Shear Strengthening Of Reinforced Concrete Beams Research Articles

Strength models of near-surface mounted (NSM) fibre-reinforced polymer (FRP) shear-strengthened RC beams based on machine learning approaches

The shear strengthening of reinforced concrete (RC) beams using near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars/strips has gained substantial research attention worldwide. However, owing to the complex failure mechanisms and many influencing parameters, the shear capacities of NSM FRP shear-strengthened beams are difficult to predict. Accordingly, this study adopted machine learning approaches to predict the shear capacity of strengthened beams. An experimental database was constructed comprising 130 rectangular/T-shaped beams and their 15 parameters, collected from the existing literature. Subsequently, a genetic-algorithm-improved back propagation neural network (GA-BPNN) trained with a Bayesian regularisation (BR) algorithm was employed, which was capable of giving accurate predictions on shear capacities of strengthened beams and own good generalisation ability. Furthermore, the GA-BPNN was used for parametric studies to investigate the parameter effects on the contributions of concrete, steel stirrups, and NSM FRP to the shear capacity. Finally, with reference to the GA-BPNN parametric analyses and existing models, a design-oriented strength model for calculating the shear capacities of NSM FRP shear-strengthened beams was proposed and optimised using the genetic algorithm. A comparison with existing models proved the higher prediction accuracy of the proposed strength model.

The Efficiency of Using Machine Learning Techniques in Fiber-Reinforced-Polymer Applications in Structural Engineering

Sustainable solutions in the building construction industry have emerged as a new method for retrofitting applications in the last two decades. Fiber-reinforced polymers (FRPs) have garnered much attention among researchers for improving reinforced concrete (RC) structures. The existing design guidelines for FRP-strengthened RC members were developed using empirical methods that are based on specific databases, limiting the accuracy of the predicted results. Therefore, the use of innovative and efficient prediction tools to predict the behavior of FRP-strengthened RC members has become essential. During the last few years, efforts have been progressively focused on the use of machine learning (ML) as a feasible and effective technique for solving various structural engineering problems. Its capability to predict the behavior of complex nonlinear structural systems while considering a wide range of parameters offers a distinctive opportunity to make the behavior of RC members more predictable and accurate. This paper aims to evaluate the current state of using various ML algorithms in RC members strengthened with FRP to enable researchers to determine the capabilities of current solutions as well as to find research gaps to carry out more research to bridge revealed knowledge and practice gaps. Scopus databases were searched using predefined standards. The search revealed ninety-six articles published between 2016 and 2023. Consequently, these articles were analyzed for ML applications in the field of FRP retrofitting, including flexural and shear strengthening of RC beams, flexural strengthening of slabs, confinement and compressive strength of columns, and FRP bond strength. The results reveal that 32% of the reviewed studies focused on the application of ML techniques to the flexural and shear strengthening of RC beams, 32% on the confinement and compressive strength of columns, 6.5% on the flexural strengthening of slabs, 22% on FRP bond strength, 6.5% on materials, and 1% on beam–column joints. This research also revealed that the application of various ML algorithms has shown a significant improvement in resistance prediction accuracy as compared with the existing empirical solutions. Supervised learning techniques were the most favorable learning method due to their good generalization, interpretability, adaptability, and predictive efficiency. In addition, the selection of suitable ML algorithms and optimization techniques is found to be mainly dictated by the nature of the problem and the characteristics of the dataset. Nonetheless, selecting the most appropriate ML model and optimization algorithm for each specific application remains a challenge, given that each algorithm is developed with different principles and methodologies.

Strengthening of RC beams in shear with novel near-surface mounted (NSM) U-shaped fiber-reinforced polymer (FRP) composites

