Flexural Strengthening Of Reinforced Concrete Beams Research Articles

Flexural behavior of RC beams externally strengthened with side-bonded CFRP laminates with variable internal reinforcement

This study investigates the flexural behavior of reinforced concrete (RC) beams externally strengthened with bottom- and side-bonded carbon fiber-reinforced polymer (CFRP) sheets with variable steel ratio. The choice of applying the CFRP sheets in a bottom- or side-bonded configuration depends on the accessibility of the beam. This experimental investigation is aimed at studying and comparing the efficacy of bottom- and side-bonded CFRP sheets for flexural strengthening of RC beams with variable internal steel ratios. The effect of steel reinforcement ratio, and the number of CFRP plies are examined by testing 10 RC beams under a four-point bending configuration. The results in terms of load-deflection response, ultimate load-carrying capacity, failure modes, and ductility are studied and compared with control unstrengthened beams. The study revealed that side-bonded beams provided flexural capacity comparable to the bottom-bonded beams for both ratios of internal reinforcement used in the study. The study also showed that both strengthening configurations were more effective when the internal steel ratio was low. In terms of ductility, the side-bonded scheme provided ductility indices comparable to the bottom-bonded beams. The findings of this study confirm the feasibility of using side-bonded fiber-reinforced polymer (FRP) sheets as a strengthening technique for RC beams when the soffit of the beam is inaccessible.

Flexural strengthening of RC beams using PGFRP bars embedded in strain-hardening cementitious composites (SHCC)

The application of the near surface mounted (NSM) fiber reinforced polymer (FRP) as an additional reinforcement at tension side of flexural members is efficient to upgrade the flexural strength. However, this technique must be applied to concrete beams having hard concrete cover to avoid premature failure induced by concrete cover deterioration. The current research aims to improve and evaluate the flexural behavior of reinforced concrete (RC) beams strengthened with embedded prestressed glass fiber reinforced polymer (PGFRP) bars, based on replacement of weak concrete cover with a layer of strain hardening cementitious composites (SHCC). For this investigation, one reference beam (without strengthening) and nine flexural strengthened beams were tested under a four-point bending scheme. All beams had the same reinforcement and geometry, 150 mm width, 300 mm total depth, a total length of 3000 mm and the effective span was 2700 mm. The test parameters were: (1) the strengthening technique (conventional NSM-PGFRP bars, NSM-PGFRP bars covered with external SHCC layer and PGFRP bars embedded in SHCC replaced cover), (2) the prestressing levels in the GFRP bars (0, 10 % and 20 % of the ultimate bar strength) and (3) the thickness of the SHCC layer (30, 40 and 50 mm). Compared to the conventional NSM strengthened beams, the conjunction of SHCC with PGFRP bars not only prevented the spalling of the concrete cover but also increased the load carrying capacity up to 26.5 % and the ductility up to 16 %. A model for the prediction of flexural capacity of the strengthened beams having SHCC replaced cover was conducted, the predicted ultimate loads have a good consistency with the test results.

Flexural strengthening of RC beams using GFRP grid bonded with sprayed polyurea

Flexural strengthening of reinforced concrete (RC) beams with fiber reinforced polymer (FRP) was investigated in this research. The bonding agents were an epoxy paste and a sprayed polyurea. Four RC beams were strengthened with FRP composites according to the following techniques: (a) sprayed polyurea with and without glass FRP (GFRP) grid reinforcement; (b) manual layup with one GFRP grid; and (c) manual layup with one GFRP sheet. Experimental results clearly shows that flexural strengthening with polyurea technique is an effective scheme. Other than fast setting, the major advantages of using polyurea over other organic or inorganic matrices are as follows: (a) no slippage of the FRP grid from the polyurea or cracking of the polyurea occurred during the tensile test; (b) no debonding of the polyurea system from strengthened RC beams was observed during the bending test. Application of the polyurea system, key experimental results, and comparison with findings from other research programs reported in literature are presented in this paper.

