Abstract:

It is hard to decide the initial slip force of normal friction damper. In order to solve this problem, a novel composite friction damping system (CFDS) is formed by connecting a nonlinear hard spring and a friction damper in series. When the earthquake intensity is smaller, the friction damper is in a state of adhesion, and nonlinear hard spring undergoes deformation to prevent the isolated layer from large drift. When the earthquake intensity is larger, the deformation of the hard spring keeps constant, while the friction damper is slip and friction damping occurs to dissipate seismic energy. The motion equations of base isolated structure with the proposed damping system are derived, and boundary conditions aimed at two different phases, stick and slip, of friction damper are pointed out. Then seismic response of the base isolated structure subjected to normal far-field earthquakes and near-fault pulse-like ones are studied. Compared with structures only installed with isolator devices, numerical simulation shows that CFDS can effectively suppress the horizontal motion of isolated layer. If the parameters of the damping system are proper, the interstorey drift and acceleration of the main structure are also reduced. Furthermore, the state of the friction damper in CFDS will switch between stick status and slip status. The influence of three parameters of the proposed damping system is also investigated in depth. It is pointed out that, since the seismic response change trend of the base isolated structure caused by the variation of CFDS parameters depends on earthquake type, optimal parameters of the CFDS is related to the peak ground acceleration and type of the earthquake, and the optimal parameters, which minimize both displacement and acceleration response of the superstructure, is not exist. So only when the proper control goal is given, the proper parameters of CFDS can be selected.

Key words: composite friction damping system (CFDS), nonlinear hard spring, friction damper, isolated, vibrations