Tensile strength of straight FRP anchors in RC structures

Abstract

Structural strengthening using externally bonded fibre reinforced polymer (FRP) materials is an established method to enhance the performance of existing structures. Although standardised design methods are available for the strengthening of simple elements, limited guidance is available to apply these designs to the complex geometries which are common in realistic applications. In particular, a current limitation of existing FRP design guidance emerges where the force carried by the FRP needs to be transferred into or through an adjacent structural element. Straight FRP anchors feature a number of advantages over other methods to transfer the load, but their behaviour is poorly understood and the lack of available design guidance hampers efficient design. Reported here are a series of experiments performed as part of on-going research aimed to develop design equations for straight FRP anchors that will assist engineers to utilise straight FRP anchors and design efficient and reliable FRP strengthening schemes for structures with complex geometries. The focus of these experiments was primarily on the fibre rupture failure mode developing in the key portion of the anchor, with fibre content having the most influence on capacity for this failure mode. The concrete used as a substrate to bond the FRP sheets was fabricated with two different strengths. The objective was to trigger different failure modes by varying the bonding strength between the FRP sheet and the concrete substrate and to compare the results obtained for both subfailure modes. Next the efficiency of each anchor test was calculated as the measured capacity of the anchor divided by the ultimate tensile capacity of the bundles as specified by the manufacturer. Finally, the measured ultimate capacity and the efficiency were compared for different anchor sizes. As a result, the efficiency of the anchors was found to reduce for larger fibre contents, and an efficiency equation was developed based on the experimental results.