Fiber-reinforced Polymer Reinforcement Research Articles

Composite Fiber Wrapping Techniques for Enhanced Concrete Mechanics

This study systematically investigates the enhancement effects of different fiber-reinforced polymer (FRP) materials on the axial compressive performance of concrete. Through experimental evaluations of single-layer, double-layer, and composite FRP reinforcement techniques, the impact of various FRP materials and their combinations on concrete’s axial compressive strength and deformation characteristics was assessed. The results indicate that single-layer CFRP reinforcement significantly improves concrete axial compressive strength and stiffness, while double-layer CFRP further optimizes stress distribution and load-bearing capacity. Among the composite FRP reinforcements, the combination with CFRP as the outer layer demonstrated superior performance in enhancing the overall structural integrity. Additionally, numerical analyses of the mechanical behavior of the reinforced structures were conducted using ABAQUS 2023HF2 finite element software, which validated the experimental findings and elucidated the mechanisms by which FRP influences the internal stress field of concrete. This research provides theoretical support and empirical data for the optimized design and practical application of FRP reinforcement technologies in engineering.

Seismic Retrofit Case Study of Shear-Critical RC Moment Frame T-Beams Strengthened with Full-Wrap FRP Anchored Strips in a High-Rise Building in Los Angeles

This paper discusses the iteration of a seismic retrofit solution for shear-deficient end regions of 19 reinforced concrete (RC) moment-resisting frame (MRF) T-beams located in a 12-story RC MRF building in downtown Los Angeles, California. Local strengthening with externally bonded (EB) fiber-reinforced polymer (FRP) fabric was chosen as the preferred retrofit strategy due to its cost-effectiveness and proven performance. The FRP-shear-strengthening scheme for the deficient end-hinging regions of the MRF beams was designed and evaluated through large-scale cyclic testing of three replica specimens. The specimens were constructed at 4/5 scale and cantilever T-beam configurations with lengths of 3.40 m or 3.17 m. The cross-sectional geometry was 0.98 × 0.61 m with a top slab of 1.59 m in width and 0.12 m in thickness. Applied to these specimens were three different retrofit configurations, tested sequentially, namely: (a) unanchored continuous U-wrap; (b) anchored continuous U-wrap with conventional FRP-embedded anchors at the ends; and (c) fully closed external FRP hoops made of discrete FRP U-wrap strips and FRP through-anchors that penetrate the top slab and connect both ends of the FRP strips, combined with intermediate crack-control joints. The strengthening concept with FRP hoops precluded the premature debonding and anchor pullout issues of the two more conventional retrofit solutions and, despite a more challenging and labor-intensive installation, was selected for the in-situ implementation. The proposed hooplike EB-FRP shear-strengthening scheme enabled the deficient MRF beams to overcome a 30% shear overstress at the end-yielding region and to develop high-end rotations (e.g., 0.034 rad [3.4% drift] at peak and 0.038 rad [3.8% drift]) at strength loss for a beam that, otherwise, would have prematurely failed in shear. These values are about 30% larger than the ASCE 41 prescriptive value for the Life Safety (LS) performance objective. Energy dissipation achieved with the fully closed scheme was 108% higher than that of the unanchored FRP U-wrap and 45% higher than that of the FRP U-wrap with traditional embedded anchors. The intermediate saw-cut grooves successfully attracted crack formation between the strips and away from the FRP reinforcement, which contributed to not having any discernable debonding of the strips up to 3% drift. This paper presents the experimental evaluation of the three large-scale laboratory specimens that were used as the design basis for the final retrofit solution.