Over the last three decades, various researchers have proven the high efficiency of the near-surface-mounted (NSM) fiber-reinforced polymer (FRP) method for strengthening reinforced concrete (RC) beams. The shear strengthening of RC beams by embedding FRP bars or strips onto the side concrete cover is a primary application of NSM FRP investigated in numerous studies. These studies revealed that despite the high bond efficiency between the NSM FRP and concrete, NSM FRP shear-strengthened beams frequently failed in debonding modes, such as FRP–concrete interfacial debonding or side concrete cover separation. Such debonding failures limit the strength utilization and strengthening efficiency of the FRP material. Anchoring measures have been proposed for NSM FRPs to mitigate such debonding failures. However, the manufacturing and installation processes of these anchoring devices are complicated. Moreover, interfacial debonding between the NSM FRPs and anchoring devices can still occur. Therefore, this study proposes a novel NSM U-shaped FRP (NUF) device for the shear strengthening of RC beams. The proposed NUF device was fabricated using a fiber sheet through a wet lay-up process. The device can effectively increase the bond efficiency between the FRP and strengthened beam. The concept, manufacturing, and installation processes of this device are discussed. Subsequently, an experiment was performed on seven full-scale RC beams. The test results showed that the proposed NUF device is able to postpone/prevent the debonding failure between NSM FRP and concrete thus largely increase the strengthening efficiency of NSM FRP method.

External Shear Strengthening of RC Beams with Anchored Geopolymer Fiber Mortar Panel: An Experimental Study

Failure due to shear deficiency in reinforced concrete (RC) structures, particularly RC beams, is one of the most common problems encountered in RC structures. As a result, the effectiveness of using externally anchored geopolymer fiber mortar panels were investigated in the scope of this experimental study. The variable of the test programmed herein was the change in anchor bolt spacing. Two strengthened beams with 200 mm and 300 mm anchor bolt spacings, respectively, were tested. In addition, one un-strengthened beam was prepared as the reference beam to compared the load-deflection behavior, shear capacity, and failure mode of the strengthened beams. All the beams were tested under monotonic loading until reached the failure load. The experimental results of all strengthening beams showed an increase in the shear strength of the RC beams by 34.9% (spacing 200 mm) and 22.8% (spacing of 300 mm) compared to the reference beam. In addition to increasing shear capacity, the failure mode of the strengthened beam with 200 mm anchors spacing changed from brittle shear failure to ductile flexural failure with increased stiffness. This indicated that geopolymer fiber mortar panel is considered a promising technique that could be utilized to repair and rehabilitate shear deficient RC beams.

Effect of maximum coarse aggregate size upon shear strengthening of RC beams using NSM-CFRP strips

Reinforced concrete (RC) is widely used because of its many desirable characteristics, such as high strength, fire resistance, and durability. However, structures that are made of concrete may need strengthening or repairing due to concrete deterioration, the harshness of the environment, steel corrosion, errors in design, and damage caused by earthquake load. The use of composite materials has recently become more popular for strengthening and repairing damaged concrete structures. It is also known that properties of the aggregates, such as shape, size, and surface texture, have important influences on the behavior of concrete. In fact, many studies have shown that changes in coarse aggregate will affect the concrete's strength and fracture properties. Towards this end, very little research has been carried out on the effect of maximum aggregate size (MAS) on the shear behavior of reinforced concrete beams. The impact of maximum coarse aggregate size on shear strengthening using the methods proposed in this study was not studied. This research is driven by both environmental and economic aspects where the use of large-size coarse aggregates provides a large volume and less void space compared to small-size aggregates. From an environmental perspective, such an approach will reduce the need for cement in concrete unit volume, hence reducing the pollution. The main purpose of this study is to examine the behavior of reinforced concrete beams under general loading and how this is affected by using different coarse aggregate sizes. This work’s main objective is to investigate the effect of maximum coarse aggregate size on the shear behavior of reinforced concrete beams and study the effectiveness of using the Near Surface Mounted (NSM) – Carbon Fiber Reinforced Polymer (CFRP) strips technique on the shear strengthening of the RC beams. The experimental variables of the study consist of different maximum coarse aggregate sizes (9.5 mm, 12.5 mm, 19 mm, and 25 mm), Carbon Fiber Reinforced Polymer (CFRP) strips spacing (75 mm and 150 mm), and concrete compressive strength (25 MPa and 40 MPa). Fourteen RC beams (150 mm × 200 mm × 1150 mm) were cast using six mixes of concrete to be prepared and tested. The experimental results showed that using maximum coarse aggregate size has a positive effect on ultimate shear strength, maximum deflections, toughness, and stiffness of strengthened RC beams. Using NSM-CFRP strips change the failure mode from pure shear for the control beams to shear-flexural failure for the strengthened beams, which is an ideal enhancement.

