Development of a hybrid anchor to improve the bond performance of multiple plies of FRP laminates bonded to concrete

Fiber reinforced polymer composites (FRPs) are currently one of the leading materials used to strengthen reinforced concrete (RC) structures against various loading actions such as flexure, shear and torsion. Due to the escalating loads being applied to existing structures, significant structural deficiencies have resulted in higher strengthening demands on many projects, resulting in large and often impractical quantities of FRPs being needed to achieve the required level of strengthening. Although FRP possesses significant advantages over traditional materials in terms of strength, the phenomenon of premature debonding currently limits the degree of material utilization achieved in practice. One means by which debonding may be addressed is by the use of anchorage systems that facilitate the utilization of more layers of FRP prior to failure. The paper presents an experimental investigation of a new hybrid anchor, comprising of 3 layers of ±45° bidirectional fiber sheets used to anchor 2 plies of FRP laminate to the concrete. The patch anchor concept is further enhanced by anchoring the ±45° bidirectional fiber sheets to the concrete with FRP spike anchors, with the dowel end of the anchor embedded into the concrete and the fan end attached to the bidirectional fiber sheet. Significant improvements in the bond performance of the FRP laminates were observed as a result of the hybrid anchor

Finite element and experimental investigation into patch anchor sizes used to enhance the bond performance of FRP-to-concrete joints

The increasing demand to strengthen existing infrastructure has resulted in growing popularity of advanced fiber composite materials (FRPs) applied to reinforced concrete (RC) members as externally bonded reinforcement. Although FRPs contain very high tensile strengths, premature debonding usually prevents the material from reaching its full potential. Research is currently underway to address this shortcoming by the provision of anchorages to the ends of FRP reinforcement. Bi-directional fiber patch anchors have been found to be one of the most effective anchorages available, which are particularly suitable in shear strengthening applications. The ongoing need for verification of the various influencing parameters such as anchor size, spacing and fiber thickness have inspired further numerical and experimental studies resulting in the present work. The paper will investigate the effect of such parameters highlighting key relationships that may be applied for future use in anchorage strength models

A prediction model for bidirectional fiber patch anchors used to enhance the performance of FRP materials bonded to concrete

Research has demonstrated that the effectiveness of the FRP when applied to concrete members is largely governed by the strength of the bond between the FRP and the concrete. As a result, failure of strengthened members is usually a result of FRP debonding from the concrete substrate. To improve the efficiency of strengthening systems and mitigate the occurrence of end debond, the provision of end anchorage using bidirectional fiber patch anchors have been recently introduced to counteract the peeling and interfacial shear stresses at the FRP ends resulting much higher material utilisations prior to debond. The tests conducted to date have provided promising results, and could be utilised directly provided that the materials matched those used in published experimental programs. However, enough data has been collected to attempt the development of a prediction model which could theoretically relate parameters such as concrete strength, laminate thickness, width and spacing and patch anchor size. Such a model is presented herein and subsequently verified with results from both experimental tests and finite element simulations. The model is proven to provide reasonable predictions in anchorage strength based on the available data

The Influence of FRP spike and patch anchors on the bond performance of FRP-to-concrete joints

It has been demonstrated that the governing failure mode of concrete structures strengthened with fiber reinforced polymer composites (FRP) is by premature debonding of the FRP material from the concrete substrate. Research has shown that one means by which the FRP-to-concrete bond performance may be improved is to provide anchorage measures that resist the interfacial shear and peeling stresses that are generated along the FRP bond line. FRP spike anchors and bidirectional fiber patch anchors are a proven means to enhance the bond performance of FRP materials when bonded to concrete. Although the above mentioned anchorage systems have shown significant promise when investigated independently, the present research aims to combine their unique properties into a hybrid anchorage system. In this study, FRP spike anchors were used to anchor bidirectional fiber patches and used to restrain FRP laminates tested in direct shear resulting in a superior anchorage strength which was demonstrated through experimental testing

Anchorage devices used to improve the performance of concrete structures retrofitted with FRP composites: a state-of-the-art review

