Laboratory study of a variable friction damper with a curved wedge

Passive friction dampers are known as devices improving structural response to earthquakes. The friction force magnitude in these dampers is usually constant. It is known that buildings with supplemental friction dampers not always return to the initial position after the earthquake, and remain in a deformed stage. A passive variable friction damper, consisting of a tube, a curved wedge, elastic strip elements and a bolted connection clip, was proposed by the authors. Its principal distinction from other existing ones is using a curved wedge element, aimed to change the friction force as a function of the displacement transferred to the damper and the wedge curvature. An additional advantage of this damper is a possibility to provide the centring capacity. The damper's mechanical properties and its hysteretic behavior are studied theoretically and verified experimentally using a small-scale model and a laboratory shaking table. A static scheme, enabling to get the force-displacement relationship of the damper for different wedge curvatures, was assumed. The results of the dynamic test are in good correlation with the proposed theoretical model. It is demonstrated that the loading and unloading lines of the damper's hysteretic loops are non-linear and are similar to those predicted theoretically. Comparison of variable friction dampers with curved and triangular wedges is performed. The theoretical model, proposed in this study, can be successfully used for design of full-scale variable friction dampers with curved wedges.