Flexural Performance of Concrete Beams Strengthened Using CFRP Sheets with Large Spike Anchors

Abstract

Fiber-reinforced polymers (FRP) have a proven strength enhancement capability when attached to reinforced concrete (RC) beams. However, the inherent brittleness of FRP composites largely sacrifices the full load-carrying capacity of externally bonded FRP strengthening systems. The use of carbon fiber-reinforced polymers (CFRP) splay anchors has demonstrated positive outcomes in terms of enhancing the capacity of strengthened members and mitigating debonding. Limited research studies have been carried out to examine the effect of CFRP splay anchor parameters on the flexural behavior of RC beams anchored with small diameter anchors. The aim of this study is to examine the effect of large anchors, specifically, anchors with a diameter of more than 14 mm. Accordingly, a total of seventeen beams were cast and tested under four-point bending test. Fifteen beams were strengthened using CFRP sheets and anchored with different configurations of CFRP spike anchors. The investigated variables in the experimental program are anchor’s dowel diameter, embedment depth, fan length, insertion angle, and number of anchors. Test results of the anchored specimens in terms of load-deflection responses, failure modes, strain in the concrete, steel reinforcement, and CFRP laminates were compared to that of the control unstrengthened and unanchored strengthened specimens. The test results indicate that CFRP anchors enhanced the strength of the CFRP laminates by 12-53% over the unanchored specimens. It was observed that larger diameter anchors provided a considerably improved strength enhancement compared to smaller diameter anchors, on average by 28%. It was also concluded that bonding CFRP laminates by well-designed CFRP anchors highly utilized the strain attained in CFRP laminates. In addition, the flexural strength of the anchored beams is predicted using the ACI440.2R-17, CSA-S806.12(R2017), and fib-14 design guidelines. Based on comparison with the experimental results, the ACI440.2R-17 and fib-14 provisions provided reasonable predictions according to the debonding/delamination equation and assuming no fully bonded action is developed due to anchorage.