Monotonic and cyclic bond behavior of confined concrete using NiTiNb SMAwires

Abstract

This study conducts bond tests of reinforced concrete confined by shape memoryalloy (SMA) wires which provide active and passive confinement of concrete.This study uses NiTiNb SMA which usually shows wide temperature hysteresis;this is a good advantage for the application of shape memory effects. The aimsof this study are to investigate the behavior of SMA wire under residual stressand the performance of SMA wire jackets in improving bond behavior throughmonotonic-loading tests. This study also conducts cyclic bond tests and analyzescyclic bond behavior. The use of SMA wire jackets transfers the bond failurefrom splitting to pull-out mode and satisfactorily increases bond strength andductile behavior. The active confinement provided by the SMA plays a major rolein providing external pressure on the concrete because the developed passiveconfinement is much smaller than the active confinement. For cyclic behavior,slip and circumferential strain are recovered more with larger bond stress. Thisrecovery of slip and circumferential strain are mainly due to the external pressureof the SMA wires since cracked concrete cannot provide any elastic recovery.