Development of Semi-active Cam-Lever Friction Device on a Small-Scale Structure Subjected to Earthquake Loads

Damping devices installed in building structures increase resilience against natural hazards such as earthquakes and high winds. Structural control devices are divided into passive, semi-active, active, and hybrid systems. Semi-active vibration control has received considerable attention because it combines the reliability of passive control systems with the versatility to adapt like active systems but with a smaller magnitude of power consumption. Among semi-active devices, variable-friction dampers are promising because they only require a variable clamping force to a surface to dissipate mechanical energy into heat. Factors that drive the adoption of new technology in structural engineering are driven by cost saving, ease of use, technology effectiveness, and reliability of response. Based on these design goals, this research focuses on the design and characterization of semi-active cam-lever friction damper devices. The proposed device applies a normal force to frictional surfaces through slipping bolts that are attached to a cam-double-lever mechanism. This configuration consists of a cam-lever that has a varying radius cam attached to a lever and a slider-crank mechanism that transforms the rotational movement of the first lever into a linear movement of an actuator. This provides a large mechanical advantage to easily adjust the position of the levers and change the tension of the slipping bolts. The feasibility of this device is studied with a small-scale prototype using additive manufacturing of components and an Arduino microcontroller to change the position of the levers. The device is installed in a single-DOF structure that is subjected to harmonic motions and earthquakes using a shake table. The results show that the mechanical advantage and the speed of response of the system are a function of the geometry of the components of the cam-levers. It is also shown that the slipping bolts can have a minimum pre-tension to make the device work as a passive device if the actuation system fails. This initial pilot study opens pathways in advanced mitigation strategies for smart structures.