Application of SRP Composite Sheets for Retrofitting Reinforced Concrete Beams: Cracking and Tension Stiffening

This paper presents the contribution of steel-reinforced polymer (SRP) composites to the serviceability of reinforced concrete beams when retrofitted, with particular emphasis on cracking behavior and tension stiffening. SRP composite sheets, consisting of high-carbon steel unidirectional fabrics embedded in epoxy resin, provide high tensile strength and modulus at a reasonable cost. Six reinforced concrete beams, five of which are retrofitted using various widths of SRP sheets with or without end anchorage, are tested in three-point bending to examine their flexural performance, including crack width and depth progression, crack patterns, flexural rigidity, and tension stiffening. A 3D non-linear finite element analysis is conducted and compared to the code provisions and experimental findings. The trend of crack width progression of the SRP-retrofitted beams includes an almost linear response with respect to the SRP strain development. Clear differences in crack spacing are observed between the mid-span and shear-span regions of the test beams. The end anchorage significantly improves flexural rigidity and narrows the crack spacing of SRP-retrofitted beams. A characteristic area, including the tension stiffening factor, is proposed to evaluate the contribution of SRP composites to the flexural rigidity of SRP-retrofitted beams.