## 4 Conclusions  
This paper conducts experiments on the active reinforcement of concrete structures with an Fe-SMA with various connecting methods, focusing on their influence on the recovery stress and reinforcement effect. The obtained conclusions are as follows:  
1. During the activation process of an Fe-SMA, the recovery force generated during the heating stage is relatively small, while the recovery force increases significantly  
Figure 16: Strain and stress on concrete side surface: (**a**) strain–activation temperature curve; (**b**) average stress. Figure 17: Strain and stress at concrete anchor hole: (**a**) strain–activation temperature curve; (**b**) local stress. during the cooling stage. When the activation temperature of the Fe-SMA reaches 250 \({}^{\circ}\)C, the recovery stress in the adhesive-bolted hybrid connection reaches 246 MPa, which is sufficient for structural reinforcement of concrete structures. 2. In the adhesive-bolted hybrid connection, the average prestress on the reinforced surface of the concrete specimen reaches \(-\)19.3 MPa, achieving good reinforcement effect to apply compression. 3. A simple bolted connection can lead to local stress concentrated in the concrete block and Fe-SMA plate around the hole, which can easily cause early cracking of the concrete. The adhesively bonded connection can effectively avoid this problem, so the application of a structural adhesive in the adhesive-bolted hybrid connection significantly alleviates the stress concentration phenomenon. 4. A simple adhesively bonded connection is prone to softening and slip of the structural adhesive during the activation process, which reduces the overall restoring force, hence having adverse effects on the structural reinforcement. Additionally, the low glass transition temperature characteristic of adhesive affects the performance of the connection between the Fe-SMA and concrete. Optimizing the performance of the structural adhesive is of great significance in practical applications. However, structural adhesive has a superior effect on applying even prestress on the surface of concrete and can be used for repairing cracks in concrete structures. In addition, the bonded connection avoids damage caused by openings in the parent structure, which can be effectively applied in the non-destructive reinforcement of structures. 5. The adhesive-bolted hybrid connection effectively combines the advantages of adhesively bonded connection and bolted connection. The experimental results show that the adhesive-bolted hybrid connection effectively reduces the local stress concentration problem of the concrete and Fe-SMA at the anchor bolt hole, while avoiding the prestress loss caused by the softening and slip of structural adhesive during elevated-temperature activation, achieving an ideal reinforcement effect. 6. Compared to the bolted connection and adhesively bonded connection, in adhesive-bolted hybrid connections, the Fe-SMA can bring greater local prestress to concrete structures and have a better effect in suppressing the further expansion of shear cracks in concrete structures. 7. The experimental findings not only provide test support for the application of Fe-SMAs in reinforcing concrete structures but also offer new perspectives for future research. Future studies could further optimize the reinforcement effectiveness of Fe-SMAs in concrete structures. Conceptualization, X.Q. and X.J. ; methodology, X.Q. and X.J. ; software, D.Z. ; investigation, D.Z. ; data curation, X.Q. ; writing--original draft preparation, D.Z. and Y.W. ; writing--review and editing, X.Q. and X.J. ; visualization, D.Z. ; supervision, X.J. ; project administration, X.Q. and X.J. ; funding acquisition, X.Q. All authors have read and agreed to the published version of the manuscript. This research was funded by the Natural Science Foundation of China [Grant No. 52278207, 52278206] and National Key R&D Program of China [Grant No. 2020 YED1100403]. Not applicable.