Optimization of kenaf fibre reinforced polymer laminate for shear strengthening of RC beams using embedded connector

Abstract

Kenaf fibre reinforced polymer (KFRP) laminate has gained its potentiality in shear strengthening of reinforced concrete beams recently, thus, method to obtain the minimal required dimension of KFRP shear strip is the utmost demand. The main aim of this research was to optimize the dimension of KFRP laminate for shear strengthening of RC beam. In experimental programme, high strength KFRP laminate and seven full scale RC beams were fabricated. The beams were shear strengthened using 7.5 mm thick and 20 mm, 30 mm and 35 mm widths of KFRP laminate, the dimensions of those shear strips were based on design strains of 0.007, 0.0045 and 0.004 respectively. Beams were also shear strengthened using CFRP laminates with similar widths of KFRP laminates for comparison. All beams were numerically analysed. Parametric study on design strain based on theoretical model was also conducted. Results showed that shear strengthened beam with 0.007 strain of KFRP laminate failed due to fracture of laminate. However, beams with laminate strains of 0.0045 and 0.004 did not show fracture or debonding of KFRP laminates, both beams had shown ductile flexural mode of failures with higher failure loads. In contrast, all CFRP laminate strengthened beams failed because of cover separation of laminates followed by shear. The failure loads of KFRP laminates strengthened beams were found to be higher as compared to those of CFRP laminates. The KFRP laminates were effectively enhanced shear capacity of strengthened beams without showing any premature failure even with the design strain of 0.0045, while, CFRP laminate showed premature cover separation failure with design strain of 0.002. Theoretical model showed that higher strength of concrete and length of laminate increased debonding or design strain of laminate. The numerical model predicted flexural and shear behaviour of shear strengthened beams. The flexural behaviour of strengthened beams based on numerical analysis were closely comparable with those of experimental findings. However, the model had limitation to predict local debonding failure of shear strip due to cracks and the effects of debonding on shear behaviour of strengthened beams.