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Abstract This paper considers the use of Nonlinear Finite Element Analysis (NLFEA) to predict the load capacity of a range of experimentally tested in-plane restrained reinforced concrete slabs which experienced internal arching effects under loading. The slabs were constructed at one third scale and strengthened with basalt fibre reinforced polymer (BFRP) or carbon fibre reinforced polymer (CFRP) bonded in place using the near surface mounted (NSM) technique. As the research was representative of existing floor slabs within reinforced concrete building frames, all test specimens were constructed with normal strength concrete (∼40 N/mm2) and 0.15% steel reinforcement. One tenth of one percent fibre reinforced polymer (FRP) was used to strengthen samples which were compared with unstrengthened control specimens. The London University Structural Analysis System (LUSAS) finite element analysis software package was used to model all test samples using experimentally derived material test values. Experiments and NLFEA models were compared with the Queen's University Belfast (QUB) arching theory which showed that LUSAS was slightly more accurate than the QUB arching theory in predicting slab capacity. However, the QUB arching theory was found to be slightly more consistent in estimating slab capacities compared with LUSAS. Yet, both of these methods were significantly better at predicting slab capacities than existing Eurocode and American Concrete Institute codes. [ABSTRACT FROM AUTHOR]

Abstract This paper outlines basalt fibre reinforced polymer (BFRP) and carbon fibre reinforced polymer (CFRP) strengthening of laterally restrained concrete floor slabs. In-plane restraint has previously been shown to enhance slab capacity due to the development of internal compressive membrane action (CMA), which is not generally included in codified strength assessments. By installing fibre reinforced polymers (FRPs) using the near surface mounted (NSM) technique, disturbance to the existing structure can be minimised. The span-to-depth ratios of test slabs were 20 and 15 and these were constructed with normal strength concrete (∼40 N/mm2) with 0.15% steel reinforcement. 0.10% FRP (either BFRP or CFRP), was used to strengthen samples which were then compared with control samples. Investigations showed that FRP strengthening and CMA are generally separate, with limited overlap in terms of their contribution to capacity increase. Recommendations are then made for designers to better determine the capacity of FRP strengthened restrained slabs. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical assessments into the compressive stress-strain behaviour of circular FRP-confined rubberised alkali-activated concrete with unidirectional sheets incorporating fibres in the hoop direction. The parameters investigated in the experimental programme include three different rubber contents of 0%, 30% and 60% volumetric replacement of the total natural aggregates and three confinement levels of 1–3 aramid FRP layers. The numerical assessment is performed in ABAQUS/CAE and a new strain hardening-softening function is developed for the compressive behaviour in the Concrete Damaged Plasticity material model, which captures the passive confinement imparted by the FRP jacket on the rubberised concrete. The numerical results are validated against the experimental results and a parametric study involving 240 models covering a wide range of parameters, including varying FRP materials (basalt, glass, aramid, and carbon), reference concrete grades, rubber replacement ratios, and confinement levels, is performed. The experimental results show an increase in the confinement effectiveness, i.e., confined-to-unconfined strength, by 66.7% and 103.4% for specimens with 0% and 60% crumb rubber replacement ratio, respectively, as the number of FRP layers increase from 1 to 3. Test specimens with 0% and 60% crumb rubber replacement ratio indicate an increase in the ultimate axial strain by 228.2% and 76.2%, respectively, as the number of FRP layers increase from 1 to 3. The observed hoop rupture strain reduces by 32.8% and 21.3% for specimens with 0% and 60% crumb rubber replacement ratio as the number of FRP layers increase from 1 to 3, showing a trend of reduction in the hoop rupture strain with higher FRP confinement layers and rubber content. The numerical results show that the enhancement in compressive strength is linearly proportional to the confinement ratio and is only marginally influenced by the FRP jacket stiffness at a given confinement ratio. The ultimate axial strain enhancement is also linearly proportional to the confinement ratio but is dependent on the FRP jacket stiffness. The compressive stress-strain curve for sufficiently confined specimens is also shown to be well represented by a bi-linear curve with hardening. Based on the findings, a design-oriented model is introduced for sufficiently confined specimens and is shown to be in close agreement with the experimental results. • Experimental and numerical assessments of axial compressive behaviour are presented. • Specimens with up to 60% volumetric rubber replacement of mineral aggregates are considered. • Different FRP jacket material properties and thicknesses are investigated. • A design-oriented constitutive model for adequately confined specimens is proposed. [ABSTRACT FROM AUTHOR]

