Shear Strengthening of Recycled Lightweight Coarse Aggregate Concrete Beams Using NSM Technique

Abstract

The NSM technique began to apply as a modern technique to treat defects in structural elements and to increase the shear and flexural strength of structural elements. For this technique to be effective, a series of practical experiments were conducted to characterize the behavior of the element strengthened by the NSM technique for flexure and shear. Shear strengthening with GFRP rods is the focus of this paper for concrete beams that contain 30% coarse aggregate replacement ratio of bonza (volumetric ratio) obtained from the rubble of demolished buildings. A total of 7 beams were loaded under four-point load test, the parameters examined were the angle of inclination and the distance between the GFRP bars, the presence and absence of stirrups and the bonza aggregate replacement ratio. The characterization of the tested beams includes failure mode, load-deflection curves, load-strain curves of stirrups, rebars and GFRP rods and the surface concrete strain in the shear zone of beam. The results showed that the use of GFRP rods used to strengthen concrete beams was relatively effective, especially in the presence of stirrups, where the gain in shear strength was 8.8% and 4.1% when the distance between the vertical GFRP bars was (200 and 300) mm, respectively, with the presence of stirrups. While the gain in shear strength was (5.9%) when the GFRP bars were inclined at 45o with presence of stirrups. The deflection of strengthened beams was greater than the deflection of unstrengthened beam, where the maximum deflection of strengthened beams reaches 29.6mm at 177kN, while the maximum deflection of unstrengthned beam was 18.9mm at 185kN.