Improving design of new buildings and retrofitting existing build, to resist the action of earthquakes, constitute an issue of primary importance. Among the emerging techniques that can be used for this purpose, reinforcing with ferrous based shape memory alloys has given promising results. These materials are cost-effective; they have excellent recentering capabilities, high damping properties and elevated resistance to corrosion. The potential of using these reinforcements when placed at the extremities of structural members of the building was investigated in this work. A comparative study was performed between this variant and the reference case where conventional steel rebars are employed. This was conducted in the case of a simple reinforced concrete frame having a symmetric configuration. The comparison has targeted moderate and strong seismic excitation. The studied structure was modeled by using SeismoStruct software to perform both pushover analysis and full nonlinear time history analysis. The obtained results have indicated that the use of shape memory alloys yields lesser demand in terms of base shear and support moment, while reducing residual deformations thanks to the recentering property of these materials.

Shape memory alloys are smart materials which have remarkable properties that promoted their use in a large variety of innovative applications. In this work, the shape memory effect and superelastic behavior of nickel-titanium helical spring was studied based on the finite element method. The three-dimensional constitutive model proposed by Auricchio has been used through the built-in library of ANSYS® Workbench 2020 R2 to simulate the superelastic effect and one-way shape memory effect which are exhibited by nickel-titanium alloy. Considering the first effect, the associated force-displacement curves were calculated as function of displacement amplitude. The influence of changing isothermal body temperature on the loading-unloading hysteretic response was studied. Convergence of the numerical model was assessed by comparison with experimental data taken from the literature. For the second effect, force-displacement curves that are associated to a complete one-way thermomechanical cycle were evaluated for different configurations of helical springs. Explicit correlations that can be applied for the purpose of helical spring's design were derived.