Influence of the Fe-based shape memory alloys on concrete shear wall structures

Seismic loading in seismic prone countries is very important and the lack of enough attention can make a irreparable damages to structures and non-structural elements. Dissipating earthquake energy just by using elastic capacity of structure, will increase the dimension and weight of structural elements like column, beam, walls and the cost of building will increases. Incoming seismic energy should be dissipated in plastic process and in this process, structure must remain stable. Shearwall is using widely because of its suitable behavior against seismic loading and good ability of energy dissipation. Sometimes it is inevitable to avoid openings in shear walls due to architectural considerations. Providing enough ductility in these shear walls is a difficult job because of stress concentration around of voids. The other problem of using shear walls is plastic deformations that make the structures useless. One way of improving ductility and self-centering ability of shear walls is using smart materials. Shape memory alloys are one of the newest smart materials that have two important behaviors, called shape memory effect and superelasticity. Removing the residual deflection after unloading of elements made by shape memory alloys by heating called shape memory effect. Superelasticity in SMAs is returning the elements to their initial shape after unloading by them. Good corrosion resistance, good fatigue behavior and weldability are the other positive behaviors of shape memory alloys. In this paper the improvement of the shear walls ductility and self-centering ability with using shape memory alloys in superelastic phase is investigated. Shape memory alloys can withstand up to 7 percent of strain without any residual deformation. In this paper shear walls modeled by shear-flexure interaction multi-vertical-line-element-model (SFI-MVLEM). This model was implemented in the Open System for Earthquake Engineering software (OpenSees). Considering interaction between shear and flexural response in shear walls has made this element superior. Superelastic reinforcement bars were embedded in plastic hinge of boundary elements, coupled beam and walls web separately. Shear wall modeled by using SMA in boundary element, coupled beam and walls web called SMAB, SMAC and SMAW respectively. To examine the effects of these alloys on energy dissipation capacity and self-centering ability of the shear walls, structure were evaluated in cyclic analysis. Place of using SMAs on shear wall in very important and can influence widely on shear wall so most optimized place of using SMAs in shear wall should recognized. Two case of optimization considered in this analyze. In first one, best place is a place that using SMAs on it causes minimum energy dissipation reduction and maximum residual displacement removing. In second one, best place is the place that causes maximum residual displacement removing with minimum usage of SMAs. In order to find the influence of SMAs on ductility of shear wall, pushover analyse was used. Using SMAs in boundary elements of shear walls made maximum increasing in ductility of shear wall but the best place for using SMAs for optimization of usage of SMAs is walls web. Based on the results, with using shape memory alloys, ductility of shear walls was increased and its residual deformation and energy dissipation capacity was decreased. The best place of using SMAs in shear wall is coupled beam for optimization of energy dissipation and residual displacement and for optimization SMA usage is walls web.