Fiber-reinforced Polymer Reinforcement Research Articles

Finite Element Analysis of the Beam-Bond Test of Steel and GFRP Bars with Concrete

The ecological thinking and the development of new materials foreground the composite structures made of FRP (fiber reinforced polymers) and concrete. Before the use in real concrete structures, the material characteristics and composite action with concrete need numerical, analytical, and experimental evaluation. The key to developing the composite action of an FRP reinforcement in concrete is a sufficient bond between the reinforcement and concrete. The GFRP (Glass Fiber Reinforced Polymer) bars as the most common and affordable alternative to steel bars are used in this study to investigate the bond with concrete on the analytical model. The finite element model simulates the beam-bond test of GFRP and steel bars to concrete. The effect of bar diameter and type of reinforcement on the bond behavior are analyzed. Finally, the results obtained from the analytical model are compared with the experimental results from the literature.

FRP Material for the Performance of Bridge Components Reinforcement and Improvement

Most bridges today suffer from ageing as a result of increased uses and the erosion of the natural environment. Engineers often need to focus on the actual strengthening needs in the projects they design, as each method has its own limitations and applicability, and there are gaps in the strengthening and improvement methods for various bridge elements. This paper provides a synthesis of some methods of strengthening bridge elements to facilitate comparison and discussion during construction. The application of Fiber Reinforced Polymer (FRP) materials in bridge engineering is then explored and the different types of FRP materials are compared. The results show that the strengthening methods are more suitable for each bridge member. For bridge decks, the analysis of various FRP reinforcement test results and crack extensions lead to the conclusion that the FRP reinforcement is closer to the modulus of elasticity of concrete and has better coordination of deformation, making it a splitting of concrete. However, when discussing the strengthening of bridge girders and pier members, the type of damage that occurs under different damage and loads is different. Therefore, there are different options and methods for different types of FRP materials.

Acoustic emission characteristics of concrete cylinders reinforced with steel-fiber-reinforced composite bars under uniaxial compression

An experimental study of the acoustic emission characteristics of concrete cylinders reinforced with steel fiber-reinforced composite bars (SFCB) under uniaxial compression was performed. SFCB-reinforced concrete cylinders, plain concrete cylinders, and fiber-reinforced polymer (FRP) bar-reinforced concrete cylinders were tested under uniaxial compression. The entire failure process of different concrete cylinders was monitored in real time using acoustic emissions (AE). Damage characteristics of the cylinders were analyzed using the AE hit number distribution, Ib value analysis method, and AE event location and energy. The Ib value characteristics were closely correlated with the microcracks and their extension inside the concrete cylinders. For the reinforced concrete cylinders, the damages were predominantly microcracks of the concrete observed before the first turning point of the load-displacement curve. Subsequently, damage to the longitudinal SFCBs and FRP bars occurred. The AE characteristic of FRP reinforcement damage was similar to that of the macroscopic crack damage in concrete, that is, with a small Ib value. According to the AE event location analysis, the plain concrete cylinder demonstrated obvious shear failure, which was primarily suppressed in the reinforced concrete cylinders owing to the confinement effect of the spiral. The AE energy released by the compression damage of the longitudinal FRP bar was higher than that released by the tensile damage of the FRP spiral. This could trigger a distinguishable high AE location source amplitude for detecting the compression damage to the FRP bar. The analysis of the AE event distribution characteristics proves that the SFCB has a stable post-yield stage, and the compressive damage process of the SFCB is relatively stable and mild compared with the FRP bars in concrete cylinders.

Numerical performance evaluation of debonding strength in fiber reinforced polymer composites using three hybrid intelligent models

Debonding of the fiber-reinforced polymer (FRP) reinforcement is considered as a significant issue in the concrete design because of shear stresses. The main problem is the potential of brittle debonding failures that can highly reduce the effectiveness of strengthening. Shear bond strength and the governing variables have been empirically analyzed several times; however, these experiments cannot provide accurate predictions due to the complexity of debonding process. In this regard, this paper is aimed to investigate the debonding strength of FRP composites using novel models of Extreme Learning Machine (ELM) in co-operation with Teaching–Learning based Optimization (TLBO), Particle Swarm Optimization (PSO) and gray wolf optimizer (GWO). By comparing corresponding values of coefficient of determination (R2) and root mean square (RMSE) in three hybrid models, the best performance in predicting the debonding strength of FRP composites was obtained for ELM-GWO in comparison with ELM-PSO and ELM-TLBO. Considering the best RMSE value as 0, GWO with RMSE = 2.5057 showed the closest value to 0 compared to PSO (2.73) and TLBO (5.58). On the other hand, since the best value of R2 is closest to 1, GWO with R2 = 0.9504 indicated a better performance compared to PSO (0.9431) and TLBO (0.7554).

