Fatigue behaviour of notched steel beams strengthened by a self-prestressing SMA/CFRP composite

Integrating a NiTiNb-based shape memory alloy (SMA) and carbon fibre-reinforced polymer (CFRP) sheet can achieve a self-stressing SMA/CFRP composite, providing an alternative active (or prestressing) strengthening technology for steel elements. In this study, the effects of retrofitting methods and fatigue load amplitudes on the fatigue behaviour of notched steel beams were experimentally investigated. The retrofitting methods included SMA patch bonding, CFRP sheet bonding, and SMA/CFRP composite bonding. Test results showed that, compared with strengthening methods of CFRP sheets or SMA patches, SMA/CFRP composite strengthening can greatly increase the fatigue lives and slow down the fatigue crack growth rate of steel beam web cracks and interfacial debonding. Besides, the strengthening effect of the SMA/CFRP composite becomes increasingly significant on notched steel beams as the fatigue load amplitude decreases. Additionally, the fatigue life of the SMA/ CFRP composite repaired beams was greater than that of the sum of the fatigue life of repaired beams with SMA or CFRP alone. Moreover, SMA/CFRP composite strengthening can effectively reduce the stiffness degradation rate compared with the other two strengthening methods.