Stiffness of Concrete Flexural Members Increases on Use of Shape Memory Alloy Bars as Reinforcement

Abstract

This paper describes the properties of Shape Memory Alloys (SMAs) and its useful aspect towards utilization in civil engineering structures. The non-linear material behavior in terms of shape memory effect, superelasticity, martensite damping and variable stiffness is presented. The values of effective moment of inertia and cracking moment, of treated and controlled Reinforced Concrete (RC) beams were determined using ACI 318, AS 3600 and CEB-FIP model codes. Treated beams were reinforced in combination with SMA and conventional steel reinforcement and controlled beams were reinforced with only steel. It was found that high yield strength property of SMA, increases effective moment of inertia and cracking moment of treated beams under self-weight and restricts growth of instantaneous and long-term deflections. With increase in load the deflections of treated beams increases than that of controlled beams due to lower modulus of elasticity of SMAs. The deflection or stiffness of SMA reinforced treated beams were more than that of similar steel reinforced controlled beams, when mid-span bending moment due to imposed load was within 30% of their respective designed moment of resistance. 

Keywords: Shape memory alloy, Superelasticity, instantaneous deflection, time dependent deflection, reinforced concrete beam.