An efficiency framework for anchorage devices used to...

Construction and Building Materials 191 (2018) 354–375

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Construction and Building Materials

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Review

An efficiency framework for anchorage devices used to enhance theperformance of FRP strengthened RC members

https://doi.org/10.1016/j.conbuildmat.2018.10.0220950-0618/� 2018 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail addresses: [email protected] (R. Kalfat), [email protected] (J. Gadd), [email protected] (R. Al-Mahaidi), scott.smith@sc

(S.T. Smith).

Robin Kalfat a,⇑, Jeremy Gadd a, Riadh Al-Mahaidi a, Scott T. Smith b

a Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Vic, Australiab School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia

h i g h l i g h t s

� Anchorage of externally bonded FRP can mitigate debonding failure.� Most effective flexural anchor types are steel anchors, p-anchors and FRP anchors.� Effective shear anchor types are the hybrid, spike and substrate strengthening.� A database has been presented which compiles the latest test results.� An anchor efficiency framework has been proposed for evaluation.

a r t i c l e i n f o

Article history:Received 16 February 2018Received in revised form 2 October 2018Accepted 4 October 2018

Keywords:ConcreteStrengtheningFRPAnchorage systemsDatabaseBond

a b s t r a c t

Concrete structures strengthened with fibre reinforced polymer (FRP) composites in both flexure shearcan be enhanced by introducing anchorage systems to suppress or delay the occurrence of prematureFRP debonding. Research has demonstrated that by ultilising FRP anchors, it is possible to increase FRPutilisation levels prior to failure resulting in greater degrees of strengthening using less material.Despite several independent research studies conducted to explore the benefits of FRP anchors, thereremains a lack of design guidelines which enable the specification of anchors in strengthening projectsworldwide. However, prior to the development of such models, a database is required which compilesthe relevant influencing parameters and corresponding FRP strains for given anchor types. The objectiveof this paper is to provide an extensive and up to date database as well as an evaluation framework basedon anchor efficiency whereby the effectiveness of each type of anchor can be clearly determined.Anchorage efficiency factors are developed for multiple FRP anchorage systems for both shear and flexureapplications based on a database of over 375 experimental data points.

� 2018 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3552. Anchorage devices for FRP reinforcement used to strengthen members in flexure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356

2.1. FRP anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3562.2. U-strap anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

3. Anchorage devices for FRP reinforcement used to strengthen members in shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
3.1. P-anchor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3583.2. FRP anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3593.3. Patch anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3603.4. Hybrid (FRP anchors + patch anchors) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3613.5. Substrate strengthening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3623.6. NSM anchor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
4. Research methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364

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R. Kalfat et al. / Construction and Building Materials 191 (2018) 354–375 355

5. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
5.1. Flexural anchor results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3645.2. Flexural anchors discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3675.3. Shear anchor results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3675.4. Shear anchor discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
6. Further work and development of design provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3727. Conclusions and recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

Conflict of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

1. Introduction

Concrete structures are generally expected to provide adequateperformance for the entirety of their service life with very littlemaintenance. However, such expectations are generally not realisedowing to factors such as concrete degradation, overloading or phys-ical damage. Concrete degradationmayhave several possible causessuch as reinforcement corrosion, chemical damage from chloride orsulphate attack, carbonation, alkali aggregate reaction leading toconcrete cracking and spalling, calcium leaching, and bacterial cor-rosion. Physical damage may be due to fire, vandalism, explosion,impact, earthquakeor other extremeevents. Traditional strengthen-ing and rehabilitation approaches have included the use ofmechan-ically fastened steel plates, near--surface mounted (NSM) steelreinforcement, concrete or steel jacketing and partial or completedemolition and replacement. However, these solutions have a repu-tation of being costly, destructive, labour intensive and time con-suming. However, the introduction of fibre reinforced polymer(FRP) composites and their use as a strengthening material has lar-gely replaced traditional strengthening methods. FRPs have beenproven to provide a suitable and cost effective solution to thestrengthening of existing concrete structures which is requireddue to: deterioration, increased loads and changes in usage.

Thematerial has severalwell documentedadvantages over tradi-tional strengthening materials, including its light weight, high ten-sile strength, durability, ease of installation and unobtrusiveness[1]. The application of FRP has been found to be more cost effectivethan traditional strengthening methods and it can negate the needto replace theoriginal structure. The cost effectiveness of applicationof FRP composites is further increased by the ongoing savings asso-ciated with lack of maintenance. As a result, FRP strengthening isenjoying a great deal of popularity in the construction industry [2].FRP’s consist of a polymer matrix embedded with microscopic fila-ments, which can be either short, continuous, unidirectional, multi-directional, woven or non-woven. The composite acquires its basicstrength and other fundamental properties such as stiffness, corro-sion resistance and thermal conductivity from the embedded fibres.The surrounding matrix binds the reinforcing fibres together thusacting as a load transfer medium between them. It also protectsthe fibres against mechanical and environmental damage. Thereare a number of FRP systems available which differ in the types offibres used (i.e carbon, glass, aramid, basalt) and the methods ofbonding (i.e externally bonded or near-surface mounted). In addi-tion, the products are are produced in the form of loosely wovenfibres, pultruded laminates or bars. FRP laminates or sheets are typ-ically applied to structuralmembers as externally bonded reinforce-ment using high strength adhesives or as near-surface mountedreinforcement. Fibres arebonded to theconcreteonly after sufficientsurface preparation consisting of grit blasting or water jetting (toexpose aggregate) followed by application of a suitable primer.

To date, several failure modes for RC beams strengthened inflexure with FRP plates have been identified from experimentalinvestigations, which has been based on Pham and Al-Mahaidi[3]. The modes are summarised as follows: (1) Concrete crushing,

(2) FRP rupture, (3) Shear failure, (4) Concrete cover separationfailure [4], (5) Plate end interfacial debonding [5], (6) Intermediateflexural or flexural-shear crack induced interfacial debonding(otherwise known as IC debonding) [6], and (7) shear induceddebonding (can also be referred to as critical diagonal crackdebonding or CDC debonding) [7]. Modes 4–7 are all prematuredebonding failures. Of these, modes 4 and 5 initiate at or nearthe plate end while modes 6 and 7 initiate away from the plateend. In addition, modes 5 and 6 and sometimes mode 7 occur atthe FRP-to-concrete interface (in the concrete) while modes 4and 7 can occur predominantly at the internal steel reinforcementlevel. Detailed accounts of all failure modes though are providedelsewhere [8]. Many factors control the likelihood of a particulardebonding failure mode such as (i) the level of internal steel rein-forcement, (ii) the distance between a plate end and the adjacentbeam support (plate end distance), (iii) FRP plate length, width,thickness and modulus of elasticity, (iv) shear-to-moment interac-tion, (v) concrete strength and (vi) section geometry [9]. Observa-tions suggest that as the plate end moves further away from thesupport, cover separation failure becomes the controlling modeand IC debonding governs when the distance between the plateend and support is relatively small [4]. In addition, the likelihoodof debonding initiating near the plate end has been found to bethe highest when the ratio of maximum shear force to bendingmoment is high, such as the higher peeling stresses generated atthe ends of the external plate. Therefore, slender beams with highshear span/depth ratios do not present a need for plate end anchor-age because failures are initiated in regions of high bendingmoment well away from the plate ends [10].

In practice, shear strengthening is usually accomplished by thebonding of FRP laminates to the sides of RC beams in the form ofexternally bonded ligatures which act to cross diagonal cracks.FRP can be installed in the form of continuous sheets or discretestrips of a certain width and spacing. Common techniques forstrengthening RC members in shear using FRP are side bonding,U-jacketing and full wrapping. Experience has shown that failureof FRP bonded to concrete as externally bonded shear reinforce-ment is closely related to the shear strengthening system utilised.The majority of experimental data highlights that almost all beamsstrengthened by enclosed wrapping typically fail due to FRP rup-ture after localised debonding [11]. In contrast, beams strength-ened by side bonding only and most strengthened by U jacketing,fail due to debonding of the FRP, which has been observed to initi-ate where the FRP intersects diagonal shear cracks in the member.Debonding then propagates to the nearer end of the plate (this istypically the free plate end). It may be noted that pure interfacialdebonding failure along the FRP-adhesive interface, adhesive-concrete interface or within the adhesive have been rarelyreported. Debonding failures almost always occur within the con-crete at the FRP-to-concrete interface. Even though advanced com-posites have a high tensile strength, in flexural, shear and torsionalretrofit applications, this strength may be little utilised due to theineffective bond between the composite and the concrete. Uponthe compilation of results from numerous tests it was seen that

356 R. Kalfat et al. / Construction and Building Materials 191 (2018) 354–375

FRP debonded on average at a strain level of about 50% of the FRPtensile capacity [12]. It has, however, been found that for heavyshear and torsional strengthening applications this utilisation levelcan be as low as 10–25% [13]. The inherent drawback has lead torecent research into CFRP-to-concrete bond strength improvementand the introduction of efficient anchorage systems.

The primary role of FRP anchorage is to prevent or delay thedebonding process. However, a lack of design guidelines foranchorage solutions means that designs must be substantiatedby representative experimental testing (ACI 440.2 [27]). With noexplicit guidance over what constitutes representative testing,the task of specifying and detailing FRP anchorage systems on realprojects quickly becomes onerous. The aim of this paper is to pre-sent a new database containing the latest anchorage data pub-lished in the research literature. The data is organised andprocessed using the same framework developed by Kalfat et al.(2013). This framework will produce a standardised anchorage effi-ciency factor for each anchorage type which quantifies the enhanc-ing contributions for each anchor.

2. Anchorage devices for FRP reinforcement used to strengthenmembers in flexure

The general categories of anchors applied to flexurally strength-ened members which are included in this paper are:

(a) FRP anchors [14,15](b) U-jacket anchors [16–18](c) p-anchor [19]

Fig. 1. FRP anc

This paper will review the latest research in the area of FRPanchorage systems produced between 2012 and 2017 andcombine the data from this period with that published in thereview paper by Kalfat et al. [20]. Other anchor types such as:Mechanically fastened metallic anchors [16,21] have beenresearched prior to 2008 and covered extensively in Kalfatet al’s [20] work.

2.1. FRP anchors

FRP anchors otherwise known as spike anchors, fibre bolts orFRP dowels are constructed using bundled loose fibres or a rolledFRP sheet to form a dowel and fan configuration (see Fig. 1). Thedowel component of the anchor is placed within a pre-drilled holein the concrete and the anchor fan is bonded onto the FRP strength-ening. The dowel can be embedded in the concrete using differentdowel angles and the fan can be bonded onto the FRP strengthen-ing using either single-fan or double-fan (i.e. bow tie)configurations.

While there is increasing amount of data on FRP anchors thatsuggest effectiveness in FRP shear strengthening applicationsbased on FRP-to concrete joint tests, a number of researchers[14,15,22–24] have extended the concept to flexural applications.Although FRP anchors have been undergoing research since 2001,one of the more recent studies by Smith et al. [15] investigatedthe influence of the following FRP anchor parameters: (1) bow-tie and single-fan anchors, (2) anchor fibre content, (3) inclinationof anchor dowel angle, (4) influence of number of anchors, and (5)influence of anchorage concentrated at plate end.

hors [15].


Several observations can be drawn from the results of thesetests, namely (a) bow-tie anchors are more resistant to fan debond-ing than single-fan anchors; (b) anchors of larger fibre content canlead to higher plate strains; (c) open dowel angles (i.e. 135�) rela-tive to the direction of load led to better load capacity when allother parameters are kept equal. To demonstrate the influence ofdowel angle, specimen S2.4 was tested using a dowel angle of67� and only 52% of the FRP plate strain capacity prior to debond-ing was found to be utilised. In contrast, specimen S2.6 utilised adowel angle of 135� which resulted in 86% strain utilisation ofthe FRP plate. This is likely due to a reduced stress concentrationat the dowel to fan transfer region. This also suggests the cornerradius on the dowel holes plays an important role in maximisingthe FRP anchor efficiency. Further, the study suggests that FRPanchor fans pointing towards the applied load (i.e. middle of thebeam) offered a more efficient solution and were more capableof transferring the tensile forces from the FRP sheet to the concretevia dowel action; (d) smaller and more numerous anchors (32anchors vs 8 anchors) resulted in an increase in load carryingcapacity of 6.5%. This increase is attributed to a more uniform dis-tribution of anchor forces along the FRP plate length resulting insmaller stress concentrations. However, the addition of discreteFRP anchors in the middle of the plate did little to increase the loadcapacity although the ductility of the slab was increased. Hence,the positioning of FRP anchors needs to be ‘‘strategic” in order toachieve substantial gains in the load and deflection capacity. Thisfinding is strengthened by Baggio [25] who demonstrated that aspecimen with 12 FRP anchors failed at a lower load than a nomi-nally identical specimen containing 8 FRP anchors. Therefore, it isnot necessarily a greater number of anchors, but where they areplaced that can improve the efficiency of the flexural FRP reinforce-ment. Selected FRP anchor layouts used by Smith et al. [15] aredepicted in Fig. 2.

