Semi-active Control of Base-isolated Structures

A numerical and experimental analysis of semi-active (SA) control strategies for controlling seismic-excited structures is presented. A physical model consisting of a two degree-of-freedom (2DOF) mechanical system with a magneto-rheological (MR) damper was developed to evaluate this concept at LNEC's shaking table. Linear elastic and viscous models were used to describe the mechanical behavior of the 2DOF mechanical system. A Modified Bouc-Wen model was used to describe the behavior of the MR damper. Four distinct control strategies were implemented for numerical and experimental evaluation. The associated controllers were tuned using the system model and the ground motions information. The strategies were the integral control law, two linear quadratic regulator strategies and a predictive controller, in conjunction with a clipped on-off algorithm. In both the numerical and experimental tests the results reveal that the response of the structure is effectively mitigated by all of the analyzed control methods. It is shown that SA systems can outperform the original structure as well as one using the best passive solution for most of the strategies. The integral control law exhibits the best performance when collocated control was considered. If more responses are available for control, the linear quadratic regulator technique exhibits even better performance.