Seismic loading is crucial in seismically vulnerable nations, and neglecting it can result in catastrophic harm to both structural and non -structural components. Columns, beams, and walls will grow in size and weight due to employing a structure's elastic ability to dissipate seismic energy, which will also raise the cost of construction. Shear walls are frequently employed due to their effective behavior under seismic loads and a strong capacity for energy dissipation. Sometimes, it is unavoidable to prevent openings in shear walls for architectural reason s. Due to load concentration in the vicinity of voids, providing sufficient ductility in these shear walls is challenging . Plastic deformations render the constructions unusable, which is another issue with shear walls. Researchers are paying more and more attention to the use of shape memory alloys (SMA) as reinforcing bars in concrete buildings. This study aims to assess the effectiveness of using superelastic Nitinol (NiTi) and Fe-based ( FeMnAlNi ) SMAs in a concrete shear wall to reduce residual displacement . One shear wall model without SMA was created with OpenSees finite element software to verify this analysis's integrity . Secondly, the steel rebar was partially replaced with different types of SMA in critical locations. Results indicated that utilization of superelastic alloys w ould result in a significant reduction of residual displacement. Additionally, a s light change in the shear wall's dissipated energy is observed compa red to the shear walls without SMA. Keywords : Shape memory alloys, Superelastisity, Finite Element Method, Reinforced concrete shear wall, self-centering. 2nd International Conference on Industrial Application of Advanced Materials and Manufacturing July. 20th to 21th, Iran University of Science and Technology, Tehran, Iran 2 Introduction Typically, the primary earthquake -resistant elements of reinforced concrete structures are structural walls. However, they often contain a few openings in line with the purpose of the architectural design, and the opening ratios, placements, and forms are frequently different. However, assessing the stiffness and shear strength of structural walls containing openings is challenging . Evaluation becomes significantly more challenging if the opening s are positioned eccentrically. Using a strut and tie model is standard to represent structural walls with eccentric openings. However, the modeling technique is not simple and requires considerable knowledge. Due to variations in design and modeling , both national and international seismic design codes include certain associated structural features and constraints. In earthquake -prone countries , seismic design plays a significant role. If this factor is not appropriately considered , significant earthquake damage will occur . Inoue et al. in (1998) , Fujita et al . (2001) , Palermo and Vecchio (2007) , and others have all worked extensively on FEM analyses of structural walls over the recent decades , but the design process always takes much longer [1-3]. The stress concentration in particular places causes compression (crushing) and tens ile (cracking) damage in concrete. Proposing ways to prevent or postpone these failures becomes extremely important when they are coupled with significant displacements and unexpected loadings that may negatively influence the shear wall carrying capacity. The persistent damage and deformations of shear walls can be influenced by the type of reinforcement utilized. Ductile materials are required to enhance the shear wall's ability to withstand significant deformations and hold onto modest residual stresses [4]. SMA The shape -memory effect and superelasticity are two distinctive features of shape -memory alloys (SMAs) . The capacity of the alloys to return to their original shape after heating them to the temperature at which they undergo phase change is known as the shape -memory effect. SMAs have a particular characteristic that sets them apart from other materials and is directly tied to the atomic structure of the alloy. Austenite, which is stable at high temperature, and Martensite, which is stable at low temperature, are the two distinct atomic structures of SMAs. The heating or stress loading of these phases can cause a reversible transition betw een them "Figure 1 ". Superelasticity and the Shape Memory Effect (SME) are two crucial properties of SMAs (SE). Fully Austenite -structured SMAs exhibit SE behavior, whereas Martensite - structured SMAs exhibit SME behavior [5, 6] . Even when it experiences si gnificant inelastic deformations, a superelastic SMA could quickly recover its original shape following unloading. The majority of applications that may use this capability are seismic ones. When heated, SMAs can revert to their predetermined forms because of a feature called SME. Figure 1. Phase transformation of the SMA [4]. "Figure 2 " depicts a superelastic SMA undergoing a loading and unloading cycle in an exemplary stress -strain diagram. The following four stress values are used to define the superelastic model at a constant temperature. There are four types of stress: starting stress from Austenite to Martensite, finishing stress from Austenite to Martensite, start ing stress from Martensite to Austenite, and ending stress from Martensite to Austenite [7]. Figure 2. Stress–strain diagram model of 1D -superelastic SMA [4]. There are several advantages and disadvantages associated with various SMAs families. Beginning in the early 1960s, SMAs were created. They have been effectively employed for medical [8, 9], robotic [10], aerospace [11, 12], automotive [13], and Their use in structural and civil engineering is growing . 2nd International Conference on Industrial Application of Advanced Materials and Manufacturing July. 20th to 21th, Iran University of Science and Technology, Tehran, Iran 3 SMAs could well withstand corrosion, fatigue, and significant deformation s. Dolce and Cardone (2001) subjected superelastic NiTi SMA wires to cyclic tensile testing and concluded that the SMAs' properties are suitable for seismic applications [14]. The utility of SMAs as reinforcement in reinforced concrete (RC) constructions was demonstrated via comprehensive analytical and experimental investigations that followed the advancement of research on these alloys. Czaderski et al. (2006) experimented on an SMA -reinforced RC beam and contrasted it with a standard RC beam. Their findings demonstrated that an RC beam with changeable stiffness and strength might be created utilizing SMAs [15]. The use of SMAs as reinforcement in concrete buildings has been the subject of much research in recent years, but concrete shear walls have not seen the same level of investigation. With the use of a finite element model, Ghassemieh et al. (2012, 2013) assessed the effective ness of the SMA -reinforced concrete shear walls (without openings) and demonstrated how this reduced the structure's overall permanent residual strain [16, 17] . Additionally, they examined how well SMA reinforcement improved the seismic response of coupled shear walls and concluded that it significantly restored the remaining displacement in the shear wall. This article examines the impact of shape memory rebars with various SMAs on the concrete shear wall's energy dissipation and residual displacement capa city. To accomplish this, a concrete shear wall with steel bars and eccentric openings is first modeled without SMA, using OpenSees software and an MVLEM macro element, which is explained later . The results of this model are examined to ensure that the results are similar to those in the experimental laboratory results for the purpose of verifi cation . After the verification phase, steel rebars are replaced with various amounts of SMA , and the ef fects of this change in residual displacement and dissipated energy are analyzed and reported for interpretation. Model Description This study adapted one specimen as an analytical object "Figure 3" . The experimental tests were carried out at Kyoto Univer sity, Japan, and used 40 percent scale models of concrete structural walls with eccentric openings [18,19] . Figure 3. Dimension of specimens (mm) [19] "Figure 3" illustrates the specimen's height and span length. "Tables 1 " and "Table 2", respectively, include a list of the sectional measurements as well as certain specifics about beams, columns, and walls. The various sorts of reinforcements are represented by D and Ф. Table 3 detail s the material characteristics of the reinforcement used for this sample. The compressive strength (MPa), tensile strength (MPa) , and young 's modul us (GPa) of the concrete are 28.9, 2.2, and 26.0, respectively. The opening ratio used as an experimental parameter is 0.46 for, defined as (h0l0/hl)1/2, where l0 and h0 are the length and height of the aperture . The l and h are the center -to-center distances between the upper and lower beams [19]. Table 1. Section and reinforcements of beam/column (mm) [19] Section dimension Main reinforcement Hoop reinforcement Side column 300×300 8-D19 2-Φ10@75 Beam 200×300 2-D13 2-Φ6@100 Foundation beam 600×400 4-D25 4-D10@100 Loading beam 400×400 2-D25 2-D10@100 Table 2. Section and reinforcements of the wall (mm) [19] Thickness (mm) 80 Wall reinforcement D6@100 Reinforcing bar of opening ( vertical ) 1-D16 Reinforcing bar of opening ( horizontal ) 2-D13 2nd International Conference on Industrial Application of Advanced Materials and Manufacturing July. 20th to 21th, Iran University of Science and Technology, Tehran, Iran 4 Table 3. Properties of reinforcements (mm) [19] rebar Yield strength (MPa) Ultimate strength (M Pa) Young modulus (GPa) D6 425 538 204 D10 366 509 180 D13 369 522 189 D16 400 569 194 D19 384 616 183 Φ6 985 1143 197 Φ10 962 1085 