A new variable damping semiactive device for seismic response reduction of civil structures

A semiactive mechanism, called a VDSA (variable damping semiactive device), is proposed to reduce the seismic response of structures. It is composed of two fixed-orifice viscous fluid dampers installed in the form of a V whose top ends are attached to a floor and their lower ends to a collar that moves along a vertical rod. By varying the VDSA position one obtains an optimal instantaneous damping added to the structure. The position of the moving end is calculated with an algorithm based on a variation of the instantaneous optimal control theory which includes a generalized LQR (linear quadratic regulator) scheme. This modified algorithm, referred to as Qv, is based on the minimization of a performance index J quadratic in the state vector, the control force vector, and an absolute velocity vector. Two variants of the algorithm are used to present numerical simulations of the controlled seismic response of a single and a MDOF (multi-degree-of-freedom) structure.