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
,
is based on the minimization of a performance index
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.
Keywords
semiactive systems, control algorithms, earthquake
engineering, seismic response, added damping