Low-force magneto-rheological damper design for small-scale structural control

Small-scale experimental testbeds fulfill an important role in the validation of multi-degree-of-freedom systems with distributed semi-active control, by providing a necessary platform for laboratory validation of key elements of control algorithms. Development of such small-scale testbeds is hampered by difficulties in actuator construction. In order to be a useful analog to full-scale structures, actuators for small-scale test beds should exhibit similar features and limitations as their full-scale counterparts. In particular, semi-active devices, such as magneto-rheological (MR)-fluid dampers, with limited authority (compared to alternatives such as active mass dampers) and nonlinear behavior are difficult to mimic over small force scales because of issues related to fluid containment and friction. In this study, a novel extraction-type small-force MR damper, which exhibits nonlinear hysteresis similar to a full-scale MR device, is proposed, and its behavior is characterized. This actuator is a necessary development to enable the function of small-scale structural control testbeds intended for experimental structural control validation studies. Experimental validation of this prototype as a structural control device is conducted using a three-story small-scale structure subjected to simulated seismic excitation. The actuator is commanded by a wired control computer that executes a linear-quadratic-Gaussian state feedback control law augmented by a modified Bouc-Wen lookup table, both previously developed for full-scale MR applications.