Dynamic Behavior of a Two-Story Building Frame Braced with SMA for Vibration Control

In this study, the dynamic behavior of a two-story building frame with Shape Memory Alloy (SMA) braces is determined experimentally in terms of its oscillatory response to earthquakes loadings. Two earthquake loadings representing the El Centro and Northridge earthquakes were generated and applied to the base of the building frame using a shake table. SMA wires, whose stiffness varies with applied current through them, were used to brace the building frame in order to control vibrations. Two types of current: constant current and pulse current were used to tune the system (2D frame) stiffness. The goal is to achieve increased damping capacity of the frame due to the martensite-austenite co-existing state. The effect of constant and pulse current on the system stiffness (i.e., deformation, acceleration) are analyzed to determine the optimum current values. For El Centro earthquake, the optimum value of the constant current is 1.8A for minimum displacement and oscillation of the system. Where as, the value of the constant current for minimization of the displacement and oscillation of the building frame is found to be 1.4A using the Northridge earthquake excitation. It is shown that the periodic pulse current used to stiffen the SMA brace is more effective than the constant current actuations. In this study, the effect of system stiffness on resonance frequency is also determined. Finally, the responses of the two-dimensional (2D) frames with and without bracing were compared. It is believed that the findings of this study will be useful in advance understanding of the behavior of building structures with SMA members under earthquake loadings.