Vibration Control of a Frame Structure Using Pulsed Current Activated Shape Memory Alloy Braces M. G. Rashed Department of Civil Engineering, AUST, Bangladesh R. Ahsan Department of Civil Engineering, BUET, Bangladesh F. S. Jumbo Independent Scholar, London, UK ABSTRACT: In this study, a frame structure is braced with SMA and its dynamic response under seismic excitation has been obtained from FE analysis by using the nonlinear FE software program MSC Marc. A Thermo-Mechanical SMA phenomenological constitutive model is used to simulate the SMA behaviour. The SMA is activated by pulsed current and the optimization gain using pulsed current input is established with respect to constant current input. From the simulation result, it is evident that the use of pulsed current resulted in reduced energy consumption by the SMA, as well as mitigating the seismic vibrations on the frame structure. Keywords: Optimization, Pulse Width Modulation, Shape memory alloy, Semi-active control. 1. INTRODUCTION The use of Shape Memory Alloy’s (SMA) in mitigating the seismic vibration response of civil infrastructure is gaining momentum. SMA has two basic properties, Super-Elasticity (SE) and Shape Memory Effect (SME). SE allows the material to recover from large deformations, while developing a hysteretic loop. SME allows the material to recover the initial shape or position which in turn can be used as re-centering mechanism. The mechanism of SMA works in two phases, Martensite which is the low stiffness phase and Austenite which is the high stiffness phase. Phase transformation occurs between Martensite & Austenite depending upon temperature & stress. Previously, SE was the focus of structural engineers because SMA reaches activation temperature and becomes Austenite at the ambient temperature of civil engineering infrastructures. The use of high temperature SMA has enabled the re-centering mechanism to work. The SMA is heated by joule-heating due to electrical current flow. The use of constant current in this purpose will result in greater power consumption which can be reduced significantly by passing pulsed current through the SMA using Pulse Width Modulation (PWM) technique [1]. Figure 1. Braced frame. Figure 2. Optimum constant current [2].