Numerical investigation on a precast bridge using GPC and BFRP reinforcements subjected to cross-fault rupture and fling step excitation

This study investigates the seismic performances of a precast bridge made of geopolymer concrete (GPC) with fibre-reinforced polymer (FRP) reinforcements subjected to cross-fault ground motions. A numerical model was developed and verified against experimental results from a previous study and then used to evaluate the bridge's performances under earthquake excitations. The study found that a simplified model was able to reliably capture the failure pattern and displacement response of the bridge, reducing simulation time significantly. Additionally, the numerical results indicated the combination of torsional and flexural cracks was the primarily damage mode of the columns, which was not observed in the experimental test. This study also revealed that while the performances of the bridge using ordinary Portland cement (OPC) and GPC were similar under low ground excitations, GPC columns were more susceptible to brittle failure under higher ground excitations due to their brittleness. The use of FRP reinforcements led to similar displacement response as steel reinforcements under low ground displacement excitation, although severe flexural and shear damages on the column of Bent 2 were observed due to the lower elastic modulus and shear resistance of Basalt FRP material than steel. To address the disadvantages of brittle GPC and low-modulus of basalt FRP reinforcements, it is suggested to reinforce GPC with fibres and/or increase stirrup ratios if green GPC and corrosion-resistant basalt FRP reinforcements are used to construct bridges for seismic resistance.

Shear performance of FRP panel-reinforced rc columns attached using corner angles and bolts without epoxy resin

As the frequency of earthquakes has risen globally, the importance of seismic design in building construction has intensified. Fiber-reinforced polymers (FRP) are increasingly utilized as seismic reinforcement materials for reinforced concrete (RC) columns because of their lighter weight and superior strength compared to concrete and steel. However, the epoxy resin commonly used for FRP reinforcement is susceptible to fire, as it exhibits a glass transition temperature below 100 °C, and its performance can vary depending on the skill of the applicator. A method was therefore proposed to involve the non-adhesive application of FRP panels using corner angles and angle connections, eliminating the need for epoxy resin. Experimental and analytical studies were conducted to assess the shear performance of FRP-reinforced RC columns without adhesive attachment. The findings revealed that the maximum shear force capacity increased by more than 1.5 times compared to traditional RC columns. By securing the corner angle and FRP panel with angle connection materials, the attachment effect can be maximized to the extent of the corner angle area, suggesting its potential for enhancing shear performance.

Machine-Learning-Based Predictive Models for Punching Shear Strength of FRP-Reinforced Concrete Slabs: A Comparative Study

This study is focused on the punching strength of fiber-reinforced polymer (FRP) concrete slabs. The mechanical properties of reinforced concrete slabs are often constrained by their punching shear strength at the column connection regions. Researchers have explored the use of fiber-reinforced polymer reinforcement as an alternative to traditional steel reinforcement to address this limitation. However, current codes poorly calculate the punching shear strength of FRP-reinforced concrete slabs. The aim of this study was to create a robust model that can accurately predict its punching shear strength, thus improving the analysis and design of composite structures with FRP-reinforced concrete slabs. In this study, 189 sets of experimental data were collected, and six machine learning models, including linear regression, support vector machine, BP neural network, decision tree, random forest, and eXtreme Gradient Boosting, were constructed and evaluated based on goodness of fit, standard deviation, and root-mean-square error in order to select the most suitable model for this study. The optimal model obtained was compared with the models proposed by codes and the researchers. Finally, a model explainability study was conducted using SHapley Additive exPlanations (SHAP). The results showed that random forests performed best among all machine learning models and outperformed existing models suggested by codes and researchers. The effective depth of the FRP-reinforced concrete slabs was the most important and proportional to the punching shear strength. This study not only provides guidance on the design of FRP-reinforced concrete slabs but also informs future engineering practice.

Machine Learning-Based Prediction Models for Punching Shear Strength of Fiber-Reinforced Polymer Reinforced Concrete Slabs Using a Gradient-Boosted Regression Tree.

