FRP Anchors Research Articles

Experimentally optimized anchored-FRP method: A high-strength, cost-effective and ease-to-install technique for concrete rehabilitation

Conventional EB-and NSM-FRP techniques tend to prematurely fail in FRP delamination, suggesting inefficient utilization of the FRP materials. Various anchorage systems have been developed by integrating FRP anchors with FRP patches or groove bond to maximize the utilization of FRP materials. This study proposes a simpler but robust method that can make full use of FRP materials while minimizing the need for groove excavation, FRP patches, epoxy adhesive and surface preparations. The reinforcement was achieved by externally bonding FRP reinforcement to the concrete surface, with bent anchors being embedded into the strengthened elements. 51 experiments were conducted to demonstrate the potentials of the proposed method, which successfully prevented premature debonding failure, thereby offering robust rehabilitation solutions with a reduction of up to 42 % in epoxy usage compared to current methodologies. The results also suggested the impact of key parameters, such as cross-sectional area, embedment depth, and multi-reinforcement arrangement, on the effectiveness of the proposed FRP technique. Based on the experimental findings, discussions and recommendations were presented to facilitate the continued advancement of the proposed FRP methodology, aiming to fully develop FRP strength and minimize the need for FRP materials and epoxy adhesive in comparison to the current anchored FRP methods.

Seismic Retrofitting of Realistic Beam–Column Joints with Shear Failure Using FRP Sheets and FRP Anchors

Seismic Retrofitting of Realistic Beam–Column Joints with Shear Failure Using FRP Sheets and FRP Anchors

Behavior of FRP-engineered cementitious composite layer and concrete interface with FRP anchors

The problem of low material utilization caused by premature interface debonding is prevalent in carbon fiber-reinforced polymer (CFRP)-reinforced concrete structures. In this study, the influence of anchors on the bonding and behavior of the FRP-engineered cementitious composite (ECC) layer and concrete interface was analyzed. A total of 42 single shear tests were performed to investigate the interface–bond behavior between the FRP-ECC layer and concrete under static load in case of anchor reinforcement. The variables mainly include the matrix type, anchor location, anchor spacing, and number of anchors. The results show that the anchor can increase the interfacial load-carrying capacity up to 85%; the maximum slip value of the interface can also be enhanced. Furthermore, the influence of the location, spacing, and number of anchors on the interface bonding performance is closely related to the effective bonding length and post-anchor bond length. The effective bonding length is 400 mm based on the strain distribution calculation and analysis. The test results provide valuable information for FRP anchor reinforcement in FRP-ECC composite layer-reinforced concrete structures.

Design of Pressure Energy-Absorbing FRP Anchors and Numerical Analysis of Mechanical Properties

Conventional FRP anchor rods have low elongation and poor impact resistance, both of which do not meet the support requirements of rock burst roadways. Therefore, a pressure energy-absorbing FRP anchor rod composed of an FRP rod body, tray, energy-absorbing sleeve and round table nut was designed. Numerical simulations were carried out to study the mechanical properties of the FRP anchor rod in static tension and impact tension, and to compare its mechanical properties with those of conventional FRP anchor rods. The results show that the pressure energy-absorbing FRP anchor rod is stretched in four stages: the front-elastic stage, constant resistance to compression, the back-elastic stage and damage, with an additional constant resistance to compression stage compared with conventional FRP anchors. The elongation, energy absorption and impact resistance time of the pressure energy-absorbing FRP anchor rods are greater than those of conventional FRP anchor rods, and the mechanical properties of the pressure energy-absorbing FRP anchor rods are better than those of conventional FRP anchor rods. As the impact velocity increases, the energy absorption rate of the pressure energy-absorbing FRP anchor increases non-linearly. The impact energy and impact velocity have less influence on the breaking load, elongation and energy absorption of pressure energy-absorbing FRP anchor rods. The research results can provide a theoretical basis for the application and parameter design of the pressure energy-absorbing FRP anchor rod, and provide support for the safe and efficient mining of the mine.

EFEKTIVITAS ANGKUR EPOKSI TERHADAP KEKANGAN EKSTERNAL BALOK BETON BERTULANG DENGAN PERKUATAN CFRP

Externally Bonded Carbon Fiber Reinforced Polymer (EB-CFRP) with U-wrap is one of the alternative external strengthening of modern reinforced concrete beams, which has been proven effective in significantly increasing flexural and deformation capacities. Although quite effective in increasing the structural capacity, external reinforcement needs to be studied further about its failure behavior, the avoided failure is called debonding, an interface bond failure between the FRP composite material and the concrete material. Epoxy has a fairly high material resistance, but its use as a reinforcing composite bonding material needs further investigation. Adding epoxy anchors at the ends of CFRP can mobilize the tensile strength in CFRP, eliminating or delaying debonding failure. Epoxy anchors (epoxy-filled grooves) are expected to be effective and flexible for application to various forms of components of reinforced concrete structures that have been reinforced with EB-CFRP. Currently, there are no standards and guidelines for applying FRP anchors. However, research has been conducted on the failure pattern of FRP anchors with U-style wrapping which can avoid debonding so that failure with FRP rupture can be achieved. This study examines the effectiveness of epoxy anchorage in improving the external strengthening of reinforced concrete beams with EB-CFRP reinforcement. The behavior of epoxy anchors in reinforced concrete beams with EB-CFRP will be investigated through experimental tests.

