Fiber-Reinforced-Cementitious-Composites Plate for Anchoring FRP Sheet on Concrete Member Qingxu Jin 1 and Christopher K. Y. Leung, M.ASCE 2 Abstract: To improve the fiber-reinforced polymer (FRP)/concrete bond capacity, this paper presents a new anchoring approach with the gluing of precast fiber-reinforced cementitious composites (FRCC) plate on top of the FRP sheets. In order to measure the improvement in ultimate load and deformation capacity and to study the failure mechanisms around the anchored area, the direct shear bond test is performed on concrete prisms with bonded FRP. Several sets of tests have been carried out with anchoring plates of different FRCC compositions and lengths. Comparison with the control sample shows that the installation of FRCC plate can significantly increase both the bond and deformation capacities (by up to 100%). On the basis of the shear bond test, two types of FRCC plate materials were found to be particularly effective and were selected for strengthening of beam members to be tested under four-point bending. Comparison with control members (without anchor) and those with conventional U-shaped FRP anchors indicates that both the ultimate load and central deflection can be improved by the new anchoring method. DOI: 10.1061/(ASCE)CC.1943-5614.0000211. © 2011 American Society of Civil Engineers. CE Database subject headings: Fiber-reinforced polymer; Composite materials; Anchors; Bonding; Plates; Shear tests; Sheets; Rehabilitation; Concrete. Author keywords: Fiber-reinforced polymer; Composite materials; Anchors; Bonding; Plates; Shear tests; Sheets; Retrofitting; Concrete. Introduction When fiber-reinforced polymer (FRP) sheets are employed for the flexural or shear strengthening of concrete members, the achievable increase in bond and deformation capacities is often limited by the sudden debonding of the FRP from the concrete substrate. Two major failure modes of FRP debonding are often observed: (1) Concrete cover separation (Ritchie et al. 1991; Garden and Hollaway 1998; Nguyen et al. 2001; Yao and Teng 2007) and (2) Intermediate crack-induced debonding (Ziraba et al. 1994; Rahimi and Hutchinson 2001; Teng et al. 2003; Oehlers et al. 2005; Yao et al. 2005). In order to increase the bond capacity of retrofitted FRP sheets and provide more obvious signs in deforma- tion before failure, the anchoring of FRP sheets has been studied for many years. In previous investigations, various anchoring methods (Fig. 1) have been proposed to enhance the load-carrying capacity of FRP and to delay its debonding. For example, U-shaped FRP jackets [Fig. 1(a)] applied on the sides and tension face of a beam can be employed to confine the FRP strip and hence to delay the debonding (Teng et al. 2002). In Ceroni (2010), concrete cover separation was observed in a beam member with FRP plate terminated at 300 mm from the support. The test results showed that a U-shaped anchor can enhance the member by 39%. For the beam member with intermediate crack-induced debonding near the midspan rather than high stresses at the plate end, a U-shaped FRP strip anchor shows much less effectiveness. In Smith and Teng (2001), intermediate crack- induced debonding was observed in tested beams with FRP plate terminated at 125 mm from the support. With a U-shaped FRP anchor placed over the end of the FRP, the load capacity only in- creased slightly from 86.4 kN to 89 kN (a 3% increase). In Leung (2006), FRP-plated beams with a U-shaped anchor at different locations along the FRP were tested under four-point loading. With the anchor at the plate end, there was essentially no increase in load capacity (0.2%). However, the anchoring effect became more sig- nificant (13.6%) when the anchor was placed closer to the loading point (750 mm from the plate end). Fig. 1(b) illustrates the anchoring of FRP with the use of a spike anchor. This method was first proposed by Neuner and Falabella (1996) and further developed by Eshwar et al. (2008). The spike anchor is made up of glass fiber bundles, with part of it impregnated with resin and cured. A hole must be drilled in the concrete member to install the anchor, and resin has to be added afterward. After the first layer (or a couple of layers) of FRP is bonded to the concrete surface, the cured part of the anchor is inserted through the wet FRP layer into the hole, whereas the loose part is spread on top of the FRP later to form a fan. Additional layers of FRP can then be applied. According to the shear bond test results by Eshwar et al. (2008), the effectiveness depends on the embedment depth of the anchor and number of anchors on the strips. As suggested by Özdemir (2005) and Orton et al. (2008), the effective embedment depth for full development of the anchor should be greater than 100 mm to ensure at least a 50 mm depth inside the core of the concrete (beyond the first layer of reinforcing steel). Recently, dif- ferent configurations of spike anchor have been studied (Niemitz et al. 2010). The results indicate that the failure mode can be converted from FRP debonding to FRP rupture. The percentage increase strongly depends on anchor configuration and varies from 16% to over 40%. 1 M.Phil., Dept. of Civil and Environmental Engineering, The Hong Kong Univ. of Science and Technology, Clear Water Bay, Hong Kong, China (corresponding author). E-mail: jinqx@ust.hk 2 Professor, Dept. of Civil and Environmental Engineering, The Hong Kong Univ. of Science and Technology, Clear Water Bay, Hong Kong, China. E-mail: ckleung@ust.hk Note. This manuscript was submitted on August 31, 2010; approved on February 9, 2011; published online on February 11, 2011. Discussion per- iod open until March 1, 2012; separate discussions must be submitted for individual papers. This paper is part of the Journal of Composites for Con- struction, Vol. 15, No. 5, October 1, 2011. ©ASCE, ISSN 1090-0268/ 2011/5-790–798/$25.00. 790 / JOURNAL OF COMPOSITES FOR CONSTRUCTION © ASCE / SEPTEMBER/OCTOBER 2011 J. Compos. Constr. 2011.15:790-798. Downloaded from ascelibrary.org by University of Michigan on 11/24/13. Copyright ASCE. For personal use only; all rights reserved.