Comparing the cyclic behavior of concrete cylinders confined by shape memory alloy wireor steel jackets

Abstract

Shape memory alloy (SMA) wire jackets for concrete are distinct from conventional jacketsof steel or fiber reinforced polymer (FRP) since they provide active confinement which canbe easily achieved due to the shape memory effect of SMAs. This study uses NiTiNb SMAwires of 1.0 mm diameter to confine concrete cylinders with the dimensions of300 mm × 150 mm(L × D). The NiTiNb SMAs have a relatively wider temperature hysteresis than NiTi SMAs; thus,they are more suitable for the severe temperature-variation environments to which civilstructures are exposed. Steel jackets of passive confinement are also prepared inorder to compare the cyclic behavior of actively and passively confined concretecylinders. For this purpose, monotonic and cyclic compressive loading tests areconducted to obtain axial and circumferential strain. Both strains are used toestimate the volumetric strains of concrete cylinders. Plastic strains from cyclicbehavior are also estimated. For the cylinders jacketed by NiTiNb SMA wires, themonotonic axial behavior differs from the envelope of cyclic behavior. The plasticstrains of the actively confined concrete show a similar trend to those of passiveconfinement. This study proposed plastic strain models for concrete confinedby SMA wire or steel jackets. For the volumetric strain, the active jackets ofNiTiNb SMA wires provide more energy dissipation than the passive jacket of steel.