Implementation of Modified Compression Field Theory to Simulate the Behavior of Fiber-Reinforced Polymer Shear-Strengthened Reinforced Concrete Beams under Monotonic Loading

The numerical modeling of structures is a widely preferable approach to investigate the structural behavior of RC beams since it delivers inexpensive predictions for confirming the required goals concurrently with reducing casting, testing time, and effort. Shear-strengthening of reinforced concrete (RC) beams using externally bonded (EB) fiber-reinforced polymers (FRPs) has attracted much attention due to the fact that the FRP strengthening technique has the ability to alter the distribution of stresses between the structural elements and increase the load-carrying capacity. A significant number of experimental studies have been carried out to test the monotonic behavior of FRP shear-strengthened RC beams. Conversely, limited numerical research has been performed to investigate such performance. The VecTor2 software is developed based on the modified compression field theory (MCFT) and is directed to examine the monotonic behavior of retrofitted specimens using fiber-reinforced polymer (FRP) composites. To the authors’ knowledge, the behavior of FRP shear-strengthened beams has not been explored in the literature using the MCFT modeling approach. The main objective of this study is to detect the software’s capability of predicting the experimental outcomes of FRP shear-strengthened RC beams. This research study is carried out in two stages. Initially, the numerical study involves the development of an accurate finite element model to simulate the control specimens. The quality of this model is assessed by comparing the numerical results with the experimental outcomes. In the second phase of the numerical study, the control beam model is modified to accommodate the presence of external FRP composites. The accuracy of this model is again measured by comparing its predictions with the experimental measurements. The goal of these phases is to ensure that the numerical model captures the actual behavior of the tested beams. Additionally, two distinctive modeling approaches are investigated to represent the behavior of FRP composites. The accuracy of the numerical models is verified through comparisons of numerical predictions to experimental results in terms of ultimate loading capacity, load–deflection relationships, and failure modes. It can be stated that the validated numerical model provides alternate means for evaluating the monotonic behavior of both strengthened and non-strengthened RC beams. The predicted results compare very well with the test results of the control specimens when discrete truss elements are employed for the FRP composites. Furthermore, the numerical model provides useful information on the crack patterns and failure modes.

Shear Strengthening of RC Beams Using Fabric-Reinforced Cementitious Matrix, Carbon Plates, and 3D-Printed Strips

Existing reinforced concrete (RC) structures suffer from degradation in their structural capacity. These structures require strengthening and retrofitting to integrate sustainability and improve their serviceability and durability. RC members strengthened with fiber-reinforced polymer (FRP) composites usually suffer from FRP debonding; therefore, researchers proposed several types of sustainable materials to overcome the shortcomings of FRP composites. Limited experimental studies have been conducted for shear strengthening of RC beams using sustainable fabric-reinforced cementitious matrix (FRCM) composites; moreover, the application of 3D-printed strips in strengthening RC beams has never been established. The current research experimentally investigates the efficiency of FRCM composites, 3D-printed sheets (CD), and CFRP plates (CP) in strengthening RC beams that are weak in shear. Various strengthening configurations were adopted, including vertical, oblique, zigzag, and several-slanted layouts. Eight simply supported beams were prepared to find the most efficient shear-strengthening configuration and material for RC beams. Test results showed that FRCM and CP are both efficient for shear strengthening in terms of maximum load capacity, initial stiffness, and ductility. However, CD showed a limited effect on enhancing the performance of shear-strengthened beams. The best shear enhancement was found in the beam strengthened with vertical CP, with improvements in load-carrying capacity, stiffness, and ductility of 43%, 23%, and 23%, respectively. The vertical and oblique strengthening configurations were more efficient than the zigzag and several-slanted layouts. The ACI 440.2R-17 model yielded accurate predictions with an average (Vc, test/Vc, ACI 440) of 1.11.

Shear strengthening of RC beams with NSM FRP strips: Concept and behaviour of novel FRP anchors

The high efficiency of the near-surface mounted (NSM) fibre-reinforced polymer (FRP) technique for improving the shear capacities of reinforced concrete (RC) beams has been proved by numerous studies. However, premature debonding failures including interfacial debonding and concrete cover separation, which could largely limit the utilization of FRP strength, were frequently observed in RC beams strengthened in shear with NSM FRP. Proper anchoring measures of NSM FRPs can mitigate or even prevent such debonding failures and thus enhance the FRP strengthening efficiency, but relevant research on anchoring measures for NSM FRP shear-strengthened beams is still limited. Against the above background, a novel FRP anchor for NSM FRP shear-strengthened beams is proposed in this paper. A test program consisting of eight full-scale RC beams is carried out to investigate the effectiveness of the proposed FRP anchor system. It can be seen from the test results that the proposed FRP anchor is capable of mitigating or preventing the FRP debonding failures and thus significantly enhancing the load-carrying and deformation capacities of RC beams strengthened in shear with NSM FRP strips, and the configuration of the anchor can largely influence the performance of strengthened beams.