Enhancing fire resistance of reinforced concrete beams through sacrificial reinforcement

Due to the superior properties of concrete, structural members made of concrete often satisfy fire requirements specified in codes and standards without special installations or the use of external insulation. A closer examination into fire codal provisions shows that they are primarily founded for new constructions or that which does not suffer from aging or in-service trauma; such as cracking, reinforcement corrosion, creep, etc., all of which can adversely affect the structural response of concrete structures, especially under fire conditions. In order to enhance the fire resistance of concrete structures, this paper presents insights into simple and cost-effective solutions by utilizing sacrificial layer(s) of reinforcement. These solutions capitalize on the natural synergy between reinforcement and concrete and have the potential to mitigate fire-induced cracking and the development of fire-induced large deformation, thereby extending the fire resistance of reinforced concrete beams. The validity and applicability of the proposed concepts are highlighted through a highly complex three-dimensional thermo-mechanical nonlinear-based finite element model. This model was utilized in a series of parametric studies to examine critical parameters influencing the fire response of concrete beams reinforced with steel and fiber-reinforced polymer reinforcement. These parameters include sacrificial reinforcement scheme, size, and material type. It was concluded that the use of sacrificial reinforcement could be beneficial for mitigation purposes or as a repair solution for postfire events.

Parametric Design Studies of Mass-Related Global Warming Potential and Construction Costs of FRP-Reinforced Concrete Infrastructure.

Fibre-reinforced polymers (FRPs) are a promising corrosion-resistant alternative to steel reinforcement. FRPs are, however, generally costly and have a high energy demand during production. The question arises whether the high performance of FRPs and possible savings in concrete mass can counterbalance initial costs and environmental impact. In this paper, a parametric design study that considers a broad range of concrete infrastructure, namely a rail platform barrier, a retaining wall and a bridge, is conducted to assess the mass-related global warming potential and material costs. Design equations are parametrised to derive optimum reinforced concrete cross-sectional designs that fulfil the stated requirements for the serviceability limit state and ultimate limit state. Conventional steel reinforcement, glass and carbon FRP reinforcement options are evaluated. It is observed that the cross-sectional design has a significant influence on the environmental impact and cost, with local extrema for both categories determinable when the respective values become a minimum. When comparing the cradle-to-gate impact of the different materials, the fibre-reinforced polymer-reinforced structures are found to provide roughly equivalent or, in some cases, slightly more sustainable solutions than steel-reinforced structures in terms of the global warming potential, but the material costs are higher. In general, the size of the structure determines the cost competitiveness and sustainability of the FRP-reinforced concrete options with the rail platform barrier application showing the greatest potential.

Use of high spatial resolution distributed optical fiber to monitor the crack propagation of an adhesively bonded joint during ENF and DCB tests

Similarly to other industrial areas, there is a strong interest for the use of bonded FRP (Fiber Reinforced Polymers) repair or reinforcement for steel structures in the case of offshore applications. However, the reliability of the adhesively bonded (FRP) shall stand as high as steel renewal, this requires additional developments, in particular, a complete understanding of the repair mechanical strength which depends on material and interfacial properties. Fracture mechanics is an interesting approach to assess the risk to undergo interlaminar fracture or steel to adhesive interfacial disbonding failure. The experimental determination of the required design values for this an approach (critical toughness) are generally obtained using common tests such as Double Cantilever Beam (DCB), End Notched Flexure (ENF) or Mixed Mode Bending (MMB) tests. These tests require a precise crack length monitoring that is currently carried out using visual observation or Digital Image Correlation (DIC) on the flank of the sample. This may induce error in crack length measurement especially if the crack doesn't remain straight during the test. The paper presents a study of crack front monitoring by a distributed optical fiber as an alternative to the standard techniques to monitor crack front and to determine the critical toughness in mode I and II through respectively, DCB (Double Cantilever Beam) and ENF (End Notched Flexure) tests. Firstly, the issues related to the use of this continuous optical fiber are raised (insertion, precision resolution, measurement noise, exploitation methodologies). Then, some experimental investigations on ENF and DCB tests are presented and analyzed using the proposed methodology to monitor crack propagation using the optical fiber strain measurement. The obtained results are compared, focusing on the proper determination of the critical toughness of the adhesive. These results show that an optical fiber bonded on the surface of the sample can be used to measure and follow the crack propagation during the test which simplifies and adds precision to the standardize critical toughness computation method.