Fiber-reinforced polymers (FRPs) are increasingly being used as a composite material in concrete slabs due to their high strength-to-weight ratio and resistance to corrosion. However, FRP-reinforced concrete slabs, similar to traditional systems, are susceptible to punching shear failure, a critical design concern. Existing empirical models and design provisions for predicting the punching shear strength of FRP-reinforced concrete slabs often exhibit significant bias and dispersion. These errors highlight the need for more reliable predictive models. This study aims to develop gradient-boosted regression tree (GBRT) models to accurately predict the shear strength of FRP-reinforced concrete panels and to address the limitations of existing empirical models. A comprehensive database of 238 sets of experimental results for FRP-reinforced concrete slabs has been compiled from the literature. Different machine learning algorithms were considered, and the performance of GBRT models was evaluated against these algorithms. The dataset was divided into training and testing sets to verify the accuracy of the model. The results indicated that the GBRT model achieved the highest prediction accuracy, with root mean square error (RMSE) of 64.85, mean absolute error (MAE) of 42.89, and coefficient of determination (R2) of 0.955. Comparative analysis with existing experimental models showed that the GBRT model outperformed these traditional approaches. The SHapley Additive exPlanation (SHAP) method was used to interpret the GBRT model, providing insight into the contribution of each input variable to the prediction of punching shear strength. The analysis emphasized the importance of variables such as slab thickness, FRP reinforcement ratio, and critical section perimeter. This study demonstrates the effectiveness of the GBRT model in predicting the punching shear strength of FRP-reinforced concrete slabs with high accuracy. SHAP analysis elucidates key factors that influence model predictions and provides valuable insights for future research and design improvements.

A Reliability-Based Design Approach for the Flexural Resistance of Compression Yielded Fibre-Reinforced Polymer (FRP)-Reinforced Concrete Beams

Fibre-reinforced polymer (FRP) reinforcement has been employed as an alternative to conventional steel reinforcement in concrete structures, which is attributed to its excellent strength and corrosion resistance. However, one drawback is that FRP reinforcements are brittle and affect the ductility of concrete structures. One of the recent effective techniques proposed to overcome ductility issues is the compression yielding (CY) concept. The CY mechanism allows the structure to fail differently than the conventional FRP-reinforced concrete structure. Thus, the existing design recommendations as per the current codes for FRP-reinforced concrete structures are not appropriate. Hence, reliability studies are crucial for the development of a functional CY beam design in order to emphasise the structure’s lifetime performance and to guarantee safety requirements. In this study, a reliability-based design approach is developed for a compression-yielded FRP-reinforced concrete beam (CY beam) using load and resistance factor design (LRFD). Firstly, the flexural failure modes of CY beams are discussed. The uncertainties involved in the development of the probabilistic model for the CY beam are defined. A case study is consequently conducted for a CY beam with random variables that are associated with the statistical characteristics of material properties and load. The reliability analysis method employed in this research is the Hasofer–Lind method. The results suggest the importance of choosing appropriate design variables and stochastic parameters for CY blocks that contribute to a higher level of reliability. The reliability index and resistance factors of a CY beam are then evaluated using the Monte Carlo Simulation computational method. The reliability index value of 3.336 is obtained from the simulation, which indicates that the CY beam demonstrates ductile behaviour. The results not only demonstrate ductile behaviour but also contribute to a possible reduction in material costs and a substantial safety margin. When compared to conventional FRP-reinforced concrete beams, for different load ratios, CY beams showed higher resistance and better reliability levels.

Experimental Study of the Flexural Performance of GFRP-Reinforced Seawater Sea Sand Concrete Beams with Built-In GFRP Tubes.

The use of seawater sea sand concrete (SSSC) and fiber-reinforced polymer (FRP) has broad application prospect in island and coastal areas. However, the elastic modulus of FRP reinforcement is obviously lower than that of ordinary steel reinforcement, and the properties of SSSC are different from that of ordinary concrete, which results in a limit in the bearing capacity and stiffness of structures. In order to improve the flexural performance of FRP-reinforced SSSC beams, a novel SSSC beam with built-in glass FRP (GFRP) tubes was proposed in this study. Referring to many large-scale beam experiments, one specimen was used for one situation to illustrate the study considering costs and feasibility. Firstly, flexural performance tests of SSSC beams with GFRP tubes were conducted. Then, the effects of the GFRP tubes' height, the strength grades of concrete inside and outside the GFRP tubes, and the GFRP reinforcement ratio on the flexural behaviors of the beams were investigated. In addition, the concept of capacity reserve was proposed to assess the ductility of the beams, and the interaction between the concrete outside the GFRP tube, the GFRP tube and concrete inside the tube was discussed. Finally, the formulas for the normal section bearing capacity of beams with built-in GFRP tubes were derived and verified. Compared to the beam without GFRP tubes, under the same conditions, the ultimate bearing capacities of the SSSC beam with 80 mm, 100, and 200 mm height GFRP tubes were increased by 17.67 kN, 24.52 kN, and 144.42 kN, respectively.

