Flexural Behavior Of Concrete Beams Research Articles

Flexural Behavior of Concrete Beams Reinforced with a CFRP Grid Exposed to Chloride-Containing Environments: An Experimental Study

Flexural Behavior of Concrete Beams Reinforced with a CFRP Grid Exposed to Chloride-Containing Environments: An Experimental Study

Experimental and Numerical Study on Flexural Behavior of Concrete Beams Using Notches and Repair Materials

In a concrete beam, cracking is generated on the tension side under the effect of flexure, shear, and torsional loadings. Accordingly, these weak concrete members require repair and/or strengthening to increase or restore their internal load capacity. In the current experimental and numerical investigations on concrete beams, the impact of using notches with different width to depth ratios on the ultimate flexural load under a three-point test was considered. Further, the flexural behavior performance of a notched concrete beam repaired using the three repair materials—cement mortar, bacterial mortar, and adhesive—was also examined. Consequently, a comparative study was implemented between the experimental and numerical results. A concrete damage plasticity (CDP) model was used for the finite element numerical analysis of the beams. The differences in numerical and experimental measured results ranged from 0.65 to 22.20% for the ultimate load carrying capacity. As the notch size increased, the ultimate load carrying capacity of the beam reduced. Additionally, a linear regression model was used to predict the ultimate load values at a notch width interval of 5 mm up to a maximum notch width of 100 mm. It was observed that the ultimate load capacity for a repaired beam increased as compared to the notched beam for all three repair materials under consideration. And the maximum ultimate load increased in the case of notched beams repaired using adhesive. Furthermore, in comparison to the cement mortar, the performance of the bacterial mortar in terms of the ultimate load was more. The bacterial mortar was found to be more sustainable and more durable as a repair material for concrete structures.

Flexural behaviour of concrete beams reinforced with fiberglass geogrid

In cold regions, especially within Canada, the degradation of non-structural concrete components in challenging environmental conditions has become a pressing issue. Traditional steel reinforcements are known to be susceptible to corrosion. With anticipated climate shifts causing variations in temperature, precipitation, and freeze-thaw cycles, there's an increasing need for more resilient reinforcement materials to deter premature cracking in non-structural concrete components. This study delves into the advantages of using low-ductility fibreglass geogrids as reinforcement layers to curb crack development and augment the flexural performance of plain concrete beams. Tests were carried out on nine concrete beams, each measuring 550×150×150 mm, with diverse reinforcement setups. The emphasis was on evaluating load-deflection characteristics, energy absorption capabilities, and modes of failure. Results suggest that lowductility fibreglass geogrid reinforcement markedly enhances the flexural strength of plain concrete, outperforming control beams. Additionally, fibreglass reinforcement showcases enhanced crack resistance and postcracking behaviour than plain beams. A Finite Element Analysis (FEA) was also executed using the Abaqus software, and its accuracy was confirmed through experimental data comparisons, yielding numerical figures for midspan deflection and peak load. This research furnishes pivotal insights into the prospective use of progressive reinforcement materials to combat environmental challenges in colder climates.

Experimental study to evaluate the flexural behavior of concrete beams reinforced with CFRP grid

Fiber reinforced polymer (FRP) is evaluated as an excellent material to replace rebar in reinforced concrete due to its advantages such as high tensile strength-to-weight ratio and high corrosion resistance. Many studies have been conducted to use FRP as substitutes for steel rebar. However, most of these studies were conducted using FRP bars, and research on using FRP grids in the construction field is focused on the field of repair and strengthening. Therefore, this study reports the results of an experimental study to evaluate the flexural behavior of concrete beam with Carbon FRP (CFRP) grid tensile reinforcements as a basic study to evaluate the feasibility of using FRP grid as a as substitutes for steel reinforcement. Thirteen test specimens were prepared for the experiments. The CFRP grids were applied to the specimens as tensile reinforcement. The concrete cover thickness, layers of the CFRP grid and the spacing between the CFRP grids were considered as test variables. The experiment results showed that the specimens without spacing between the CFRP grids were destroyed by side CFRP grid fracture. Also, as the CFRP grid layer increased, the ultimate load increased by 53% to 94%, and when the cover thickness decreased by 10 mm, the ultimate load decreased about 10%. The ratios of the nominal flexural strengths calculated according to the CSA S806–12 and ACI 440.1R-15 standards were 1.004 and 1.09, respectively. Thus, the use of the CSA S806–12 standard enables a relatively accurate prediction of the nominal flexural strength of concrete beams reinforced with CFRP grids.

