innovative sma-based retrofitting techniques for concrete columns

Shape memory alloys (smas) are advanced metallic materials that exhibit two distinct behaviors: the shape memory effect (sme), which enables the recovery of pre-stress through heating in the martensitic phase, and the superelasticity (se), which allows for reversible strain recovery upon unloading in the austenitic phase. the main families of smas include cu-based, fe-based, and ni-ti alloys. however, the high cost of ni-ti limits its widespread use in civil engineering applications. this review paper synthesizes and compares previous experimental and numerical studies on the use of smas as longitudinal or transverse reinforcements in reinforced concrete (rc) columns and cylinders. this paper is divided into two main sections that introduce the research using the se (enhancing self-centring behavior) and sme (in pre-stressing application) features of sma in the last decades. the results showed that using smas in the plastic hinge region of the column was an excellent idea for reducing residual deformation and increasing the ductility of the column under seismic loading.  the results related to utilizing sme features in the column enhanced its stiffness and lateral strength. in contrast, in se cases, the existence of sma showed reverse consequences, causing a decrease in the column's stiffness, although its strength occasionally declined. it underscores the need for further research toward cost-effective alloys, improved bonding, and the development of design guidelines for sma-reinforced rc structures.