The anchorage of fiber-reinforced polymer (FRP) composites when applied to reinforced concrete (RC) structures as externally bonded reinforcement is an effective means to achieve higher levels of fiber utilization prior to premature debonding failure. Commonly documented anchorage methods for FRP-to-concrete applications demonstrating encouraging results include FRP U-jackets, FRP anchors (also known as spike anchors, among other names), patch anchors (utilizing unidirectional and bidirectional fabrics), nailed metal plates (also known as hybrid bonding), near-surface mounted rods, mechanical fastening, concrete embedment, and mechanical substrate strengthening. Anchorages applied to FRP systems have been verified through experimental testing and numerical modeling to increase the ductility, deformability, and strength of the member and also prevent, delay, or shift the critical mode of FRP debonding failure. Although the benefits of anchorage solutions have now been widely acknowledged by researchers, further studies are required in order to establish reliable design formulations to negate the requirement for ongoing laboratory verification by industry. The present paper is a state-of-the-art review of experimental studies conducted in the area of FRP anchorage systems applied to FRP-strengthened RC flexural members. Available experimental data are compiled and catalogued and an anchorage efficiency factor for each anchorage type under investigation is assigned in order to quantify the anchor’s efficiency. Finally, current shortcomings in knowledge are identified, in addition to areas needing further investigation

The West Gate Bridge: strengthening of a 20th century bridge for 21st century loading

Retrofitting of existing concrete structures and civil infrastructure has become necessary due to environmental degradation, changes in usage and heavier loading conditions. The use of advanced carbon fiber composite materials (CFRP) as externally bonded reinforcement has found wide application in recent years and has proven to be an effective method of improving the structural performance of existing structures. A good example of this is the West Gate Bridge in Melbourne, Australia for which the following case study is presented. Key innovations in CFRP technology developed specifically for this project have been described in the areas of design and testing of CFRP anchorage technology, involving the utilization of unidirectional and bidirectional fabrics together with mechanical substrate strengthening. These have all resulted in increases in material utilizations and enabled successful transfer of combined shear and torsional forces. Key aspects of the detailing, application, quality control and monitoring program adopted in the project are also presented along with the key aspects which resulted in the successful execution of this world class project

Genetic programming in the simulation of Frp-to-concrete patch-anchored joints

Although fiber reinforced polymer composites (FRPs) have proven to be one of the most efficient materials for strengthening existing reinforced concrete (RC) structures against various loading actions, premature debonding remains the major factor limiting their full utilization. Experiments have demonstrated that anchorage systems such as bidirectional fiber patch anchors are an effective method to improve the bond performance of FRP when bonded to concrete substrates and they can be applied to existing strengthening systems to achieve a given level of strengthening using less material. The present research aims to use available experimental data on patch-anchored joints to develop a new anchorage strength model using genetic programming. The model incorporates a number of input parameters which have been found to influence the strength of the anchor: concrete strength, laminate thickness, laminate width, patch anchor size and strength of adhesive. The genetically programmed model is compared with predictions from a semi-empirically derived model and provides less error and better correlations with the available data

Torsional strengthening of concrete members using near-surface mounted CFRP composites

To increase the strength of concrete members, numerous research studies on flexure and shear have been reported using carbon fibre-reinforced polymer (CFRP) with the near-surface mounted (NSM) strengthening technology, as it is considered a promising technology. However, to date research on torsional strengthening has been provided only for the externally-bonded reinforcement technique (EBR) and no studies have been conducted on NSM strengthening technology. In this paper, reinforced concrete (RC) beams with CFRP are considered and ATENA software is used to build a 3-D model of the beams and to analyse the beam structure. Finite element and experimental results of the control beam and beams strengthened for torsion with CFRP sheets using the EBR technique are compared. Further computer analysis of beams strengthened with CFRP laminate using the NSM strengthening technology is achieved by considering many parameters. The type of the adhesive, the method of strengthening, and the spacing between the grooves were examined. The performances of the beams and the ultimate strengths of the control and beams strengthened using the EBR technique were predicted with high accuracy by the models employed. According to the results for the beams strengthened using the NSM technique, the overall torsional behaviour of the beams with CFRP was improved by different percentages and the beams became stronger

PANI pseudopolyrotaxanes as new conducting materials

International audienc

Formulation de molécules antifongiques par inclusion dans des cyclodextrines

International audienc