195 Loading description After modeling the shear wall, it is recommended to apply the loading depicted in "Figure 4" to the wall that was applied in the experiment and then compare the model's findings with those obtained for validation [19]. Figure 4. Horizontal loading assign ed to shear wall This loading has fourteen cycles , each of wh ich is performed twice. The relative displacement values for the cycles are ±0.04 %,±0.1 %,±0.25 %, ±0.5 %,±0.75% ,±1.0%,±1.5%respectively The model mentioned above could have an excellent relation ship with the laboratory results, as seen in "Figure 5" [19]. Figure 5. Verification of the numerical analysis Finite element modeling A two -dimensional Multiple -Vertical -Line- Element -Model (MVLEM ) is created using the MVLEM element approach to simulate the behavior of flexure -dominated RC walls [20- 22]. As shown in Figure 1a, a single model element contains six global degrees of freedom, three of which ar e situated in the middle of the rigid top and bottom beams. A sequence of uniaxial elements (or macro -fibers) attached to the rigid beams at the top and bottom (e.g., floor) levels replicate the axial/flexural response of the MVLEM, while a shear spring po sitioned at a height ch from the bottom of the wall element describes the shear response (Figure 1a). The model element's flexural and shear responses are independent. The point on the element's central axis at height ch is where the wall element's top and bottom faces are rotated in relation to one another (Figure 1b). Rotations and associated transverse displacements are computed based on the wall curvature, determined by the section and material parameters, and correspond to each element's bending moment at height ch (Figure 1b). Vulcano et al. (1988) suggested a value of c=0.4 based on a comparison of the model response and the outcomes of the experiments [20]. Figure 6. a) MVLEM Element, b) MVLEM Rotations and Displacements [20] The properties of various SMAs used in this study are shown in "Table 4 ". These values are directly used in the OpenSees modeling software. -2-1.5-1-0.500.511.52 0 20 40 60Lateral Displacement (%) Time (s) 2nd International Conference on Industrial Application of Advanced Materials and Manufacturing July. 20th to 21th, Iran University of Science and Technology, Tehran, Iran 5 Table 4. Mechanical properties of FeMnAlNi and NiTi [23] Results and discussions Since the primary goal of this article is to evaluate how equal amounts of memory alloy and steel affect the behavior of the shear wall, the design criteria have not been utilized to replace the steel with memory alloy, and the same quantity of steel has been taken out of the plastic joint on the first story of macro model . As shown in "Figures 7 -9", the use of shape memory alloy in the shear wall will reduce the area under the diagram and , as a result , reduce the dissipated energy of the wall, which is due to the flag -shaped diagram of these alloys and the area under the diagram which is less than the steel rebars alone. Figure 7. Hysteresis analysis result with SMAs in c olumn Figure 8. Hysteresis analysis result with SMAs in the middle wall Figure 9. Hysteresis analysis result with SMAs in Beam The impact of shape memory alloy on residual structur al displacement is seen in "Figure 10 " and "Figure 11 " In all instances where shape memory alloy is utilized in place of steel reinforcement, reduced residual displacement is seen, especially at higher cycles . According to the findings shown in that figure. The least residual displacement is often experienced when shape memory alloy is used in columns in both Fe -based and NiTi SMAs . The use of memory alloy in the middle wall and coupled beam come second in reducing the residual displacement. Figure 10. Influence of SMA on residual displacement in positive cycles Figure 11. Influence of SMA on residual displacement in negative cycles Due to their flag -shaped response, it is safe to assume that the reduction in residual displacement strongly correl ates to the reduction of dissipated energy from the structural system. The detailed Properties FeMnAlNi NiTi austenite to martensite starting stress (MPa) 320 300 austenite to martensite finishing stress (MPa) 442 450 martensite to austenite starting stress (MPa) 210 200 martensite to austenite finishing stress (MPa) 122 100 superelastic plateau strain length (%) 5 5 modulus of elasticity (GPa) 98 30 2nd International Conference on Industrial Application of Advanced Materials and Manufacturing July. 20th to 21th, Iran University of Science and Technology, Tehran, Iran 6 comparison between the dissipated energy and residual displacement of each type of analysis is presented in "Table 5 ". Table 5. influence of SMA on energy dissipation and remained displacement Dissipated Energy (kJ) Maximum negative Residual Displacement (mm) maximum positive Residual Displacement (mm) Without SMA 154.34 -31 25 Fe-Based in Wall 131.34 -31 16 NiTi in Wall 123.62 -31 18 Fe-Based in Beam 135.62 -25 22 NiTi in Beam 128.37 -26 22 Fe-Based in Column 74.23 -5 6 NiTi in Column 74.23 -5 3 Additionally, as shown in "figure 12 ", the structure will experience the highest total dissipated energy if it is exclusively reinforced with steel. Using shape memory alloy in the coupled beam, middle wall, and column will re duce the system's dissipated energy . Figure 12. influence of SMA on energy dissipation Two techniques may describe the best location for replacing steel rebars with SMA . In the first scenario, the ideal location is where the usage of shape memory alloy results in the highest dissipated energy while causing the system to leave the least residual displacement. The second state of optimality is also related to the rate of SMA utilization. The place where the least amount of SMA usage causes the lowest residual displacement. A dimensionless number is used for each of the above states. This dimensionless number for the first scenario is obtained by dividing the percentage of reduction in the residual displacement of the last cycle by the percentage of reduction in the total dissipated energy compared . The larger this dimensionless number is the more appropriate location for using shape memory alloys instead of steel reinforcement. For the second scenario of optimality , the dimensionless number is obtained by dividing the percentage of residual displacement reduction by the percentage of shape memory alloy utilization in the shear wall. In this case, the larger the dimensionless number, the place of replacement is more appropriate. In "Table 6", the first state of optimality, i.e., optimality of residual displacement -dissipated energy , has been investigated and reported in the 5th column . According to this table, using the memory alloy in the column , in terms of the optimality of the first scena rio, is the most optimal place among the available options for using the SMA in shear wall s. The second stage of optimization, optimum consumption, is also examined in the 6th column . From the optimality point of view in the second scenario , the ratio with the least residual displacement to the least usage of SMA is the most optimal place among the available replacement regions in the shear wall. Thus, the coupled beam is the best place on average , but it is apparent that the exact best location depends on the type of SMA used. The re sidual displacement and dissipated energy reduction in "Table 6" are obtained from comparing SMA reinforced cases with the steel model 's results . "Table 7" show the initial stiffness and ultimate strength for different types of SMA as a replacement form of steel reinforcement. This table indicates that due to the different dynamic properties of SMAs, discussed previously in "Table 4", the initial stiffness and ultimate strength of Nitinol are lower than its Fe -based counterpart. 2nd International Conference on Industrial Application of Advanced Materials and Manufacturing July. 20th to 21th, Iran University of Science and Technology, Tehran, Iran 7 Table 6. Evaluation of two optimization scenarios Table 7. Influence of SMA on initial stiffness and ultimate strength initial stiffness (kN/m) ultimate strength (kN) Without SMA 179142 677.7 Fe-based in wall 175186 668.2 NiTi in wall 173779 652.7 Fe-based in beam 176391 677.1 NiTi in beam 174570 651.7 Fe-based in column 170536 739.8 NiTi in column 165987 623.8 Conclusions Steel has a more substantial capacity to dampen energy than shape memory alloys in all cycles, according to the shape memory alloys' flag -shaped strain stress diagram and their smaller area under the diagram compared to the surface under the steel diagram. The most significant reduction in energy damping capabilities will occur in columns made of shape memory alloys. Using these alloys in the wall and coupled be am results in the most considerable reduction in energy damping ability after the columns. The most significant decrease in residual deformation in the shear wall is brought on by applying shape memory alloy in the column elements. Using SMA in the couple d beam and the wall will minimize the deformation roughly equally after the columns . Different changes in residual deformation and dissipated energy are observed based on the position and the type of SMA material . For instance, When Fe-based SMAs are utiliz ed to their full potential, the wall is where they have the most significan t impact on reducing residual deformation while using the least amount of material . However , different forms of SMA do not compare similarly. It is impossible to pinpoint the exact ideal region for decreasing residual displacement because of SMAs ' various behaviors. In this study, it is observed that t he gap between dissipated energy of various SMAs will also close as SMA usage increases.