Monotonic and cyclic flexural performance of timber beams strengthened with glass fiber-reinforced polymer rods using near-surface mounted technique

Wood has gained widespread use as a construction material for structures. The strengthening of timber structures using fiber-reinforced polymer (FRP) reinforcement remains challenging. This paper presents an experimental investigation of timber beams strengthened with glass FRP (GFRP) rods subjected to flexure. Sixteen specimens, including four un-strengthened beams (control beams) and twelve strengthened beams, were tested. The beam dimensions were 45 mm in width, 95 mm in depth, and 1800 mm in length. The GFRP rods were retrofitted the beam soffit applying near-surface mounted (NSM) method. The test variables included the GFRP ratios by volume (i.e., 0 %, 0.59 %, 0.88 %, and 1.32 %) and the loading types of monotonic and cyclic loading conditions. The flexural performance of the beams, including the capacity, mid-span deflection versus load, displacement at the peak load, initial stiffness, energy absorption, and failure mode are assessed. Additionally, the cross-section equilibrium analysis of the GFRP-reinforced timber beams is implemented to compare against the experimental results. The experimental results indicated that the GFRP rods can enhance the flexural effectiveness of the strengthened beams subject to both monotonic and cyclic tests. Compared with the reference beams, the GFRP-retrofitted beams showed an increase by 20 %− 61 % in load-carrying capacity, by 58 %− 71 % in initial stiffness, and by 35 %− 96 % in energy absorption under monotonic loading. Meanwhile, under cyclic loading, the GFRP-reinforced timber beams exhibited an increase by 22 %− 75 % in maximum load, by 58 %− 90 % in initial stiffness, and by 19 %− 37 % in energy absorption. On other hand, the flexural moment resistance of GFRP-reinforced timber beams predicted by the section analysis depicts a good agreement compared to experimental results.

Investigating the efficiency and reliability of different lap-splice configurations in NSM BFRP rods for strengthening RC beams

The use of near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement has shown great promise for flexural and shear strengthening of reinforced concrete (RC) members. However, the continuity of NSM FRP rods is often interrupted due to length constraints, necessitating lap splices to transfer forces between spliced rods. The performance of lap splices depends on design configuration factors, including anchorage shape, splice length, and connection method. This research describes an experimental investigation into the bond behaviour and failure mechanisms of various lap splice designs for NSM basalt FRP (BFRP) rods in RC beams. The parameters investigated were end anchorage shape (straight or Embedded Through-Section (ETS) anchors), and connection type (overlay rods or face-to-face with FRP sheet wrap). A total of 8 simply supported RC beams strengthened with different NSM BFRP lap splice configurations were tested under four-point bending. The load-deflection response, strain distribution, and failure modes were evaluated. Test results showed that beams with NSM FRP rods with ETS anchors exhibited higher bond strength and ductility than face-to-face connections. The outcomes of this study can help optimize lap splice design and detail provisions for NSM FRP systems in future strengthening applications.

Flexural loading test of a tunnel lining concrete model strengthened with carbon-fiber composite cables

In general, incorporating fiber-reinforced polymer reinforcements into arch-shaped tunnel lining concrete (TLC) is challenging. To overcome this, the TLC can be strengthened by combining a flexible carbon-fiber composite cable (CFCC) with the near-surface mounted (NSM) technique. Thus, this study evaluated the load-carrying capacity of arched concrete members strengthened by NSM–CFCC and investigated the effectiveness of the strengthening system for TLC. To measure the load-carrying capacity of arched concrete members, a specialized loading system was fabricated to conduct flexural loading tests on TLC models. The primary test models were the reference TLC models without reinforcement. TLC models bonded with a carbon-fiber sheet (CFS), and NSM–CFCC-strengthened TLC models, and two types of NSM–CFCC TLC models were tested. Eight TLC models were constructed using the conventional NSM technique in which the CFCC was embedded into a cementitious material-filled groove. The results revealed that the TLC member was not perforated by a flexural crack, even in non-strengthened concrete, owing to the arch effect. The load-carrying capacity of the NSM–CFCC TLC was remarkably higher than that of the reference and CFS strengthening models. The ultimate failure of all TLC members was caused by the crushing of the upper concrete. A finite difference analysis (FDA) for the loading test was also performed using commercial software FLAC3D. The numerical simulation results were found to be in good agreement with the cracking behavior of the strengthened TLC members observed in the experiment. These results suggest that the strengthening system using NSM–CFCC is effective for the TLC.

