Heat Activated Prestressing of Shape Memory Alloys for Active Confinement of Concrete Sections

This paper presents the results from the experimental investigation on heat activated prestressing of Shape Memory Alloy (SMA) wires for active confinement of concrete sections. Active confinement of concrete is found to be... [ view full abstract ]

This paper presents the results from the experimental investigation on heat activated prestressing of Shape Memory Alloy (SMA) wires for active confinement of concrete sections. Active confinement of concrete is found to be much more effective than passive confinement. Active confinement achieved using conventional prestressing techniques faces many obstacles due to practical limitations. A class of smart materials that has recently drawn attention in civil engineering is the shape memory alloy which has the ability to undergo reversible hysteretic shape change known as shape memory effect. The shape memory effect of SMAs can be utilized to develop a convenient prestressing technique for active confinement of concrete sections. In this study a series of experimental tests are conducted to study thermo-mechanical behaviour of Ni48.46Ti36.03Nb15.42 (wt.%) SMA wires. Although, numerous studies on active confinement of concrete using NiTiNb SMA have been carried out in the past, no particular study on Ni48.46Ti36.03Nb15.42 exists in the literature. A series of tests were conducted in this study to characterize the material properties of Ni48.46Ti36.03Nb15.42 for active confinement of concrete sections. Parameters such as heat activated prestress (HAP), residual strain and the range of strain that can be used for effective active confinement after HAP were investigated in detail. The influence of pre-strain and temperature on HAP was also investigated. It was found that a significant amount of HAP can be developed in pre-strained Ni48.46Ti36.03Nb15.42 upon heating, most of which is retained at room temperature. A substantial amount of strain recovery upon unloading and after heating was recorded in all tests. The range of strain available for effective active confinement was also found to be significant. This study demonstrates that the chemical composition of NiTiNb along with level of pre-strain and the corresponding transformation temperature range significantly affects the HAP, which in turn can affect the efficacy of the retrofitting strategy in which NiTiNb is used as a means to apply active confinement.