Flexural strengthening of RC beams using sisal fibre reinforced polymer (SFRP) composite with anchorage systems

This research paper presents a study on the use of sisal fibre reinforced polymer (SFRP) composite as a sustainable alternative to artificial fibre reinforced polymers (FRPs) for strengthening reinforced concrete (RC) beams. Three anchorage systems, namely SE, SEM, and EE, were developed to prevent delamination of the SFRP composite from the RC beams, and their effectiveness was evaluated. The effects of SFRP composite layers, configuration, and main reinforcement ratio on the flexural capacity of RC beams were investigated. Experimental results from four-point loading tests on 15 simply supported RC beams showed that the SFRP composite improved the ductility and load-carrying capacity of the beams. Numerical analysis supported the experimental findings and successfully simulated the load-displacement curve, failure load, and failure modes of the RC beams. The research contributes to sustainable and environmentally friendly methods of strengthening RC beams and concludes that the SEM anchorage system was the most efficient in avoiding SFRP delamination, and strengthening configuration B (U-shaped) resulted in a significantly higher increase in the ultimate load-carrying capacity of RC beams due to improved bonding at the side faces of the beams.

Fatigue properties of RC beams reinforced with ECC layer and steel plate

Pasting steel plates on the tensile side of reinforced concrete (RC) beams to improve their flexural capacity is a standard strengthening method. However, the increase in the RC beam bearing ability is limited, and it is easy to induce “over-reinforced beam” failure. In this paper, therefore, the ECC layer and steel plate are employed for the flexural strengthening of RC beams and the static, and fatigue properties of RC beams are investigated through experiments. A total of seven test beams were made. The static failure test and fatigue performance test were conducted to measure the ultimate bearing ability, flexibility, strain of steel and concrete, mid-span deflection, and residual bearing ability of the three kinds of RC beams after specific fatigue times. The experimental results demonstrate that the flexural capacity of the RC beam with the ECC layer and steel plate is more than twice that of the non-reinforced beam, and its flexibility is 1.77 times that of the non-reinforced beam. The residual bearing ability is 96.2% of the static loading test after 200 thousand times of fatigue loading. Additionally, no apparent damage occurs after 2 million times of fatigue loading, and the residual bearing ability is 94.2% of the static loading test. The strain range of the tensile rebar and concrete of the beam reinforced with the ECC layer and steel plate significantly decrease. Thus, RC beams reinforced with the ECC layer and steel plate possess a good fatigue performance.

Flexural strengthening of RC beams with built-in basalt-fibre-reinforced polymer T-plates

Basalt-fibre-reinforced polymers (BFRPs) are expected to be excellent materials for the repair and rehabilitation of civil infrastructure due to their sound mechanical properties, high corrosion resistance and low cost. However, reported studies investigating reinforced concrete (RC) beams externally strengthened with BFRP are limited. The objective of this work was thus to determine the effect of BFRP strengthening on the flexural performance of RC beams. Four RC beams with a rectangular cross-section were fabricated, strengthened using different BFRP reinforcement techniques and tested under four-point bending until failure. The failure mode, crack widths, number of cracks, load–deflection response curves and ductility of the beam systems were recorded and analysed. The experimental results showed that, compared with a control beam, the stiffness and ultimate capacity of the strengthened beams were increased by 8–23% and 14–30%, respectively. To predict the load-carrying capacity and deflection of the test specimens, three-dimensional finite-element (FE) modelling was performed using Abaqus software to simulate the behaviour of RC beams strengthened with BFRP plates. The predictions of the FE model matched the experimental results well in terms of the mid-span deflection and load-carrying capacity.

Using NSM pre-stressed rebars for flexural strengthening of RC beams subjected to constant loading

The present study introduces an innovative technique for flexural strengthening of reinforced concrete (RC) beams subjected to constant loading and explores its efficacy through experimental evaluation. The technique involves the application of near-surface mounted (NSM) pre-stressed rebars, which exploits the advantages of both the NSM technique, as an effective one commonly used in strengthening RC beams, and pre-stressing, as an effective technique to eliminate excessive cracking and deformation. The experimental program consists of eight identically reinforced RC beams. Before strengthening, longitudinal grooves are cut out along the tensile face of the specimens in which steel bars are placed and anchored by end plates and an epoxy adhesive. Some of the bars are pre-stressed to a predetermined level using an end bolt and a torque-meter wrench. The test results indicate that the NSM pre-stressed steel rebars lead not only to almost identical amounts of significant increases in the ultimate flexural capacity of RC beams but also to decreased initial cracking and deflection.