Contribution of Longitudinal NSM-CFRP Bars on the Shear Strength of RC Beams with Varying Depths and Concrete Strengths

To assess experimentally the effect of flexural near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) bars mounted on the sides of beams on the shear strength of reinforced concrete (RC) beams, 18 shear-deficient RC beams were built, strengthened with flexural NSM-CFRP bars, and tested under three-point bending until failure. The variables of the experimental program included the beam depth, the concrete compressive strength, and the flexural fiber-reinforced polymer (FRP) reinforcement ratio. It was observed that the strengthened beams exhibited up to 35% increase in shear capacity over the control beams. It was also observed that the increase in shear strength provided by concrete after strengthening was higher for beams with normal strength concrete when compared to those with higher strength concrete. The results have also revealed that the percent change in shear strength provided by concrete for the strengthened beams decreased with the increase in beam depth. Experimental data from this study showed that current standards become unconservative for beams with large depths. Five different beam shear strength models found in the literature were utilized to predict the shear strength of the tested beams. The models that exhibited the closest agreement with the experimental data were those of the University of Houston and the second order simplified modified compression field theory. It was concluded that flexural longitudinal NSM bars are a viable solution to enhance the shear strength of RC beams and that the shear strength provided by concrete can be accurately quantified using published models.

Structural Performance of Lightweight Aggregate Concrete Reinforced by Glass or Basalt Fiber Reinforced Polymer Bars.

Lightweight aggregate concrete (LWC) and fiber reinforced polymer (FRP) reinforcement are potentially more sustainable alternatives to traditional steel-reinforced concrete structures, offering several important benefits. To further the knowledge in this area, the physical–mechanical properties of LWC produced with 0%, 50%, and 100% expanded clay aggregate were assessed. Subsequently, the flexural behavior of LWC beams reinforced with steel reinforcement and glass and basalt FRP bars was tested. The results of the experimental program allowed quantifying of the effect of expanded clay aggregate incorporation on LWC properties. The use of FRP reinforcement was also compared to steel-reinforced concrete beam behavior. The results of this study can provide additional support for the use of innovative materials such as LWA and FRP reinforcement.

Parametric study and improved capacity model for RC beams strengthened with side NSM CFRP bars

Near Surface Mounted (NSM) fiber reinforced polymer (FRP) technique with rods/strips attached at the bottom face (B-NSM) has become widely used method for retrofitting concrete structures but has several practical limitations such as accessibility problems and premature debonding. A viable alternative by attaching the NSM FRP reinforcement at the side faces (S-NSM) has recently been presented and showed excellent effectiveness in limited research studies. In this study, a robust finite element (FE) model, featuring state-of-the art modelling techniques and nonlinear properties, is developed to study the flexural behaviour of reinforced concrete (RC) beams strengthened with S-NSM FRP bars. After validating its load, strain, and failure mode predictions with 6 full-size beam experiments, the model was used in an extensive parametric study on 108 new models, evaluating the effects of FRP bar diameter (df), strengthening length (SL), groove elevation (hg), tensile steel reinforcement ratio (ρs), and concrete compressive strength (fc’). In general, the beam ultimate load (Pu) increased with SL, df, ρs, and fc’. The beam ductility also seems to be affected by the studied parameters but in general was satisfactory, averaging 2.30 to 2.73. A regression-based formula was presented for the effective FRP bar length, beyond which the brittle concrete peel-off failure is prevented, and Pu becomes constant. A sectional analysis was also performed coupled with regression, resulting in the development of a simple equation to calculate the FRP strain at beam failure and consequently an improved analytical model for predicting Pu.