Evaluation of Early Crack Detection of Hybrid FRP Anchors

Evaluation of Early Crack Detection of Hybrid FRP Anchors

Blast retrofit of one-way reinforced concrete members using externally bonded FRP and FRP anchorage

This paper presents the results of nine as-built and carbon fiber reinforced polymer (CFRP) retrofitted reinforced concrete panels subjected to simulated blast loading using a pneumatically operated shock tube. The objective of the study was to characterize the blast response of CFRP retrofitted reinforced concrete panels, with and without supplemental mechanical anchorage applied to the CFRP. The results indicate that retrofitting can significantly increase the strength and stiffness of reinforced concrete flexure members and greatly enhance the displacement time-history response over non-retrofitted members. Debonding of the externally bonded CFRP was the failure mode for all retrofitted members. FRP anchors, designed to prevent or delay debonding failures through mechanical end-anchorage, were found to substantially enhance the performance of panels experiencing critical diagonal crack debonding. However, the FRP anchors were found to have no substantial effect on retrofit performance for the case plate-end interfacial debonding failures. In addition, the displacement time-histories for as-built and FRP retrofitted panel obtained through detail single degree of freedom analysis were found correlate well with those obtained experimentally. Finally, a discussion on the practical considerations of using externally bonded FRP retrofits to resist blast loads and recommendations for protective design are presented.

A machine‐learning‐based constitutive bond‐slip model for anchored CFRP strips externally bonded on concrete members

AbstractStrengthening is often required for reinforced concrete, steel, and masonry structures or structural elements when they possess insufficient performance against external loads such as earthquakes. Recently, the use of carbon fiber‐reinforced polymers (CFRP) has been considered a viable strengthening technique alternative to traditional methods. The major concern is premature debonding failure hindering the efficient use of CFRP systems. FRP anchor systems have been used to avoid this phenomenon. This paper employs a machine learning (ML)‐based algorithm (support vector regression) to propose predictive models to simulate the bond‐slip behavior of anchored CFRP strips externally bonded to the concrete surface. A comprehensive database was constructed using the previous reports on the bond‐slip behavior of FRP‐to‐concrete joints anchored with CFRP strips. Afterwards, the collected database was used to train and validate the proposed models. The input parameters cover all possible factors, that is, compressive strength of concrete, width of concrete block, anchor hole diameter, anchor hole depth, number of anchors at one row, number of anchors at one column; elastic modulus, width, bonding length, and thickness of CFRP strip. The output parameters are maximum shear capacity, residual shear capacity, displacement values at peak shear, and residual shear. Results imply that the proposed models have high prediction accuracies with low error rates. Proposed models are also presented in code format to be easily incorporated into analysis software for practical use.

Repairing and strengthening of reinforced concrete cantilever slabs using Glass Fiber–Reinforced Polymer (GFRP) wraps

This study represents the behavior of reinforced concrete cantilever slabs repaired and strengthened using GFRP experimentally; then a 3D finite element model using “ANSYS” was constructed to test the validity of analytical models in capturing the experimental cases. Additionally, the experimental results are compared with theoretical calculations per the ACI and ECP codes to test the validity of codes equations. Finally, more numerically models are applied to review the effect of various parameters on the behavior of cantilever slabs strengthened with GFRP. Also, the theoretical calculations consistent with the ACI and ECP codes are compared with numerical results obtained using the ANSYS finite element program for parametric study.The using GFRP as a top mesh on cantilever slabs increased the strength and therefore the deflection of the cantilever was increased due to the more additional load that resisted by Fibers. The strengthened slabs were provided more ductility, more strength capacity and higher deflection than the repaired slabs. The slabs strengthened/repaired with GFRP Wraps additionally to glass anchors get more strength capacity than slabs strengthened/repaired with GFRP Wraps only. For (ACI) and (ECP) codes the identical in predicting the share of flexure strength increasing but need adding amplification factor about 1.25. (ACI) and (ECP) codes do not capture the effect the FRP anchors in flexure strength increasing, but it can be reached that these needs adding amplification factor about 1.12 above the case of strengthening without anchors. An analytical model using ANSYS software program can present a good simulation for the failure loading, deflections and debonding of fiber for the cases of strengthening and repairing. This encourages continuing the parametric study. From the parametric study, it can reach that the greater the cantilever length, the more the deflection but the lower the load carrying capacity although of the more the use of fiber glass in strengthening. The greater the thickness of the strengthening cantilever slab, the lesser the deflection value but the more the load carrying capacity.

