A simple model for maximum diagonal crack width estimation of shear-strengthened pre-damaged beams with CFRP strips

This paper presents an experimental study on diagonal crack width estimation of Shear-Strengthened Pre-damaged Beams with CFRP strips (SSPBCs). Several parameters including pre-damaged degree, shear-span ratio and CFRP strips spacing are considered. The crack formation of shear-strengthened undamaged or low pre-damaged beams with CFRP strips is caused by reaching the ultimate tensile strain of concrete while that of shear-strengthened high pre-damaged beams with CFRP strips is due to the relative slip between stirrups and concrete. The development rate of diagonal crack increases as shear-span ratio, CFRP strips spacing or pre-damaged degree increases. The increase in CFRP strips spacing, pre-damaged degree or the decrease in shear-span ratio enhances the number of diagonal crack. The diagonal crack width of SSPBC increases as shear-span ratio, CFRP strips spacing or pre-damaged degree increases. When the normal service load ( P 1 = 120 kN ) is applied, the diagonal crack width of shear-strengthened pre-damaged beam SA3-A2 with shear-span ratio of 3.49 is 1.45 times than that of shear-strengthened pre-damaged beam SA2-A2 with shear-span ratio of 2.17. The diagonal crack width of shear-strengthened beam SA2-A2 with 150 mm CFRP strips spacing is 0.22 mm while that of shear-strengthened beam SA2-B2 with 100 mm CFRP strips spacing is 0.16 mm. The diagonal crack width of shear-strengthened high pre-damaged beam SA3-A3 is 40% higher than that of shear-strengthened undamaged beam SA3-A1. The ultimate strain of CFRP strips increases as CFRP strips spacing or shear-span ratio increases while the impact of pre-damaged degree on ultimate strain of CFRP strips is not distinct. On the basis of ordinary RC beams diagonal-crack-width model, a simple model for predicting the maximum diagonal crack width of SSPBCs is suggested considering the impact of pre-damaged degree, and the estimated values agree well with test data.