Control of Civil Structures Using a Semiactive Stiffness System Based on Variable Amplification

Various semiactive systems have been proposed to control the seismic response of civil structures. These include semiactive fluid, friction, and stiffness devices. Energy dissipation in these devices occurs through a variety of mechanisms. The purpose of the present study is to propose a new semiactive stiffness system that dissipates energy based on the principle of hysteresis. The system consists of a novel variable amplification device (VAD) connected to a simple spring. When integrated with other semiactive components, the stiffness of the VAD-spring system can be adjusted based on feedback from the structure’s response. This is done by changing the amplification factor of the VAD according to a semiactive control algorithm tailored specifically to the device’s unique characteristics. The proposed system is simulated for an eight-story building subject to multiple seismic excitations. The response of the building using the VAD-spring system is compared with the maximum amplification case and that obtained using the active variable stiffness system. Results indicate that the VAD-spring system is an effective means of controlling vibrations in seismically excited buildings.