This paper proposes a novel self-centering negative stiffness damper (SCNSD), which combines superelastic shape memory alloy (SMA) and prepressed springs in parallel for damping enhancement. A mechanical model of the damping force is established and experimental tests are conducted for verification. The influence of the negative stiffness provided by the prepressed springs is investigated by parametric analysis. A single-degree-of-freedom (SDOF) structure is used as a case to study the damping effectiveness of the proposed damper. The low limit of the negative stiffness is established, and the additional equivalent damping ratio is deduced theoretically. Frequency response under harmonic excitation is evaluated by using the average method. Numerical simulation is carried out to explore the damping effectiveness of the SCNSD for suppressing the seismic response of the SDOF structure. These numerical simulation results show that the SCNSD can achieve a larger damping ratio due to the effect of the negative stiffness, and the acceleration and displacement response of the SDOF system can be reduced remarkably.

The degradation of seismic performance for RC bridge piers induced by chloride corrosion has previously been studied by treating the earthquake as a unilateral cyclic loading. Such studies do not consider the true response of the pier under the joint effect of corrosion damage and real multi-dimensional earthquake action. Thus, in the present study, the cyclic behavior of rectangular bridge piers subjected to the coupling effects of chloride corrosion and bidirectional loading was numerically investigated. First, the corrosion-induced deterioration of material mechanical properties is introduced. Second, the numerical model of two corroded piers is built and validated with the test results in the literature. Then, the time-dependent biaxial seismic performance of a rectangular bridge pier under the circular-shaped (CS) biaxial displacement pattern, square-shaped (SS) biaxial displacement pattern, uniaxial displacement in the X-direction (UX) pattern, and uniaxial displacement in the Y-direction (UY) pattern is analyzed using the validated model. The simulation results conclude that the trajectory of biaxial loading paths and corrosion levels significantly influence the peak force, deformation capacity, and dissipated energy of the piers. The biaxial loading path effect for the corrosive pier includes two stages with different biaxial force trajectory characteristics. Compared with the uncorroded pier, the corrosion level of 13.7% and biaxial loading induces up to a 40% reduction in strength and a 54% decrease in the residual ultimate displacement of the corroded pier. For the same corrosion degree, the dissipated energy under the SS biaxial displacement path is the largest among the four loading paths.

Coastal bridge piers suffer random performance deterioration owing to the presence of complex nonuniform corrosion characteristics and material uncertainties. Some of these piers will also be threatened by random earthquakes during a long-term service period, and therefore, structural safety needs to be probabilistically assessed by the seismic reliability method. To deal with this problem, we present a method to calculate the time-dependent reliability of the coastal bridge pier, comprehensively considering the randomness of a seismic event, nonuniform corrosion, and material uncertainty. First, the time-dependent M–N interaction diagrams are established by using the Monte Carlo simulation method. On the basis of the interaction diagrams, the moment resistance reduction function and time-dependent moment resistance distribution are determined. Subsequently, the moment demand under the seismic load is determined using the Poisson model and the response acceleration spectrum. Then, the formulas to calculate the time-dependent reliability of a nonuniform corroded pier are derived on the basis of the theorem of total probability. The proposed method is illustrated with a case study of a coastal bridge pier. It was found that the increase in corrosion damage would obviously increase time-dependent reliability. Furthermore, the increase in submerged zone height delayed the year when the failure section shifts from the pier bottom to the bottom of the splash and tidal zone, and it reduces the failure probability of the coastal pier. The research results presented herein show that the nonuniform corrosion manifestations influence the failure mode–related time-dependent seismic reliability of the coastal bridge pier.

Negative-stiffness damper is a promising device to mitigate cable vibrations effectively. In contrast to traditional rigid supports, recent study has found that flexible supports are actually beneficial for enhancing the performance of negative-stiffness dampers. This study extends the understanding of the impact of support flexibility under nonlinear condition, followed by an optimization process to obtain required negative-stiffness dampers and corresponding supports. First, taking damping nonlinearity into account, a unified model is established for the negative-stiffness damper with flexible support. Theoretical equivalent negative stiffness and damping are obtained for a linear case, followed by numerical verification. Thereafter, equivalent parameters under a friction case are presented. Experiments are conducted to validate the analytical derivation. Then, problem formulation is developed for the controlled cable. Optimization process is proposed to determine the required negative-stiffness damper and support for multimodal cable vibration. A series of numerical simulations are performed to demonstrate the design process. Moreover, nonlinear examples are presented to show the potential for improving control performance. As indicated by the research results, a flexible support is capable of amplifying the equivalent negative stiffness and damping under linear and nonlinear conditions. For multimodal cable vibration, it is sufficient to determine the optimized negative stiffness and support by only considering the highest mode. Nonlinear negative-stiffness dampers exhibit superior performance due to the leakage of vibration energy toward high-order modes.

Cables are widely utilized as load-carrying members due to their excellent mechanical properties. However, the inherent damping of cables is usually extremely low, thereby causing undesired vibrations to occur frequently under various external excitations. This study investigates the utilization of rigid restraints with a built-in tuned mass damper to mitigate the vibration of cables. First, the configuration of a rigid restraint with a built-in tuned mass damper is presented, followed by the development of a problem formulation for controlled cables using such a device. A discrete model is further established to describe the dynamic behavior of the system. Thereafter, a series of numerical simulations are conducted. The influence of the mass ratio of the tuned mass damper and installation position is analyzed. Then, examples are presented to verify the control effectiveness under sinusoidal excitations. As indicated by the numerical results, the proposed device can mitigate cable vibration exceptionally well. Taking aerodynamic effects into account, model cables and control devices are manufactured. Two installation positions, namely, quarter-span and mid-span, are considered. Wind tunnel tests are performed. As shown by the experimental tests, the proposed rigid restraint with a built-in tuned mass damper can suppress the first two modal vibrations. Overall, the rigid restraint with built-in tuned mass damper can mitigate cable vibration, though several issues should be further addressed.