Flexural strengthening of reinforced concrete beams using geopolymer-bonded small-diameter CFRP bars

In this study, the strengthening system for reinforced concrete (RC) members using geopolymer-bonded small-diameter carbon fiber-reinforced polymer (CFRP) bars was proposed and investigated for the first time. An experimental program was conducted to evaluate the efficiency of the FRP-reinforced geopolymer matrix (FRGM) system for the flexural strengthening of RC beams. A total of 11 RC beams were tested, including ten strengthened beams and one reference beam. The influences of three major factors on the strengthening performance were investigated, including the bonding method (geopolymer vs. epoxy), fiber reinforcement in the matrix (plain geopolymer vs. steel or polyvinyl alcohol fiber-reinforced geopolymer), and the number/diameter of CFRP bars (7Φ3, 2Φ6, and 2Φ10). It was found that the strengthened beams showed significantly higher stiffnesses, yield loads, and ultimate loads than the reference beam and the geopolymer-bonded FRGM layer showed similar strengthening efficiency with the epoxy-bonded FRGM layer. For the FRGM strengthening system, the use of short fibers in the geopolymer matrix further improved the crack control capacity. An analytical investigation was conducted to predict the load capacities of the strengthened beams. Finally, a practical application case was presented to demonstrate the feasibility of this method in strengthening the concrete superstructure at The Port of Zhanjiang (Guangdong, China). The findings lay the groundwork for using this FRGM system to repair reinforced concrete structures.

Flexural strengthening of RC beams with NSM-GFRP technique incorporating innovative anchoring system

Reinforced concrete (RC) beams may require flexural strengthening due to the corrosion of reinforcing bars or changes in the design load. The near surface mounted (NSM) and externally bonded (EB) techniques, using either glass or carbon fibre-reinforced polymer (GFRP or CFRP) composites, are used for strengthening deficient RC beams. However, RC beams strengthened with both techniques are susceptible to the debonding failure of the FRP composites. This paper proposes an innovative anchoring system for NSM strengthening of the RC beams, which comprises an L-shaped GFRP bar anchor (L-anchor), U-shaped CFRP strips (U-strips) and double plate (DP-anchor). The developed strengthening technique is termed as NLUD technique. Seven RC beams were cast and tested under four-point bending. The experimental results showed that RC beams strengthened with the NLUD technique achieved significantly higher flexural load. The NLUD technique prevented the debonding failure of GFRP bars of the strengthened RC beams.

Externally Bonded CFRP for Flexural Strengthening of RC Beams with Different Levels of Soffit Curvature

Abstract This paper reports a comprehensive study on the behavior of concavely curved soffit reinforced concrete (RC) beams strengthened in flexure with carbon fiber-reinforced polymer (CFRP) compo...

Flexural strengthening of RC beams with textile-reinforced mortar composites focusing on the influence of the mortar type

This paper presents an experimental study on the flexural strengthening of reinforced concrete (RC) beams with externally bonded layers of textile-reinforced mortar (TRM), as a means of improving their flexural response. The main aim of this study was to investigate the effect of the mortar type in the performance of TRM strengthening system, while varying the type of the textile and the number of the textile layers. In total, nine medium-scale RC beams were manufactured and tested as simply supported under 4-point bending. One beam was tested as-built without strengthening and served as control specimen. The rest of the beams were first strengthened with different configurations and then were subjected in monotonic bending. The parameters under investigation included: a) the mortar type (two different mortars were used, M1 and M2), b) the number of strengthening layers (three versus six), and c) the type of the textile (basalt-fibre with small mesh-size versus glass-fibre textile with large mesh-size). The main difference between mortars M1 and M2, was the use of synthetic polymers as additives in mortar M1. It was overall concluded that there is a strong influence of the mortar type on the flexural capacity increase, on the flexural stiffness response after yielding, as well as on the failure modes. Combined effects between the different type of mortars and the rest of the investigated parameters were also revealed.

