Behaviour of reinforced concrete beams strengthened by carbon fiber reinforced plastic sheets

The use of fiber reinforced plastic (FRP) as reinforcement for concrete structures hasbeen growing rapidly in recent years. This study was intended to examine andevaluate the structural behaviour of reinforced concrete RC beams strengthened withcarbon fiber reinforced plastic (CFRP) sheets experimentally and analytically.Sixteen full-scale RC beams of dimensions 200 x 450 x 4000 mrrr’ were used in thisstudy, where both strengthening in flexure and in shear were considered.Nine beams were used for studying the flexural strengthening of RC beams:two reference beams with different internal steel reinforcement and sevenstrengthened ones with external CRFP sheets adhered to the soffits of these beamsalong the span length by an epoxy adhesive. The sheets had the cross-sectional areaof 1.2 mm thickness by 100 mm width. Factors considered in this study were theeffect of strengthening with the CFRP sheet, the effect of precracking the beam toabout its service load and its strengthening while unloaded, the effect of precrackingthe beam to about its service load and its strengthening while loaded, and the effectof the presence of end anchorages for anchoring the CFRP sheet at its ends. Inaddition, the internal and external reinforcements were in turn varied to examinetheir effects on the behaviour of the strengthened beams. Theoretical calculationswere made and compared to the experimental results.Based on the outcome of the study of this group of beams concerning theshort-term behaviour, it was found that a finer cracking distribution and an increasein the stiffness and strength up to failure were obtained due to strengthening. Theductility was reduced but strengthened beams still possessed sufficient ductility.Results also showed that the sheet-peeling mode offailure should be considered inthe design of the strengthened beams as this mode of failure can occur prematurely,particularly in beams of low internal steel reinforcement. Precracking a beam toabout its service load before it was strengthened while unloaded resulted in analmost similar behavior to the reference beam, which was strengthened withoutprecracking with almost the same ultimate load but with a small reduction in thestiffness leading to an increase in the midspan deflection of about 10% at the level of