Influence of FRP anchors on FRP-to-concrete bonder interfaces

Abstract

Existing reinforced concrete (RC) structural members such as beams, columns and joints can be strengthened and repaired with externally bonded high-strength and light-weight fibre-reinforced polymer (FRP) composites. The effectiveness of such strengthening can, however, be limited by premature debonding of the FRP at strains well below the strain capacity of the FRP. Such failures are also generally sudden and give rise to brittle member behavour. It is therefore important to prevent or even delay debonding failure in order for the FRP strengthening to be more effectively and efficiently used. Anchorage of the FRP strengthening is a logical solution and to date several different types of anchorage systems have been developed and tested. Anchors made from FRP, which are herein referred to as FRP anchors, are singled out for deeper inspection in this doctoral program of research. FRP anchors are an attractive form of anchorage as they are non-corrosive, relatively easily made by hand, and can be used in a variety of shaped RC elements ranging from beams to walls. There have been limited systematic studies though conducted on anchorage devices including FRP anchors. This knowledge gap forms the scope of the program of doctoral research reported herein. This dissertation is concerned with investigating the ability of FRP anchors to anchor externally bonded FRP in flexural strengthening applications. This is done by investigating the influence of FRP anchors on FRP-to-concrete bonded interfaces. Following a review of relevant literature, tests on FRP-to-concrete joints anchored with FRP anchors are reported as well as tests on FRP-strengthened RC slabs anchored with FRP anchors. The joint tests are used to investigate and understand the influence of key geometric and material properties such as, but not limited to, anchor type and position as well as plate length. The optimal arrangement of FRP anchors enabled significant increases in FRP plate strain utilisation to be achieved in the joints. Two modelling approaches based on regression analysis as well as partial interaction modelling are developed for the modelling of the joint tests. In the latter method of analysis, the complete debonding process is able to be simulated. The test and modelling results of the joint specimens are then used to design anchorage schemes for application to RC slabs strengthened in flexure with externally bonded FRP plates. The slab test results show the importance of strategic FRP anchor installation for enhancing the strength, ductility and deformability of FRP-strengthened RC slabs. Future research needs are finally presented in light of the outcomes of the experimental and analytical components of the research reported herein.