Shear strengthening of RC beams using FRCM system made with industrial wastes

In the present study, industrial wastes were used as a partial replacement for cement to form cement-based repair mortars, and the feasibility of using these mortars as the matrix in fiber reinforced cementitious matrix (FRCM) system for shear strengthening of reinforced concrete (RC) beam specimens was investigated. Accordingly, an experimental program comprising two parts was carried out. Firstly, the properties of the mortars were examined through compressive strength, tensile strength, sulfuric acid resistivity, and electrical resistivity tests. Finally, 6 shear-critical RC beam specimens were manufactured, two of which remained un-strengthened acting as control specimens. Two specimens were strengthened in shear by carbon fiber reinforced polymer (CFRP) strips and two specimens were strengthened by fiber reinforced cementitious matrix (FRCM) layers made with prepared mortars. The shear capacity of the specimens was measured through 3-point bending test. The parameters investigated in the beam specimens included the effect of shear strengthening system (FRP/FRCM) and shear span/depth ratio. It was shown that the specimens strengthened by the FRCM system made with waste materials had similar or slightly better performance compared to the FRP strengthened specimens.

Experimental and analytical study for shear strengthening of reinforced-concrete beams using a prefabricated geopolymer–mortar panel

This study investigated the performance of geopolymer–mortar panels (GMPs) in improving the shear capacity of reinforced-concrete (RC) beams. A GMP with a thickness of 15 mm was prefabricated and fixed to the shear span of beams using mechanical anchors. Five RC beams were constructed and tested under a four-point bending monotonic load: one unstrengthened, three strengthened with a GMP, and one strengthened with a Portland-cement-mortar panel. The investigated parameters included (a) anchor-bolt spacing, (b) presence of a wire mesh, and (c) binding material types. The results indicated that the GMP is an effective technique for improving the shear capacity of RC beams. The maximum gain in the shear capacity of the strengthened beams ranged from 14.1% to 34.9% with respect to the unstrengthened beam. Moreover, the results suggested that the failure mode of the beam changed from brittle to ductile failure if an anchor bolt spacing of 200 mm and wire mesh were used at the GMP. Based on these findings, the GMP can be used as an alternative method for shear-strengthening RC beams in building applications owing to its high strength and ductility. Finally, an analytical model based on the simplified-modified–compression-field theory model was proposed to predict the shear capacity of RC beams strengthened with the GMP. The analytical model was in reasonable agreement with the test results.

Examination of parameters impacting flexural and shear strengthening of RC beams

Structural performance of reinforced concrete (RC) structures should be improved due to new design standards, strength reduction, and/or functional changes throughout their service life. To reach a sufficient level of structural performance, the following two options can be considered: reconstruction or strengthening of structures. Although reconstruction has some advantages in terms of using current technological developments, this option can lead to some negative consequences such as interruption of the building's service life, relatively high cost, and sustainability issues. Therefore, strengthening an existing structure mostly stands out as the first choice. The techniques used in strengthening applications can be grouped into two different methods: traditional (addition of new structural members) and non-conventional (seismic base isolation, local retrofitting, and jacketing). Among innovative methods, the fibre-reinforced polymer strengthening method attracts attention due to several advantages including practical applicability, as well as shear and bending capacity increase. Its application to the outer surface of structural members using resin reduces deterioration. Plus, fibres oriented in various directions spread stresses in different directions, therefore, provide effective force distribution. In this study, the effect of carbon fibre reinforced polymer (CFRP) orientation and RC material properties in the strengthening RC beams were investigated using MATLAB software. Accordingly, all stages of the design process are presented for RC beam strengthening considering both flexural and shear effects based on the American Concrete Institute (ACI) 440.2R standard. Through compiling MATLAB code, calculation time reduces, and material characteristics can be obtained more accurately. Plus, using curves obtained by MATLAB coding, shear and bending capacity increases can be observed. According to our findings, the application of one-layer CFRP plate to an RC beam increases the bending capacity by 50.6% and shear capacity by 33.6%. However, as the number of layers increases, the capacity increase rate reduces.

