Analytical Study of Flexural Strengthening of Reinforced Concrete Beams by Using Externally Bonded Cfrp Sheets

Abstract

Externally bonding carbon fiber reinforced polymer (CFRP) sheets with an epoxy resin is an effective technique for strengthening and repairing reinforced concrete (RC) beams under monotonic loads. In this study, three types of beam were adopted. They are Laboratory scale Beam (4000x150x300 mm), Building Specific Beam (5000x300x450 mm) & Bridge Specific Beam (20000x500x1800 mm). A total of seventy eight RC beams were analyzed. For the study of effective percentage of CFRP, six control beams, eighteen beams reinforced with 0.17% to 1.0% CFRP corresponding to 0.33% rebar and eighteen beams reinforced with 0.17% to 1.0% CFRP corresponding to 0.75% rebar are analyzed. For the study of effect of offset of CFRP from support, twenty seven beams with 0% to 40% offset of CFRP from support corresponding to 0.5% CFRP & 0.33% rebar and nine beams with 0% to 40% offset of CFRP from support corresponding to 0.17% CFRP & 0.75% rebar on Laboratory scale beam are analyzed. The percentage of rebar and CFRP are expressed in terms of cross-section of beam and percentage of offset of CFRP is expressed in terms of span of beam. All specimens were subjected to a four-point bending test under monotonic loading where load, defection, mid-span strain and failure mode were recorded up to failure. Analysis of beam is done with the help of non-linear FEM software Marc2003. From analytical study it was found that the load carrying capacity of the strengthened beam increases from 30% to 50% at cracking, 25% to 95% at yielding and 80% to 200% at ultimate, the increment of load carrying capacity of the beam depends on the geometry of the beam, percentage of rebar and percentage of CFRP. The failure mode of the beam depends on the amount of rebar and CFRP. From analysis it was found that the optimum percentage of CFRP for fully utilization is 0.5% corresponding to the 0.33% rebar and 0.17% corresponding to 0.17% rebar. The load carrying capacity of the beam, corresponding to the final deflection allowed in the design (IS 456-2000), can be increased from 12% to 80%. From analysis, it was seen that keeping offset of CFRP from the support more than 25% is not good. On the other hand, by keeping offset of CFRP less than 25%, it increases the cost only but not strength. With the increase in percentage of CFRP, the mid-span deflection of the beam is reduced. With the increase in offset of CFRP from the support more than 25%, the mid-span deflection of beam is increased.