Flexural and Shear Strengthening of RC Beams with FRP –An Experimental Study

Abstract

This study deals with experimental investigation for enhancing the flexural and shear capacity of RC beams using Glass fiber reinforced polymers (GFRP) and Carbon fiber reinforced polymers (CFRP). Fifteen concrete beam specimens with dimensions of 110mm width, 200mm height and 1300mm length were fabricated in the laboratory. As per practical consideration of pre-stressed bridge girders, one 30mm diameter longitudinal hole was provided below the neutral axis in the tension zone in all the beams for future strengthening, service lines and other consideration. The
geometry of all beams was kept constant, while steel reinforcement varied as per initial design. Out of 15 beams four were control beams. One beam was made without any steel reinforcement strengthened with two layers of GFRP fabrics U- jacketed over the full span. Five beams were weak in flexure, strengthened using GFRP fabrics with varying configurations in higher flexural zone. Four beams were weak in shear, (tied with two 6-Ø stirrups in each support, one 6-Ø stirrup at mid span to keep the grill intact for concreting) strengthened using GFRP fabrics with varying configurations in higher shear zones near both supports. One beam was made weak in shear, strengthened with CFRP fabrics in higher shear zones near both supports. All the beams
were simply supported at both ends with 1000mm effective span, 150mm bearings, loaded under more realistic loading conditions, i.e. uniformly distributed loaded (UDL) and tested up to failure by gradually increasing super imposed load. The preparation of concrete surface was done with
great care and showed no bond failure in all U-jacketed and inclined stripped beams. One beam bonded with GFRP fabric in the soffit bottom only failed due to debonding. The flexural and shear capacities of the beams are compared with the theoretical prediction using codal provisions. The experimental deflection of beams are also compared with the theoretical predictions. The beams weak in flexure after strengthening showed remarkable flexural strength with 33% to 83% increase in cracking load capacity with respect to the control beam depending on the configuration of GFRP. The four beams weak in shear after strengthening showed 25% to
81% increase in cracking load capacity with respect to the control beam depending on the configuration of GFRP. One beam shear strengthened with CFRP showed remarkable increase of 131% in cracking load capacity and rigidity with respect to the control beam which is highest in the series of tested beams. There was increase in the stiffness of all strengthened beams compared to the control beams.