Grid U-Wrap Anchorage for Reinforced Concrete Beams Strengthened with Carbon Fiber-Reinforced Polymer Sheets

This paper presents the feasibility and effectiveness of an alternative anchor system for reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) sheets. Continuum U-wrap anchors that enclose the longitudinal CFRP sheets are conventionally employed to impede the premature delamination of the sheets. This method, however, is not cost-effective and completely blocks the bonded region, thereby disrupting any technical maintenance and visual inspections on the shear span of the beam. Grid CFRP U-wraps are proposed to address these concerns. Twenty beams are tested to examine the effects of the following parameters: anchorage types (continuum and grid U-wraps), grid configurations, shear-span coverage ratios (25 to 100%), bonding schemes (epoxy and silyl-modified polymer [SMP] adhesives), and loading conditions (monotonic and cyclic). Of interest are the flexural capacity of the strengthened beams, failure modes and crack propagation, and strain development that represents the behavior of the CFRP-concrete interface. The grid U-wraps alter the failure characteristics of the beams in conjunction with the interrupted formation of diagonal tension cracks. The use of SMP alleviates stress concentrations at the beam corners, preserving the integrity of the grid U-wraps. Cyclic loading brings about the progressive shearing of the CFRP sheet; accordingly, the capacity of the strengthened beams decreases. When SMP-epoxy hybrid bonding is used, the grid U-wraps result in flexural responses comparable with those of their continuum counterparts. Statistical inference techniques clarify the relationship between the anchorage configuration and the coverage ratio.