## 4 Results and Discussions  
### Effect of SMA Activation  
In this section, the FE model with 5 Fe-SMA bars was used to investigate the effect of Fe-SMA activation on the bending response of the RC beam and the cracking behavior. For this purpose, one FE simulation was conducted without activating the Fe-SMA bars while another simulation was carried out with the activation. The activation of the Fe-SMA bars in this section was done with a single FE step, i.e., all 5 Fe-SMA bars were activated numerically at once. Figure 4 shows the bending load-deflection behavior of the FE models with 5 SMA bars, with and without the activations of the Fe-SMA bars. The bending deformations up to the bending defection of 10 mm was considered to prevent divergency in the FE solutions due to the severe cracking in the concrete. Figure 5 shows the bending load-deflection behavior of the FE models with 5 SMA bars, with and without the activations. In the figure, the experimentally obtained load-deflection curves are also depicted for comparisons. In the FE simulation results, it can be clearly seen that the activation of Fe-SMA bars significantly increased the bending resistance of the RC beam. In the case without Fe-SMA activation, the non-linear response of the simulated load-deflection curve started at the applied load of approximately 50 kN, whereas the non-linearity started to appear at a load of \(\sim\)130 kN in the case with the Fe-SMA activation. This shows that the developed FE simulation model can effectively take account of the prestressing effect due to the FE-SMA activation. When comparing the experimentally obtained load-deflection curves with the simulated curves, the FE model without Fe-SMA activation reproduced the experimentally obtained curve very well, as shown in Figure 5. This means that the developed FE simulation model can consider all the major strengthening effects by the Fe-SMA bars and the rebars on the bending deformation of the RC beam when the Fe-SMA bars are not activated. However, the FE model with Fe-SMA activation overestimated the applied load for the bending of the RC beam in comparison to the experimentally obtained behavior by approximately 20-30 kN, in the whole range of the bending deflection tested. Since the only difference between the two FE models (and also between the two RC beams used in the experiments of the bending curves presented in Figure 4) is in the stress states due to  
Figure 4: Idealized stress-strain curves used for FE simulations. (**a**) Compressive stress-strain curve for concrete and (**b**) tensile stress-strain curve for Fe-SMA bar. the Fe-SMA bar activations, the reason for the discrepancy between the FE simulation and the experiment in the case of Fe-SMA activation can be due to the inaccurate prediction of the prestressing effect of the Fe-SMA bars. One possible explanation for the overestimated prestress of the Fe-SMA is the imperfect bonding between the Fe-SMA bars and the concrete in the experiments. In the experiments, there was no anchoring between the concrete and the Fe-SMA bars and the Fe-SMA bars had nearly flat surfaces [31]. If there was debonding or slip of the interfaces between the Fe-SMA bars and the concrete in the experiments, this could make the present FE simulation have an overestimated prestress state while activating the Fe-SMA bars where perfect bonding between the bars and the concrete was assumed. To take into account the realistic bonding behavior between the Fe-SMA bars and the concrete, sophisticated FE simulations with consideration of bonding-debonding [36] or with specialized interface elements for the consideration of slip [35] are needed, which is beyond the scope of current FE simulations.