Baggio [25] performed similar experiments to Smith et al. [15]and tested an RC beam strengthened with 2 layers of FRP sheetand 8 FRP anchors (230C-2L-8A) which showed a 18% increase inload capacity relative to an unstrengthened control specimen.However, this would have been higher if premature anchor failuredid not occur. The test specimen failed due to concrete cone failurearound the anchor dowel. Baggio [25] attributed the concrete coneand cover failure to the low concrete strength of the beams(34 MPa). However, Smith et al. [15] used a similar concretestrength and the same dowel embedment depth of 100 mm(min) with no such failure. Hence, it is suggested that for300 mm wide FRP plates, more FRP anchors are required acrossthe width to avoid such failure, rather than deeper embedment.

Fig. 2. Various FRP anchor La

More anchors across the width is compatible with recommenda-tions by Wei et al. [26] who suggested that more uniform straindistributions in the FRP plates leads to a more effective solution.

2.2. U-strap anchors

The term U-strap anchors is used to cover both discrete stripsused by Fu et al. [17] and wider jackets used by Hasnat et al.[16]. U-straps, U-strips, U-wraps and U-jackets are all terms usedto describe types of U-strap anchors. U-strips are generally of les-ser width, with U-wraps and U-jackets considered to be muchwider.

According to Fu et al. [17], vertical FRP U-straps at soffit plateends reduce the likeliness of concrete cover separation failurethrough the following two mechanisms: (1) reducing the interfa-cial peeling (normal) stresses between the concrete and the soffitplate; and (2) restraining the propagation of horizontal crack atthe level of tension steel bars. However, the width of the verticalU-straps should be sufficient in order to suppress concrete coverseparation failure. The study found that a narrower vertical U-jacket can only shift the location of concrete cover separation fromthe plate end to the inner side of the vertical U-jacket. SelectedFRP-strap configurations used by [17] are depicted in Fig. 3.

Of particular interest Fu et al. [17] evaluated the models cur-rently included within the ACI440.2 [27], Concrete Society Techni-cal Report no. 55 [28] and the Chinese national standard [29] todetermine area of the transverse clamping FRP U-strap reinforce-ment to mitigate concrete cover separation failure. The area oftransverse clamping used by Fu et al. [17] was successful in miti-gating concrete cover separation failure, however was 27 timesless than the required area predicted by the ACI 440.2 [27], 6 timesless than the area predicted by Concrete Society Technical Reportno. 55 [28] and approximately 3 times less than the area requiredby the Chinese national standard [29]. The above results are consis-tent with the experience of the authors. Hence, the model devel-oped by Reed et al. [30] which is currently implemented withinthe ACI 440.2 [27] to determine area of the transverse clampingFRP U-strap reinforcement provides gross overestimations in U-strap area which cannot practically be implemented in most cases.

The Chinese National Standard [29] stipulates that in order forU-straps to suppress concrete cover separation failure, two FRPU-straps with their net spacing not greater than the beam depthare required to be installed at the end of the FRP tension plate.Where the tension plate is comprised of wet-lay-up FRP, the widthand thickness of the U-strap anchors is recommended to be greaterthan half the width and thickness of the FRP tension plate

youts, Smith et al. [15].

Fig. 3. Selected FRP U-strap layouts [Reprinted with permission from [17]].


respectively. For pultruded FRP soffit plates, the width of each U-strap is recommended to be greater than 100 mm with a U-straparea greater than 25% of the soffit plate area. The U-strap widthrecommended by the Chinese National Standard [29] is consistentwith Concrete Society Technical Report no. 55 [28] which recom-mends that the width of the U-strap should be equivalent to theentire anchorage length of the FRP. Hence for the specimens usedby Fu et al. [17], the width of the U-straps should be approximately200 mm to cover the full FRP anchorage length. Fu et al. [17] inves-tigated U-strap widths of 60 mm, 90 mm and 120 mm respectivelywhere U-strap widths of 60 mm and 90 mm were not effective insuppressing concrete cover separation failure. Hence the recom-mended U-strap width provided by the Concrete Society TechnicalReport no. 55 [28] is conservative but practical in most cases.

In addition to the mitigation of concrete cover separation fail-ure, Fu et al. [31] explored the use of partial height U-straps to sup-press intermediate crack induced debonding. However, the studyfound that the use of vertical U-straps in the IC debonding zonehas a limited effect on suppressing this failure mode, since only10% increase in strength was noted due to the anchors.

Several models are now available in the literature to determinethe area of U-jacket anchors to suppress the failure mode of con-crete cover separation. The data from which these models arederived is still limited though. The majority of the experimentalstudies on U-jacket anchors have utilised relatively narrow beamwidths (200–300 mm wide) and more studies are required toassess the performance of U-straps applied to band beams or largescale box girders with beam widths greater than 300 mm. Further,where U-straps have been demonstrated as effective, the testbeams were often over-strengthened in shear in order to ensureflexural failure. However, shear cracking of the beam can be thevery mechanism that initiates cover separation failure. Hence, itis suggested that future studies should consider variability in thesteel shear reinforcement of test specimens to help address theseissues.

A key parameter which influences the performance of U-jacketanchors is the jacket inclination angle. Generally, all studies whichdirectly compared vertically orientated U-straps with inclined U-straps have found inclined straps to be more effective. Fu et al.[17] directly compared 90 mmwide vertical U-straps with inclinedcounterparts. Specifically, the study found that 90 mm wide verti-cal U-straps failed to prevent concrete cover separation failure,however 90 mm inclined U-straps successfully shifted the failuremode to IC debonding. Further, when using a wider U-jacket of120 mm, inclined U-straps were found to be 35% more effectivethan vertical ones. Inclined U-straps were found to transfer someof the tensile force from the soffit plate to the beam sides therebyrelieving the interfacial bond stresses between the soffit plate andthe concrete. Even after IC debonding of the soffit plate, the beamswere able to carry further load due to the restraint provided by the

inclined U-straps until eventual debonding of the U-jacketoccurred.

3. Anchorage devices for FRP reinforcement used to strengthenmembers in shear

A review and discussion of recent shear anchoring solutions ispresented in this section. The concepts presented herein are basedon the relevant papers identified in the literature containing FRPstrain data. Strain data is essential in deriving the anchor effective-ness factors presented in later in the paper. The shear anchorageconcepts have been divided into five categories for discussion:

1. FRP Anchors [33–35]2. Patch Anchors [36,37]3. Hybrid Anchors [38,39]4. Substrate Strengthening [13,40,41]5. NSM anchors [42–44].

Further to the above 5 anchorage types, other anchorage meth-ods such as the use of metallic anchors [72], CFRP embedment intobeam flanges [45,46] and CFRP rope through web [47] have beencovered elsewhere in Kalfat et al. [20].

3.1. P-anchor

The p-anchor is a recent anchoring method tested for flexuralstrengthening applications. The concept was conceived by Mosta-pha and Razaqpur [19] and involves the bonding of an integralCFRP head plate with two monolithic legs over or through theFRP soffit plate. The head plate is 200 long � 50 mm wide � 3 mmthick and each leg is 10 mm in diameter and 90 mm long (referFig. 4). The concept is not dissimilar to the earliest forms ofmechanical anchorages which were steel plates adhesively bondedand mechanical fastened over the FRP reinforcement, e.g Wu andHuang [32]. The difference is that the p-anchor is integrally man-ufactured from CFRP and its legs are bonded into the concrete sub-strate to provide restraint to the FRP reinforcement. This isaccomplished by a transfer of the FRP soffit plate forces to theanchor head and later to the concrete through the anchor legsvia dowel action. The advantages of the p-anchor over the tradi-tional metallic mechanical anchorage are its durability and corro-sion resistance.

Mostapha and Razaqpur [19] demonstrated that the p-anchorcould prevent IC debonding on FRP reinforced T-beams. Theyinvestigated several layouts, from p-anchors located only at theplate ends to anchors over the entire span. The different layoutsinvestigated the application of p-anchors through a 220 mm wideFRP soffit plates (i.e. the top two configurations in Fig. 5), as well as

Fig. 4. p-anchor [Reprinted with permission from [19]].


over a thinner 90 mm wide FRP reinforcing plate (i.e. the bottomconfiguration in Fig. 5).

Mostapha and Razaqpur [19] were not able to assess anchorbenefit from 1 ply of FRP sheet as all specimens (with or withoutanchorage) failed by FRP rupture. Similarly, the 2 ply FRP reinforc-ing showed control beams and anchored beams exhibited little dif-ference in maximum load. However, testing of the anchored 4 plyand 8 ply laminates showed improved load capacity due to the p-anchors. When thin plates with regularly spaced anchors wereused for 4 and 8 ply FRP reinforcement, the increase in the maxi-mum recorded FRP strains compared to the unanchored controlspecimens were 83% and 117% respectively. This equates to acapacity increase of 20% and 44% respectively. Generally, installa-tion of the p-anchors at the ends of the CFRP laminates was notable to mitigate intermediate crack induced debonding as theycould not interact with the debonding crack at initiation pointaway from the plate end. However, installation of anchors alongthe span as well as at the plate ends resulted in a much higher loadrequired to attain IC debonding and FRP rupture provided that asufficient quantity of anchors were distributed along the span.Mostapha and Razaqpur [19] concluded that for the anchor to workeffectively, the FRP laminate strips must be placed within the legsand the anchors should be uniformly spaced along the whole span.Results indicated a p-anchor pitch of no more than 200 mm maybe required to achieve a meaningful increase in beam capacity.As a result, any benefit must be weighed up against the challengeof drilling a large number of 90 mm deep holes into the soffit,whilst avoid damaging the tensile steel reinforcement.

3.2. FRP anchors

Several research groups are developing anchor technology andare also categorising their structural behaviour in the context ofanchoring FRP-to-concrete joints e.g. [33–35]. Of note, Zhang

Fig. 5. Various p-anchor layouts tested [R

et al. [35] have increased the capacity of FRP-to-concrete jointsby 117% with strategically placed and oriented FRP spike anchors.The slip capacity of such joints has also been observed to increaseby several hundred percent.

Other researchers have investigated the behaviour of FRPanchors to enhance the performance of FRP U jackets used tostrengthen beams in shear. A recent study conducted by Koutasand Triantafillou [24] assessed the performance of FRP anchorsapplied to the ends of FRP U-jackets. The following parameterswere investigated: anchors embedded in the web or the flange,CFRP or GFRP anchors and anchor spacing. The various configura-tions are presented in Fig. 6.

The study reported that the control beam with unanchored U-jackets failed at 157 kN. The specimen with three anchorsembedded horizontally in the web (i.e. at 90�) failed at 169 kNby anchor pull-out. However, when the embedment angle waschanged to 155� (i.e. configuration (d) in Fig. 6) the failure loadincreased to 228.5 kN, a 46% improvement in the load capacitycompared to the unanchored specimen. Hence, anchors placedinside the slab with a near vertical orientation are considerablymore effective than those placed horizontally inside the web.When examining the maximum strains reached in the CFRP priorto debonding, the unanchored U-jackets reached maximumstrains of 2200 me, whereas the addition of inclined FRP anchorsincreased the U-jacket strains to 3800 me. The failure mode was acombination of anchor pull-out and rupture which demonstratesthe ability of inclined FRP anchors to transfer forces from the FRPU-jackets into the slab. Interestingly, five inclined anchors overthe shear span only achieved a failure load of 240 kN. Therefore,Koutas and Triantafillou [24] concluded that perhaps reducedanchor spacing is not as important as the number of anchorsthat are adjacent to the critical shear crack. Both GFRP and CFRPanchors demonstrated similar performances as the predominantfailure mode was anchor pull-out via concrete cone failure which

eprinted with permission from [19]].

Fig. 6. FRP anchor configuration for [Reprinted with permission from [24]].


is less influenced by the properties of the fibre. The anchorembedment length used in the study was 70 mm. Thus the useof deeper a embedment length to improve the anchor capacityshould be investigated.

Ozedin et al. [48] also investigated the use of FRP anchors torestrain the ends of FRP U jackets into beam flanges. 20 mm wideCFRP, GFRP and high modulus CFRP U-jackets were used as shearstrengthening. Each U jacket was anchored into the beam flangesusing FRP anchors with the dowel end embedded at 45� anglesand an embedment depth of 60 mm. Although an enhancementin FRP U jacket strains were achieved prior to debonding comparedwith unanchored specimens, relatively low levels of FRP strainswere achieved compared with predictions from various designguidelines. Ozedin et al. [48] stipulated that the design guidelinesprovide an over estimation of FRP debonding strain, particularly forhigh modulus FRP laminates. However, the concrete strength usedin this study was only 12.4 MPa which is well below the minimumstrength recommended for bonding of FRP. In this sense, since thedesign guidelines used in the study to verify the experimentalresults were obtained from specimens with higher concrete com-pressive strengths (>20 Mpa) the conclusions drawn from thisstudy can be misleading.

[24] noted the peak strain location in the FRP shear straps coin-cided with the position of the critical shear crack. This was con-firmed by Baggio et al. [14] and Ozedin et al. [48] who observedthe highest readings in strain gauges immediately adjacent toshear cracks. Hence it is imperative that sufficient strain gaugesbe placed along the length of the FRP to capture the peak strainvalue. Although the FRP strains reported by Koutas and Triantafil-lou [24] were measured at nine discrete locations most of the datawas not presented due to a lack of confidence in the ability of thegauges to capture the peak strains. Kalfat and Al-Mahaidi [38]demonstrated a preference for digital image correlation (DIC) pho-togrammetry as the optimal method for capturing strain distribu-tion along the length of the FRP laminate. Although it is preferableto use DIC for detailed strain measurements, where strain gaugesare used, it is recommended that the spacing no greater than 50–100 mm is to be used in order to ensure that peak strains arecaptured.

