Experimental study on flexural strengthening of RC beams with NSM technique by different orientation of CFRP laminate

Abstract

This paper gives the brief description on the use of laminates manufactured using Carbon Fiber Reinforced Polymer (CFRP) as strengthening material for the purpose of assessing the flexural strength in RC beams using Near Surface Mounted (NSM) technique. The main objective of this work was to assess the strengthened RC beam by considering the orientation of laminate as the main priority in NSM strengthening. This study gives the brief description about the utilization of tensile strength of laminate and efficiency of adhesive for different orientation of laminate. The strengthening methodologies adopted in this research work are Near Surface Mounted Laminate with Vertical Orientation (NSMLV), Near Surface Mounted Laminate with Vertical Orientation having Anchorages (NSMLVA) and Near Surface Mounted Laminate with Horizontal Orientation (NSMLH). The dimension of beam used was 200 mm (Breadth) X 200 mm (Depth) X 2300 mm (Length) and the effective span of the beam was considered as 2100 mm. All beams were designed as per Indian design code requirement to operate in under reinforcement criteria. A total of eight beams were casted, out of which two were used as control beams and the remaining were strengthened with different NSM techniques. The groove size used for NSMLV and NSMLH technique were different. The premature debonding takes place in NSMLV technique by not utilizing the tensile strength of laminate to greater extent, to overcome this drawback CFRP fabrics were used as the anchorages in four critical locations where debonding is predominate and this method was expressed as NSMLVA technique. This work was mainly focused on improving the ultimate load carrying capacity by satisfying the serviceability requirement as per codal provisions. The four-point bending test was performed for all the test specimens. In comparison with the control beams, all strengthened beams showed improved ultimate loads by satisfying the serviceability requirement. The ultimate load shows an increase of 21.74 %, 40.22% and 71.74% for NSMLV, NSMLVA and NSMLH technique respectively compared to control beams. The Stiffness of beam was increased by 14% and 30% respectively for NSMLVA and NSMLH technique compared to control beams. NSMLH technique maximizes ultimate load, which is 71.74% higher, and fulfills the serviceability requirements. In comparison with NSMLV and NSMLVA, the NSMLH Technique is the most effective method of strengthening which bears debonding to maximum extent and increases ultimate load by greater margin.