The long-term performance of the bond between carbon fibre reinforced polymer composite (CFRP) fabrics and concrete substrate is crucial to estimations of the reliability of externally strengthened concrete structures. This paper presents the experimental results and analysis of 162 pull-off tests using nine concrete slabs under various environmental conditions, i.e., wet/dry cyclic exposure and full-immersion exposure of 3.5% salt-water at a temperature of 60 °C. The main objective of this study was to assess the effects on the bond performance of CFRP-strengthened concrete slabs during 12 months of exposure in a marine environment. Five types of failure modes were observed in the tested samples. The test results confirmed that 12 months of exposure in a marine environment had a low effect on the epoxy performance between CFRP and concrete. The results also indicated the marginal increase of pull-off strength values after 12 months of environmental exposure. [ABSTRACT FROM AUTHOR]

With increasing numbers of strength-deficient concrete infrastructure assets, strengthening and repair of concrete structures is becoming an issue of international importance. This study examines the bond behaviour of deep embedment (DE) glass fibre reinforced polymer (GFRP) and carbon FRP (CFRP) bars embedded into concrete prisms using an epoxy adhesive. The experimentally investigated parameters were the embedment length, FRP bar type and diameter, concrete compressive strength and hole diameter. The increase in embedded length enhanced the pull-out capacity for both GFRP and CFRP bar types. However, the bond strength and initial stiffness of the bond stress-slip curves decreased with the increase in embedded length. The specimens with DE CFRP bars had higher pull-out capacities and better bond performance than the corresponding specimens with DE GFRP bars. For the specimens with DE CFRP bars, the pull-out capacity increased with the increase in bar diameter and concrete strength but these two parameters did not affect the behaviour of the specimens with DE GFRP bars. The increase in hole diameter reduced the initial stiffness of the specimens with DE GFRP bars but affected neither the failure mode nor the failure loads. For the first time, this paper presents a mathematical model for predicting the bond strength of DE FRP bars. The mathematical model was validated against experimental results and demonstrated to produce accurate predictions. It is envisaged that both the mathematical model and the experimental results will contribute to the development of future design guidelines for DE concrete shear strengthening. [ABSTRACT FROM AUTHOR]

The use of natural fibre reinforcement in polymer and concrete composites has in recent years attracted significant research interest. When coconut fibre reinforced concrete (CFRC) is confined by flax fibre reinforced polymer (FFRP), the strength of FFRP-CFRC composite is significantly enhanced. While researchers have studied the effect of FFRP confinement on compressive strength, their work has mainly focussed on the outside confinement of CFRC. In contrast, this study considers a double confinement, i.e. CFRC is confined respectively by large and small FFRP tubes both externally and internally. The experimental results show that in comparison with single confinement, double confinement enhances the axial compressive strength and strain of the FFRP-CFRC composite, even though less concrete is used. [ABSTRACT FROM AUTHOR]

This paper presents the results of a research project to study the seismic resistance of fibre reinforced polymer (FRP) strengthened concrete members after fire exposure. Specifically, the paper presents results of FRP strengthened reinforced concrete columns exposed to a standard fire including temperatures measured during the test and a discussion of the loads applied to the columns. Finally, the paper also presents the impact of lateral loading on structural columns after fire to assess the effectiveness of structural resistance of fire-damaged FRP strengthened building elements in case of an earthquake. Numerical models to simulate the lateral behaviour are presented and the predictions are compared to the test results. Since the FRP strengthened columns were insulated with fire protection, the lateral load resistance of the unstrengthened column was reduced by less than 5% due to fire exposure. [ABSTRACT FROM AUTHOR]

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Abstract: A numerical method for estimating the curvature, deflection and moment capacity of FRP reinforced concrete beams is developed. Force equilibrium and strain compatibility equations for a beam section divided into a number of segments are numerically solved due to the non-linear behaviour of concrete. The deflection is then obtained from the flexural rigidity at mid-span section using the deflection formula for various load cases. A proposed modification to the mid-span flexural rigidity is also introduced to account for the experimentally observed wide cracks over the intermediate support of continuous FRP reinforced concrete beams. Comparisons with experimental results show that the proposed numerical technique can accurately predict moment capacity, curvature and deflection of FRP reinforced concrete beams. The ACI-440.1R-06 equations reasonably predicted the moment capacity of FRP reinforced concrete beams but progressively underestimated the deflection of continuous ones. On the other hand, the proposed modified formula including a correction factor for the beam flexural rigidity reasonably predicted deflections of continuous FRP reinforced concrete beams. It was also shown that a large increase in FRP reinforcement slightly increases the moment capacity of FRP over-reinforced concrete beams but greatly reduces the defection after first cracking. [Copyright &y& Elsevier]