Impact of developed hybrid polypropylene fiber inclusion on the flexural performance of concrete beams reinforced with innovative hybrid bars

This paper investigates the impact of incorporating a hybrid combination of structural polypropylene fibers on the flexural behavior of concrete beams reinforced with steel, GFRP, and innovative hybrid bars. A new ductile hybrid bar with equivalent bilinear stress-strain characteristics has been developed to address steel corrosion and FRP ductility issues. Fourteen half-scale RC beams were fabricated and tested under four-point loading configuration to study the flexural response. The tensile reinforcement types (steel, GFRP, and hybrid), hybrid reinforcement ratios (0.85 %, 1.26 %, and 1.70 %), reinforcement hybridization schemes (hybrid-hybrid, hybrid-GFRP, and GFRP-steel), and hybrid fiber ratio (0.0 %, 1.0 %, and 2.0 %) are the major parameters studied. The test results were recorded and analyzed in terms of mid-span deflection, cracking load, flexural capacity, and failure mechanism. The results demonstrated that the addition of hybrid fibers and using hybrid bars significantly improved the peak strength, ductility index, and bending stiffness. Moreover, the hybrid-reinforced concrete beams exhibit large inelastic deformations similar to steel-reinforced concrete beams. The inclusion of hybrid fibers improves the post-peak response of the tested beam due to fiber bridging capabilities. For design purposes, a simplified formula proposed by ACI 544 for predicting the nominal flexural capacity of hybrid fiber concrete beams reinforced with hybrid bars was presented, compared with experimental results and validated with 44 specimens from other studies. The predicted and test results were in good agreement with a standard deviation of 0.12. Additionally, 3D nonlinear finite element analysis was developed to validate the test results, demonstrating reasonable accuracy in predicting the flexural behavior of the beams.

Tests and finite element modeling of concrete beams reinforced with reused steel bars

AbstractThis paper presents the experimental study and finite element modeling of the flexural behavior of concrete beams reinforced with reused steel bars as longitudinal reinforcements. The experimental program and results of eight reinforced concrete (RC) beams constructed with and without reused steel bars are described in detail. The replacement percentages of brand‐new bars with reused steel bars in the tested beams were 50% and 100%. The reused steel bars were coated with and without epoxy. Steel fibers with fractions of 0.5% and 1.0% of the concrete volume were added to the concrete mixes. The load‐deflection relationship, ductility index, toughness, and failure modes of the tested beams are presented and discussed. It is shown that utilizing reused steel bars decreases the ultimate load of RC beams but increases their deflection at the ultimate load compared with the control beam. Increasing the steel fiber ratio increases the ultimate load and the deflection at the ultimate load of RC beams incorporating reused steel bars. However, the zinc‐rich epoxy used to coat the reused steel bars does not affect the behavior of the beams. Three‐dimensional nonlinear finite element (FE) models of the tested beams were developed using ABAQUS and validated against the test results. The developed FE models are capable of accurately simulating the experimentally observed behavior of RC beams with reused steel bars.

