This manuscript presents a method for controlling the quality of installation for spike anchors designed to delay delamination of externally bonded fiber reinforced polymers. The protocol includes the preparation of the drill hole and the insertion process. The most influential parameters on the efficiency of the anchors are discussed.
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Method Article
Installation Method to Enhance Quality Control for Fiber Reinforced Polymer Spike Anchors
In This Article
Summary
Abstract
Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they can delay or even prevent debonding failure. However, a major concern faced by designers is the premature failure of the anchors due to stress concentration. Poor installation quality and preparation of the clearance holes can result in stress concentration that provokes this premature failure. This paper deals with an installation method that aims to reduce the impact of the stress concentration and to provide a proper quality control of the preparation of the drill hole. The method involves three parts: the drilling and cleaning of the holes, the smoothing of the hole edges with a customized drill bit, and the installation of the anchor itself, including the impregnation of the anchor dowel and its insertion. Anchor fans (the free length of the spikes) are then bonded to the external FRP reinforcement. For the end anchorage, and in the case of reinforcements with multiple plies, it is recommended that the anchor fan be inserted between two plies to assist the stress-transfer mechanism.
The proposed procedure is complemented with a design approach for spike anchors, based on an extensive database. It is proposed that the design follow a number of steps, namely: selection of the anchor diameter and subsequent tensile strength of the connector (that is to say, the anchor before fanning out the free end), evaluation of the reduction in the tensile strength due to bending, provision of enough embedment to prevent slippage failure, and consideration of the number and spacing of anchors for a given reinforcement. In this sense, it should be noted that further research is needed in order to obtain a general expression for the contribution of spike anchors to overall bond strength of FRP reinforcements.
Introduction
FRP anchors offer a promising way to enhance the performance of externally bonded FRPs applied to existing structures, given that they can delay or even prevent debonding failure1,2. However, a major concern for designers entails the premature failure of the anchors in shear due to stress concentration in the bending region. Installation quality and preparation of the clearance holes are crucial to limit this stress concentration that provokes such premature failure.
This paper deals with an installation method that aims to reduce the impact of the stress concentration and to provid....
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Protocol
1. Anchor Installation Method
NOTE: This method includes the hole drilling, cleaning, and smoothing of the hole edge, as well as impregnation and insertion of the anchor.
- Drill the hole to the required embedment length and with the specified diameter.
- Use an appropriate drilling tool (that is to say, electrical hammer or diamond core). For concrete structures, the criteria for selection of drilling tools are the same as in adhesive anchors, and can be found in previously published work10,11. For an electrical hammer, drill with a maximum spee....
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Results
Tests were conducted on isolated connectors to evaluate the effectiveness of the smoothing method. In addition, two methods of impregnation and insertion of the connectors were compared. The wet method involved impregnating the anchors immediately before insertion, as in the presented protocol. The hardened (or pre-impregnated) method consisted of impregnation of the embedded region of anchors in advance, at least 24 h before insertion.
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Discussion
A step-by-step protocol for installation and design of FRP spike anchors is presented. To the best of the authors' knowledge, no detailed protocols on spike anchors have been developed regarding the effect of installation parameters and process on anchor capacity.
The proposed smoothing drill bit is beneficial in the performance of spike anchors, by means of reducing the stress concentration, and has proven its efficacy in reducing the scatter of the tests performed on isolated anchors. Th.......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
The authors wish to express their gratitude to Sika SAU for their support and, particularly for their supply of the material for the anchors and for the reinforcements. Betazul is especially acknowledged for their help with the customized drill bit and with the preparation of the video.
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Concrete | The concrete for support has a dosage made by the authors, and a strength class no lower than C40 | ||
| SikaWrap anchor C | SIKA | This material has been used for the FRP spike anchors. SikaWrap Anchor C is a unidirectional, carbon fiber rope, sheathed in an elastic gauze. The gauze can be cut onsite to create a fan end that anchors CFRP fabrics and plates used in the structural strengthening of masonry and concrete. | |
| Sikadur 330 | SIKA | Impregnating resin, apt for manual saturation methods. The product was used for impregnating the anchor dowel before insertion | |
| Sikadur 30 | SIKA | Thixotropic, two part epoxy resin applied by spatula and therefore suitable for virtually any application, including overhead | |
| Drill bit | Betazul | Drill bit employed to smooth the holes that was designed by the authors and developed by Betazul SA | |
| Hammer drill | Hilti | Tool for the execution of anchor holes on masonry and concrete, for different drilling ranges | |
| Wire brush | Hilti | Hit series | For the proper brushing of drilled holes of varying diameters and embedment depths |
| Blow-out pump | Hilti | Hit series | Manual blow-out pump |
| SikaWrap-230 C | SIKA | Unidirectional woven carbon fiber fabric for dry application process | |
| Aluminium Bubble Roller | Fibre glast | For laminations where increased pressure is necessary to release air bubbles. They are straight across the width of the head and provide excellent air relief for nearly all applications. | |
| Brush | For impregnation of FRP bundle and sheet | ||
| 600 kN testing machine | Proeti | DI-CP/S | This is used for the shear test of anchors, in order to evaluate the efficacy of the proposed insertion method |
| Cable ties | Cable ties are needed to fasten the end of the anchor dowel in order to prevent fanning out of the fibers during insertion | ||
| Measuring tape | The measuring tape is necessary to control the embedment length as well as the diameter of the drill bit and hole clearance | ||
| Steel wire | Required to assist insertion | ||
| Rigid (steel) bar | A rigid bar of any material (in this case, it was made with a steel bar) is needed to control the embedment length |
References
- Grelle, S., Sneed, L. An evaluation of anchorage systems for fiber-reinforced polymer (FRP) laminates bonded to reinforced concrete elements. Struct Cong. , 1157-1168 (2011).
- Kalfat, R., Al-Mahaidi, R., Smith, S. Anchorage devices used to improve the performance of reinforced concrete beams retrofitted with FRP composites: State-of-the-art review. J Compos Constr
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