3.3. Patch anchors

Patch anchors consist of bi-directionally orientated fibre sheetsbonded to the ends of the FRP laminate and adjacent concrete [36].The first experimental program was devised by Al-Mahaidi andKalfat [36] which involved testing FRP-to-concrete joints anchoredwith unidirectional fibre and (±45�) bidirectional fibre patchanchors. Each patch anchor was used to anchor 2 mmthick � 120 mm wide FRP laminates bonded to the concrete withepoxy resin. The results were that anchored joints experiencedincreases in strength of 93–109% as well as end slippage of 4–8times above the unanchored counterparts. The results were largelyattributed to a distribution of fibre-adhesive stresses which areusually confined to the width of the FRP laminate over a greaterwidth of concrete due to the action of the patch anchor. Based onthe results of this study, the FRP patch anchor was implementedon the Westgate Bridge strengthening project in Melbourne[49,50], resulting in large scale material savings and a more timelyinstallation process may also represent the largest FRP applicationproject worldwide to date.

Due to the success of the initial experimental program, an addi-tional study was executed which focused on investigating theinfluencing parameters such as: laminate thickness, laminatewidth and patch anchor size, and the results presented in Kalfatand Al-Mahaidi [51]. Furthermore, the study utilised a standardlaminate geometry consisting of 1.4 mm thick � 100 mm wideFRP laminates which were anchored and tested in a near end sup-ported single shear pull test. Through an inspection of the strainswithin the bidirectional fibres, it could be determined that theanchored laminates could be spaced as closely as 250 mm withoutany reduction in anchorage strength. The experimental resultshighlighted two possible failure modes associated with separatonof the the anchored FRP laminate from the concrete: (1) completedebonding of the patch anchor, together with the laminate fromthe concrete (patch anchor debond) as depicted in Fig. 2, or (2) slip-page of the FRP laminates from between the two layers of bidirec-tional fibres (laminate slippage). Laminate slippage was found tooccur at lower loads, was considered an undesirable failure modeand was observed when using laminate widths less than 120 mm


and anchor lengths less than 300 mm. It was attributed to an insuf-ficient bond area between the FRP laminate and the two layers ofbi-directional fibre sheet.

The next stage in evaluating the performance of patch anchorswas to implement them on large scale post tesnsioned beamsstrengthened in shear with FRP laminates. Large scale beam appli-cations are capable of capturing variables ommited from joint testssuch as: size effect, the influence of combined flexural/shear stres-ses, diagonal tension cracking (potentially intersecting the FRPwithin the anchorage zone), loss of aggregate interlock, and web/-concrete crushing. Jumma et al. [52] tested three large-scale post-tensioned T-beams with a depth of 1050 mm and span of5000 mm. The beams were heavily reinforced in flexure with8 � 32 mm diameter longitudinal bars and one 32 mm stress bartensioned to 600 kN. One beam was strengthened with 100 mmwide � 1.4 mm thick CFRP laminates at 300 mm spacing in a sidebonded configuration. The second beam was strengthened usingside bonded FRP laminates with 2 layers of bidirectional fibre patchanchors installed at each end of the laminates.

The unstrengthened control beam (C) failed in shear at a loadlevel of 1216 kN, whereas the strengthened beams (ST1 & ST2)failed at 1454 and 1614 kN respectively by FRP debonding at max-imum FRP strains of 2953–3435 me. The addition of patch anchorsin specimens (STA1 and STA2) increased the beam failure load to1967 kN and 1948 kN and the laminate strains to 4114–4960 me.The level of FRP strains achieved in the patch anchored beams wereconsistent with those recorded in joint tests by Kalfat and Al-Mahaidi [37], however further large scale beam testing is requiredto explore the effects of laminate spacing, different beam

Fig. 7. Debonding failure depicted for (a) strengthened specim

Fig. 8. Construction overview: (a) FRP spike anchors; (b) Concrete blocks with three 18fabric sheet with 50 mm adhesive tapers. [38].

dimensions, spans and reinforcement. The failure modes for thestrengthened beams with and without anchors is depicted in Fig. 7.

3.4. Hybrid (FRP anchors + patch anchors)

The hybrid anchor was developed to further enhance the effec-tiveness of the patch anchor concept by using spike anchors toincrease the bond performance between the ± 5� patch anchorsand the concrete via dowel action. A study by Kalfat and Al-Mahaidi [38] found that 2.8 mm thick laminates anchored withbidirectional fibre patch anchors alone yielded strength enhance-ments 2–3 times that of the unanchored specimen, and that theaddition of spike anchors resulted in a strength enhancement ofover 5 times that of the unanchored specimen. An overview ofthe construction process of the hybrid anchor is depicted in Fig. 8.

When comparing the unanchored laminate to the hybrid patchanchor using a single ply of FRP of 1.4 mm thickness, Kalfat and Al-Mahaidi [39] found the FRP laminate strain utilisation levelsincreased from 2000 me to 9000 me, a 450% increase respectively.This increase was attributed to the dowel action provided by theFRP anchors where a dowel angle of 90 degrees was used. Speci-mens failed by patch anchor debonding and FRP (spike) anchorrupure (refer Fig. 9). Based on research by Smith et al. [15], it islikely that the benefit of the hybrid anchor may be furtherenhanced by using a dowel embedment angle greater than90 deg to the direction of plate force.

Kim et al. [53] was the first to apply the hybrid anchor conceptto large scale beam applications, where 1220 mm deep RC beamsrepresentative of full-scale bridge sections were strengthened in

en (unanchored), (b) Strengthened with Patch anchors.

mm diameter holes; (c) Specimen prior to application of final layer of bidirectional

Fig. 9. Summary of failure modes (a) Type 0 Control specimen – Concrete cover separation failure; (b) Type D1 – Patch anchor debond; (c) Type D2 – Patch anchor debond andspike anchor rupture; [38].

Fig. 10. Hybrid FRP + patch anchor configuration for [53].


shear using FRP U-jackets anchored with hybrid anchors (referFig. 10). The hybrid anchor implemented by Kim et al. [53] con-sisted of a bidirectional patch with fibre orientations of 0� and90� with respect to the direction of fibres in the U jacket. 2 no.FRP (spike) anchors were placed in between each layer of unidirec-tional fibre which comprised the patch with the fan end of theanchor bonded to the patch and the dowel end inserted into theconcrete. Two FRP anchors were installed at the ends of each254 mm wide FRP U jacket utilising a fan angle of 60� and embed-ment depth of 102 mm. The U jackets comprised of 1 or 2 layers of0.28 mm thick unidirectional fibre with a young modulus of102 GPa. Where hybrid anchors were used to at the ends of0.28 mm and 0.56 mm thick FRP U-jackets, the peak FRP strainsdeveloped were 9700 me and 4800 me respectively. Although theresults from the study are noteworthy, the impact of the researchand its applicability to strengthening projects is limited due to therelatively small thickness of FRP employed. Small thicknesses ofFRP are capable of developing FRP strains greater than 4000 meprior to debonding without without the necessity for anchorage.Since most FRP design guidelines such as ACI 440.2 [27] and Con-crete Society Technical report no: 55 [28] prohibit U jacket or sidebonded FRP strains in excess of 4000 me to ensure that aggregateinterlock of the concrete is maintained, there is little practicaluse in implementing an anchorage system for such low FRP thick-nesses. It is recommended that future research into anchorage sys-tems applied to shear strengthened members focus on higherdegrees of shear strengthening and the use of thicker FRPlaminates.

3.5. Substrate strengthening

Research conducted by Kalfat and Al-Mahaidi [13] and Al-Mahaidi et al. [54] explored the introduction of a 40 mmwide � 40 mm deep mechanical chase cut into the concrete withinthe anchorage zone to enhance substrate properties and increasethe anchorage strength. The purpose of the chase was to preventthe critical mode of FRP debonding, which naturally occurs a fewmillimetres beneath the concrete/adhesive interface and utilisesthe superior mechanical properties of the epoxy to distribute bondstresses to a greater depth within the concrete prism. In addition toalmost doubling the anchorage capacity, significantly higher bondstresses of up to 11 MPa were recorded in the strengthened sub-strate specimens, while only 5.0 MPa was achieved in control spec-imens. This corresponded to a 95–100% increase in ultimatecapacity, a 118% increase in bond strength, and a 83–93% increasein the maximum FRP strain prior to failure.

The above research was later improved upon in Kalfat and Al-Mahaidi [40] by reducing the depth of the chase from 40 mm to20 mm so that the depth of the chase could be limited to the con-crete cover zone. The experimental program consisted of eightspecimens and three alternative anchorage configurations testedin direct shear. Specimens with 30–40 mm wide � 20 mm deepconcrete chases within the concrete cover zone in both transverseand longitudinal directions were constructed over which a FRPlaminate was bonded (refer Fig. 11). The chases were filled withepoxy resin to act as a mechanical key in order to improve thestrength of the FRP-to-concrete bond. The study discovered that

Fig. 11. Substrate strengthening configurations for [40].


the introduction of a longitudinal mechanical chase cut into theconcrete over the anchorage length was more effective than atransverse chase orientation which resulted in higher FRP maxi-mum elongations, bond stress, slip and load-carrying capacities.This suggests the chase area directly under the FRP laminate ismore effective in increasing the bond capacity. More specifically,the longitudinal chase increased the anchorage strength of thejoints by 135–138% compared with 69–72% for the transversechase. When comparing the results from the 40 mmwide � 20 mmchase with a previous study by Kalfat and Al-Mahaidi [13] whichutilized 40 mm wide � 40 mm deep chase dimensions, it wasobserved that the reduction in chase depth did not adversely affectthe degree of strength enhancement.

Alam et al. [41] explored a novel anchoring technique involving25 mm deep � 30 mm diameter recesses within the concrete sub-strate over which the FRP laminate was bonded. The circularrecesses were filled with epoxy to provide a better transfer offorced between the FRP laminate and the concrete. Another batchof specimens were prepared by filling the holes with adhesive andinserting 25-mm-length steel bars up to 25 mm in diameter whichacted as a shear connector. 300 � 150 � 150 mm concrete prismswere fabricated and the strength of the FRP-to-concrete joint wasinvestigated within the context of a direct shear test configuration(refer Fig. 12). The FRP laminates used were 1.2 mm thick with amodulus of elasticity of 165 GPa. The results indicated that 2 no.30 mm diameter steel connectors increased the FRP laminatestrains by 54% while the adhesive connectors increased the FRPstrains by 42% compared with the unanchored specimen. Hence,FRP strains of up to 3700–4000 me were achieved due to theanchors. The above anchorage concepts falling into the category

Fig. 12. Adhesive connector configuration for

of mechanical substrate strengthening have demonstrated promis-ing results at the level of a direct shear test, however should beinvestigated further and applied to large scale beams strengthenedin flexure and shear using FRP.

3.6. NSM anchor

In order to address the problems associated with traditionalanchors, an innovative anchoring system was developed by Khalifaet al. [42] using FRP materials only. Although the system was orig-inally named U-anchors, since this term can be confused with U-jacket anchors used for flexural strengthened members, it has beenrenamed herein to NSM anchors. NSM anchors can be applied toenhance the performance of wet lay up FRP laminates by endanchorage around a FRP bar embedded within the concrete. Agroove is required to be cut into the concrete the dimensions(depth and width) of which should be 1.5 times the diameter ofthe FRP bar used to anchor the FRP laminate. Where the grooveis required to be installed within a beam web as depicted inFig. 13c, the corner of the grove should be rounded using a mini-mum radius of 13 mm [43].

After constructing the groove to the required size, a GFRP bar isembedded within the groove with epoxy paste over the wet lay uplaminate as depicted in Fig. 13d. The NSM, anchor has been devel-oped specifically to anchor the ends of FRP U-jackets used for shearstrengthening. Khalifa et al. [42] investigated the feasibility andeffectiveness of the NSM anchors to increase the shear capacityof RC T-beams strengthened with CFRP U-wraps, and no debondingwas observed at failure. Raghu et al. [44] conducted a similar studyconsisting of 5 � 2640 mm long RC T beams with different shear

[Reprinted with permission from [41]].

Fig. 13. NSM anchor used for shear strengthening of RC beams [Reprinted with permission from [43]].


strengthening schemes. The beams tested consisted on a controlspecimen (JS1) and specimens strengthened using 1 and 2 pliesof 0.165 mm thick CFRP U-jackets (JS2 & JS4). NSM anchors appliedto 1-ply and 2-ply U-jackets in specimens JS3 and JS5. Althoughstrain gauges were installed at discrete locations along the heightof the U-jacket, the peak U-jacket strain could not be captured;however the FRP strain at failure was estimated by extrapolation.Interestingly, the failure modes of both NSM anchored specimensinvolved fibre rupture of the FRP U-jackets. Both the above studiesused an NSM anchor applied after the re-entrant corner (Fig. 13b).However, Eshwar [43] investigated the effects of NSM anchorsinstalled after re-entrant corner (Fig. 13b) as opposed to anchorsinstalled before the re-entrant corner (Fig. 13c). When comparingthese two anchor locations, it was found that anchors placed afterthe re-entrant corner were up to 40% more effective. The samestudy also investigated the influence of the groove size and FRPbar diameter on NSM anchor effectiveness and found that the min-imum groove size range should be 1.5 or 2.5 times the NSM bardiameter, with a larger groove size being more advantageous butless practical. The minimum bar diameter recommended for NSManchors is 10 mm.

