The tuned mass damper (TMD) can be applied to suppress earthquake, wind, and pedestrian- and machine-induced vibration in factory buildings or large span structures. However, the traditional TMD with a fixed frequency will not be able to perform effectively against the frequency variations in multiple hazards. This paper proposed a frequency-adjustable tuned mass damper (FATMD) to solve this limitation of current TMD. The FATMD presented in this paper is composed of a simple assembly consisting of a supported beam with a mass, in which the frequency of the FATMD is changed by adjusting the span of the beam. The kinematic equation of a single degree of freedom (SDOF) structure installed with an FATMD is established to analyze the effect of the damping ratio, mass ratio, and stiffness on the vibration damping. The fundamental frequency of the FATMD at different spans is verified by simulation and experiments. Forced vibration experiments with different excitation frequencies are also conducted to verify the performance of the FATMD. The results show that the proposed FATMD can effectively suppress the vertical vibration of structures at different excitation frequencies, including frequencies at a range higher than what a traditional TMD may not be able to suppress. Additionally, the proposed FATMD is applied to a long-span pedestrian bridge which vibrates frequently due to the walking of pedestrians, the running of escalators, and earthquakes. The numerical results indicate that the FATMD can effectively reduce the vertical vibration of the pedestrian bridge under the excitations of pedestrians, escalators, and earthquakes.

The suspended mass pendulum (SMP) conventionally used is a type of frequency sensitive vibration control device. It is vulnerable to detuning due to large amplitude oscillations, which can lead to a significant loss in vibration control performance. Although active or semi-active control systems can solve the problem of frequency detuning, the reliability and stability of the sensors and actuators in the control system are difficult to guarantee for large-scale civil structures. To overcome this issue, this study proposes a passive adaptive suspended mass pendulum (PASMP) that uses a curved support. First, the mathematical equations describing the curved support are derived to show that it can keep the frequency of the pendulum constant at large swing angles. Then the kinematic equations of a single-degree-of-freedom (SDOF) structure installed with the PASMP are established. A parametric analysis is conducted to verify how the parameters of the control system, including the excitation period, pendulum length and mass ratio, affect the dynamic responses of the main structure. Furthermore, to verify the effectiveness of the PASMP and the validity of the theoretical analysis, a two-story frame structure is chosen as the model structure in shaking table tests. Also, the proposed PASMP is applied to a transmission tower to numerically verify its effectiveness of vibration suppression under different seismic excitations. The numerical and experimental results demonstrate that the PASMP can more effectively suppress the vibration of structures than the conventionally used SMP.

Summary The analysis model of a suspended mass pendulum (SMP) control system is usually simplified as a planar model, which only considers the swing angle in‐plane. However, out‐of‐plane vibrations of a pendulum are inevitable and are significantly more complex than that assumed in the planar model. To overcome the limitations of the current planar model, this study proposes a spatial model of the pendulum. The kinetic equations of the spatial SMP model coupled with a single degree of freedom structure are established considering the swing angle of the SMP in‐plane and out‐of‐plane. The vibration characteristics of the pendulum and their influence on the dynamic response of the structure are numerically analyzed. Compared with the numerical results of the planar model, the vibrations of a pendulum are more accurately simulated by the spatial model, even when the rotation angle of pendulum out‐of‐plane is greater than 20°. A parameter study is performed considering the influencing parameters of the control system, including the excitation periods, pendulum length, mass ratio, and amplitudes of the horizontal rotation angle at the maximum displacement of the structure. The results show that the horizontal rotation angle of the pendulum negatively affects the vibration suppression of the structure. Furthermore, to verify the vibration control effectiveness of the spatial SMP model, a transmission tower was controlled under eight types of seismic excitations. The results reveal that the SMP has a clear mitigation effect on the seismic response of the tower.

Linear dampers have been widely applied for suppressing the dynamic responses of structures to mitigate their damage. However, the primary disadvantage of the classical linear damper is that it is vulnerable to detuning, which has become an issue of great importance recently due to a great reduction in vibration control performance. To overcome the shortcoming, this study develops a negative stiffness bistable damper (NSBD) composed of a simple assembly consisting of a bistable buckling beam with a mass. Energy is dissipated through the transformation between the bistable states. The constitutive equation of the NSBD is derived to analyze the effects of the stiffness ratio, the arch-span ratio, and the damping ratio on its restoring capabilities. The vibration reduction effect of the NSBD is experimentally evaluated under different sinusoidal and seismic excitations in shaking table tests. The obtained results reveal that the NSBD can effectively restrain structural displacements.

In this paper, a dynamic stress analysis of seismic vibration isolator was carried out by using ANSYS. The vibration isolator consisted of Si-Cr springs and magnetorheological dampers. The stress and deformation of the springs were calculated when an impact load was applied to the isolator. From the simulation for six different springs, in terms of their wire dimeter and coil diameter, an optimum shape of the springs to minimize the stress and deformation was determined.