Experimental study on anchoring of FRP-strengthened concrete beams

This study aims at determining an effective technique for anchoring reinforced concrete beams strengthened using FRP composites. Fourteen reinforced concrete beams were cast and strengthened with FRP. Twelve of them were anchored using three different techniques: FRP anchor; bolted steel plates ancho, and FRP sheet and bolted steel plate’s anchors, and two beams were unanchored and left as a control. The beams then were tested under four-point bending to assess their structural performance in terms of failure modes, and load-displacement relations. The experimental results have clearly shown that the unanchored beams suffered from premature debonding failure, while the FRP-anchored beams experienced concrete cover separation failure, and the presence of end anchorages in the bolted steel plates and FRP sheet and bolted steel plate’s anchor's beams had shifted the failure mode to a less critical one. The anchored beams showed an increase in the ultimate load-carrying capacity accompanied by a reduction in mid-span deflection in different percentage with respect to the control beam. It was also observed that the FRP and/or steel U-jackets increase the shear capacity of the anchorage zone, therefore result in higher anchorage efficiency of FRP-strengthened concrete beams. The results also revealed that the FRP sheet and bolted steel plate’s anchors U configuration was the best anchorage system in terms of the structural performance factor. Developing an anchor system to prevent plate end debonding failure is vital for the successful design of strengthening systems using FRP composites.

Evaluation of Settlement Model of Hybrid FRP Anchors

Evaluation of Settlement Model of Hybrid FRP Anchors

Straight FRP anchors exhibiting fiber rupture failure mode

The purpose of the work was to characterize the behavior of FRP anchors installed at the end of FRP sheets and develop a methodology to calculate the capacity when the anchors exhibited the fiber rupture failure mode. To do so an extensive experimental program was undertaken and the force transfer mechanism between the anchor and the structure was studied in depth. A theoretical model and then an adapted simplified model were developed and empirically calibrated with the experimental results, which yielded a number of design equations. The main observation from the experimental results is that the anchor was weaker when the fanning angle increased and the efficiency dropped as the anchor increased in size. The final contribution to the knowledge is a method to calculate the capacity of anchors installed at the end of FRP sheets when exhibiting fiber rupture failure mode.

Impacts of configurations on the strength of FRP anchors

The usage of FRP anchors to prevent FRP strips from premature debonding failure is gaining acceptance in strengthening applications of concrete members. FRP anchors can fully develop the strength of FRP strips when they are properly designed. However, existing equations do not well include the comprehensive impact of the spike embedment depth, the bend ratio, the strength ratio of FRP anchor to FRP strip and the dowel angle on the anchor strength. Based on 64 tests failed in anchor rupture, this study proposes a comprehensive equation to determine the anchor strength. Comparisons between equation based predictions and 12 experimental results indicate the advantage of the proposed equation against existing equations. Then, the study propose a feasible technique, i.e. the bidirectional FRP patch, to improve the efficiency of current FRP anchors. Compared with equation based predictions for those FRP anchors without FRP patches, experimental results obtained from 20 specimens with FRP patches indicate significant increases on the anchor strength. This observation favors the usage of FRP patches to improve the efficiency of FRP anchors.

Characterization of Shear Strength of FRP Anchors

A critical performance aspect of FRP retrofitted concrete elements is the bonding of the FRP sheet to the concrete surface. In general, the performance is limited by the debonding of the loaded FRP sheets from the concrete surface. One method to delay debonding and enhance the capacity is the use of FRP anchors which interlock the FRP sheet to the concrete body. FRP anchors are made of rolled FRP fibres epoxied into in predrilled boreholes. There are a considerable number of studies on FRP strengthening methods available, and also FRP anchors attract more attention of the research community recently. However, to date FRP anchors were tested in a system together with the FRP sheet attached to the concrete, inhibiting the development of general design models. Moreover, the anchor behaviour was never tested for cyclic loads, though most applications are for seismic retrofitting schemes and cyclic shear loading generally results in reduced load capacity due to fatigue failure. To overcome the deficit in knowledge, shear tests on various FRP anchors were carried out. For these tests, FRP anchors were installed in concrete specimens on a separating steel section. The FRP anchor was then directly loaded to determine the capacity of the isolated component. This paper describes the testing approach and procedure. Details on the experimental results for static tests are presented and an outlook on seismic tests is given.

