This paper gives a survey of the original concept of incorporation of 'artificial nonlinearity' or 'artificially added nonlinearity' into structural control schemes aiming at reducing seismic response of structures, and then presents the significance of 'artificial nonlinearity' integrated into semiactive control schemes. The original concept, which covers the basic philosophy from passive type to active type of control, was proposed about 50 years ago. The recent development of control schemes based upon hysteretic energy dissipation is actually the realization of such a concept with the background of modern technologies. Compared with today's base isolation scheme, the significance of 'artificial nonlinearity' is discussed. Then, with main focus on semiactive control schemes, the effectiveness and significance of artificial nonlinearity are presented along with the philosophy of autonomous-decentralization. After demonstrating how the seismic responses depend upon the resulting ductility factors of bilinear hysteresis, the effect and significance of a controllable damper with variable slip-force levels are demonstrated.
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