Shear strengthening of RC beams with NSM FRP. I: Review of strength models

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) technique is known as a promising alternative to the externally bonded (EB) FRP technique for strengthening reinforced concrete (RC) members, on account of its many advantages such as high bond efficiency with concrete and good durability. Shear strengthening of RC beams by near-surface mounting the FRP bars/strips into the concrete cover on beam sides is one of the most prevalent applications of NSM FRP. Abundant experimental studies have been conducted to investigate the behaviour of NSM FRP shear strengthened beams, and many strength models for predicting the contribution of NSM FRPs to the shear capacity of the beam have been proposed. The present paper presents a comprehensive review of these strength models, in which all the models collected from the existing literature are first classified into three categories based on their used approach and then summarized and discussed. This paper not only aims to bring a deep understanding of the existing strength models for NSM FRP shear strengthened RC beams, but also provides a background and basis for the assessment of these models by using the newly-generated experimental database in the companion paper.

Shear Enhancement of RC Beams Using Low-Cost Natural Fiber Rope Reinforced Polymer Composites

The aim of this research work is to investigate the efficiency of newly developed Natural Fiber Rope Reinforced Polymer (NFRRP) composites to enhance the shear strength of reinforced concrete (RC) beams. Two types of NFRRP composites were made using low-cost hemp and cotton fiber ropes. The effectiveness of this NFRRP confinement in increasing the shear, energy dissipation, and deformation capacities of concrete beams was studied. The effect of these natural fiber ropes with different configurations on beams was investigated. The responses of seven RC beams with different spacing arrangements of natural fiber ropes were evaluated in terms of shear enhancement, deflection, energy dissipation capacity, effect of strengthening configuration, rope types, and ultimate failure modes. The NFRRP composites exceptionally enhanced the load carrying abilities, energy dissipation, and deformation capabilities of RC beams as compared to the control beam. The ultimate load carrying capacities of natural hemp and cotton Fiber Rope Reinforced Polymer (FRRP) composite confined beams were found to be 63% and 56% higher than that of the control beam, respectively. Thus, the shear strengthening of RC beams using natural fiber ropes is found to be an effective technique. Finite Element Analysis was also carried out by using the Advanced Tool for Engineering Nonlinear Analysis (ATENA) software. The analysis results compare favorably with the tests’ results.

Effectiveness of SHCC strips reinforced with glass fiber textile mesh layers for shear strengthening of RC beams: Experimental and numerical assessments

In the present study, the potential of the use of strain-hardening cementitious composite strips internally reinforced with glass fiber textile mesh layers (GFTM-SHCC) as a strengthening system for shear-critical reinforced concrete (RC) beams is examined. For this purpose, thirteen simply supported beams incorporating two bare control specimens were tested under a three-point loading scheme. The GFTM-SHCC strips were applied inside 20 mm grooves within the beams' substrate so as to prevent the likelihood of premature debonding failure and to significantly enhance the utilization of the adopted strengthening system. The considered key parameters were the layers' number of the GFTM within the SHCC strip (2, 4, or 6), the spacing between GFTM-SHCC strips (90, 150, or 225 mm), the GFTM-SHCC orientation angle (45°, 60°, or 90°), and the strengthening configurations (side-bonded, U-wrapped, or fully-wrapped). Moreover, the location of the strengthening strips relative to the internal stirrups, if they exist, (aligned or un-aligned), was of interest.The effectiveness of GFTM-SHCC was evaluated in terms of failure patterns, ultimate shear capacity, and the gain in ductility. Experimental results revealed the effective implementation of the GFTM-SHCC strengthening strips in improving the ultimate shear capacity and the deformation characteristics of the tested specimens; however, their behavior relied on the test parameters. The shear carrying capacity and the ductility of the strengthened RC beams using GFTM-SHCC strips were in the range of 47–142% and 21–172%, respectively, higher than their counterpart control specimens. Furthermore, among all strengthening configurations, fully-wrapped strengthened RC beams demonstrated the highest gains in shear capacity, while inclined GFTM-SHCC strips with orientation angles of 45° and 60° outperformed vertical strips significantly. An analytical model to predict the ultimate shear capacity of the strengthened RC beams was derived and verified against the experimental results. To further assess the potential of the GFTM-SHCC strips for the shear strengthening of RC beams, a three-dimensional (3D) non-linear finite element model (FEM) was created using ABAQUS software and verified against the experimental records. After affirmation of the satisfactory predictive performance of the numerical model, a parametric study was performed to compare the shear responses of RC beams strengthened with intermittent GFTM-SHCC strips with continuous ones (strengthened along the whole shear span zone).

