Effect of Stiffness and Confinement Ratio On the Behavior of Concrete Confined by SMA Wires

In this article, it is discussed how the stiffness and confinement ratio of the confining material affect on the behavior of concrete confined by shape memory alloy (SMA) wires.  SMA wire jacket has been proved as an effective confining material to improve concrete behavior; for example, increasing peak strength and failure strain.  The stiffness and confinement ratio of FRP (Fiber Reinforced Polymer) jackets have been discussed well and thus their effects are well known.  However, the analysis of the stiffness and confinement ratio of the SMA wire jacket is not conducted yet.  This study also investigates the effect of stiffness and  confinement ratio of steel jackets and compares the results with those of the SMA wire jackets.  In general, the stiffness ratios of the SMA wire jackets are relatively smaller than those of the steel jackets and most of them belong to the category of lower stiffness ratio since the Young's moduli of the SMAs are smaller than that of steel.  The active confining pressure does not improve the lower stiffness ratio effect since the amount of the active confining pressure is relatively small.