Abstract: This paper reports test results of 12 concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars subjected to a four point loading system. All test specimens had no transverse shear nor compression reinforcement and were classified into two groups according to the concrete compressive strength. The main parameters investigated in each group were the beam depth and amount of GFRP reinforcement. Two modes of failure were observed, namely flexural and shear. The flexural failure is mainly occurred due to tensile rupture of GFRP bars either within the mid-span region or under the applied point load. The shear failure is initiated by a major diagonal crack within the beam shear span. This diagonal crack extended horizontally at the level of the GFRP bars indicating bond failure. Simplified methods for estimating the flexural and shear capacities of beams tested are presented. The flexural capacity is estimated based on the compatibility of strains and equilibrium of forces. Comparisons between the flexural capacity obtained from the theoretical analysis and that experimentally measured in the current investigation and elsewhere show good agreement. To predict the shear capacity of the beams tested, four methods recently proposed in the literature for GFRP-reinforced concrete beams are used. These methods have been developed by modifying the shear capacity formula for steel-reinforced concrete beams to account for the difference in the axial stiffness of GFRP and steel bars. It has been shown that the theoretical predictions of the shear capacity obtained from these methods are inconsistent and further research needs to be carried out in order to establish a rational method for the shear capacity calculation of GFRP-reinforced concrete beams. [Copyright &y& Elsevier]

Abstract: Advanced composites are widely used for the strengthening of existing concrete structures. Current design guidelines give basic requirements on how to model the enhancement of structural performance of concrete members using surface bonded FRP (fibre reinforced polymer) reinforcement. With respect to this, it is of interest to evaluate the ductility requirements which are explicitly or implicitly imposed by design guides. Based on an evaluation of four major design guidelines in Europe, Japan and North-America, and a small parametric study, the ductility aspect of the design of FRP strengthened concrete members is verified. It appears that the ductility of flexural members strengthened with FRP should be considered with care, as reduced deformability is obtained at ultimate, though generally a minimum deformability is implicitly obtained in a proper design. At the other hand, ductility enhancement by means of FRP confinement is explicitly considered in the design guidelines. [Copyright &y& Elsevier]

Confinement of reinforced concrete columns by circumferential fibre reinforced polymer (FRP) wraps is a promising application of FRP materials for structural strengthening and seismic upgrading of deteriorated or under-strength members. However, if this technique is to be used in buildings, parking garages, and industrial structures, then the ability of FRP materials and FRP-wrapped columns to withstand the effects of fire must be demonstrated and evaluated. This paper presents the results of parametric studies conducted using a previously presented and partially validated numerical fire simulation model to investigate the effects of a number of parameters on the fire behaviour of FRP-wrapped reinforced concrete columns. It is demonstrated that appropriately designed and adequately protected FRP-wrapped reinforced concrete columns are capable of achieving fire endurances equivalent to conventionally reinforced concrete columns. Furthermore, this study also suggests that a holistic approach to the fire design of FRP-wrapped members is required, rather than an approach based on the specific performance of the FRP materials. Design recommendations for the fire-safe design of FRP-wrapped concrete columns are presented and discussed. [ABSTRACT FROM AUTHOR]

This paper presents tests where hybrid composite beams have been investigated. The hybrid beam consists of a glass fibre I-beam with carbon fibre strengthened bottom flange and a rectangular concrete block in the compressive zone. The interaction between the concrete and composite beam were obtained in two ways; casting in shear connectors of steel and bonding by epoxy adhesive. As a reference, a beam without concrete in the compressive zone was also tested. The idea of combining carbon, glass and concrete was to utilize the stiffness contribution from the carbon and the compressive strength from the concrete. The glass fibre I-beam would then take up the main part of the shear force. The results from the test showed that a good composite action could be achieved between carbon, glass and concrete. However, it could also be noticed, as expected, that an I-beam is not the ultimate form due to stability problems. In the tests, problems arose due to lateral instability, but this was solved by placing stiffeners manufactured from wood between the flanges of the Fibre Reinforced Polymer beam over the supports. With a few modifications of the hybrid beam it is believed, that it would be possible to create both a technical and economical hybrid profile that benefits from carbon, glass and concrete. [Copyright &y& Elsevier]