Predicting the shear strength of rectangular RC beams strengthened with externally-bonded FRP composites using constrained monotonic neural networks

Fiber-reinforced polymer (FRP) composites bonded externally to reinforced concrete beams have shown promise for increasing shear load-carrying capacity. However, accurately predicting the shear strength contribution of FRP remains challenging due to the complexity of the shear failure mechanisms and interactions between the contributing components. Existing design provisions have limitations in modeling this behavior. Recently, machine learning has shown promise for addressing such complex problems but lacks transparency. Therefore, this study developed a data-driven Constrained Monotonic Neural Network (CMNN) approach implemented using Python libraries Keras and Tensorflow, which integrates domain knowledge to provide reliable FRP shear-strength predictions. This framework directly encodes expected monotonic input-output relationships through constraints, harnessing both predictive power and monotonicity guarantees. A comprehensive database of 273 beam tests was used to train and evaluate the model. Bayesian optimization through the Optuna framework and 4-fold cross-validation were used to tune the hyperparameters of the CMNN model. Extensive evaluation demonstrated the CMNN model's superior accuracy, yielding an R² value over 0.9, a CI above 0.93 and a low MAE under 16 kN on both training and unseen test data. The model also outperformed existing design code provisions, achieving significantly optimal performance metrics across various strengthening configurations. The analysis of the predictions revealed logical sensitivity trends aligned with the principles of shear mechanics. Such physics-informed machine learning presents a next-generation technique for performance-based structural design, contributing an effective and interpretable tool to advance knowledge on quantifying the shear capacity contribution of externally bonded FRP reinforcement in concrete beams.

Behavior of concrete voussoir flexible arch bridges reinforced with FRP composites

Flexible arch bridges, which can be pre-fabricated, transported and assembled on-site, have become increasing popular. This study presents an experimental investigation into the behavior of concrete voussoir flexible arch bridges reinforced with fiber-reinforced polymer (FRP) sheets by loading four arch specimens to failure at their left third-spans. The variables included the concrete voussoir strengths, bond quality between FRP and concrete voussoirs, and the FRP reinforcement locations. The results showed that two specimens with good bonding between FRP sheets and concrete voussoirs failed from sudden FRP rupture, while the other two specimens experienced FRP debonding and ultimately exhibited a four-hinge collapse mechanism. For the specimens with good FRP bonding, the typical load-deflection curve obtained at the loading point was an approximately monotonic increasing line, while load reductions and recoveries, as well as slope deteriorations were noted for the specimens experienced FRP debonding. It is also compared that bond quality could be more important than concrete voussoir strength, as the specimens with good bonding had higher ultimate load capacities. Applying one additional FRP sheet at intrados of arch could significantly enhance the initial ascending slope by 100%, but it cannot enhance the peak load as the FRP sheet at extrados of arch was more efficiently utilized in preventing more hinge formations at extrados joints.

Shear strength model of FRP-reinforced concrete beams without shear reinforcement

