Flexural response and crack assessment of high-strength concrete beams reinforced with steel and GFRP rebars using three-dimensional digital image correlation

The aim of this study was to improve the flexural performance and deformability of high-strength concrete (HSC) specimens by incorporating steel rebars and glass-fibre-reinforced polymer (GFRP) rebars as hybrid reinforcement. As a further step towards enhanced deformability, discrete short polyvinyl alcohol fibres (PVAF) were included. Six types of HSC beams were fabricated using M70 grade concrete with and without PVAF, strengthened with steel rebars alone, GFRP rebars alone and both GFRP and steel rebars as hybrid reinforcement (HYRC). Four-point bending tests were conducted to evaluate the flexural behaviour of the beams. Crack monitoring and failure modes were assessed using digital image correlation (DIC) and a conventional method. To ensure ductile failure, an appropriate reinforcement ratio for the HYRC beams was theoretically investigated. As the different types of reinforcement demonstrated unique deformation properties and failure mechanisms, a novel deformability method is proposed by considering load and displacement. The results obtained from both the DIC technique and conventional measurement were in good agreement, with the difference in observations being 1.8–3.8%. The results also revealed that, compared with the control beam, incorporating PVAF in HYRC beams enhanced the load-carrying capacity by 44%, the ductility index by 70% and first crack resistance by 36%.