Flexural strengthening of RC beams with BFRP or high strength steel bar–reinforced ECC matrix

This paper has investigated the flexural behavior of reinforced concrete (RC) beams strengthened with BFRP (basalt fiber reinforced polymer) or HSS (high strength steel) bar reinforced ECC matrix. A total of six strengthened RC beams and one control RC beam were tested under four-point bending up to their failure. The test variables included the cement matrix (ECC and polymer mortar), the reinforcements type (BFRP and HSS bars) as well as the reinforcement ratio (0.94% and 1.41%) of the strengthening layer. Two failure modes including the rupture of BFRP bars and the rupture of ECC matrix followed by the slippage of the steel bars were obtained in the strengthened beams. The rupture of BFRP bars dominated the failure of beams strengthened with BFRP bar reinforced cement matrix owing to the limited tensile strength of BFRP bars, and the percentage of enhancement in flexural capacity ranged from 18.6% to 47.8% compared with the control beam. The beams strengthened with HSS bar reinforced ECC matrix all failed due to the rupture of ECC matrix followed by the slippage of HSS bars, mainly owing to the high stiffness and strength of the HSS bars, leading to larger enhancements in flexural capacity at a range of 60.0–75.6%. In addition, a beam strengthened with BFRP bar reinforced polymer mortar was also tested with the purpose of conforming the advantage of ECC over polymer mortar as the matrix of the strengthening layer. The test results showed that the application of ECC matrix with BFRP bars resulted in larger enhancement in the yield and ultimate loads compared to the use of polymer mortar matrix. The difference between the two strengthening systems confirmed the excellent strain compatibility of BFRP bars and ECC matrix. Finally, a flexural theoretical analysis based on three possible failure cases was proposed, and its reliability was verified through comparing the test results and the theoretical predictions.

Innovative flexural strengthening of RC beams using self-anchored prestressed CFRP plates: Experimental and numerical investigations

This paper presents an innovative method of prestressing carbon fibre reinforced polymer (CFRP) plates used as externally bonded reinforcement for flexural strengthening of reinforced concrete (RC) beams. The proposed method aims to achieve self-anchorage of the prestressed CFRP plate and thus eliminate the need for conventional mechanical anchorage at its ends. Experimental tests of RC beams in four-point bending were conducted to investigate the strengthening efficiency of the self-anchored prestressed CFRP plate. The experimental results showed that using the self-anchored prestressed CFRP significantly improved the flexural performance of the strengthened beam in terms of bending stiffness, crack widths, and load-carrying capacity. The utilisation ratio of the prestressed CFRP plate reached 81% at its debonding. Numerical analyses using nonlinear finite element (FE) method were conducted to model the tested specimens. Based on the reliable simulation of flexural cracks and crack-induced CFRP debonding, parametric studies were conducted using FE analyses, in order to investigate the effect of prestressing levels and the CFRP plate’s stiffness on the flexural behaviour. Recommendations were then made for selecting a proper prestressing level and the mechanical properties of CFRP plates.

Flexural Performance of RC Beams Strengthened with Externally-Side Bonded Reinforcement (E-SBR) Technique Using CFRP Composites.

Reinforced concrete (RC) structures necessitate strengthening for various reasons. These include ageing, deterioration of materials due to environmental effects, trivial initial design and construction, deficiency of maintenance, the advancement of design loads, and functional changes. RC structures strengthening with the carbon fiber reinforced polymer (CFRP) has been used extensively during the last few decades due to their advantages over steel reinforcement. This paper introduces an experimental approach for flexural strengthening of RC beams with Externally-Side Bonded Reinforcement (E-SBR) using CFRP fabrics. The experimental program comprises eight full-scale RC beams tested under a four-point flexural test up to failure. The parameters investigated include the main tensile steel reinforcing ratio and the width of CFRP fabrics. The experimental outcomes show that an increase in the tensile reinforcement ratio and width of the CFRP laminates enhanced the first cracking and ultimate load-bearing capacities of the strengthened beams up to 141 and 174%, respectively, compared to the control beam. The strengthened RC beams exhibited superior energy absorption capacity, stiffness, and ductile response. The comparison of the experimental and predicted values shows that these two are in good agreement.

