Complete analytical thermomechanical model of double friction pendulum devices

Friction Pendulum Devices (FPDs) are strongly attracting the attention of both Ac-ademic and Technical Communities of Engineers concerned with the development of strategies for the protection of structures against earthquakes. Several versions of such devices can be found on the market, ranging from the Single, to the Double and up to the so-called Triple Friction Pendulum. Those devices are characterized by an increasing number of kinematic pairs and corresponding sliding plates. Even though their effectiveness has extensively been proven by means of numerous experimental campaigns carried out worldwide, it seems that many aspects concerning their mechanical behavior still need to be clarified. These aspects concern, among others: 1) the sequence of sliding on the several concave surfaces, 2) the in-fluence of temperature on the frictional properties of the coupling surfaces, 3) the possibility of alternation of mechanical sticking and slipping phases, 4) the possibility of impact-induced rupture of some components, and so on. Those aspects are less clear the larger the number of concave surfaces the device is composed of. With the aim to contribute to a better understating of the mechanical behavior of the multiple friction pendulum devices, a new mechanical inter-pretation of their behavior was formulated and the relevant model was developed. Such model is based on a rigorous, though simplified, mechanical approach. Starting from the analysis of a double pendulum device, which comprises two stainless steel concave plates facing each other and a convex-faced pad coated with polytetrafluoroethylene (PTFE), the mechanical model envisages the decomposition of each time-instant of the dynamic time-history in two phases. For each phase the device is modelled by an open kinematic chain of rigid bodies differently constrained between each other. Moreover, the model is based on the fulfillment of 1) geometric compatibility, 2) kinematic compatibility, 3) dynamical equilibrium and 4) thermo-mechanical coupling.