4. Research methodology

This research paper extends and updates the database ofresearch on FRP anchors published by Kalfat et al. [20]. Themethodology involved a thorough literature search, which targetedpapers published prior to 2012. However, only those studies whichreported the FRP strains were utilised. In order to comparativelyassess each anchorage, the concrete strength (f’c), fibre modulus(Ef), number of plies (n) and fibre thickness (tf), were used to stan-dardise the strain data from experimental results collected from anumber of researchers. Fibre modulus, number of plies and fibrethickness all affect the magnitude of FRP-to-concrete bond stressesat the interface at a given level of FRP strain. Whereas the concretestrength is the key parameter which governs the bond resistance ofthe interface. It is therefore important to consider these factorswhen determining the strain efficiency of any strengthened sys-tem. An anchorage effectiveness factor has been defined on thebasis of the maximum strain reached in the FRP plate prior to fail-ure, ef, max, and the effective FRP strain to resist intermediatecrack debonding [27]. The resulting expression presented in Eq.(1), which is used to define the anchorage effectiveness factor forbending (kfab).

kfab ¼ ef ;max

0:41ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffif0c=ðnEf tf Þ

q ð1Þ

In order to evaluate the various types of anchorages used toincrease the effectiveness of FRP shear strengthened members, aclassification and evaluation approach is adopted based on theeffective strain approach given in ACI440.2 [27]. The FRP effectivestrain is used to determine the anchorage effectiveness factor forshear (kfas), refer Eqs. (2)–(6).

kfas ¼ ef ;max

kvefuð2Þ

kv ¼ k1k2Le11;900efu

� 0:75 ð3Þ

Le ¼ 23;300

ntfEfð Þ0:58ð4Þ

k1 ¼ f0c

27

!2=3

ð5Þ

k2 ¼dfv�Ledfv

for u�wrapsdfv�2Le

dfvfor 2 side bonded

8<:

9=; ð6Þ

The equations have been based on factors such as: concretestrength (f’c), fibre thickness (tf), number of plies (n), fibre modulus(Ef), depth of FRP ligature (dfv) and maximum fibre elongation (ef,max). Following this approach, anchorage effectiveness is deter-mined by dividing the maximum experimental FRP strains (withanchors) by the predicted strain to cause debonding (withoutanchors). It should be noted that when collating the relevant datafor the derivation of anchor effectiveness factors, the concretecompressive strength was often derived from cast cubes. Thiswas converted to a cylindrical strength before using the aboveequations.

5. Results and discussion

5.1. Flexural anchor results

The anchor effectiveness factors for flexurally strengthenedconcrete members (i.e. kfab) are derived using Eq. (1) and pre-sented in Table 1. The results are further consolidated into a tablerating the average effectiveness of each anchor type in comparisonto the unanchored configuration (see Table 2).

The data presented in Table 1 can be further processed to nor-malise the average anchor effectiveness factor for each specifictype of anchorage with respect to the average for the control spec-

Table 1Flexural anchor effectiveness data.

Reference Specimen Comments f’c(MPa)

tft(mm)

Ef(GPa)

ef,max

(le)kfab Failure#

Control Specimens – Bonded Flexural FRP only 0.76 (Average)[55] A-200P 200 mm Support 55.0 1.20 150 3860 0.54 IC[55] A-200P 420 mm Support 55.0 1.20 150 3420 0.48 ED[55] B-200P 200 mm Support 55.0 1.20 150 2890 0.40 ED[18] E1a 6 PLY – 3 � 12 mm dia bars 53.7 1.06 209 3036 0.47 ED[18] E3a 6 PLY – 2 � 12 mm dia bars 53.7 1.06 209 3502 0.55 ED[18] E1b 6–3 � 12 mm dia bars 53.7 1.06 209 3414 0.53 ED[18] E5a 9 PLY CFRP 53.7 1.06 209 2329 0.36 ED[34] S2 Un-anchored control 41.4 0.50 239 6649 0.87 ED[56] W1.1 CFRP – surface smooth (CS1) 35.0 1.02 71 6039 0.67 IC[56] W1.2 Surface (CS1) 35.0 1.02 71 7443 0.82 IC[56] W2.3.1 Surface (CS2-CS3) 35.0 1.02 71 6490 0.72 IC[56] W6.9.1 Surface (CS6-CS9) 35.0 1.02 71 5214 0.58 IC[25] 230C-1L-NA Flexural FRP: 1 layer of 230C (300 mm wide) – Series II 34.0 0.38 65 10,700 0.70 FR[25] 230C-2L-NA Flexural FRP: 2 layers of 230C (300 m wide) Series II 34.0 0.76 65 7,800 0.73 CPD[25] 600C-1L-NA Flexural FRP: 1 layer of 600C (300 mm wide) Series II 34.0 1.30 24 7,000 0.52 PPD[25] 600C-2L-NA Flexural FRP: 2 layers of 600C (300 mm wide) Series II 34.0 2.60 24 3,620 0.38 ED[57] B1/CFRP Flexural FRP: 1 sheet (100 mm wide) 20.0 0.45 75 2,400 0.24 ED[17] CB Flexural FRP: 1 plate (165 mm wide) 46.6 1.33 258 2,485 0.52 ED[16] S(AT1)C Flexural FRP: 1 plate (100 mm wide) 48.3 1.20 120 9,000 1.20 ED[16] S(AT1)T Flexural FRP: 1 plate (100 mm wide) 48.3 1.20 120 7,000 0.93 ED[19] B1-F1-N Flexural FRP: 1 ply (220 mm wide) 55.0 0.17 227 16,700 1.06 FR[19] B1-F2-N Flexural FRP: 2 plies (220 mm wide) 55.0 0.33 227 14,000 1.26 IC[19] B1-F4-N Flexural FRP: 4 plies (220 mm wide) 55.0 0.66 227 9,300 1.18 IC[19] B1-F4-N-b90 Flexural FRP: 4 plies (90 mm wide) 55.0 0.66 227 8,600 1.09 IC[19] B1-F8-N-b90 Flexural FRP: 8 plies (90 mm wide) 55.0 1.32 227 6,000 1.08 IC[19] B2-F1-N Flexural FRP: 1 ply (220 mm wide) 55.0 0.17 227 16,700 1.06 FR[19] B2-F2-N Flexural FRP: 2 plies (220 mm wide) 55.0 0.33 227 10,000 0.90 IC[19] B2-F4-N Flexural FRP: 4 plies (220 mm wide) 55.0 0.66 227 10,000 1.27 IC[15] S2.2 Flexural FRP: 3 layers (100 mm wide) 30.3 0.39 232 6,821 0.91 CPD[58] 100 mm wide � 1 mm thick plate comprising 3 layers CFRP

sheet45.3 1.00 237 6,301 0.91 IC

FRP Anchor 1.23 (Average)[34] S3 FRP anchors along whole span (Type A) 41.4 0.50 239 7676 1.00 ED[34] S4 FRP anchors along whole span (half no. anchor as S3) (Type

A)44.1 0.50 239 8025 1.02 ED

[34] S5 Shear span FRP anchors (Type A) 44.1 0.50 239 8884 1.13 ED[34] S6 Plate end FRP anchors (Type A) 45.4 0.50 239 6696 0.84 ED[34] S7 Shear span FRP anchors (Type B) 45.4 0.50 239 11,566 1.44 ED[34] S8 Shear span FRP anchors (Type A + Type B) 45.4 0.50 239 11,348 1.42 ED[25] 230C-2L-8A Series II, 2 layers of 230C, 8 anchors 34.0 0.76 65 8,980 0.84 AF[25] 600C-2L-12A Series II, 2 layers of 600C, 12 anchors 34.0 2.60 24 4,570 0.48 ED[25] 600C-2L-8A Series II, 2 layers of 600C, 8 anchors 34.0 2.60 24 4,660 0.49 ED[15] S2.10 3 � 2 Type SA200 @ 75 mm + 2 TypeSA100 middle 34.7 0.39 232 12,660 1.58 CPD + FR

+ AF[15] S2.3 4 � Type BA400 (90 deg dowel) @ 200 mm (@ ends) 30.3 0.39 232 12,836 1.72 PPD + FR

+ AF[15] S2.4 4 � Type SA200 (67.5 deg dowel) @ 200 mm (@ ends) 34.7 0.39 232 8,077 1.01 CPD + AF[15] S2.5 4 � Type SA200 (90 deg dowel) @ 200 mm (@ ends) 30.3 0.39 232 11,299 1.51 CPD + AF[15] S2.6 4 � Type SA200 (135 deg dowel) @ 200 mm (@ ends) 30.3 0.39 232 13,386 1.79 CPD + FR

+ AF[15] S2.7 8 � 2 Type SA50 @ 100 mm spacing each end 34.7 0.39 232 14,863 1.86 PPD + FR

+ AF[15] S2.8 2 � 2 Type SA200 @ 150 mm spacing each end 34.7 0.39 232 8,968 1.12 CPD + AF[15] S2.9 3 2 Type SA200 @ 75 mm spacing each end 34.7 0.39 232 13,621 1.70 CPD + FR

+ AF

FRP U-Strips/Jacket

0.84 (Average)

[56] P1.1 4 CFRP U-jackets 35.0 1.40 131 4842 0.85 IC[56] P2.3.1 4 CFRP U-jackets 35.0 1.40 131 4598 0.81 IC[56] P6.9.1 4 CFRP U-jackets 35.0 1.40 131 5027 0.89 IC[56] P2.3.2 Full U-jacket 35.0 1.40 131 5076 0.90 IC[56] P6.9.2 Full U-jacket 35.0 1.40 131 5281 0.93 IC[55] A-420U 90� U-jacket anchor 55.0 1.20 150 8760 1.22 CC / ED[55] B-200U 90� U-jacket anchor 55.0 1.20 150 3750 0.52 CC / IC[18] A1a 1 U-jacket – 3 � 12 mm dia bars 53.7 1.06 209 4100 0.64 IC[18] A1b 3 U-jackets at 180 mm c/c – 3 � 12 mm dia bars 53.7 1.06 209 5350 0.84 IC[18] E3a2 1 U-jacket – 2 � 12 mm dia bars 53.7 1.06 209 3500 0.55 IC[18] E5a2 3 U-jackets at 180 mm c/c – 3 � 12 mm dia bars 53.7 1.59 209 4307 0.83 IC[56] W1.3 4 U-jackets 2 No. each end. (CS1) 35.0 1.02 71 6314 0.70 ED[56] W1.4 4 U-jackets 2 No. each end. (CS1) 35.0 1.02 71 3876 0.43 ED[56] W1.5 4 U-jackets 2 No. each end. (CS1) 35.0 1.02 71 6685 0.74 ED[56] W2.3.2 4 CFRP U-jackets 2 No. each end. (CS2-CS3) 35.0 1.02 71 7791 0.86 ED[56] W2.3.3 4 CFRP U-jackets 2 No. each end. (CS2-CS3) 35.0 1.02 71 7386 0.82 ED

(continued on next page)


Table 1 (continued)


tft(mm)

Ef(GPa)

ef,max

(le)kfab Failure#

[56] W2.3.4 4 CFRP U-jackets 2 No. each end. (CS2-CS3) 35.0 1.02 71 6814 0.75 ED[56] W6.9.2 4 CFRP U-jackets 2 No. each end. (CS6-CS9) 35.0 1.02 71 8057 0.89 ED[56] W6.9.3 4 CFRP U-jackets 2 No. each end. (CS6-CS9) 35.0 1.02 71 6253 0.69 ED[56] W6.9.4 4 CFRP U-jackets 2 No. each end. (CS6-CS9) 35.0 1.02 71 6422 0.71 ED[56] W1.6 7 CFRP U-jackets (CS1) 35.0 1.02 71 8349 0.92 ED[56] W1.7 11 CFRP U-jackets (CS1) 35.0 1.02 71 8962 0.99 FR[56] W2.3.5 11 CFRP U-jackets (CS2-CS3) 35.0 1.02 71 8381 0.93 FR[56] W6.9.5 11 CFRP U-jackets (CS6-CS9) 35.0 1.02 71 10,074 1.11 FR[56] W1.8 Flexural FRP + Full U-jacket (CS1) 35.0 1.02 71 6647 0.73 FR[56] W2.3.6 Full U-jacket (CS2-CS3) 35.0 1.02 71 8937 0.99 FR[59] B1 Single notched beam with side plates 49.2 0.22 235 6628 0.52 IC[59] B2 Single notched beam with side plates 49.2 0.22 235 6625 0.52 IC[59] B3 Double notched beam with side plates 49.2 0.22 235 7299 0.58 IC[59] B4 Double notched beam with side plates 49.2 0.22 235 6492 0.51 IC[59] B5 Double notched beam with FRP plate 49.2 0.22 235 10,217 0.81 IC[59] B6 Un-notched beam with FRP plate 49.2 0.22 235 10,489 0.83 IC[59] B7 Pre-cracked bonded with FRP plate 49.2 0.22 235 9399 0.74 IC[59] B8 Un-notched beam with FRP plate 49.2 0.22 235 9954 0.79 IC[16] S(AT3c)C (Each end – L/4), 2 layers, C = 2 � 8 mm top/bot reinforcing 48.3 1.20 120 11,800 1.57 AF[17] V1L1W120 1 � 120 mm wide U-strips. 54.9 1.33 258 4,061 0.78 IC[17] V1L1W60 1 � 60 mm wide U-strips. 50.4 1.33 258 3,258 0.66 ED[17] V1L1W90 1 � 90 mm wide U-strips. 50.4 1.33 258 4,180 0.84 ED[17] V2L1W60 2 � 60 mm wide U-strips. 50.4 1.33 258 3,472 0.70 ED[57] B1/CFRP/CMAS 110 mm wide U-wrap @ ends + single GFRP spike anchor. 20.0 0.45 75 9,900 0.99 IC[58] V90W150H350 Vertical 150 mm wide, 350 mm high U-strip @ 90 deg. 45.3 1.00 237 8285 1.46 IC + RU[31] B2S1 3 Vertical 150 mm wide U-jackets @ 412.5 mm spacing 51.1 0.67 251 8153 1.14[31] B3S1 2 Vertical 150 mm + 300 mm wide U-jackets @ 750 mm

