Shear Strengthening of Short Span Reinforced Concrete Beams with CFRP Sheets

This paper presents the results of a series of tests on short span reinforced concrete beams which were strengthened in shear with various arrangements of externally bonded carbon fibre reinforced polymer (CFRP) sheets. The objective of the tests was to determine the effect of changing the area and location of the CFRP sheet within the shear span. A total of fifteen 150 mm x 300 mm x 1,675 mm concrete beams were tested of which four were un-strengthened control specimens. The remaining 11 beams were strengthened with varying configurations of CFRP sheets. Parameters varied in the tests included the area of CFRP sheet, its anchorage length and the distance of the CFRP sheet from the support. The experimental results revealed that the CFRP is more effective when it is placed close to the supports and even small areas of CFRP can give significant increases in shear strength. The experimental results were compared with the three different existing shear prediction models for estimating shear contribution of CFRP sheets. A simple strut-and-tie model is presented which gives reasonable predictions of shear strength for the beam specimens, which were strengthened with CFRP over the full depth of the beam. The superposition method of design is replaced in EC2 by the variable angle truss model in which all the shear is assumed to be resisted by the truss mechanism. A simple regression equation is proposed for the calculation of effective stress in FRP to be used in EC2.