Flexural response of FRP-strengthened lightweight RC beams: hybrid bond efficiency of L‐shape ribbed bars and NSM technique

This paper presents the results of an experimental study on employing near surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement technique, and L‐shape ribbed bars, for flexural strengthening of lightweight reinforced concrete (RC) beams. 18 RC beams including 14 lightweight RC beams and four normal-weight concrete beams were designed. The beams were strengthened with glass fiber-reinforced polymer (GFRP) bars and carbon fiber-reinforced polymer (CFRP) laminate in bending tests. Test parameters included: (1) different FRP materials (glass bars and carbon sheets), (2) longitudinal steel reinforcement ratio, and (3) type of strengthening technique used (NSM reinforcement or hybrid). The ultimate tensile strength, deflection, compressive and tensile strain of concrete, and failure mode of the beams were examined under four-point flexural test. Results showed that the ultimate strength of all RC beams increased between 33 and 105% compared to the control beam. The ultimate strength of beams reinforced with CFRP in the mid-span region was 10% higher than that of beams strengthened at both ends, although the former exhibited 28% lower ultimate deflection. The ultimate strength and deflection of RC beams strengthened with combined steel reinforcing bars and GFRP bars were 10% and 108% higher, respectively, compared to those of RC beams strengthened with GFRP bars only. Hybrid L‐shape ribbed bars beams showed a considerably higher ductility (up to 170% increase in the ultimate deflection) compared to other beams. The comparison of the experimental results of the ultimate strength of the beams with ACI440-2R guidelines indicated a reasonable and conservative prediction of the code expression.

Bond-dependent coefficient and cracking behavior of lightweight self-consolidating concrete (LWSCC) beams reinforced with glass- and basalt-FRP bars

Crack width is one of the issues that can often control the design of flexural elements reinforced with fiber-reinforced polymer (FRP) bars due to the relatively low modulus of elasticity. This paper aims at investigating the cracking behavior of lightweight self-consolidating concrete (LWSCC) beams reinforced with glass- and basalt-FRP (GFRP and BFRP) bars and evaluating the bond-dependent coefficient (kb) values. Fifteen reinforced concrete specimens 200 mm in width, 300 mm in height, and 3100 mm in length were prepared and tested up to failure. Twelve specimens were made using LWSCC, while the other three were made with normal-weight concrete (NWC) as reference specimens. The test variables were concrete density (LWSCC and NWC); reinforcement type (GFRP and BFRP bars) with various surface conditions (sand-coated and helically grooved); and longitudinal reinforcement ratio. The experimental results show that the FRP-reinforced LWSCC (FRP-LWSCC) beams exhibited cracking behavior similar to that of the counterpart FRP-reinforced NWC (FRP-NWC) beams. The FRP-LWSCC beams had a linear crack response up to failure by concrete crushing, regardless of the amount and surface condition of the FRP reinforcement. Moreover, the recorded crack widths of the FRP-LWSCC beams are presented and compared to those predicted according to FRP design provisions. The comparisons indicate that the crack widths of the FRP-LWSCC beams can be estimated with the FRP design provisions with a variable degree of conservativeness. Furthermore, the determination of the kb factor reveals that the sand-coated GFRP and BFRP bars yielded smaller kb values than the helically grooved GFRP and BFRP bars.

Evaluation and modification of bend corner strength prediction models of FRP reinforcement

AbstractThe bend corner of Fiber‐reinforced polymer (FRP) reinforcement has been shown significantly lower tensile strength than the straight portion. To date, various prediction models were developed for the bend corner strength. In this study, three types of six prediction models are reviewed and evaluated based on a most extensive database to date, including tests from 15 investigations from 1999 to 2020. The validities of the models for cross‐section types and test methods are analyzed. The logarithmic and linear regression models are further modified. The macro‐mechanical model provides the best predictions for the whole database with similar validity for test specimens with different cross‐section types. The linear regression and logarithmic models show lower accuracy and inconsistency in cross‐section types. The different test methods adopted in the literature show limited influence on the bend corner strength and the performance of the prediction models. The proposed cross‐section geometry factor can effectively consider the cross‐section types and the modified linear regression and logarithmic models could provide more accurate predictions. The model evaluations and modifications in this study could provide a more comprehensive understanding of the calculation philosophy of the bend corner strength of FRP reinforcement, which could be used for the future updates of shear design provisions for FRP reinforced concrete structures.