Flexural strengthening of RC beams using aluminum alloy plates with mechanically-fastened anchorage systems: An experimental investigation

Externally bonded reinforcement (EBR) has emerged as one of the promising techniques for flexural strengthening of reinforced concrete (RC) members due to its practicality and structural effectiveness. However, shortcomings like premature failure modes, cost, labor, and installation time limited its use. Mechanically fastened (MF) Aluminum Alloy (AA) plates instead have the potential to overcome some of these drawbacks by providing strength and ductility, while influencing the failure modes. In this investigation, 16 RC beams were prepared, one beam was left un-strengthened (CB), one was strengthened with an externally bonded (EB) AA plate (CBE), and the remaining 14 beams were strengthened with MF AA plates that varied based on expansion anchor bolts (EAB) sizes, spacing, layout, and the presence or absence of epoxy. The test results indicated that all the specimens with MF AA plates exhibited approximately 30% increase in strength accompanied with drastic increase in ductility up to about 84% compared to specimen CBE. Analytical predictions were made to numerically assess the advantages of using MF systems where ACI 318-19 outperformed ACI 440.2R-17 due to the sufficient composite behavior that allows the AA plates to behave similar to steel reinforcement such that the section has an additional lever arm. It is concluded that the implementation of epoxy and EAB as an alternative anchorage technique serves as a viable approach in enhancing the strength and ductility of RC beams strengthened with AA plates.

Effects of tensile reinforcing steel ratio and Near-Surface-Mounted bar development length on the structural behavior of strengthened RC beams

Abstract The use of near-surface mounted (NSM) Glass fiber reinforced polymer (GFRP) bars is one of the most popular and effective techniques for strengthening reinforced concrete (RC) beams. This paper presents an experimental research program to study the flexural strengthening of RC beams comparing two areas of bottom tensile reinforcing steel and three development lengths of NSM GFRP bars. The beam test results indicated that the beam flexural strength increased up to 110% and 58% for the cases of low and high tensile reinforcing steel ratios, respectively. The effect of the tensile reinforcing steel area on the critical value of the development length of NSM GFRP bars was also investigated. It was found that decreasing the axial stiffness ratio, reduced the strengthening efficiency and the critical development length of the NSM GFRP bars. Finally, a 3D Finite Element (FE) model using ANSYS was constructed and was validated using the experimental results. Good agreement was seen between experimental and FE model results.

Flexural strengthening of reinforced concrete beams using hybrid near-surface embedded/externally bonded fabric-reinforced cementitious matrix

The efficacy of hybrid near-surface embedded/externally bonded (NSE/EB) fabric-reinforced cementitious matrix (FRCM) for flexural strengthening of reinforced concrete (RC) beams was assessed experimentally. Bending tests were conducted on eight RC beams: 6 strengthened and two reference beams. The test parameters were (a) the internal tensile reinforcement ratio and (b) the FRCM fabric type (glass, polyparaphenylene benzobisoxazole (PBO), and carbon). The experimental results revealed that the hybrid NSE/EB-FRCM could effectively be used for the flexural strengthening of RC beams based on the test parameters. The strengthened beams exhibited an enhanced flexural behavior as evidenced by their increased load-carrying capacity (Pu) that ranged between 24.7% and 109%. The maximum enhancement in the load-carrying capacity was measured in carbon FRCM strengthened beams owing to the higher axial stiffness of carbon FRCM relative to PBO and glass FRCM. The strengthening efficacy of the FRCM was increased with an increase in the FRCM axial stiffness. An increase in the internal tensile reinforcement ratio showed an adverse effect on the gain in Pu. The stiffness factor (βf) was used to study the combined effect of the test parameters. An almost linear relationship was observed between the increase in Pu and βf with a good coefficient of correlation of 97%. Moreover, the strengthening system has increased the post-crack stiffness of the beam with an average increase of 52%. Finally, the prediction of the ACI 549 provisions was examined and compared with the experimental results.