The current design codes for evaluating the shear strength of concrete beams reinforced with fiber-reinforced polymer (FRP) bars predominantly rely on a semi-empirical approach through test data calibration without a robust theoretical background. This approach may lead to either overestimation or underestimation, resulting in significant scattering in strength predictions. This study proposed a modified approach to enhance the existing unified shear-strength model developed for steel-reinforced concrete (RC) beams based on the compression zone failure mechanism, for predicting the shear strength of FRP-RC beams without shear reinforcement. The proposed model integrates strain and stress approaches, accounting for the distinctive characteristics associated with FRP reinforcement. Additionally, the overall shear resistance capacity of the FRP-RC beam is considered as the sum of contributions from the intact concrete of the compression zone and the aggregate interlock mechanism. The reliability of the proposed model is verified by comparing its predictions with a comprehensive database comprising 264 FRP-RC beam specimens without shear reinforcement reported by 41 research groups. Furthermore, the accuracy of the proposed model was assessed through a comparative analysis with existing evaluation methods, encompassing machine learning-based models, empirical models, theoretical models, and design codes. The results indicate that the proposed model satisfactorily predicts the shear strength of FRP-RC beams within a wide range of design parameters. In comparison with machine learning-based models, the proposed theoretical model exhibits a similar level of accuracy in terms of the mean shear strength ratio and coefficient of determination (R2) values but with less scattering, indicated by lower coefficient of variation (COV) and root mean square error (RMSE) values. In addition, the proposed model outperforms existing empirical and theoretical models, as well as current design codes, by significantly enhancing prediction accuracy, demonstrated by lower COV, RMSE, and higher R2 values. Finally, a parametric study was conducted to investigate the effects of the key parameters on the shear strength of FRP-RC beams using both the proposed model and representative existing evaluation methods.

Experimental study on shear performance of PET FRP-strengthened RC beams without stirrups

The shear behavior of simply supported RC beams strengthened with polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) was studied in this paper. The test variables include strengthening schemes (i.e., U-wrapping and full-wrapping) and FRP reinforcement ratios. A comprehensive and meticulous investigation was conducted on the failure mode of RC beams, shear force-deflection curves, the development process of shear cracks, the evolution of FRP strain, and the interaction between FRP and concrete. The shear capacity and deformation were increased by 42.5–123.2% and −16.34–96.89% using the fully wrapped scheme, respectively. The improvement in shear capacity was 42.5–72.55% when the U-wrapped scheme was adopted. The PET FRP fully wrapped beams exhibited a type of ductile shear failure. The strain of PET FRP in the fully wrapped specimen exceeded 4% without fracture, ensuring the deformation capacity after the peak load. The shear deformation caused the increase in post-peak mid-span deflection. The U-wrapped specimens showed debonding failure, with the debonding strain of PET FRP being more than that of conventional FRP. Finally, six design guidelines for PET FRP shear contribution were evaluated for both U-wrapped and fully wrapped schemes.

Shear behavior of circular concrete short columns reinforced with GFRP longitudinal bars and CFRP grid stirrups

Although fiber-reinforced polymer (FRP) reinforcements have become popular, the post-pultrusion bending leads to significant deficiency in bent portions of FRP hoops and spirals. This study adopts flexible carbon FRP (CFRP) grids as stirrups, and investigates the shear behavior of circular short columns reinforced with GFRP bars and CFRP grid stirrups. Six specimens with different shear reinforcement ratios, axial load ratios and types of stirrups (CFRP grids and steel hoops) were tested to shear failures. The failure modes, crack and strain developments, and shear load-horizontal displacement responses were presented for discussion. All specimens experienced shear-compression failures, and the critical diagonal crack widths increased approximately linearly with shear loads. The typical shear load-horizontal displacement curve consisted of three branches: a linear elastic branch, a cracking branch with progressive slope deteriorations, and an almost flat failure branch. Increasing CFRP grid stirrup ratio could not only enhance strength and ductility performance, but also alleviate the slope degradations, while increasing axial load ratios could enhance the initial cracking loads, restrain crack propagations, and reduce the lateral displacements. In terms of strength performance, steel hoops could be replaced by CFRP grid stirrups even with smaller stirrup ratio. Additionally, analytical investigations suggested that the effective stresses and strains of CFRP grid stirrups at failure may be lower than code limits.

Mechanical behaviour of TRM and FRP-reinforced concrete voussoir masonry specimens

This research investigates, both experimentally and analytically, the mechanical performance of masonry specimens made with special lightweight concrete voussoirs joined with cement mortar and reinforced with TRM (Textile Reinforced Mortar) made of either fibreglass mesh, TRM with basalt mesh or FRPs (Fiber Reinforced Polymers). The specimens represent a segment of an arch. A total of 18 specimens were tested, with one-third featuring each reinforcement solution. Another variable studied was the number of sides reinforced with TRM or FRP, either one or three. The specimens were tested under eccentric compression to analyze the effectiveness of the reinforcements. An analytical model was calibrated with the experimental results and used to extrapolate the experimental results in terms of strength capacity. The specimens that exhibited the best mechanical behaviours were those reinforced with TRM using basalt mesh. The FRP reinforcement experienced prematurely debonding with the voussoirs.

