Experimental Study of Sliding Friction Damper for High-Performance Steel Structures

Passive energy dissipation devices are widely utilized in buildings to minimize structural and non-structural damage under seismic loading. Commonly used devices include, among others, yield, viscous and friction dampers. While the use of yield dampers, such as buckling-restrained braces (BRBs), has been fairly well established in the earthquake engineering practice, arguably, uncertainties regarding the amount of cyclic hardening of the BRB yield core necessitate the BRB qualification testing for the design of the BRB’s non-dissipative elements. An additional concern may be the residual deformations along the building height in the aftermath of earthquakes. Similarly, viscous dampers may exert forces that are influenced by the dynamic load imposed on a building due to their sensitivity to temperature and imposed velocity. Maintenance of viscous dampers due to potential leakage may be another complexity. While friction dampers do not generally experience the aforementioned issues, their use in seismic applications is still evolving. One reason could be that their performance is strongly dependent on the selected friction pad material type. Ideally, friction pads should have a static friction coefficient between 0.3 and 0.4 under high-pressure (between 10 and 20 MPa). They should also exhibit stable force-displacement hysteretic response under cyclic loading. All-in-all, the selection of a suitable friction pad material for structural applications is non-trivial. In this regard, friction pads commonly used in braking applications of the automobile industry may be effective to address long-term effects associated with corrosion and delamination of friction pads. In order to investigate their applicability in the context of seismic engineering, a sliding friction damper prototype is developed and tested under various loading histories at the EPFL Structures Laboratory. The damper is designed for a maximum axial force of 450 kN and can accommodate a maximum axial displacement of ± 80 mm. The force-displacement response of the friction damper is investigated by testing two friction pad types under two different pressure levels at the sliding interface. Cyclic tests with constant and increasing amplitudes are conducted at different rates to depict their influence on the force-displacement response of the friction damper. Furthermore, a pulselike loading protocol is carried out in order to test the friction damper under conditions similar to those of an actual seismic event. The evolution of the static and dynamic friction coefficients is examined by monitoring both the sliding force and bolt preload. The experimental results suggest that under sliding motion, the examined friction pads provide a fairly constant sliding force, thereby exhibiting similar static and dynamic friction coefficients. Furthermore, the force-displacement hysteretic response of the friction damper is fairly stable and repeatable. Finally, similar static friction coefficients are obtained for different slip loads and sliding velocities, suggesting that the behavior of the tested friction pads is nearly pressure- and velocity-independent.