## 4 Results and Discussions
### Effect of SMA Activation
Although the FE simulation for the RC beam bending with Fe-SMA activation overestimated the experimentally obtained bending load, the FE simulation could capture the overall trend of load-deflection behavior of the experiment, as shown in Figure 4. The FE simulation results predict the onset of non-linear bending deflection at around 1.5 mm deflection due to the cracking of the concrete, which is consistent with the load-deflection behavior observed in the experiment. The slope in the load-deflection curve in the RC beam bending obtained in the FE simulation is in very good accordance to that of the experimentally obtained curve in the wide range of the bending deflection up to 10 mm. Figure 6 shows the evolutions of cracking and crushing patterns with increasing bending deflection predicted by the FE simulations with and without the activation. From the figure, it can be easily confirmed that the cracks in the RC beam without Fe-SMA activation is more severe and widely spread than those with the activation. At a relatively low bending deflection of 2 mm, the concrete in the RC beam without Fe-SMA activation already showed long and severe cracks mainly along the stirrups near the center of the RC beam. Long vertical cracks along the stirrups as well as inclined shear cracks in between the stirrups were found to be the main cracking mechanisms, as shown in Figure 6. Near the bottom of the RC beam, concrete crushing patterns also appeared, which are due to the localized bending deformation of the cracked concrete elements near the bottom. With increasing the bending deflection, the cracking patterns become more widely spread. Figure 5: Comparison of experimental results and FE simulations for bending load-deflection responses of RC beams with 5 Fe-SMA bars, with (W) and without (W/O) activation of SMA bars. In comparison to the case without Fe-SMA activation, the RC beam with activated Fe-SMA showed less severe and more localized cracking pattern, as shown in Figure 6. This is due to the prestressing effect by the activation of the Fe-SMA bars, which reduces the tensile stress near the bottom of the RC beam and consequently hinders the onset of cracking in the concrete beam. With increasing the bending deflection, the cracking pattern in the RC beam in this case did not spread far from the center of the RC beam. Evolutions of equivalent stress fields of the concretes with bending deformations, predicted by the FE simulations of the RC beams with and without Fe-SMA activation are shown in Figure 6. Regardless of the bending deflection, near the top of the RC beam, concrete in the RC beam with the Fe-SMA activation was in a higher stress than that in the beam without the activation. This was because the prestressing associated with the Fe-SMA activation produces additional compressive stress near the top of the RC beam. With increasing bending deflection, the high compressive stress region spreads more widely in the concrete with the Fe-SMA activation than that without the activation, as shown in Figure 7.  
The results shown in Figures 5-7 reflect that the prestressing effect due to the activation of the Fe-SMA bars can be numerically considered with the simple FE model proposed in this study. The FE model with activated Fe-SMA shows much higher resistance to the bending deformation, less severe cracks at the same bending deflection and more widely  
Figure 6: Cracking and crushing patterns developed in FE simulation of bending of the RC beam on \(x\)-\(y\) plane, for RC beams with 5 Fe-SMA bars with and without activation. Figure 7: Evolutions of equivalent stress fields of concrete with bending predicted by FE simulations of RC beam with 5 Fe-SMA bars with and without activation. spread compressive stress region in the stress fields in the FE solutions than that without Fe-SMA activation.