Assessment of punching shear strength of FRP-RC slab-column connections using machine learning algorithms

Recently, the use of fiber-reinforced polymer (FRP) bars replacing steel reinforcement has been widely applied to overcome the corrosion issue, particularly concrete slab-column connections using FRP bars as flexural reinforcement (FRP-RC slabs). However, experimental studies showed that the use of FRP differentiates the punching shear behavior from steel-RC slabs. Various methods have been proposed to predict the punching shear strength of FRP-RC slabs, but existing design equations need improvement because their accuracy is low with wide scatteredness. Thus, this study aims at pioneering the application of machine learning (ML) algorithms for the prediction of the punching shear strength of FRP-C slabs without shear reinforcement. For this purpose, an experimental database with 104 specimens was compiled, with the input variables of the shear span-to-effective depth ratio, column perimeter-to-effective depth ratio, effective slab depth, concrete compressive strength, FRP reinforcement ratio, and ultimate tensile strength and elastic modulus of FRP. Three ML algorithms, including support vector regression (SVR), random forest (RF), and extreme gradient boosting (XGBoost), were evaluated for the application. To develop the ML-based models, a grid search method with a 5-fold cross-validation approach was used in the training process to determine the optimal hyperparameters. The performance of the ML-based models was estimated using various statistical estimators and compared with the current design codes and existing models. The comparisons showed that all three ML-based models could accurately predict the punching shear strength of the FRP-RC slabs without any significant and evident bias with the input variables. The XGBoost-based model displayed the best prediction with the coefficient of determination (R2) of 0.962, the root mean square error (RMSE) of 0.061 MN, mean absolute error (MAE) of 0.035 MN, and mean absolute percent error (MAPE) of 8.931% for testing dataset. The correlation coefficient, feature score, and sensitive analysis for the input variables indicated that the effective slab depth has the most substantial influence on the prediction performance. The prediction by the XGBoost-based model was more accurate and robust than that by the SVR- and RF-based models, current design codes, and existing models. These analysis results proved that the XGboost-based model can be used in the design and evaluation of FRP-RC slabs reliably and precisely.

Influence of Bond Characterization on Load-Mean Strain and Tension Stiffening Behavior of Concrete Elements Reinforced with Embedded FRP Reinforcement.

Based on the characterization of the bond between Fiber-Reinforced Polymer (FRP) bars and concrete, the structural behavior of cracked Glass-FRP (GFRP)-Reinforced Concrete (RC) tensile elements is studied in this paper. Simulations in which different bond-slip laws between both materials (FRP reinforcement and concrete) were used to analyze the effect of GFRP bar bond performance on the load transfer process and how it affects the load-mean strain curve, the distribution of reinforcement strain, the distribution of slip between reinforcement and concrete, and the tension stiffening effect. Additionally, a parametric study on the effect of materials (concrete grade, modulus of elasticity of the reinforcing bar, surface configuration, and reinforcement ratio) on the load-mean strain curve and the tension stiffening effect was also performed. Results from a previous experimental program, in combination with additional results obtained from Finite Element Analysis (FEA), were used to demonstrate the accuracy of the model to correctly predict the global (load-mean strain curve) and local (distribution of strains between cracks) structural behavior of the GFRP RC tensile elements.

Structural behavior of FRP connector enabled precast geopolymer concrete sandwich panels subjected to one-side fire exposure

Precast concrete sandwich panel (PCSPs), consisting of two reinforced concrete (RC) wythes (i.e., interior and exterior), a core insulation layer and connectors, can help to improve the building energy efficiency. This study is concerned with the fire and post-fire residual performance of an innovative PCSP system, in which fiber-reinforced polymer (FRP) reinforced geopolymer concrete is used as the two wythes and FRP tubes are used as the connectors. Six PCSP specimens were fabricated and five of them were tested under one-side fire exposure. The experimental parameters included the concrete type (geopolymer and conventional concrete), the reinforcement type (basalt FRP reinforcement and steel reinforcement), the connector type (plate-type and hexagonal tubular type), and the RC wythe thickness. After the fire exposure, all the specimens were tested under concentric loading to evaluate their residual axial load capacity. In addition, numerical analysis was conducted to facilitate a better understanding on the experienced temperature field of the PCSPs. It was found that the PCSPs with geopolymer concrete exhibited a decrease of the axial load capacity by 88.5% after 4 h one-side fire exposure while they performed better than that with conventional concrete. Besides, the reinforcement type, RC wythe thickness and the connector type are key factors influencing the post-fire structural performance of the PCSPs.

