Suspended piping systems often suffer from severe damages when subjected to seismic excitation. Due to the high flexibility of the piping systems, reducing their displacement is important for the prevention of damage during times of disaster. A solution to protecting piping systems during heavy excitation is the use of the emerging pounding tuned mass damper (PTMD) technology. In particular, the single-sided PTMD combines the advantages of the tuned mass damper (TMD) and the impact damper, including the benefits of a simple design and rapid, efficient energy dissipation. In this paper, two single-sided PTMDs (spring steel-type PTMD and simple pendulum-type PTMD) were designed and fabricated. The dampers were tested and compared with the traditional TMD for mitigating free vibration and forced vibration. In the free vibration experiment, both PTMDs suppressed vibrations much faster than the TMD. For the forced vibration test, the frequency response of the piping system was obtained for three conditions: without control, with TMD control, and with PTMD control. These novel results demonstrate that the single-sided PTMD is a cost-effective method for efficiently and passively mitigating the vibration of suspended piping systems. Thus, the single-sided PTMD will be an important tool for increasing the resilience of structures as well as for improving the safety of their occupants.

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.

The condition of an offshore wind turbine (OWT) should be monitored to assure its reliability against various environmental loads and affections. The modal parameters of the OWT can be used as an indicator of its condition. This paper combines the Kalman filter, the random decrement technique (RDT), and the stochastic subspace identification (SSI) methods and proposes an RDT-SSI method to estimate the operational frequency of an OWT subjected to ambient excitation. This method imposes no requirement on the input/loads; therefore, it is relatively easy for field application. An experimental study with a small-scale OWT was conducted to verify the accuracy of the proposed RDT-SSI method. The test results implied that the frequency estimated by the RDT-SSI method is close to that estimated by an impact hammer test. Moreover, the small-scale OWT was buried at different embedment depths to simulate the influence of the scouring phenomenon, and the frequency of the OWT decreased with decreasing embedment depth. Additionally, the bolts at the root of the turbine blades were also loosened to investigate their influence on the frequency. As more blades were loosened, the identified frequency of the OWT also decreased, indicating that the proposed RDT-SSI method can be employed for the health monitoring of an OWT.

High-rise structures are normally tall and slender with a large height-width ratio. Under the strong seismic action, such a structure may experience violent vibrations and large deformation. In this paper, a spring pendulum pounding tuned mass damper (SPPTMD) system is developed to reduce the seismic response of high-rise structures. This SPPTMD system consists of a barrel limiter with the built-in viscoelastic material and a spring pendulum (SP). This novel type of tuned mass damper (TMD) relies on the internal resonance feature of the spring pendulum and the collision between the added mass and barrel limiter to consume the energy of the main structure. Based on the Hertz-damper model, the motion equation of the structure-SPPTMD system is derived. Furthermore, a power transmission tower is selected to evaluate the vibration reduction performance of the SPPTMD system. Numerical results revealed that the SPPTMD system can effectively reduce structural vibrations; the reduction ratio is greater than that of the spring pendulum. Finally, the influence of the key parameters on the vibration control performance is conducted for future applications.

The pounding tuned mass damper (PTMD) is a novel vibration control device that can be used for many different structures. The PTMD utilizes a viscoelastic delimiter to enhance its vibration control effectiveness and robustness though pounding between the tuned mass and the viscoelastic material. However, the viscoelastic material is subjected to repeated poundings during its service life, which influences the property of the material and degrades its energy dissipation ability. Therefore, this study investigates the fatigue behavior of the viscoelastic material under impact loading. An experimental apparatus, which can generate and sense the lateral impacts, is designed and fabricated to facilitate the fatigue study of the viscoelastic material subject to impact loading. Based on experimental data, the pounding stiffness and the hysteresis loops are employed to characterize the behavior of the material. It is revealed that the impact fatigue process can be divided into two phases: the cyclic-hardening phases and the cyclic-softening phase. The energy dissipation is firstly reduced, and then increased, by the repeated impacts. In summary, with a total of 360,000 impacts, the viscous elastic material is still effective in dissipating impact energy.