Integrating SMA and CFRP for fatigue strengthening of edge-cracked steel plates

Inclined fatigue cracks of U-ribs and diaphragms in orthotropic steel-box girders are challenging to be repaired using prestressing techniques. Integrating shape memory alloys (SMAs) and carbon fibre reinforced polymers (CFRPs) can achieve a hybrid self-prestressing strengthening approach for such fatigue cracks. To examine the strengthening effect of this approach on inclined cracks, 39 specimens were prepared in four groups and tested under static and fatigue tensioning in this study. Both static and fatigue test results showed that SMA/CFRP composite strengthening effectively retard steel cracking. Compared to control specimens, SMA/CFRP composite strengthening enhanced the notch tip yield load by 128% and 111% for specimens with a notch inclination of 0 degrees and 30 degrees, and the corresponding fatigue life by 7.62 and 8.69 times, respectively. Besides, the strengthening effect of combining SMA and CFRP (SMA/CFRP composite) on cracked steel plates was greater than that of either SMA or CFRP alone, particularly for the steel plates with an inclined crack. Finally, the calculation of mixed -mode I/II effective stress intensity factors confirmed the superior strengthening effect of SMA/CFRP compos-ite on steel plates with an inclined crack. The findings of this study can provide a reference for the reinforcement of orthotropic steel-box girders.