Reliability of shear-deficient RC beams strengthened with CFRP-strips

Abstract Effectiveness of externally bonded FRP-strips on the side faces of RC beams in the strengthening of shear-deficient RC beams is well established. However, how the design parameters such as fiber orientation, strip-width, and spacing between the FRP-strips influences the reliability of strengthened beams is not very well known. In the present study, a simplified probabilistic procedure based on Monte Carlo Simulation technique has been presented to study the influence of externally bonded FRP-strips on the reliability of shear-deficient RC beams. To illustrate the procedure, reliability analysis was carried out for the six RC beam specimens of 2 m span. Two of these specimens were shear-deficient control specimens, and the remaining four were the similar beams which were shear-strengthened using CFRP-strips. Out of these four strengthened specimens, in the first two specimens, CFRP-strips were externally bonded at 30° whereas in the other two CFRP-strips were attached at 90° with the longitudinal axis of the beam. All these beams were tested in the lab until failure to obtain their ultimate load carrying capacities. Reliability analysis was then carried out for a range of applied nominal loads, varying from service to ultimate. Three parametric studies (i) effect of fiber orientation; (ii) effect of strip width; and (iii) effect of strip-spacing on reliability of strengthened beams were carried out for two different service loads, taken 60% and 70% of tested beams’ capacity. The results indicate that when the service load is 60% (or less) of the ultimate load, beam is sufficiently reliable for all the values of the fiber orientation ranging from 30° to 60° from the longitudinal axis of the beam. However, when the applied load is 70% (or more) of the ultimate load, it is difficult to achieve the desired reliability just by attaching the inclined CFRP strips at a certain angle. The desired reliability, in this case, can be achieved by altering the strip-width or strip-spacing or the both.