Shear Strengthening of RC Beams with FRP Composites: Database of FE Simulations and Analysis of Studied Parameters

The use of externally bonded fiber-reinforced polymer (EB-FRP) composites for shear strengthening of reinforced concrete (RC) beams presents many challenges given the complex phenomena that come into play. Premature bond failure, the behavior of the interface layer between FRP composites and the concrete substrate, the complex and brittle nature of shear cracks, and the adverse interaction between internal steel stirrups and EB-FRP are some of these phenomena. Compared to experimental investigations, the finite element (FE) technique provides an accurate, cost-effective, and less time-consuming tool, enabling practicing engineers to perform efficient, accurate nonlinear and dynamic analysis as well as parametric studies on RC beams strengthened with EB-FRP. Since 1996, many numerical studies have been carried out on the response of RC beams strengthened using FRP. However, only a few have been related to RC beams strengthened in shear using EB-FRP composites. In addition, the analytical models that have been reported so far have failed to address and encompass all the factors affecting the contribution of EB-FRP to shear resistance because they have mostly been based on experimental studies with limited scopes. The aim of this paper is to build an extensive database of all the studies using finite element analysis (FEA) carried out on RC beams strengthened in shear with EB-FRP composites and to evaluate their strengths and weaknesses through various studied parameters.

Comparative analysis of design guidelines for FRP contribution to shear capacity of strengthened RC beams

In the past few years, strengthening and retrofitting of reinforced concrete (RC) structures using externally bonded (EB) fiber-reinforced polymers (FRP) laminates has been deemed as a promising rehabilitation technique. Structural applications of FRP include flexural and shear strengthening of RC beams and confinement of columns. Many guidelines and standards were developed to predict the contribution of FRP to the strength of structural members. For shear strengthening applications, in particular, most of the design guidelines tend to underestimate the capacity of the strengthened members, whereas other models provide unsafe predictions. The accuracy of the models is dependent on many factors, such as but not limited to the wrapping scheme, amount of internal shear reinforcement, shear crack angle, concrete compressive strength, number of FRP layers, and FRP type. For this purpose, this paper focuses on comparing and evaluating the accuracy of the available FRP shear design guidelines. The design standards that are considered in this study are the ACI440.2R-17, CSA-S806.12 (R2017), fib bulletin 90, and TR55. The accuracy of the design models was assessed against an experimental database collected from the literature. The database included RC beams externally strengthened in shear with different FRP types, configurations, and wrapping schemes. In addition, the database included strengthened beams with varying types of anchors. Results showed that most design codes provide reasonable predictions to the FRP shear strength in case of U-wraps. However, the guidelines are significantly conservative in case of complete wraps and anchored specimens. Overall, the ACI440.2R-17 and TR55 predictions are very conservative while fib bulletin 90 and CSA-S806.12 predictions are accurate and can be safely used to design FRP shear strengthened members.

Evaluation on the effect of anchor embedment depth on the flexural capacity of concrete prisms

