Impact loads may cause serious or even fatal damage to the structure (component), in most existing specifications in China, and there are no special terms that take impact load into consideration. So, the response analysis of the structure (component) under impact loads is very important. In this paper, the sensitivity analysis was conducted for the 22 parameters of the Holmquist–Johnson concrete (HJC) constitutive model of concrete, and the sensitive parameters of the HJC model are identified with A, B, G, Pl, μl, and fc respectively. LS-DYNA nonlinear transient finite element analysis code was used for this paper. Based on the validation of finite element modeling and choosing midspan deflection of RC beams and impact loads as response indices, some influencing factors on RC beams under falling weight impact were investigated, such as the mass and speed of falling weight, impact position, the strength of concrete and rebar, longitudinal reinforcement ratio, and the span of the beam.
The circumferential joint of a shield tunnel is prone to damage under strong earthquakes, affecting the safety of the tunnel. This paper adopts an innovative shape memory alloy (SMA) flexible circumferential joint for longitudinal seismic mitigation of the tunnel. The SMA joint is composed of SMA ring springs and ordinary bolts. The SMA joint design is performed for a shield tunnel, and a simplified model of the SMA joint is proposed. Based on the generalised response displacement method, the longitudinal seismic mitigation analysis of the tunnel is conducted, the arrangement of SMA joints is discussed, and the seismic mitigation performance is evaluated. Results show that the SMA joint design method can efficiently complete the joint design, and the SMA joint model can accurately reflect the joint performance. SMA joints can reduce the stiffness of tunnel joints and have a good energy dissipation effect, which is suitable for shield tunnel seismic mitigation. An appropriate SMA joint arrangement can concentrate the tunnel joint deformation and effectively reduce the opening width between the tunnel segment rings. It can also dissipate energy and reduce the internal force of the tunnel joint, thus enhancing the seismic safety of the tunnel.
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