## 6 Reinforcement of Concrete Beams with Fe-SMA
### Flexural Performance Enhancement  
The flexural reinforcement of concrete beams can increase the stiffness, reduce the deflection under load, decrease crack width, and inhibit crack propagation, to improve the bearing capacity and durability of concrete beams. The available research has shown that the NSM technology and embedding the Fe-SMA strips/bars into the shotcrete layer can achieve a satisfactory reinforcement effect. Crucially, it can solve the problem of ductility reduction and brittle failure of concrete beams reinforced by prestressed CFRP, which is extremely valuable for engineering applications.  
[PERSON] et al. [72] and [PERSON] et al. [114] demonstrated the reliability of NSM technology through connection tests, and the Fe-SMA strips/bars can transfer prestress effectively. As shown in Figure 21, [PERSON] et al. [97] employed the NSM method with Fe-SMA strips to repair concrete beams. The reinforcement measures could decrease crack widths, deflections, and stress in the internal steels. The cracking load of the beams reinforced by the Fe-SMA strips increased by 80% after activating Fe-SMA to introduce prestress. [PERSON] et al. [79] reinforced the beams using the Fe-SMA strips with cross-sectional areas of 30 mm\({}^{2}\), 60 mm\({}^{2}\), and 90 mm\({}^{2}\), the cracking load was increased by 26.95%, 81.40%,  
Figure 19: Shear strengthen of the concrete beam with Fe-SMA strips [15].  
Figure 20: Shear reinforcement of the concrete beam [33,111]: (**a**) external Fe-SMA strips, (**b**) embedding Fe-SMA bars.  
and 89.22%, respectively, and the yield load was increased by 19.71%, 43.0%, and 74.11%, respectively.  
[PERSON] and [PERSON] [80, 81] used the CFRP and Fe-SMA bars to repair concrete beams. The ultimate strength of the beams reinforced with CFRP bars was marginally higher than that of beams reinforced with Fe-SMA bars, but the ductility of CFRP-strengthened beams was obviously decreased. The brittle failure occurred due to the sudden fracture of CFRP bars in the CFRP-strengthened beams, whereas beams reinforced with Fe-SMA bars failed due to concrete crushing following the yield of steel and Fe-SMA bars.  
As shown in Figure 22a, [PERSON] et al. [71] embedded the ribbed Fe-SMA bars in the shotcrete layer to reinforce concrete beams. The upward deflections were reversed 0.17 mm and 1.18 mm, respectively, when the number of Fe-SMA bars was two and four. The counterforce under deflections of 4 mm increased by 163% and 265% after reinforcement, and the cracking load of the beams dramatically increased. Notably, the shotcrete layer may crack due to material shrinkage, resulting in a stiffness decrease in the beams; hence, it is valuable to control the shrinkage cracking of the shotcrete layer. [PERSON] et al. [99] reinforced concrete beams with the Fe-SMA strips through nail-anchor connections at the end region (as shown in Figure 22b). The deformation in the nail anchorage during and after activation was small compared to the entire length of Fe-SMA strips. Neither shear failure of the nails nor concrete py-out was observed at the anchorage when the concrete was crushing.