spacing51.1 0.67 251 8038 1.13

[31] B4S1 2 Vertical 150 mm + 480 mm wide U-jackets @ 660 mmspacing

52.7 0.67 251 7434 1.03

Inclined FRP U-Strips 1.74 (Average)[60] U1-45–1 Inclined U-jacket anchor, 1 place 27.3 0.17 230 15,000 1.36 FR[60] U1-45–2 Inclined U-jacket anchor, 2 places 27.3 0.17 230 15,000 1.36 FR[17] I1L1W120 Inclined 120 mm wide U-strip @ 45 deg. 54.2 1.33 258 5,504 1.07 IC[17] I1L1W90 Inclined 90 mm wide U-strip @ 45 deg. 54.9 1.33 258 4,292 0.83 IC[17] I1L2W120 2 � Inclined 120 mm wide U-strip @ 45 deg. 54.9 1.33 258 5,592 1.08 IC[58] I45W100H350 Inclined 100 mm wide, 350 mm high U-strip @ 45 deg. 45.3 1.00 237 10,725 1.89 IC[58] I45W150H350 Inclined 150 mm wide, 350 mm high U-strip @ 45 deg. 45.3 1.00 237 11,938 2.11 IC[58] I45W200H350 Inclined 200 mm wide, 350 mm high U-strip @ 45 deg. 45.3 1.00 237 14,787 2.61 CC[58] I45W400H350 Inclined 400 mm wide, 350 mm high U-strip @ 45 deg. 45.3 1.00 237 14,538 2.56 CC[58] I45W150H141 Inclined 150 mm wide, 141 mm high U-strip @ 45 deg. 45.3 1.00 237 10,798 1.90 IC[31] B3S2 Inclined U-jacket, 0.716 mm thick � 318 mm wide U-Jacket 27.8 0.67 251 10,612 2.02 FR[31] B4S2 Inclined U-jacket, 0.716 mm thick � 318 mm wide U-Jacket 28.3 0.67 251 11,127 2.10 FR

Prestressed U-jacket Anchor 0.78 (Average)[18] A2a 1 Prestressed U-jacket – 3 � 12 mm dia bars 53.7 1.06 209 4571 0.71 IC[18] A2b 3 Prestressed U-jackets at 180 mm c/c – 3 � 12 mm dia bars 53.7 1.06 209 5416 0.85 IC

FRP + Steel Anchorage 2.22 (Average)[61] A1.2 Steel Anchorages Type A/Type B 30.0 1.20 152 9600 1.83 ED[61] A1.3 Steel Anchorages Type A/Type B/Type C 30.0 1.20 152 10,500 2 ES / ED[61] A2.2 Steel Anchorages Type A/Type B – Arr1 30.0 1.20 152 10,000 1.9 ES / ED[61] A2.3 Steel Anchorages Type A/Type B – Arr2 30.0 1.20 152 11,000 2.09 ES/ED/CC[61] A3.2 Steel Anchorages Type A/Type B 30.0 1.20 152 10,200 1.94 ED[61] A3.3 Steel Anchorages Type A/Type B/Type C 30.0 1.20 152 12,000 2.28 ES[62] B4a Steel Clamp at Laminate ends, 400 N.m 42.3 1.20 155 10,070 1.63 ED[62] B6 Steel Clamp at Laminate ends, 400 N.m 41.3 1.20 155 7800 1.28 ES[16] S(AT2)C C = 2 � 8 mm top/bot reinforcing 48.3 1.20 120 12,500 1.66 ED[16] S(AT2)T T = 2 � 20 mm top, 2 � 8 mm reinforcing 48.3 1.20 120 8,000 1.07 ED[21] PRS-EB 1 � 1.2 mm � 50 mm wide EB FRP, Anchor is prestress

clamp.21.3 1.20 165 10,369 2.44 Debonding

[21] PRS-2N20 2 � 2 mm � 16 mm wide NSM FRP, Anchor is prestressclamp.

24.3 2.00 131 14,355 3.64 ED

[21] PRS-2N20-BL330 PRS-2 N20 with extra 400 mm of bond length! 48.6 2.00 131 19,610 3.51 FR[21] PRS-2N20-AN PRS-2 N20 + 6 off CFRP U-strips at each end. 47.6 2.00 131 20,650 3.74 FR

p-anchor 1.30 (Average)[19] B1-F1-E3 1 ply + 3 each end 55.0 0.17 227 16,700 1.06 FR[19] B1-F2-E3 2 plies + 3 each end 55.0 0.33 227 9,300 0.84 IC[19] B1-F2-E3-M9 2 plies + 3 each end + 9 along span 55.0 0.33 227 12,400 1.12 IC[19] B1-F2-E4-M11 2 plies + 4 each end + 11 along span 55.0 0.33 227 13,000 1.17 IC[19] B1-F4-E2-M15-

b904 (90wide) plies + 2 each end + 15 along span 55.0 0.66 227 15,700 2.00 FR


Table 1 (continued)


tft(mm)

Ef(GPa)

ef,max

(le)kfab Failure#

[19] B1-F4-E3 4 plies + 3 each ends 55.0 0.66 227 9,500 1.21 IC[19] B1-F4-E3-M9 4 plies + 3 each end + 9 along span 55.0 0.66 227 9,900 1.26 IC[19] B1-F8-E3-M17-

b908 (90wide) plies + 3 each end + 17 evenly distributed 55.0 1.32 227 13,000 2.34 FR

[19] B2-F1-E3 1 ply + 3 each end 55.0 0.17 227 14,300 0.91 FR[19] B2-F2-E3 2 plies + 3 each end 55.0 0.33 227 12,000 1.08 IC

IC + RU = U-jacket rupture followed by soffit plate debonding; CC = Concrete crushing.# IC = intermediate crack-induced debonding; ED = end debond; ES = end slippage; FR = fibre rupture; AF = anchor failure; CPD = complete plate debonding; PPD = partial

plate debonding.

Table 2Normalised flexural anchor effectiveness (by type).

Anchor type kfab,n ST dev

Control 1.00 0.39Prestressed U-jacket Anchor 1.02 0.13FRP U-Strips/Jacket 1.09 0.31FRP Anchor 1.61 0.57p-anchor 1 0.63Inclined FRP U-Strips 2.28 0.77FRP + Steel Anchorage 2.90 1.11


imen – without anchors (i.e. kfab = 0.76). The normalised anchorageeffectiveness factors are presented in Table 2.

5.2. Flexural anchors discussion

The anchorage effectiveness factors presented in Tables 1 and 2provide a comparative framework to assist designers and research-ers in the specification of appropriate anchor types for a givenstrengthening application. However, the normalised anchorageeffectiveness factors cannot be used as a constant value to increasethe effective FRP strain for a given anchor type with respect to theunanchored condition. Owing to the degree of variability in effec-tiveness for a given anchor type. The variability was noted whenexamining the average and standard deviation values for the nor-malised anchor effectiveness factors observed in Table 2. This vari-ability is dependent on parameters such as: concrete strength, FRPthickness, FRP modulus of elasticity, anchor properties and thenumber of anchors. Hence, the development of more specific mod-els are required for each type of anchor which capture the influ-ence of the above parameters. Nevertheless, the databasepresented and anchor effectiveness framework may serve futureresearchers in the development of more specific models. Suchmodels will require development within the context of the anchordelaying a certain failure mode to occur at a higher level of FRPstrain or suppressing a failure mode entirely, shifting it from eitherIC debonding to end debonding or vice versa.

Of the types of anchorage systems used to suppress enddebonding FRP U straps were found to be very effective whenappropriately detailed with the correct U-strap width and area ofvertical fibres. Therefore, the failure mode of U-strap anchoredmembers typically shifted from end debonding to IC debonding.Since the anchor effectivess factors were derived on the basis ofmitigating IC debonding, both prestressed and non prestressedU-jackets were found to have an anchor effectiveness factors of1.02 and 1.09 which suggested that they did not delay the occur-rence of IC debonding. However, inclined U-straps were able torelieve some of the interfacial shear stresses between the FRPand the concrete in the intermediate zone which was observedto suppress end debonding while also delaying the occurrence ofIC debonding.

Both FRP anchors and p-anchors were implemented in theintermediate regions within the span with the objective of sup-pressing IC debonding and achieved similar levels of success. Onaverage, FRP anchors and p-anchors resulted in average, nor-malised anchor effectiveness of 1.61 and 1.70 respectively. How-ever, standard deviations in the results between 0.57 and 0.63are evidence of the degree of scatter in the results which dependon variables such as the number of anchors, where the anchorswere placed and the anchor properties.

Although, steel anchorages (mechanically fastened) showed thehighest anchor effectiveness (2.9) the data was based on 4 studiesand 14 data points and further studies are required to generate ahigher level of confidence in the outcomes. However, steel anchorswere demonstrated to be successful in suppressing end debondingif placed at the FRP laminate ends and IC debonding if placedthroughout the span.

5.3. Shear anchor results

The anchor effectiveness factors for shear strengthened con-crete members (i.e. kfas) are derived using Eqs. (2)–(6) and pre-sented in Table 3. The results are further consolidated intoTable 4 depicting average normalised effectiveness factors for eachanchor in addition to the standard deviations.

The data presented in 3 can be further processed to normalisethe average anchor effectiveness factor for each specific type ofanchorage with respect to the average for the control specimen –without anchors (i.e. kfas = 1.12). The normalised anchorage effec-tiveness factors are presented in Table 4.

5.4. Shear anchor discussion

The performance of the above anchorage systems for shearstrengthened members has been determined by evaluating themaximum FRP strains achieved prior to debonding. However, themajority of the data summarised in Tables 3 and 4 which formedthe basis of the average, normalised effectiveness factors werebased on FRP-to-concrete joint assemblies rather than full scalebeam tests. While FRP-to-concrete joint assemblies can provide agood indication of the ability of a given anchor to suppress FRPdebonding, large-scale beam testing is required to consider omit-ted factors such as: size effect, combined flexural/shear stresses,diagonal shear cracking (potentially intersecting the FRP withinthe anchorage zone) and other failure modes, such as: web shearcrushing, loss of concrete aggregate interlock or concrete crushingwhich can limit the degree of enhancement achieved. Therefore, itis recommended that future research focus on application of theabove mentioned anchors to large scale beam tests.

A review of the literature noted very little research on FRPanchorage systems were applied to large scale beams strengthened

Table 3Shear anchor effectiveness data.


tft(mm)

Ef(GPa)

ef,max

(me)kfas Failure#

Control Specimens – No Anchorage 1.12 (Average)[63] Spec-2 Side bonded CFRP 31.9 0.12 231 2000 0.41 S + CSF[63] Spec-4 U-jacketing CFRP 29.1 0.12 231 1600 0.35 S + CSF[1] A-SO3-2 U-jacket strips, 50 @ 125 mm 27.5 0.20 228 4700 1.41 CSF[1] A-SO3-4 One ply continuous U-jacket 27.5 0.20 228 4500 1.35 CSF[1] C-BT2 One ply continuous U-jacket 35.0 0.20 228 4500 1.15 CSF[1] B-CW2 Two plies (90�/0�) 27.5 0.30 228 2700 0.99 CSP[1] A-SW3-2 Two plies (90�/0�) 19.3 0.30 228 2300 1.07 CSP[1] A-SW4-2 Two plies (90�/0�) 19.3 0.30 228 1900 0.88 CSP[64] Type 0 WG9–Control Specimen 62.0 2.00 210 2535 1.36 CSF[41] C1-0 30.5 1.20 165 2,600 1.45 DB[47] S0-EB CFRP Sheet, No stirrups 28.0 0.38 65 2,500 0.60 DB[47] S0-LS 6 L-strips @ 175 mm, No Stirrups 28.0 1.40 120 4,300 2.55 DB[47] S1-EB CFRP Sheet, Stirrups @ 260 mm 28.0 0.38 65 2,800 0.67 DB[47] S1-LS 6 L-strips @ 175 mm, Stirrups @ 260 mm 28.0 1.40 120 3,200 1.90 DB[47] S3-EB CFRP Sheet, Stirrups @ 175 mm 28.0 0.38 65 3,900 0.94 DB[47] S3-LS 6 L-strips @ 175 mm, Stirrups @ 175 mm 28.0 1.40 120 2,700 1.60 DB[13] WG9 Type 0 62.0 2.00 210 2,706 1.45 DB[37] 0.1 Type 0 69.2 1.40 210 2,875 1.16 DB[37] 0.2 Type 0 69.2 1.40 210 3,062 1.24 DB[37] 0.3 Type 0 69.2 1.40 210 3,100 1.26 DB[38] D0.1 Type D0 28.7 2.80 195 1,410 1.47 CSF[38] D0.2 Type D0 28.7 2.80 195 1,610 1.68 CSF[39] 0.1 Type 0 28.7 1.40 195 2,097 1.46 CSF[39] 0.2 Type 0 28.7 1.40 195 2,201 1.53 CSF[19] P3 27.0 1.03 70.55 2,000 0.67 DB[19] P4 27.0 1.03 70.55 2,500 0.84 DB[24] U2C CFRP U-Jacket 22.2 0.12 230 2,200 0.61 DB[48] FBwoA-CFRP CFRP Strips (20 mm wide @ 120) 12.4 0.13 238 1,587 0.72 DB[48] FBwoA-Hi-