Pull-off bond behavior of anchored random-chopped FRP composites bonded to concrete

An externally bonded random-chopped FRP composite can efficiently strengthen concrete structures, though premature debonding is commonly reported, which can be prevented using an anchorage system. In this paper, the pull-off bond strength of anchored random-chopped FRP composites bonded to concrete was tested by direct pull-off tests. The effects of different parameters, in this case the anchorage depth, the diameter of the FRP anchors, and the concrete compressive strength levels were investigated. Finally, analytical models from the literature were used to predict the pull-off bond behavior of the samples. The test results revealed that the FRP anchors efficiently prevented cohesive failures of random-chopped FRP composites-to-concrete bonded samples and significantly increased their pull-off bond strength compared to unanchored control samples. The prediction results of the pull-off bond behavior according to Kim and Smith’s model were in good agreement with the experimental data.

Influence of geometrical and installation parameters on performance of CFRP anchors

This paper presents an experimental study of the geometrical and installation parameters affecting the maximum strength, failure mode and load-slip response of FRP anchors. In this study, single-shear tests were conducted on isolated carbon fibre ropes embedded in concrete to identify the variables that have a greater influence on the capacity of FRP anchors. Special attention was paid to variables influencing the stress concentration in the bending region. The parameters under evaluation included fabrication and installation method, embedment length, smoothing of the hole edge, hole diameter and dowel angle. The results demonstrate that increasing the embedment length leads to a proportional increase of maximum stress. Dowel angle and smoothing techniques can be combined to improve the anchor’s performance, as it was observed that both parameters reduce stress concentration and therefore enable higher bend strength.

Structural behavior of strengthening masonry in-filled frames subjected to lateral load using bonded and un-bonded CFRP

Lateral loads annually destroy many reinforced concrete structures in different countries. However, there is a necessary need to retrofit masonry infill walls to utilize them as lateral load resisting elements. For this purpose, an experimental program has been carried out on half scale specimens to characterize the behavior of single story brick masonry in-filled frames under the effect of lateral loads. The effectiveness of different strengthening techniques is investigated using Carbon–fiber Reinforcement Polymer (CFRP). The steel reinforcement at the beam-columns joints of all specimens was detailed as hinged connection. FRP sheets and FRP strips were used as strengthening agents for the tested specimens. They were utilized in two different cases, bonded or unbonded to the masonry wall. In addition, the FRP anchor technique was used to increase the efficiency of bonding the strengthening agents with the frames and the walls. The load–displacement behavior, FRP strain, crack pattern, steel strain, and mode of failure of the tested specimens were investigated. The results showed that the used strengthening methods are effective, with high increase in strength and ductility. In addition, an analytical model was presented and solved. Based on this model, simplified empirical equation to design the required amount of FRP needed to resist lateral loads was proposed. The equation showed a good agreement with both the experimental result and finite element output.

Pullout behavior of FRP anchors in masonry

Pullout behavior of FRP anchors in masonry

Shear strengthening of reinforced concrete T‐beams with fully or partially bonded fibre‐reinforced polymer composites

AbstractA series of 10 reinforced concrete T‐beams, designed deficient in shear, were tested in order to investigate the shear performance achieved through externally applied U‐shaped FRP composite strips. Key variables of the study were: type of FRP composite, type of surface bonding and type of end anchorage for the strips. Carbon fibre‐reinforced polymer (CFRP), glass fibre‐reinforced polymer (GFRP) and high modulus of elasticity carbon fibre‐reinforced polymer (Hi‐CFRP) strips were the special composite types with different elastic moduli, full or partial bonding of the strips to the beam surface were the variables for the type of surface bonding. All partially bonded FRP strips were free from surface bonding, whereas epoxy‐bonded FRP anchors were used at their ends close to the slab‐to‐beam connection. Those strips with full surface bonding have either epoxy‐bonded FRP anchors at their ends or the strip ends were without anchorage. The test results revealed that shear‐deficient beams may well be strengthened by the externally applied FRP strips. However, the level of strength enhancement and the failure pattern is closely influenced by the composite's elastic modulus, the type of surface bonding and the type of end anchorage for the FRP strip itself. The enhancement of the Hi‐CFRP strips did not live up to expectations. The use of unbonded FRP for shear strengthening yielded promising results.

Theoretical and Numerical Study on a New Hybrid FRP Wrapped Anchor

A new hybrid FRP wrapped anchor is developed to solve the poor ductility of FRP anchor. The designability of functionally graded material (FGM) makes it possible to connect the high ductility metal to FRP material. Numerical and analytical methods are compared in solving plane stress FGM cantilever beam problem. The results show the analytical method's simplification in constraint makes it inaccurate in solving displacements. Consequently, the numerical method is employed to analyze the hybrid FRP wrapped anchor in the ideal condition. The results indicate the hybrid FRP wrapped anchor solved the current problem theoretically.