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.

In this study, based on the high energy-dissipating capacity of viscoelastic dampers with shearing deformation, damped stay cable crossties were proposed to mitigate the vortex-induced vibration (VIV) of stay cables in long-span bridges. Viscoelastic dampers were installed at the connection points of cable crossties to dissipate the kinetic energy of stay cable vibration. Three stay cable models incorporating different numbers of damped crossties were set up in a wind tunnel. Experimental investigations on the control efficacy of the proposed damped stay cable crossties and their parametric influence on the mitigation of the VIV of stay cables were conducted. Numbers of the damped crossties connected with a target main stay cable at different locations were experimentally studied, when the first three modal VIV of three stay cable models were excited respectively. On the basis of the test results, the oscillation behavior of the VIV of the three stay cable models with and without control was ascertained. The experimental results indicated that the proposed damped stay cable crossties can significantly reduce the VIV of stay cables by increasing the stiffness and damping of the cables, and can enhance the modal frequency and the onset wind velocity of the VIV of stay cables due to the increased stiffness.

Magnetorheological (MR) dampers are common methods that are used to mitigate cable vibrations with high effectiveness. Under the long-term effect of external loads and harsh environment, MR dampers will probably suffer from various durability problems, especially fluid leakage. Hence, accurate modeling and evaluation of the effect of fluid leakage of MR dampers are of great significance for bridge maintenance. This paper will investigate the mechanical behavior of MR dampers with fluid leakage after long-term operation and will evaluate their residual performance for cable vibration control. First, three MR dampers with fluid leakage will be selected from a real bridge, followed by a laboratory test to illustrate their damping force characteristics. Based on the experimental results, a theoretical model will be proposed to predict the mechanical behavior of the leaked dampers. A parametric analysis will then be conducted to show the effect of fluid leakage on the damping capacity. Then, one full-scale cable will be idealized as a taut string and the equation of motion for the cable-leaked MR damper system will be formulated. Additional modal damping provided by the MR damper will be determined numerically. The results show that fluid leakage could cause considerable slipping in the damping force. This slipping could lead to a remarkable reduction of the achieved additional modal ratios for the cables. The results of this paper could be of practical significance for the assessment of cable dampers performance and their maintenance on real bridges.

Piping systems are important nonstructural components of most types of buildings. Damage to piping systems can lead to significant economic losses, casualties, and interruption of function. A survey of earthquake disaster sites shows that suspended piping systems are flexible and thus prone to large deformation, which can lead to serious damage of the piping systems. The single-sided pounding tuned mass damper (PTMD), which is an emerging vibration suppression tool, has the potential to serve as a cost effective and non-invasive solution for the mitigation of vibration in suspended piping systems. The operating frequency of the single-sided PTMD can be tuned similarly to a tuned mass damper (TMD). The single-side PTMD also possesses high energy dissipation characteristics and has demonstrated outstanding performance in vibration control. One of the key factors affecting the performance of the PTMD is the damping material, and there is a constant search for the ideal type of material that can increase the performance of the PTMD. This paper explores the use of shape memory alloy (SMA) sponge as the damping material for two types (spring steel and pendulum types) of PTMDs to mitigate the vibration of a suspended piping system. The PTMDs are tested both in free vibration and in forced vibration. The results are compared with no control, with a TMD control, and with a viscoelastic (VE) material PTMD control. The results show that in free vibration tests, SMA–PTMDs attenuate the displacement of the piping system significantly. The time to mitigate vibration (i.e., reduce 90% of the vibration amplitude) is reduced to 6% (for spring steel type) and 11% (for pendulum type) of the time taken to mitigate vibration without control. In forced vibration tests, the overall magnitudes of the frequency response are also lowered to 38% (spring steel) and 44% (pendulum) compared to vibration without control. The results indicate that SMA has the potential to be a promising energy dissipating material for PTMDs.