CFRPCFRP Strips (20 mm wide @ 120) 12.4 0.14 640 381 0.28 FR

[23] CN(47)-1 37.8* 0.39 226 3,529 1.07 DB[23] CN(47)-2 37.8* 0.39 226 3,511 1.06 DB[23] CN(55)-1 44.1* 0.39 226 3,519 0.96 DB[23] CN(55)-2 44.1* 0.39 226 3,586 0.98 DB[65] CNE-227-1 50 mm FRP plate (4 plies) 39.4* 0.52 227 3,400 1.19 DB[65] CNE-227-2 50 mm FRP plate (4 plies) 39.4* 0.52 227 2,300 0.80 DB[65] CNT-2-1 50 mm FRP plate (2 plies) 39.4* 0.26 227 4,900 1.14 DB[65] CNT-2-2 50 mm FRP plate (2 plies) 39.4* 0.26 227 4,600 1.07 DB[65] CNT-3-1 50 mm FRP plate (3 plies) 39.4* 0.39 227 3,900 1.15 DB[65] CNT-3-2 50 mm FRP plate (3 plies) 39.4* 0.39 227 3,700 1.09 DB[65] CNT-4-1 50 mm FRP plate (4 plies) 39.4* 0.52 227 3,400 1.19 DB[65] CNT-4-2 50 mm FRP plate (4 plies) 39.4* 0.52 227 2,300 0.80 DB[65] CNT-5-1 50 mm FRP plate (5 plies) 39.4* 0.66 227 3,000 1.19 DB[65] CNT-5-2 50 mm FRP plate (5 plies) 39.4* 0.66 227 2,500 0.99 DB[65] CNW-100-1 100 mm FRP plate (3 plies) 44.1* 0.39 224 4,200 1.14 DB[65] CNW-100-2 100 mm FRP plate (3 plies) 44.1* 0.39 224 3,300 0.90 DB[65] CNW-125-1 125 mm FRP plate (3 plies) 44.1* 0.39 227 3,300 0.90 DB[65] CNW-125-2 125 mm FRP plate (3 plies) 44.1* 0.39 227 3,400 0.93 DB[65] CNW-150-1 150 mm FRP plate (3 plies) 44.1* 0.39 227 4,400 1.20 DB[65] CNW-150-2 150 mm FRP plate (3 plies) 44.1* 0.39 227 3,800 1.04 DB[65] CNW-50-1 50 mm FRP plate (3 plies) 44.1* 0.39 227 4,900 1.34 DB[65] CNW-50-2 50 mm FRP plate (3 plies) 44.1* 0.39 227 3,900 1.07 DB[65] CNW-75-1 75 mm FRP plate (3 plies) 44.1* 0.39 224 4,400 1.20 DB[65] CNW-75-2 75 mm FRP plate (3 plies) 44.1* 0.39 224 3,700 1.01 DB[22] CN lfrp = 250 mm 44.1* 0.39 227 3,484 0.95 DB[66] Ws0L2-1 2 plies FRP Sheet 47.4* 0.33 276 5,400 1.44 DB[52] CFRP laminates applied to sides of large scale PT girders 67.0 1.40 195 2953 1.42 DB[52] CFRP laminates applied to sides of large scale PT girders 67.0 1.40 195 3435 1.65 DB

CFRP Rope Through Web 3.64 (Average)[47] S0-LS-Rope 6 L-strips @ 175 mm, No Stirrups 28.0 1.40 120 6,400 3.80 CC[47] S1-LS-Rope 6 L-strips @ 175 mm, Stirrups @ 260 mm 28.0 1.40 120 6,000 3.56 CC[47] S3-LS-Rope 6 L-strips @ 175 mm, Stirrups @ 175 mm 28.0 1.40 120 6,000 3.56 CC

CFRP Anchor into flange 1.22 (Average)[24] U2C-AN3Cin 2 layers of FRP, 3 inclined FRP anchors, 34 g/m, 70 mm

embedment22.2 0.23 230 3800 1.52 DB

[24] U2C-AN5Cin 3 layers of FRP, 5 inclined FRP anchors, 34 g/m, 70 mmembedment

22.9 0.23 230 3800 1.49 DB

[24] U2G-AN3Gin 2 layers of CFRP, 3 inclined GFRP anchors, 59 g/m, 70 mmembedment

22.9 0.72 72.4 3800 1.48 DB

[48] FBwA-CFRP 1 Layer of 20 mmwide FRP anchored with 60 mm embedmentat 45� angle

12.4 0.13 238 3375 1.17 DB


Table 3 (continued)


tft(mm)

Ef(GPa)

ef,max

(me)kfas Failure#

[48] FBwA-GFRP 1 Layer of 20 mmwide FRP anchored with 60 mm embedmentat 45� angle

12.4 0.16 73 4260 0.83 DB

[48] FBwA-Hi-CFRP

1 Layer of 20 mmwide FRP anchored with 60 mm embedmentat 45� angle

12.4 0.14 640 1282 0.82 DB

FRP Anchor (spike) 1.88 (Average)[40] M3.1 Type M3, 2 off @ 75 mm (long.) 28.7 1.40 195 3,918 2.73 LAF[40] M3.2 Type M3, 2 off @ 75 mm (long.) 28.7 1.40 195 4,284 2.99 CSF[48] FBwA-CFRP CFRP Strips (20 mm wide @ 120) 12.4 0.13 238 3,375 1.52 FR[48] FBwA-Hi-

CFRPCFRP Strips (20 mm wide @ 120) 12.4 0.14 640 1,282 0.94 FR

[48] PBwA-CFRP CFRP Strips (20 mm wide @ 120) – U-strip NOT bonded 12.4 0.13 238 4,138 1.87 FR[48] PBwA-Hi-

CFRPCFRP Strips (20 mm wide @ 120) – U-strip NOT bonded 12.4 0.14 640 3,309 2.42 FR

[23] BF-200-1 1 � Bow tie, 90 deg 44.1* 0.39 226 6,216 1.70 DB[23] BF-200-2 1 � Bow tie, 90 deg 44.1* 0.39 226 6,828 1.86 DB[23] BF-300-1 1 � Bow tie, 90 deg 44.1* 0.39 226 6,547 1.79 DB[23] BF-300-2 1 � Bow tie, 90 deg 44.1* 0.39 226 7,023 1.92 DB[23] BF-400-1 1 � Bow tie, 90 deg 44.1* 0.39 226 6,780 1.85 DB[23] BF-400-2 1 � Bow tie, 90 deg 44.1* 0.39 226 7,898 2.16 DB[23] BF-400-3 1 � Bow tie, 90 deg 44.1* 0.39 226 7,552 2.06 DB[23] DA-101.3-1 1 � Single fan, varying dowel angle 37.8* 0.39 226 6,686 2.02 DB + AF[23] DA-101.3-2 1 � Single fan, varying dowel angle 37.8* 0.39 226 6,923 2.10 DB + AF[23] DA-112.5-1 1 � Single fan, varying dowel angle 44.1* 0.39 226 8,474 2.31 DB + AF[23] DA-112.5-2 1 � Single fan, varying dowel angle 44.1* 0.39 226 7,514 2.05 DB + AF[23] DA-123.8-1 1 � Single fan, varying dowel angle 37.8* 0.39 226 8,100 2.45 DB + AF[23] DA-123.8-2 1 � Single fan, varying dowel angle 37.8* 0.39 226 7,675 2.32 DB + AF[23] DA-135-1 1 � Single fan, varying dowel angle 44.1* 0.39 226 9,221 2.52 DB + AF[23] DA-135-2 1 � Single fan, varying dowel angle 44.1* 0.39 226 8,458 2.31 DB + AF[23] DA-157.5-1 1 � Single fan, varying dowel angle 37.8* 0.39 226 9,129 2.76 DB + AF[23] DA-157.5-2 1 � Single fan, varying dowel angle 37.8* 0.39 226 8,961 2.71 DB + AF[23] DA-45-1 1 � Single fan, varying dowel angle 44.1* 0.39 226 4,987 1.36 DB + AF[23] DA-45-2 1 � Single fan, varying dowel angle 44.1* 0.39 226 3,933 1.07 DB + AF[23] DA-67.5-1 1 � Single fan, varying dowel angle 37.8* 0.39 226 4,490 1.36 DB + AF[23] DA-67.5-2 1 � Single fan, varying dowel angle 37.8* 0.39 226 5,091 1.54 DB + AF[23] DA-90-1 1 � Single fan, varying dowel angle 44.1* 0.39 226 7,102 1.94 DB + AF[23] DA-90-2 1 � Single fan, varying dowel angle 44.1* 0.39 226 7,442 2.03 DB + AF[23] SF-200-1 1 � Single fan, 90 deg 44.1* 0.39 226 7,102 1.94 DB[23] SF-200-2 1 � Single fan, 90 deg 44.1* 0.39 226 7,442 2.03 DB[23] SF-200R-1 1 � Single fan reversed, 90 deg 44.1* 0.39 226 5,041 1.38 DB[23] SF-200R-2 1 � Single fan reversed, 90 deg 44.1* 0.39 226 6,329 1.73 DB[23] SF-200R-3 1 � Single fan reversed, 90 deg 44.1* 0.39 226 5,843 1.60 DB[65] PE-227-1 50 mm FRP plate (4 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.52 227 5,700 1.99 DB[65] PE-227-2 50 mm FRP plate (4 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.52 227 6,000 2.09 DB[65] PT-2-1 50 mm FRP plate (2 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.26 227 9,700 2.26 DB[65] PT-2-2 50 mm FRP plate (2 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.26 227 8,000 1.87 DB[65] PT-3-1 50 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.39 227 6,600 1.95 DB[65] PT-3-2 50 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.39 227 6,600 1.95 DB[65] PT-4-1 50 mm FRP plate (4 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.52 227 5,700 1.99 DB[65] PT-4-2 50 mm FRP plate (4 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.52 227 6,000 2.09 DB[65] PT-5-1 50 mm FRP plate (5 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.66 227 4,400 1.75 DB[65] PT-5-2 50 mm FRP plate (5 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.66 227 5,700 2.26 DB[65] PT-5-3 50 mm FRP plate (5 plies), 1 � Single 60 deg fan, 90 deg 39.4* 0.66 227 4,700 1.87 DB[65] PW-100-1 100 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 44.1* 0.39 227 4,900 1.34 DB[65] PW-100-2 100 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 44.1* 0.39 227 6,400 1.75 DB[65] PW-100-3 100 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 44.1* 0.39 227 4,700 1.29 DB[65] PW-125-1 125 mm FRP plate (3 plies), 1 � Single 64 deg fan, 90 deg 44.1* 0.39 227 3,700 1.01 DB + AF[65] PW-125-2 125 mm FRP plate (3 plies), 1 � Single 64 deg fan, 90 deg 44.1* 0.39 227 4,700 1.29 DB + AF[65] PW-150-1 150 mm FRP plate (3 plies), 1 � Single 74 deg fan, 90 deg 44.1* 0.39 227 5,600 1.53 DB + AF[65] PW-150-2 150 mm FRP plate (3 plies), 1 � Single 74 deg fan, 90 deg 44.1* 0.39 227 4,900 1.34 DB + AF[65] PW-50-1 50 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 44.1* 0.39 227 6,400 1.75 DB[65] PW-50-2 50 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 44.1* 0.39 227 5,900 1.62 DB[65] PW-75-1 75 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 44.1* 0.39 224 6,200 1.68 DB[65] PW-75-2 75 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 44.1* 0.39 224 5,500 1.49 DB[65] PW-75-3 75 mm FRP plate (3 plies), 1 � Single 60 deg fan, 90 deg 44.1* 0.39 227 5,500 1.51 DB[22] A1 lanc = 75 mm, lend = 175 mm, lfrp = 250 mm 44.1* 0.39 227 6,164 1.69 DB[22] A2 lanc = 125 mm, lend = 125 mm, lfrp = 250 mm 44.1* 0.39 224 6,016 1.63 DB[22] A3 lanc = 175 mm, lend = 75 mm, lfrp = 250 mm 44.1* 0.39 224 5,715 1.55 DB[22] A4 lanc = 225 mm, lend = 25 mm, lfrp = 250 mm 44.1* 0.39 224 4,813 1.31 DB[22] B1 lanc = 75 mm, lend = 25 mm, lfrp = 100 mm 44.1* 0.39 224 3,459 0.94 DB[22] B2 lanc = 125 mm, lend = 25 mm, lfrp = 150 mm 44.1* 0.39 227 3,886 1.06 DB[22] B3 lanc = 175 mm, lend = 25 mm, lfrp = 200 mm 44.1* 0.39 227 4,154 1.14 DB[22] B4 lanc = 225 mm, lend = 25 mm, lfrp = 250 mm 44.1* 0.39 224 4,813 1.31 DB[22] B5 lanc = 75 mm, lend = 125 mm, lfrp = 200 mm 44.1* 0.39 224 6,467 1.76 DB



