A leverage-type variable friction damper for seismic protection of structural systems

A friction damper (FD) can be an effective energy dissipation device for the seismic protection of structural systems. The level of the constant slip force in a passive FD is a critical design parameter, since it will determine the amount of energy dissipated by the damper in an earthquake. A passive FD will behave like a bracing without energy dissipation capacity when the seismic load is lower than the slip force, while the amount of energy dissipated by the passive FD may not be sufficient if the seismic load is much higher than the designed slip force. In order to improve the control performance, a novel leverage-type variable friction damper (LVFD), whose friction force can be adjusted in real time through a leverage mechanism, depending on the earthquake intensity, is introduced in this study. Different from most existing variable FDs that are usually controlled by adjusting the clamping force applied on friction interfaces, the LVFD system combines a passive FD and a leverage mechanism with a movable central pivot. By simply controlling the pivot position, the frictional damping force generated by the LVFD can be adjusted in real time; therefore, precision control of the clamping force, which is usually substantially larger than the slip force, can be avoided. Furthermore, by considering 16 different ground motions with two different intensities, the adaptive feature and control performance of the LVFD for the seismic protection of a 3-story shear structure is further demonstrated numerically, by comparing with those of its counterpart passive FD systems.