Fatigue life improvement of steel structures using self-prestressing CFRP/SMA hybrid composite patches

•Fatigue is a mode of failure that affects the majority of steel structures.•Self-prestressing CFRP/SMA patches are developed for fatigue repair and retrofit.•The proposed concept uses the shape memory effect of SMA wires embedded in CFRP.•An extensive experimental study is conducted to validate the strengthening technique.•The hybrid patches significantly enhance the fatigue life of cracked steel structures. While prestressed CFRP patches are considered as attractive alternatives to traditional welding or bolting methods for enhancing the fatigue life of cracked steel structures, they commonly require hydraulic actuators and pumps, and complex setups and installations for prestressing, limiting the applicability of this method. The primary objective of this research is to investigate the use of shape memory alloys (SMAs) in combination with CFRP composites to develop self-prestressing CFRP/SMA hybrid patches. The concept of the self-prestressing is to embed prestrained SMA wires into the CFRP patches and activate them through direct heat or electric current, thereby, generating prestressing forces in the cracked member. Two types of NiTi SMA wires, namely, the body-temperature and as-drawn heat-treated NiTi SMA wires are used in the fabrication process of the patches. The results demonstrate that the developed self-prestressing CFRP/SMA hybrid patches can be used as simple and effective solutions to significantly enhance the fatigue life of cracked steel structures.