Hybrid NSE/EB technique for shear strengthening of reinforced concrete beams using FRCM: Experimental study

Abstract

The externally bonded (EB) fabric reinforced cementitious matrix (FRCM) has successfully been used as a structural strengthening for various applications including flexural and shear strengthening of reinforced concrete (RC) beams, flexural strengthening of RC slabs and column confinement. However, the EB-FRCM system is characterized by poor FRCM/concrete bond leading to premature debonding of FRCM off the concrete substrate, particularly for thicker FRCM. The present paper reports on an experimental study on the efficacy of a pioneer form of hybrid near surface embedded and externally bonded technique using FRCM composites (NSEEB-FRCM) for shear strengthening of RC beams. With such a technique, higher thickness of FRCM composites can be applied with less likelihood of debonding that is normally experienced when using the EB-FRCM system. Thirteen shear-deficient medium-scale RC beams were constructed, strengthened in shear and tested under three-point bending test. The test parameters were: (a) FRCM type (polyparaphenylene benzobisoxazole, carbon, and glass), (b) strengthening configuration (full versus intermittent strips), and (c) number of fabric layers. The percentage enhancement in the shear capacity of the beams ranged from 43% to 114% indicating the successful implementation of the strengthening methods provided. An average enhancement in shear capacity of 83%, 72% and 62% were observed in carbon FRCM, glass FRCM and PBO-FRCM, respectively. The failure mode of the strengthened specimens was sensitive to the type and configuration of FRCM in addition to the number of FRCM layers. The strengthening systems also resulted in higher deflection at failure and energy absorption value of the strengthened beams with an average of 94% and 204% relative to the reference specimen, respectively.