Flexural strength of Glass fiber reinforced polymer concrete beam with artificial Fine aggregate

Reinforced concrete Structures with usual steel reinforcements pose a serious threat in aggressive climate factors due to the increasingly rapid concern of corrosion. Because of their resistance to corrosion, high strength-to-weight ratios, and ease of handling, Glass Fiber Reinforced Polymer (GFRP) bars are becoming the emerging technology of the future. Another major issue is scarcity of river sand for making concrete. Hence a research was carried out on concrete mix with artificial M sand for partial fragment of river sand and GFRP bars replacing conventional steel reinforcement.Consequently, an attempt was explored on flexural strength of M40 grade concrete beam reinforced with GFRP (glass fiber-reinforced polymer) reinforcement and mixed with artificial sand or M sand as fine aggregate. A comparative analysis was made between tensile strength of GFRP reinforcement and conventional reinforcement, flexural behaviour of rectangular conventional concrete beam and concrete beam using M sand reinforced with GFRP reinforcement. From the test result, it was found that the beam with combination of GFRP and M sand is achieving 12% higher flexural strength than ordinary conventional concrete beam and withstanding higher deflection.

Experimental testing of residual strain and displacement development in pretensioned BFRP reinforced concrete beams

The utilisation of fibre reinforced polymers (FRPs) as reinforcement for concrete elements has attracted attention mainly due to their high tensile strength, light weight and corrosion resistance. Lately, there has been an interest in basalt FRPs as a more economically competitive and environmentally friendly option. Basalt FRP is manufactured from a widely available volcanic rock in a process which does not require any additives, giving it an edge over the currently more popular glass-fibre reinforced plastic (GFRP) reinforcement. Pretensioning of FRP reinforcement with low longitudinal modulus of elasticity, such as GFRP and BFRP has been proposed as an effective solution to the concerns regarding the serviceability performance of flexural elements reinforced with these composite materials. In previous research it has been demonstrated that prestressing even at low levels can significantly reduce deflections and postpone cracking of BFRP reinforced concrete elements. This research presents an experimental investigation of pretensioned BFRP reinforced concrete tested under quasi-static loading and unloading cycles at 5kN load increments until failure. A comparison with an unprestressed sample is also provided to examine the effectiveness of prestressing at improving the structural performance of the beams. The samples were equipped with internal strain gauges and linear displacement transducers to monitor the development of strains in the reinforcement, deflections and concrete surface strains during testing. Close monitoring of the anchorage zone and the development of cracks was also conducted. Based on the experimental results it can be concluded that the prestressing of BFRP reinforced beams delays the development of residual strains and residual displacements upon unloading. Furthermore, the increase in the prestress level further reduced the residual strain and displacements.

Out-of-Plane Strengthening of Unreinforced Masonry Walls by Glass Fiber-Reinforced Polyurea

Fiber-reinforced polymer reinforcement or polyurea reinforcement techniques are applied to strengthen unreinforced masonry walls (UMWs). The purpose of this experimental study is to verify the out-of-plane reinforcing effect of sprayed glass fiber-reinforced polyurea (GFRPU), which is a composite elastomer made of polyurea and milled glass fibers on UMW. The out-of-plane strengths and ductile behaviors based on various coating shapes are compared in this study. An empirical formula to describe the degree of reinforcement on the out-of-plane strength of the UMW is derived based on the experimental results. It is observed that the peak load-carrying capacity, ductility, and energy absorption capacity gradually improve with an increase in the strengthening degree or area. Compared with the existing masonry wall reinforcement method, the GFRPU technique is a construction method that can help improve the safety performance along with ease of construction and economic efficiency. Doi: 10.28991/CEJ-2022-08-01-011 Full Text: PDF

Bond Tests on Clay Bricks and Natural Stone Masonry Externally Bonded with FRP.

Nowadays, the solution of durability problems of existing buildings has a key role in civil engineering, in which there is an ever-increasing need for building restorations. Over the past 50 years, there is a growing interest in a new composite material, fibre-reinforced polymer (FRP), suitable for increasing the resistance and the stability of existing buildings and, consequently, for extending their service life. In this context, the effectiveness of the strengthening system is related to the bond behaviour that is influenced by several parameters such as bond length, the stiffness of the reinforcement, the mechanical properties of the substrate, environmental conditions, etc. This paper aims to analyse the main experimental results from shear tests performed on two kinds of masonry substrates and different types of FRP reinforcements. The purpose is to highlight the role played by many parameters to the bond behaviour of these systems: the mechanical properties of substrates; the stiffness of reinforcements; the type of supports (i.e., unit or masonry unit). The obtained experimental results underlined that the specimens realised with masonry unit show an increase in debonding load and different stress transfer mechanisms along the bonded length with respect to the specimens with a unit substrate. The analysis of the data revealed that the presence of mortar joints cannot be neglected because it influences the interface global performance.