of the contact surface and the hysteresis characteristics of the SMA material can dissipate energy. 12,28 SMA ring springs are highly effective damping functional elements and have a good absorption effect on steel structures. [29][30][31] Therefore, in the present study, SMA ring springs are used as 'elastic washers' in tunnel circumferential joints to compose SMA flexible circumferential joints for longitudinal seismic mitigation in tunnels.…”