SEISMIC PERFORMANCE EVALUATION OF STEEL BUILDING RETROFITTED BY NEW HIGH PERFORMANCE SEMI-ACTIVE CONTROL BRACING SYSTEM

Innovative devices to control of structures under seismic excitation are becoming an interesting problem in earthquake engineering. In this paper a new ribbed bracing system (RBS) is proposed capable of performing as a variable stiffness system that can be used for controlling structural deformations and frequency shifting to compensate seismic energy. RBS has two important advantages. Because of ribbed system, the compressive member is rigidly moved like a piston and cylinder and therefore it is a buckling prevented system. Also RBS can act as a semi-active device and decrease the response of structure in two different manners; at first type RBS is closed in all stories during earthquake that called completely closed RBS (CCRBS). In second type of RBS by using of storey drift as a control criterion, RBS become on or off in stories during seismic excitation that called semi-active RBS (SA-RBS). RBS is semi-active control system because it has no need to any actuator and large power supply, but just a battery-size power supply to switch the ribbed mechanism to be on or off. Nonlinear dynamic analysis of system has been carried out and performances of above RBS systems and conventional bracing system (CBS) have been investigated. Numerical results show the efficiency of CC-RBS in reducing structural damage and improving seismic energy. Also base shear is reduced when SA-RBS is used and structural damage is more uniform in this case.