Punching Shear of FRP-RC Slab–Column Connections: A Comprehensive Database

Several design standards have been developed in the last two decades to estimate the punching capacity of two-way reinforced concrete (RC) slabs reinforced with fiber-reinforced polymer (FRP) reinforcement. FRP-RC design standards include the recently published ACI 440.11-22, CSA/S806-12, and JSCE-2007. These models are either based on empirical data or semi-empirical methods and calibrated using different databases. Additionally, these standards do not have provisions for connections with shear reinforcement. Therefore, a reliable worldwide database for developing and assessing the applicability of such provisions with test results is vital. This study presents a worldwide and up-to-date database for punching shear of FRP-RC slabs. The database includes 197 tested connections, comprising interior and edge connections, with and without shear reinforcement, and a wide range of materials and cross-sectional properties. The database was used to evaluate the accuracy of the mentioned standards in predicting the punching shear capacity. For connections without shear reinforcement, it was determined that the three design standards yielded similar performance with different conservatism levels. ACI 440.11-22 yielded the most conservative results, with average Vexp/Vpred ratios of 2.04 compared to 1.28 and 1.3 for other models. For connection with shear reinforcement, specimens with Evf> 100 GPa resulted in Vexp/Vpred ratios less than 1.0 for ACI and CSA standards.

Insight into the shear failure mechanism of Wound FRP reinforced concrete beams through numerical simulations considering interface damage and material anisotropy

Utilizing the inherent flexibility of high-strength fibres, Fibre-Reinforced Polymers (FRP) can be engineered as optimized reinforcing cages for concrete structures through the application of advanced digital fabrication techniques. However, existing codified design methods and numerical investigations found in the literature fall short in providing an accurate characterization of the actual performance of FRP reinforcement in concrete structures. This work presents a novel Finite Element (FE) modelling approach for concrete beams reinforced with FRP in non-traditional arrangements, accounting for reinforcement-concrete interface behaviour and FRP material anisotropy. Validation against experimental tests of flexible Wound-FRP (W-FRP) reinforced beams demonstrates accurate predictions of load-displacement curves, crack propagation, and load-strain curves. The study delves into shear failure mechanisms, emphasizing FRP reinforcement behaviour and damage evolution at reinforcement-concrete interfaces. Further parametric analysis explores the impact of W-FRP inclination angle and spacing, revealing their significant influence on beam stiffness and ultimate capacity. Specifically, the horizontal tensile force component in inclined links and increased modulus of links with reduced spacing enhance stiffness. Altered crack propagation due to W-FRP patterns, coupled with resulting damage development at concrete-stirrup interfaces and stress evolution in W-FRP stirrups, are key contributors to varied ultimate capacity. Moreover, higher performance of W-FRP stirrups with smaller spacing and reduced cross-section area further bolsters ultimate capacity. This research advances the modelling of FRP-reinforced concrete, offering potential solutions for optimizing FRP material utilization in concrete structures.

Flexural performance of reinforced concrete beams strengthened using near-surface-mounted carbon-fiber-reinforced polymer bars: Effects of bonding patterns

The near-surface-mounted (NSM) fiber-reinforced polymer (FRP) technique is effective for enhancing the load carrying capacity of strengthened reinforced concrete (RC) beams. However, this technique significantly reduces the deformability of strengthened RC beams. To overcome this, the present study combines the NSM strengthening method with the partial bonding technique: the strengthening FRP reinforcement is partially bonded onto the concrete substrate). Six full-scale 4.3 m long RC beams strengthened with NSM FRPs using various bonding patterns were tested. The results indicated that mechanical interlocking grooves slightly improve the load carrying capacity, but have a negligible effect on the deformability of the strengthened beams. A decrease in the bond length increased deformability by 27.2 %, with only a 7.6 % drop in load capacity compared to that of the beam with full bonding. An advanced finite element model was developed and validated to confirm an optimal bond length of 930 mm for maximum flexural performance.