Using fiber-reinforced polymer (FRP) composites to strengthen and retrofit existing reinforced concrete (RC) structures has gained wide acceptance owing to the superior properties of FRPs such as high strength-to-weight ratios and corrosion resistance. Externally bonded FRP (EB-FRP) laminates can be applied to enhance the flexural and shear capacities of RC beams and improve the ductility of RC columns. However, the premature debonding of FRP laminates from the concrete substrate is a major concern and usually results in a brittle member failure. To tackle this issue, many studies proved that adequate anchorage systems could improve the FRP-to-concrete bond, and therefore results in delaying the FRP debonding and further developing the tensile strength of the FRP laminates. One of the most commonly used anchorage systems is FRP spike anchors. Compared to other anchorage systems (for e.g., metallic anchors), FRP anchors have high compatibility with the FRP laminates. In addition, FRP spike anchors are noncorrosive and have high tensile strengths. Although several studies addressed FRP spike anchors in flexural and shear strengthening of RC beams and slabs, the literature still lacks comprehensive information on the effect of all anchor parameters on the performance of the strengthening system. As a result, the aim of this study is to investigate the effect of anchor embedment depth on the behavior, strength, and effectiveness on the FRP spike anchorage system. Six concrete prisms were cast and strengthened with carbon FRP (CFRP) laminates and spike anchors then tested in flexure under four-point bending tests. Test results showed that installing anchored CFRP laminates increased the capacity of the plain concrete prism by 80-120%. Anchoring the laminates at different embedment depths of 50mm, 75mm, 100mm, and 125mm enhanced the capacity of the unanchored prisms by 11%, 13%, 15%, and 33% respectively. Thus, it was concluded that increasing the anchor embedment depths increased the ultimate load carrying capacity of the prisms.

Shear strengthening of RC beams using NSM CFRP bonded using cement-based adhesive

The shear strength of existing Reinforced concrete (RC) members can be improved by bonding Carbon fibre reinforced polymers (CFRPs) as Near-surface mounted (NSM) or Externally bonded reinforcement (EBR). CFRPs are typically bonded to RC members using epoxy resins which have low glass transition temperatures resulting in poor fire performance. In an effort to improve the fire performance of CFRP strengthened members, researchers have developed Cement-based adhesives (CBAs) and verified their efficacy using NSM CFRP-to-concrete joint tests, however no applications have been conducted on full-scale RC beams strengthened in shear using NSM CFRP and CBA. This study attempts to fill this gap and involves testing fourteen RC beams strengthened in shear using NSM CFRP textile bonded using CBA. The experimental results showed that CFRP textile bonded using CBA in NSM configurations significantly improved the shear capacity of the RC members. Further, comparisons were made between CBA and epoxy resins as bonding agents and it was found that CBA achieved comparable results to epoxy when used in the configuration explored. The results of NSM-CFRP strengthened beams with CBA showed shear strength improvements of 97% and 70% using CFRP textile and laminate, respectively. Therefore, the use of CBA in the NSM CFRP strengthening techniques is considered a good substitute for epoxy resins for bonding CFRP to concrete members.

Shear strengthening of RC beams with corrosion-damaged stirrups using FRP grid-reinforced ECC matrix composites

This paper presents an experimental investigation of the shear behavior of reinforced concrete (RC) beams with corrosion-damaged stirrups strengthened using a fiber-reinforced polymer (FRP) grid-reinforced engineered cementitious composite (ECC) matrix. A total of 18 beam specimens, including four referential beams and 14 strengthened beams, were prepared and tested. After corroding the stirrups to the expected ratio using the electrochemically accelerated method, the lateral corrosion-damaged concrete cover was removed, and then repaired using the FRP grid-reinforced ECC matrix (FGREM). The main test parameters included the stirrup corrosion level, shear-span ratios, and types and strengthening amounts of the FRP grid. Based on the experimental results, the shear bearing capacity of the beams with corrosion-damaged stirrups improved significantly after being restored using this technique. The embedded FRP grid could effectively share the shear force borne by the stirrups and the ECC improves the deformation characteristics and energy absorption of the specimen owing to its excellent strain-hardening behavior. Furthermore, a theoretical calculation formula was proposed to predict the shear bearing capacity of the strengthened beams based on the truss-arch model, which was confirmed to be safe and accurate after being assessed using the modified version of the demerit points classification (DPC) method.

Efficiency of shear strengthening of RC beams with externally bonded FRP materials – State-of-the-art in the experimental tests

This paper presents a study of the shear capacity of reinforced concrete (RC) beams strengthened in shear with externally bonded (EB) fiber reinforced polymer (FRP) composites, based on the performance of existing published tests. The main objective of this study is to create a comprehensive overview of the performance of different shear strengthening configurations and the failure modes observed in experimental tests. In addition, the influence of the following parameters on the strengthening efficiency has been analyzed: shear span to depth ratio (a/d), existing steel transverse reinforcement ratio (ρsw), concrete strength (fck), size effect (d), longitudinal reinforcement ratio (ρsL), strengthening configurations, type of FRP: sheets or laminates (CFRP, GFRP), and FRP axial stiffness (AfEf).