Experimental and theoretical investigation on the hybrid CFRP-ECC flexural strengthening of RC beams with corroded longitudinal reinforcement

This paper reports an experimental and theoretical investigation on the flexural behavior of hybrid engineered cementitious composite (ECC) and carbon fiber reinforced polymer (CFRP) strengthened reinforced concrete (RC) beams with different corrosion levels of longitudinal reinforcement. A certain thickness of damaged concrete cover was removed and replaced by ECC, and CFRP sheets were attached to the soffit of the ECC layer to form the so-called hybrid CFRP-ECC strengthening. Experimental results show that the ECC strengthening could recover the capacity close to that of a virgin beam if the corrosion ratio was less than 10%. Bonding CFRP to ECC in the hybrid CFRP-ECC strengthening prevented CFRP debonding due to the multiple micro-cracking behavior of ECC, thus significantly enhanced the flexural capacity of a beam. The cracking of the remaining upper concrete was better restrained due to the excellent cracking control ability of ECC. In addition to experimental work, theoretical models were proposed to predict the capacity of hybrid CFRP-ECC strengthened beam with corroded flexural steel bars under different failure modes. Model results are found to be in good agreement with test data.

Experimental and analytical study on flexural strengthening of RC beams via prestressed EBROG CFRP plates

The present manuscript reports results obtained from both experimental and analytical studies on the behavior of reinforced concrete (RC) beams strengthened in flexure using prestressed carbon-fiber-reinforced polymer (CFRP) plates via the externally bonded reinforcement on grooves (EBROG) method. A major concern in strengthening beams with prestressed FRP plates is the proper transfer of prestressing force to the beam. The present study pioneers the use of EBROG technique in prestressed CFRP plates considering the proven superiority of the bond efficiency created by the EBROG technique over that by the EBR. For the purposes of this study, seven RC beams with cross-sections of 200 × 300 mm and lengths of 2600 mm were subjected to the four-point loading test in order to investigate the effects of different parameters including prestressing level, using anchorage system, and the strengthening technique employed. Experimental results indicated that the EBROG technique, in the absence of any end anchorage, was well capable of transferring the prestressing stresses to the beam, which obviously led to significant reductions in strengthening costs. Compared to the specimens strengthened through the EBR technique, those strengthened via the EBROG technique exhibited an enhanced flexural behavior as evidenced by their increased load carrying capacity, ductility, and CFRP debonding strain that were higher by 18, 53, and 36%, respectively. It was also observed that prestressing CFRP plates attached via EBROG method was able to postpone the debonding and increase the strength efficiency of the FRP plates. A maximum enhancement of 20% in ultimate load-carrying capacity was measured in prestressed beams strengthened via the EBROG technique relative to the non-prestressed ones.

Nonlinear behavior analysis of flexural strengthening of RC beams with NSM FRP laminates

This paper proposes an analytical method for predicting the nonlinear behavior of reinforced concrete (RC) beams after flexural strengthening with near surface mounted (NSM) fiber reinforced polymer (FRP) laminates. With a gradual increase in the beam curvature and a step-by-step numerical integration method, an algorithm model was designed for predicting the load-deflection response of RC beams strengthened with the NSM technique. Based on the bond mechanism between the NSM FRP laminates and the surrounding concrete, the available calculation methods of the load bearing capacity of RC beams with NSM FRP laminates were derived according to the bearing capacity model for the strengthened RC structure with FRP materials. Using the proposed model, the load-deflection responses of five flexural strengthened RC beams with NSM carbon FRP (CFRP) laminates were analyzed and verified against the experimental results. The presented results indicate that the proposed model based on the available test data can accurately analyze the tensile stresses of the NSM CFRP laminates. Moreover, the results prove the feasibility of the designed algorithm model in precisely predicting the nonlinear behavior of RC beams strengthened with NSM CFRP laminates. The proposed algorithm model could provide a much needed link between structural design and nonlinear behavior analysis of RC structures strengthened with the NSM technique.