Table 3 (continued)


tft(mm)

Ef(GPa)

ef,max

(me)kfas Failure#

[22] B6 lanc = 125 mm, lend = 125 mm, lfrp = 250 mm 44.1* 0.39 224 6,016 1.63 DB[22] B7 lanc = 175 mm, lend = 125 mm, lfrp = 300 mm 44.1* 0.39 227 5,896 1.61 DB + AF[22] B8 lanc = 225 mm, lend = 125 mm, lfrp = 350 mm 44.1* 0.39 227 7,504 2.05 DB + AF[22] C1 lanc = 75 mm, lend = 25 mm, lfrp = 100 mm 44.1* 0.39 224 4,512 1.23 DB[22] C10 lanc = 75 mm, lend = 250 mm, lfrp = 325 mm 44.1* 0.39 227 7,504 2.05 DB[22] C11 lanc = 75 mm, lend = 275 mm, lfrp = 350 mm 44.1* 0.39 227 7,236 1.98 DB + AF[22] C2 lanc = 75 mm, lend = 50 mm, lfrp = 125 mm 44.1* 0.39 227 5,092 1.39 DB[22] C3 lanc = 75 mm, lend = 75 mm, lfrp = 150 mm 44.1* 0.39 224 6,317 1.72 DB[22] C4 lanc = 75 mm, lend = 100 mm, lfrp = 175 mm 44.1* 0.39 227 6,432 1.76 DB[22] C5 lanc = 75 mm, lend = 125 mm, lfrp = 200 mm 44.1* 0.39 224 6,317 1.72 DB[22] C6 lanc = 75 mm, lend = 150 mm, lfrp = 225 mm 44.1* 0.39 224 4,963 1.35 DB[22] C7 lanc = 75 mm, lend = 175 mm, lfrp = 250 mm 44.1* 0.39 227 6,164 1.69 DB[22] C8 lanc = 75 mm, lend = 200 mm, lfrp = 275 mm 44.1* 0.39 227 7,772 2.13 DB + AF[22] C9 lanc = 75 mm, lend = 225 mm, lfrp = 300 mm 44.1* 0.39 227 7,102 1.94 DB + AF[67] B40R1-1 40 mm embedment, 1 anchor, 45 mm from concrete edge 49.6 0.67 230 5,600 1.94 AP + PD[67] B40R1-2 40 mm embedment, 1 anchor, 45 mm from concrete edge 49.6 0.67 230 3,900 1.35 AP + PD[67] B40R1-3 40 mm embedment, 1 anchor, 45 mm from concrete edge 49.6 0.67 230 4,000 1.39 AP + PD[67] B60R1-1 60 mm embedment, 1 anchor, 45 mm from concrete edge 49.6 0.67 230 6,600 2.29 AP + PD[67] B60R1-2 60 mm embedment, 1 anchor, 45 mm from concrete edge 49.6 0.67 230 6,400 2.22 AP + PD[67] B60R1-3 60 mm embedment, 1 anchor, 45 mm from concrete edge 49.6 0.67 230 5,600 1.94 AP + PD[67] B60R2-1 60 mm embedment, 1 anchor, 135 mm from concrete edge 49.6 0.67 230 4,200 1.46 AP + PD[67] B60R2-2 60 mm embedment, 1 anchor, 135 mm from concrete edge 49.6 0.67 230 4,200 1.46 AP + PD[67] B60R2-3 60 mm embedment, 1 anchor, 135 mm from concrete edge 49.6 0.67 230 5,800 2.01 AP + PD[67] B60R3-1 60 mm embedment, 1 anchor, 225 mm from concrete edge 49.6 0.67 230 4,400 1.53 AP + PD[67] B60R3-2 60 mm embedment, 1 anchor, 225 mm from concrete edge 49.6 0.67 230 3,400 1.18 AP + PD[67] B60R3-3 60 mm embedment, 1 anchor, 225 mm from concrete edge 49.6 0.67 230 3,600 1.25 AP + PD[67] C60R1R2-1 60 mm embedment, 2 anchors, 45 & 135 mm from concrete

edge49.6 0.67 230 7,100 2.46 PS&PD

[67] C60R1R2-2 60 mm embedment, 2 anchors, 45 & 135 mm from concreteedge

49.6 0.67 230 7,400 2.57 AP/R&PD


49.6 0.67 230 8,000 2.78 AR&PD


49.6 0.67 230 5,300 1.84 AP&PD


49.6 0.67 230 7,000 2.43 AP&PD


49.6 0.67 230 5,200 1.80 AP&PS/D

[67] D60R1R1-1 60 mm embedment, 2 anchors, 45 from concrete edge –Transverse

49.6 0.67 230 8,300 2.88 AR&PD


49.6 0.67 230 5,600 1.94 AR&PD


49.6 0.67 230 6,600 2.29 AP/R&PD


49.6 0.67 230 5,000 1.73 AR&PD


49.6 0.67 230 4,000 1.39 AP&PD


49.6 0.67 230 3,100 1.08 AP&PD

[67] E60R11R22-1 60 mm embedment, 4 anchors, 45 & 135 mm from concreteedge

49.6 0.67 230 8,100 2.81 PS&PD


49.6 0.67 230 7,100 2.46 AP/R&PD


49.6 0.67 230 8,000 2.78 AR&PD


49.6 0.67 230 10,200 3.54 AR&PS/D


49.6 0.67 230 8,000 2.78 PS&PD


49.6 0.67 230 8,800 3.05 AR&PS/D

CFRP + Full wrap through flanges 4.80 (Average)[68] B3/30/H/22 Full Wrap through 45�holes cut higher into flanges 22.3 1.60 121 6050 4.09 S[68] B4/30/G/25 Full Wrap through 45�holes cut higher into flanges + holes

grouted24.6 1.60 121 7700 4.88 S

[68] B5/30/C/27 Full Wrap through 45�holes cut higher into flanges 26.7 1.60 121 9050 5.43 S

CFRP + Embedment inflange

4.07 (Average)

[45] Beam 0.75D CFRP L-strips + 120 mm Embedment in flange 31.1 1.30 137 8884 4.58 ARS[45] Beam 0.6D CFRP L-strips + 120 mm Embedment in flange 30.9 1.30 137 7298 3.78 ARS[45] Beam 0.5D CFRP L-strips + 120 mm Embedment in flange 31.6 1.30 137 7515 3.84 CPO


Table 3 (continued)


tft(mm)

Ef(GPa)

ef,max

(me)kfas Failure#

Metallic Anchors 1.83 (Average)[69] No. 24 angle with through bolt 18.0 0.12 229 6000 1.51 FF + FR[63] Spec-3 L-shaped CFRP + Steel Anchorage 30.7 0.12 231 4700 0.83 S + FR[63] Spec-5 U-jacketing CFRP + Steel Anchorage 30.7 0.12 231 6000 1.06 S + FR[63] Spec-6 L-shaped CFRP + Steel Anchorage 30.8 0.12 231 4700 0.83 FF[63] Spec-7 Extended U-Jacket CFRP + Steel Anchorage 30.6 0.12 231 7800 1.38 FF[70] S-M-D U-jacketing CFRP (unbonded) + Anchorages 43.0 0.18 230 4200 0.74 S[71] JS3A 1 ply CFRP ligatures + Anchor 20.7 0.17 228 7500 2.06 FR[1] C-BT6 Continuous U-jacket with end anchor 35.0 0.20 228 6300 1.36 FF[71] JS6A 2 ply AFRP ligatures + Anchor 20.7 0.30 117 3400 0.90 FR[71] JS5A 2 ply CFRP ligatures + Anchor 20.7 0.33 228 5650 2.32 FR[72] TB1S1 U-jacketing CFRP + Steel Anchorage 25.6 0.86 63.6 4260 1.26 CSF + T[72] TB1S2 Extended CFRP U-Jacket + Steel Anchorage 25.6 0.86 63.6 4700 1.39 CSF + T[72] TB1S3 Full wrapping + Steel Anchorage 25.6 0.86 63.6 7690 2.28 CSF[72] TB3S4 Combined U-wrapping and Extended U-Jacket + Steel

Anchorage25.6 0.86 63.6 7590 2.25 CSF

[66] Ws12L2-2 2 plies FRP Sheet, 12 mm wide steel neck 47.4* 0.33 276 10,000 2.66 AF[66] Ws14L2-2 2 plies FRP Sheet, 14 mm wide steel neck 47.4* 0.33 276 11,300 3.00 FR[66] Ws16L2-3 2 plies FRP Sheet, 16 mm wide steel neck 47.4* 0.33 276 12,200 3.24 FR[66] Ws18L2-1 2 plies FRP Sheet, 18 mm wide steel neck 47.4* 0.33 276 10,200 2.71 FR[66] Ws20L2-1 2 plies FRP Sheet, 20 mm wide steel neck 47.4* 0.33 276 10,900 2.90 FR[66] Ws5L1-2 2 plies FRP Sheet, 5 mm wide steel neck 47.4* 0.17 276 10,500 1.87 AF

FRP BidirectionalPatch

2.52 (Average)

[36] WG8 Bidirectional fibre (1ply, ±45)+ Unidirectional fibre (2 ply), 0� 62.0 2.00 210 7500 4.02 PASF/LR[36] WG10 Bidirectional fibre (2ply), ±45 62.0 2.00 210 4900 2.63 CSF[36] WG11 Bidirectional fibre (2ply), ±45 62.0 2.00 210 5300 2.84 CSF[36] WG12 Bidirectional fibre (1ply), ±45 + 50 mm lip 62.0 2.00 210 5800 3.11 CSF / PLR/

PFR[37] 1.1 Type 1 – Bi-dir. Patch (+/�45 2 plies) – 400W � 300L 69.2 1.40 210 4,406 1.78 AF[37] 1.2 Type 1 – Bi-dir. Patch (+/�45 2 plies) – 400W � 300L 69.2 1.40 210 4,922 1.99 AF[37] 2.1 Type 2 – Bi-dir. Patch (+/�45 2 plies) – 400W � 250L 69.2 1.40 210 3,819 1.55 AF[37] 2.2 Type 2 – Bi-dir. Patch (+/�45 2 plies) – 400W � 250L 69.2 1.40 210 4,328 1.75 AF[37] 3.1 Type 3 – Bi-dir. Patch (+/�45 2 plies) – 300W � 300L 69.2 1.40 210 5,378 2.18 AF[37] 3.2 Type 3 – Bi-dir. Patch (+/�45 2 plies) – 300W � 300L 69.2 1.40 210 4,801 1.94 AF[37] 3.3 Type 3 – Bi-dir. Patch (+/�45 2 plies) – 300W � 300L 69.2 1.40 210 5,600 2.27 AF[37] 3.4 Type 3 – Bi-dir. Patch (+/�45 2 plies) – 300W � 300L 69.2 1.40 210 5,091 2.06 AF[37] 4.1 Type 4 – Bi-dir. Patch (+/�45 2 plies) – 200W � 300L 69.2 1.40 210 4,950 2.00 AF[37] 4.2 Type 4 – Bi-dir. Patch (+/�45 2 plies) – 200W � 300L 69.2 1.40 210 4,504 1.82 AF[37] 4.3 Type 4 – Bi-dir. Patch (+/�45 2 plies) – 200W � 300L 69.2 1.40 210 4,124 1.67 AF[37] 4.4 Type 4 – Bi-dir. Patch (+/�45 2 plies) – 200W � 300L 69.2 1.40 210 4,514 1.83 AF[38] D1.1 Type D1 – Bi-dir. Patch (+/�45 3 plies) 28.7 2.80 195 3,700 3.86 AF[38] D1.2 Type D1 – Bi-dir. Patch (+/�45 3 plies) 28.7 2.80 195 3,530 3.68 AF[39] 1.1 Type 1 – Bi-directional Patch (+/�45 2 plies) 28.7 1.40 195 6,180 4.31 CSF[39] 1.2 Type 1 – Bi-directional Patch (+/�45 2 plies) 28.7 1.40 195 5,451 3.80 CSF[52] Bi-dir. Patch (+/�45 2 plies) applied to large scale PT girders 67.0 1.40 195 4114 1.98 DB + AF[52] Bi-dir. Patch (+/�45 2 plies) applied to large scale PT girders 67.0 1.40 195 4960 2.38 DB + AF

FRP Hybrid Anchor (Spike + Patch) 4.82 (Average)[38] D2.1 Type D2 – 3 FRP Anchors + Bi-dir. Patch (+/�45 3 plies) 28.7 2.80 195 4,990 5.20 AF[38] D2.2 Type D2 – 3 FRP Anchors + Bi-dir. Patch (+/�45 3 plies) 28.7 2.80 195 4,530 4.72 AF[39] 2.1 Type 2 = Type 1 + 3 FRP Anchors 28.7 1.40 195 9,209 6.42 CSF + AF[39] 2.2 Type 2 = Type 1 + 3 FRP Anchors 28.7 1.40 195 9,429 6.58 CSF[39] 3.1 Type 3 = Type 2 + 1 Uni-directional Fibre 28.7 1.40 195 8,276 5.77 AF[39] 3.2 Type 3 = Type 2 + 1 Uni-directional Fibre 28.7 1.40 195 9,347 6.52 AF[53] L-S CFRP Strips (254 mm wide), anchored with 2 spike anchors

+ patch to anchor27.0 0.28 102 9700 1.90 FR

[53] H-S-2 CFRP Strips (254 mm wide), anchored with 2 spike anchors+ patch to anchor

