Flexural and shear behaviour of lightweight RC beams strengthened by NSM GFRP bars

This research has presented an experimental study to improve the flexural and shear strengths of lightweight reinforced concrete (LWRC) beams using near surface mounted (NSM) glass fiber reinforced polymer (GFRP) bars. Utilizing NSM GFRP bars in shear strengthening of the LWRC beams is elatively new practical approach and this study is on of the first experimental studies conducted about this topic. The main parameters investigated are location, number, diameter, bond length, spacing, angle of inclination, and material of the NSM bars used to strengthen the LWRC beams. The LWRC beams specimens were composed by completely replacing natural coarse aggregate with lightweight expanded clay aggregate (LECA) in the concrete mixture. The experimental program consists of twelve LWRC beams with cross-section dimensions of 160 × 250 mm (width × height) and total length of 1700 mm. The beam specimens were divided into two groups according to the strengthening objective: the first group consists of six LWRC beams strengthened in flexure; while the second group includes six LWRC beams strengthened in shear. One beam in each group was unstrengthened and considred as control beam, while the other specimens were strengthened by NSM GFRP bars in different arrangements and configurations. All LWRC beams are subject to two points loading until failure. The experimental results have shown that using side near surface mounted (SNSM) GFRP bar improves the ultimate load capacity of the LWRC beam by about 30% compared to control beam. Furthe, the experimental results revealed that when 50% of the epoxy adhesive is replacement by cement mortar at the beam mid-span, the ultimate load capacity of the NSM strengthened LWRC beams is almost similar to that when 100% epoxy adhesive was used. It was also observed that the inclined alignment of the NSM GFRP bar increases the loading capacity by about 149% compared to that of the control beam with failure mode being changed from shear to flexural failure. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.