## 4 Results and Discussions
### Effect of Activation Sequence  
In the experiments, the Fe-SMA bars were activated by heating them to ~160 \({}^{\circ}\)C by electric resistance heating [31]. The activations of the Fe-SMA bars were done one-by-one due to the practical limitation of the electric power supplier used in the experiment. In this section, the possible influence of the activation sequence on the prestressing effect and the bending resistance of the RC beam reinforced by the Fe-SMA bars was analyzed by the FE simulations. The same model used in Section 4.1, i.e., the FE model for the RC beam with 5 Fe-SMA bars, was used. The Fe-SMA bars in the FE simulations in this section were sequentially activated in the same order as in the experiment [31]. The FE simulation results were compared with the results of the same model but with activation of all 5 Fe-SMA bars activated at once. Figure 8 shows the normal \(x\)-axis stress distributions along each Fe-SMA bar after activation, calculated by the FE simulations. Figure 8a shows the normal stress distributions of the Fe-SMA bars in the case of sequentially activated Fe-SMA bars. The activations of the Fe-SMA bars were carried out in the order of SMA1, SMA2,..., SMA5 in the simulations, as schematically shown by an insert of the figure. The normal stress distributions of the Fe-SMA bars in the case of a single activation are shown for comparison in Figure 8b. It is worth noting that, during the activation, a thermal contraction of 0.002233 mm/mm along the \(x\)-direction was applied in each Fe-SMA bar. The corresponding prestress when the Fe-SMA bar is strictly restrained along the \(x\)-direction is ~335 MPa. As shown in Figure 8a, it can be seen that the stress produced by the Fe-SMA bars are about 320-323 MPa in the case of the sequential activation. Therefore, the prestress obtained by the sequential activation of the Fe-SMA bars is about 10% less than the maximum prestress that can be obtained by the Fe-SMA bars with fully constrained condition. In this case, the \(x\)-axis stress along the Fe-SMA bars is almost the same without pronounced variation along the \(x\)-direction, except near the end of the RC beam where the stress drops sharply to zero due to the absence of the constraining concrete material outside the RC beam. When the Fe-SMA bars were activated at once, the \(x\)-axis stress near the center of the RC beam was about 335 MPa, which corresponds very well to the maximum prestress that can be obtained by the activation of the Fe-SMA. The stress decreased moderately and linearly with increasing the distance from the center, and then sharply dropped to zero near the end of the RC beam, as shown in Figure 8b. The results in Figure 8 indicate that the sequential activation of the Fe-SMA bars produces slightly less prestress than the activation of the Fe-SMA bars at once. Near the center of the RC beam, the Fe-SMA bars activated at once produced \(x\)-axis stress very close to the ideal value of 335 MPa, while the sequentially activated Fe-SMA bars produced stress approximately 10% less than the prestress obtainable by the fully constrained condition. The moderate decrease in the prestress in Figure 8b with increasing the distance from the center of the RC beam in the Fe-SMA can be easily understood by the elastic shortening effect of the concrete. While the concrete material is elastically shortened during the activation of the Fe-SMA bars, the bars are not under fully fixed conditions but under elastic boundary conditions. Therefore, the Fe-SMA bars are shortened especially near the end of the RC beam due to the upward bending and \(x\)-direction shortening of the RC beam, which can reduce the prestress produced by the Fe-SMA bars in comparison to the ideal, fully constrained condition [37]. In the case of sequential activation, the elastic shortening of the concrete can occur in a more complex manner depending on the three-dimensional positions of each Fe-SMA bar and the order of the activation.