External confinement by the wrapping of FRP sheets (or FRP jacketing) provides a very effective method for the retrofit of reinforced concrete (RC) columns subject to either static or seismic loads. For the reliable and cost-effective design of FRP jackets, an accurate stress–strain model is required for FRP-confined concrete. In this paper, a new design-oriented stress–strain model is proposed for concrete confined by FRP wraps with fibres only or predominantly in the hoop direction based on a careful interpretation of existing test data and observations. This model is simple, so it is suitable for direct use in design, but in the meantime, it captures all the main characteristics of the stress–strain behavior of concrete confined by different types of FRP. In addition, for unconfined concrete, this model reduces directly to idealized stress–strain curves in existing design codes. In the development of this model, a number of important issues including the actual hoop strains in FRP jackets at rupture, the sufficiency of FRP confinement for a significant strength enhancement, and the effect of jacket stiffness on the ultimate axial strain, were all carefully examined and appropriately resolved. The predictions of the model are shown to agree well with test data. [Copyright &y& Elsevier]

• Pull-out tests conducted on basalt FRP bars in geopolymer concrete. • Analytical analysis of bond between basalt FRP bars and geopolymer concrete. • Determination of bond-slip relationship for basalt FRP-geopolymer concrete system. • Exploring the effects of bar diameter and embedment length on bond behaviour. • Investigation of bond mechanisms through a parametric study. This paper presents an experimental and analytical study of the bond behaviour of basalt fibre reinforced polymer (BFRP) bars in geopolymer concrete (GPC). Pull-out tests were conducted on ribbed BFRP bars embedded in GPC cubes considering different bar diameters (6, 8 and 10 mm) and embedment lengths (5 d b , 10 d b and 15 d b) to investigate their effects on bond behaviour in terms of bond-slip response, bond strength and failure mechanisms. Results indicate that the chemical adhesion is low, and the bond is mainly dependent on mechanical interlocking which stopped when pullout occurred by local crushing of the GPC with the BFRP ribs remaining undamaged, suggesting high rib shear strength. A theoretical bilinear model was used to describe the local bond-slip relationship and the bond interface properties. There exists nonlinear bond stress distribution, especially for longer embedment lengths and lower load levels with a bond stress concentration factor of 3.9. A parametric study was performed to estimate the influences of bar diameter, embedment length and elastic modulus on maximum pull-out load, based on which the load transfer mechanisms between BFRP bars and GPC were explored, and a formula for predicting the bond strength was proposed in comparison with experimental data. [ABSTRACT FROM AUTHOR]

• Recent studies on hybrid FRP-SWSSC structures were reviewed. • Both short-term and long-term performance were presented. • Different types of FRP reinforcement for SWSSC structures were covered. • Research gaps and recommendations for future works were introduced. The use of hybrid seawater sea sand concrete (SWSSC) and fibre reinforced polymer (FRP) composites and, as alternatives for ordinary concrete and conventional carbon steel reinforcement, in coastal areas has attracted researchers' attention. The present paper systematically reviews more than 100 experimental and numerical studies focused on environmental aspects and structural performance of hybrid FRP-SWSSC concrete structures. Besides introducing the ecological benefits of using such advanced and environmentally friendly materials, short and long-term structural performance of FRP-SWSSC structures under different loading configuration and environmental conditions are discussed. Structural performance of different systems, including FRP reinforced SWSSC beams, SWSSC filled FRP tubes, FRP strengthened/wrapped SWSSC members, and glass FRP (GFRP) profiles-SWSSC composite members are presented and discussed. In addition, microstructural properties of materials under different environmental conditions are introduced. Eventually, recommendations for prospect investigations are made. A foundation is provided with this overview which will enable a better understanding of the mechanical and microstructural properties of FRP-SWSSC structures. This overview can also be used to develop design guides for material systems in aggressive environments, particularly in coastal areas. [ABSTRACT FROM AUTHOR]

Seven reinforced concrete (RC) T-beams, comprising two unstrengthened (control) beams and five beams strengthened in shear with embedded FRP bars, were tested to failure. The test parameters were steel-to-FRP shear reinforcement ratio and tension reinforcement ratio. A nonlinear finite element (FE) model was developed, validated and used to conduct parametric studies. The experimental and FE results showed that the concrete and FRP contributions to shear resistance as well as the total shear force capacity all decrease with increasing steel-to-FRP shear reinforcement ratio. The tension reinforcement ratio influenced the failure mode of the tested and modelled beams but had insignificant impact on shear strength enhancement. The experimental results were compared with the FE and Concrete Society Technical Report 55 predictions. The FE model correctly reproduced the experimental results and gave accurate predictions, with a mean predicted-to-experimental ratio of 1.04, whereas TR55 gave conservative predictions, with a mean predicted-to-experimental ratio of 0.42. [ABSTRACT FROM AUTHOR]