27.0 0.56 102 4800 1.41 AF

CFRP + Unidirectional fibre Patch 1.75 (Average)[64] WG3 Unidirectional fibre (2ply), 90� 62.0 2.00 210 3242 1.74 CSF[64] WG4 Unidirectional fibre (2 ply), 90� 62.0 2.00 210 3142 1.68 CSF[64] WG5 Unidirectional fibre (2 ply), 0� 62.0 2.00 210 3470 1.86 CSF[64] WG6 Unidirectional fibre (2 ply), 0� 62.0 2.00 210 3239 1.74 CSF[64] WG7 Unidirectional fibre (2 ply), 0� 62.0 2.00 210 3245 1.74 CSF

Substrate Strengthening 2.60 (Average)[13] WG1 WG1 – Substrate strengthened 62.0 2.00 210 4640 2.49 ASF[13] WG2 WG2 – Substrate strengthened 62.0 2.00 210 4881 2.62 ASF[40] M1.1 Type M1, 1 � Longitudinal channel 28.7 1.40 195 5,184 3.62 CSF[40] M1.2 Type M1, 1 � Longitudinal channel 28.7 1.40 195 5,952 4.15 CSF[40] M2.1 Type M2, 3 � Transverse channels 28.7 1.40 195 3,891 2.71 CSF[40] M2.2 Type M2, 3 � Transverse channels 28.7 1.40 195 3,669 2.56 CSF[41] C1S-1A 1 � 30 mm dia adhesive connector 30.5 1.20 165 2,900 1.61 DB



Table 3 (continued)


tft(mm)

Ef(GPa)

ef,max

(me)kfas Failure#

[41] C1S-1S 1 � 30 mm dia steel connector 30.5 1.20 165 3,500 1.95 DB[41] C1S-2A 2 � 30 mm dia adhesive connector 30.5 1.20 165 3,700 2.06 DB

[41] C1S-2S 2 � 30 mm dia steel connector 30.5 1.20 165 4,000 2.22 DB

NSM Anchors 2.40 (Average)[43] A-0-1 15 mm � 37.8 mm groove 37.8 0.17 228 11,000 2.02 AP[43] A-3-1 10 mm dia GFRP bar in 15 mm � 37.8 mm groove 37.8 0.17 228 10,000 1.84 AP[43] A-3-2 10 mm dia GFRP bar in 15 mm � 37.8 mm groove 37.8 0.17 228 10,000 1.84 AP[43] A-4-3 13 mm dia GFRP bar in 19 mm � 37.4 mm groove 37.4 0.17 228 12,000 2.22 FR[43] A-4-3a 13 mm dia GFRP bar in 19 mm � 30.3 mm groove 30.3 0.17 228 17,000 3.62 FR[43] A-3-1-4 10 mm dia GFRP bar in 15 mm � 29.1 mm groove 29.1 0.17 228 9,000 1.97 FR[43] B-3-1 10 mm dia GFRP bar in 15 mm � 29.1 mm groove 29.1 0.17 228 10,000 2.19 AP[43] B-3-2 10 mm dia GFRP bar in 24 mm � 27.6 mm groove 27.6 0.17 228 10,000 2.27 AP[43] B-4-3 13 mm dia GFRP bar in 19 mm � 27.6 mm groove 27.6 0.17 228 11,000 2.49 FR[43] B-4-3-a 13 mm dia GFRP bar in 19 mm � 27.6 mm groove 27.6 0.17 228 12,000 2.72 FR[44] JS3A 10 mm dia GFRP bar in 15 mm � 37.8 mm groove 27.6 0.17 228 10,000 2.27 FR[44] JS5A 10 mm dia GFRP bar in 15 mm � 37.8 mm groove 27.6 0.33 228 9,800 3.32 FR

DB = plate debonding; ARS = anchorage failure at soffit; CSF = concrete separation failure; FF = flexural failure; FR = fibre rupture; PFR = partial fibre rupture; AF = Anchorfailure; AR = Anchor rupture PASF = partial adhesive separation failure; S = shear failure; CSP = concrete splittiing; LR = laminate rupture; PLR = partial laminate rupture;PFR = partial fibre rupture; T = torsional failure of concrete. CPO = concrete pull-out failure; AP + PD = Anchor pullout + plate debonding; PS + PD = Plate split + platedebonding; CC = Concrete crushing.

Table 4Normalised shear anchor effectiveness (by type).

Anchor type kfas,n ST dev

Control 1.00 0.34CFRP Anchor into flange 1.09 0.30CFRP + Unidirectional fibre Patch 1.56 0.06Metallic Anchors 1.63 0.72FRP Anchor (spike) 1.67 0.46NSM Anchors 2.13 0.57FRP Bidirectional Patch 2.25 0.78Substrate Strengthening 2.32 0.68CFRP Rope Through Web 3.25 0.12CFRP + Embedment in flange 3.63 0.40CFRP + Full wrap through flanges 4.28 0.60FRP Hybrid Anchor (Spike + Patch) 4.30 1.84


in shear with FRP. Of the studies which had been conducted, evenfewer reported the maximum FRP strains achieved prior todebonding, while most simple reported the maximum loadsattained prior to failure. Without recording the peak strains in eachFRP stirrup, the potential usefulness of the research is impacted asit is difficult to implement the research outcomes into the develop-ment of design guidelines. Attention also needs to be paid to pro-viding an adequate number of strain gauges along the full height ofthe FRP stirrups to ensure that the peak strain is captured. This canbe expedited through the use of digital image correlation (DIC)photogrammetry systems which can provide full field strain mea-surements best suited to capturing strain localisations.

When examining the average, normilised anchor effectivenessfactors presented in Table 4, the unanchored control specimensfailed by debonding with an average effectiveness factor ofkfas = 1.12. This provides a level of confidence in the ACI model rep-resenting the effective FRP delamination strain with some degreeof accuracy. It can be observed that FRP anchors (spike) with thedowel end inserted into the beam flange and the fan end bondedto the FRP stirrup exhibited a kfas,n value of 1.09. However, thevalue was determined based on two studies and six data points.One of the two studies by Ozden [48], was based on a concretestrength of 12.4 MPa which is well below the minimum require-ments for bonding FRP. As a result, the maximum FRP strainsreported by Ozden [48] were well below the expected valued bothfor the unanchored and anchored cases. If the data from Ozden [48]is omitted from the database, then the average, normalised effec-tiveness of FRP spike anchors increases from 1.09 to 1.33.

It should be noted that while average effectiveness factors canprovide a useful cross anchor comparative tool, individual compar-isons between anchored and unanchored specimens within thesame study need to be made to more accurately quantify theincrease in FRP utilisation as a result of a given anchor. For exam-ple, El-Saikaly [47] demonstrated that CFRP rope through the webprovided an effective anchorage for the FRP U-straps (i.e. peakkfas = 3.64 for specimen S0-LS-Rope). However, when investigatingthe unanchored specimen, the effectiveness factor for specimenS0-LS, is kfas = 2.55. Therefore, the actual increase in FRP utilisationfor that particular concept is 47%, rather than 225% quoted inTable 4.

Table 4 suggests the most promising concept is the hybridanchoring system consisting of FRP Patch restrained with FRP(spike) anchors. However, the unanchored control specimens pro-duced an average effectiveness factor of kfas = 1.54. This means theconcrete separation failure occurred at a strain 54% higher than thedelamination strain predicted by Eqs. (2)–(6). The average anchoreffectiveness factor for the associated anchored specimens yieldedkfas = 5.87. That is an actual improvement in FRP utilisation of 281%.

Ignoring the limited test results and variability within eachanchor type, the most effective concepts are the hybrid FRP anchorwith patch, the CFRP rope anchors through the web and substratestrengthening. It should be noted that the data on the CFRP ropeanchors is from testing representative flexural members. In con-trast, the hybrid anchor and substrate strengthening conceptsshould be extended to beam tests.

6. Further work and development of design provisions

The database presented in this paper is the first step in thedevelopment of design provisions for each anchorage type.Although the anchorage efficiency factor can provide a useful toolfor evaluating the effectiveness of each type of anchor when usedin a given strengthening application, it does not capture all theparameters specific to each anchorage type, therefore more specificdesign equations require development. The task of developing suchequations may progress as sufficient data has become available.

For flexurally strengthened members, anchorage systems canbe divided into two categories: (1) those developed to suppressend cover separation failure such as U-strap anchors, and anchorsto suppress IC debonding such as: FRP anchors, p-anchors and


metallic anchors. Anchors specified to address concrete cover sep-aration failure should be designed to suppress the failure modeentirely, thus shifting the failure to either IC debonding or FRP rup-ture. The task for determining the area of transverse U-strapanchors to mitigate concrete cover separation failure has largelybeen accomplished and the current models available in the Chinesenational standard [29] and Concrete Society Technical Report no.55 [28] have been found to provide reasonable predictions of thetransverse U-strap width, thickness and spacing. It should be notedthat the above equations apply to vertical U-strap orientations onlyand are not applicable to inclined U-jackets.

Development of design equations for FRP anchors, p-anchorsand metallic anchors is complicated by the fact that partial FRPplate delamination is required to engage the dowel action of theanchors. Further, in most cases partial delamination of the FRPplate is expected to have occurred well before failure of theanchored FRP soffit plate is attained. Thus, when designing suchanchorage systems to delay or suppress IC debonding, in order toprevent FRP partial delamination at service, the FRP plate strainat serviceability load should always be less than the strain to causeIC debonding in the unanchored condition. In most cases, FRPanchorage systems to address IC debonding cannot be designedto achieve rupture of the FRP plate. Although FRP rupture has beennoted by some researchers, relatively thin thickness of FRP platewere used together with closely spaced anchors. Hence, designand specification of FRP anchors, p-anchors and metallic anchorsto address IC debonding requires a framework which considersthe following parameters: FRP plate thickness, FRP plate width,FRP plate modulus of elasticity, concrete strength, anchor type,anchor properties, anchor location and anchor number. The aboveparameters may be considered in a series of design equationswhich specify the permissible FRP plate strain after which ICdebonding will occur. However, such equations are yet to be devel-oped and they are left for ongoing research.

Implementation of FRP anchorage systems to enhance the per-formance of FRP side bonded plates or U-jackets used in shearstrengthening applications is less complex than for flexural mem-bers due to the absence of multiple debonding failure modes. Aseries of design equations and guidelines for the use of patchanchors to enhance the performance of FRP laminates used inshear strengthening applications has already been introduced byKalfat and Al-Mahaidi [73,74]. The models by Kalfat et al. [74,75]were capable of predicting patch anchor response, when varyingparameters such as: concrete strength, laminate width, laminatethickness, laminate modulus, patch anchor length and patchanchor width. In addition, the model has been verified to estimatethe maximum laminate strains and loads reached prior to debondto a reasonable level of accuracy.

Further, del Rey Castillo [75] recently developed a designapproach for FRP anchors in FRP shear strengthened members. Aseries of equations are presented which capture the influence ofdowel insertion angle, anchor splay/fan behaviour as well as mul-tiple failure modes such as: concrete cone failure, concrete cone+ bond failure, dowel pull-out, fan to sheet debonding, and fibrerupture. The design approach involves: (1) determining the result-ing tensile force in the FRP sheets using the effective strain and themodulus of elasticity of the FRP. This force will be transferred viathe anchors to the substrate and to permit the development ofthe assumed effective strain in the FRP sheets. (2) Calculating thenumber of anchors to be installed, considering that the anchorshave to cover the whole width of the FRP sheet and calculatingthe required tensile force per anchor. (3) Once the tensile forceper anchor is determined, the required cross sectional area of theFRP anchor, dimensions of the drilled hole and fan/splay dimen-sions can be determined.

Development of models and guidelines for other anchorage con-cepts is currently hampered by insufficient experimental data.However, as data becomes available additional design equationsand methodologies can be developed in due course.

7. Conclusions and recommendations

Anchorage of externally bonded FRP results in higher strainlevels in the FRP prior to debonding which enables the strength-ened member to achieve a higher capacity using less material.The paper has presented an up to date database, summarisingthe latest research findings in the area of FRP anchorage systemsat the time of publication. The data has been processed such thatan effectiveness factor could be assigned to each anchor type forgeneral performance assessment and cross comparisons.

The three most effective flexural anchor types based on avail-able research at the time of publication are steel anchors, p-anchors and FRP anchors. The benefit of mechanical anchorageon flexural FRP reinforcement is well known. However, the benefitof the FRP and p-anchors are that they are both manufactured fromFRP which makes them less susceptible to durability issues such ascorrosion compared with steel anchor systems.

Although the normalised shear anchor effectiveness values arederived from limited data, the three most effective shear anchortypes based on recent research are the hybrid FRP anchor withpatch, the CFRP rope through web and substrate strengthening.Out of these three concepts only the CFRP rope through the webwas tested on flexural concrete members. The other two conceptsdemonstrated their effectiveness through joint-tests. It is recom-mended that where possible, future testing of anchor conceptsfor shear be tested using large scale beam tests as opposed to jointassemblies.

There is currently still a lack of data to develop effectivenessfactors with any statistical reliability. Ideally more data wouldallow the variability of different parameters within the sameanchoring concept to be isolated to determine their effects onanchor effectiveness (e.g. anchor size and anchor layout). Thiscan only be accomplished with increased testing.

Conflict of interest

The authors declare that they have no conflict of interest.

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