Seismic Response of Adjacent Structures Connected with Semi-Active Variable Friction Dampers

In this paper, the responses of two adjacent structures connected with semi active variable friction dampers (SAVFD) under various earthquake excitations are investigated. By controlling the clamping force, SAVFD is able to adjust its slip force and remain in slip state during an earthquake of arbitrary intensity. The objective of this study is to evaluate the optimum value of the gain multiplier and its importance in the structural response reduction of coupled structures. The optimum gain multiplier, defined as the ratio of damper force to critical damper control force, is investigated for the SAVFD connected, adjacent structures subjected to four different types of earthquake ground motions. A numerical study is carried out for two adjacent, multi-degree-of-freedoms (MDOF) structures connected with SAVFD. The investigation is also carried out to determine the effectiveness of dampers in terms of the reduction of structural responses namely, displacement, acceleration, and shear forces of adjacent, connected structures. In addition, to minimize the cost of the dampers, the study is conducted with only 50 percent of total dampers at optimal locations, rather than placing the dampers at all floor levels. The predictive control with direct output feedback concept is considered, and the results are compared with uncontrolled and passive control cases. Results show that by using SAVFD to connect the adjacent structures of different fundamental frequencies, earthquake-induced responses of either structure can be effectively reduced. Further, it is observed that two adjacent MDOF structures connected with 50 percent of the total dampers at proper locations reduces earthquake induced responses as much as when they are connected at all floor levels; thus, the cost of the dampers can be significantly reduced.