Analytical Study of SDOF Systems with Superelastic Shape Memory Alloy Properties

Abstract

This study looks at the influence of superelastic Shape Memory Alloys (SMAs) on the response of a single degree of freedom (SDOF) oscillator. SMAs are a metallic class of materials which possess unique properties that include stress plateaus, hysteretic damping, and large ductility with small residual strains. Superelastic SMAs have the ability to return to their original shape from strains of up to 8%. This study investigates the effects of the unique stress-strain behavior of SMAs on displacement demand, absolute acceleration, and residual deformation of a SDOF system under code level earthquakes. First, the paper investigates the differences in the response of an elastoplastic (EP) and a superelastic system. A double trigger-line model is used to capture the SMA’s hysteretic properties. Previous research has noted that SMAs have varying mechanical properties depending on thermomechanical processing. Therefore, the effects of several different SMA properties on the structural response are investigated. This paper investigates the importance of damping on the response of the SDOF for a suite of ground motions. The results show that shape memory alloys are much less effective in reducing the peak response of a SDOF system in the short period range, as compared to an EP system. As the strength reduction factor increases, peak displacements increase for both the SMA system and the EP system. However, the EP system, in some cases, has large residuals, compared with perfect recentering for the SMA system. Finally, the paper takes an initial look into the effects of using a parallel system consisting of a SMA and an EP element. The parallel system has over three times the energy dissipation in the hysteresis as the SMA system while maintaining significant recentering capabilities compared to the EP system.