Effect of U-wrap anchors on the strength and ductility of externally bonded RC beams with mortar bonded GSM sheets

Abstract

Strengthening of deficient reinforced concrete (RC) structures had been one of the major concerns of researchers over the past few decades. Thus, new materials are being discovered to ease the process of externally strengthening RC structures. One of the various strengthening materials is Galvanized Steel Mesh (GSM) that is available in different cord densities. High and low cord-density GSM sheets can be externally bonded to RC structures using epoxy adhesives, while only low cord-density GSM sheets can be externally bonded with cement Mortar. In this experimental study, low cord-density GSM sheets (3.15 cords/cm) were bonded with cement mortar to the soffit of RC beams surfaces. A total of four RC beams were cast, three of which were externally strengthened in flexure with GSM sheets and bonded with mortar and the remaining beam was kept as a control un-strengthened specimen. In order to avoid the brittle delamination failure mode, one of the strengthened specimens was anchored with end U-Wrap carbon-fiber reinforced polymer (CFRP) sheets, while the other strengthened specimen was anchored with intermediate U-Wrap CFRP sheets, and the remaining third strengthened specimen was not anchored, to serve as a control strengthened specimen. All specimens were subjected to four-point loading test and the load-deflection response curve of each specimen was recorded. It was observed that flexural strengthening using GSM sheets increased the ultimate-load capacity of strengthened specimens by a range of 41.8 to 51.4 %, when compared to control un-strengthened specimen. While, no strength increase was observed when comparing anchored strengthened specimens to non-anchored strengthened specimens. However, the ductility of end anchored specimens increased by 142.1 and 270% when compared to control and non-anchored specimens, respectively. In addition, the ductility of intermediate anchored specimens increased by 134.1 and 257.3 % when compared to control and non-anchored specimens, respectively. Thus, it can be concluded that GSM laminates if properly anchored can enhance the strength and ductility of RC beams in flexure.