STATE OF ART REVIEW OF SHAPE MEMORY ALLOY USED IN CIVIL STRUCTURES AS SEISMIC CONTROL DEVICE

Abstract

Shape memory alloys (SMAs) are a kind of smart materials that remember their original shapes and can be utilized as an actuators that shape, stiffness, position, natural frequency and other mechanical characteristics in response to temperature or electromagnetic fields. SMAs exhibit two different phases i.e. martensite and austensite. Temperature and internal stresses (that play a role in super elasticity) determines the phases that SMA exhibits. The aim of this paper is to discuss about SMAs and its application in civil engineering structures like cable stayed bridges, elevated highway bridges, simply supported bridges and buildings as seismic control device. SMA is used as aactive, semi-active andpassive damper in civil structures. Passive damper has energy dissipation capacity and recentering ability. The recentering property areachieved by SMAs in austenite phase while dissipation ability of austenite is not so muchtherefore detwinning behaviour of SMA in martensite phase is considered increasing the damper's dissipating ability. NiTi SMAs showhigh level of superelastic hysteresis and energy dissipation and it solidify after transformation to stress-inducedMartensite, at roughly 6 to 8% strain. This property aremainly used for utilizing SMAs for hinge restrainer purposes for bridges. By using SMA's actuation property, Intelligent reinforced Concrete (IRC) was developed. IRC utilises strandedmartensite SMA wires for post tensioning and by monitoring electric resistance change of shape memory alloy wires, the strain allocation within concrete are obtained. If there is occurrence of cracks either by earthquakes or explosions, then by heating SMA wire strands results in its contraction and the cracks get reduced. It is observed from the study that SMA is effectively used as a seismic control device for civil structures.