Experimental investigation on the flexural behavior of concrete beams reinforced with HRB635 high-strength steel reinforcement

High-strength steel reinforcement offers promising application prospects in buildings with large spans and loads, as it can reduce steel congestion and simplify construction process. To investigate the mechanical behavior of flexural members reinforced with high-strength steel and measures to control crack width, in this study, static loading tests were conducted on 17 full-scale reinforced concrete (RC) beams with HRB635 high-strength steel reinforcement, six of which were reinforced with steel fiber. The failure mode, flexural strength, ductility, crack width, and deflection of the specimens were investigated, and the effects of different key parameters, including the reinforcement ratio and diameter, concrete strength, and steel fiber volume fraction were also analyzed. Test results indicated that the tensile strength of HRB635 reinforcement could be fully utilized, while the ductility ratios of high-strength steel reinforced concrete (HSS-RC) beams were less than those of beams with normal strength reinforcement. The maximum crack widths of most specimens without steel fibers exceeded the threshold defined in GB 50010-2010, indicating that the design of HSS-RC beams may be controlled by the requirements of serviceability limit state. Furthermore, the crack widths predicting methods defined in GB 50010-2010 and EN 1992-1-1 are more accurate for HSS-RC beams, while the deflection predicting methods defined in GB 50010-2010 and ACI 318-19 both underestimated the deflection of HSS-RC beams. This study could provide a theoretical basis for the engineering application of HRB635 high-strength steel reinforcement.

Investigation of flexural behaviour of composite rebars for concrete reinforcement with experimental, numerical and machine learning approaches.

Three different types (with glass, basalt and hybrid fibres) of composite rebars manufactured using the pultrusion process were loaded in four-point bending tests. All tests were carried out with acoustic emission sensors to better understand the mechanisms of damage. The data obtained were investigated using standard parameter analysis and also using unsupervised machine learning techniques called K-means. It was found that the best number of clusters is four or five. The numerical model using the finite-element method was calibrated on the basis of the experimental data. Further research will focus on numerical modelling of flexural behaviour of concrete beams reinforced with the presented composite rebars. The presented paper focuses on the characterization of the mechanical properties of composite rebars using a micromechanical approach, as well as analysis of progression damage processes appearing under flexural loading, using different perspectives provided by techniques such as acoustic emission analysis with machine learning-based clustering and numerical simulations. The presented research confirms that the proposed experimental-numerical approach can be applied in order to describe the flexural behaviour of Fibre Reinforcement Polymer (FRP) rods, which is relevant for investigating more complex cases of FRP concrete structures. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 1)'.

Experimental and numerical investigation of flexural behaviour of concrete beams reinforced with GFRP bars

To solve the issue of corrosion, the use of glass fibre reinforced polymer (GFRP) bars in reinforced concrete (RC) has emerged as a feasible option for conventional steel bar RC. Given that GFRP RC beams have different mechanical properties and behaviours than steel counterparts, a thorough investigation of the load–deflection behaviour, failure modes, and overall performance of GFRP RC beams via experimental, analytical, and numerical studies is required. Therefore, this study encompasses the experimental, analytical, and numerical investigation of GFRP RC beams. Total of 9 beams are experimentally investigated, three (3) reinforced with steel bars (10 mm dia) while six (6) reinforced with GFRP bars (10 mm and 16 mm dia). Experimental results reveal that GFRP RC beams exhibit lower load carrying capacity and more deflection than their steel equivalents, respectively. GFRP RC beams have a 32.4 % lower ultimate load and a 16 % higher ultimate deflection than steel RC beams for the same reinforcing ratio. Steel RC beams failed under tension control, whereas GFRP RC beams failed under compression control. Analytical models, primarily based on effective flexural stiffness, are used to predict the load–deflection behaviour of GFRP RC beams. Nonlinear numerical modelling of GFRP RC beams is carried out using ATENA 2D. The load–deflection responses obtained from analytical and numerical studies are compared with experimental results and found to be in good agreement. After the validation of numerical models, the behaviour of GFRP RC beams has been investigated using a thorough parametric research, which looked at the impact of concrete compressive strength, longitudinal reinforcement ratio, GFRP bar elasticity modulus, and shear span to depth ratio.

Flexural Behavior of Concrete Beams Reinforced with CFRP Grid

Flexural Behavior of Concrete Beams Reinforced with CFRP Grid

Flexural behavior of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures

To study the flexural behavior of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures, flexural tests were conducted on twelve concrete beams reinforced with high-strength steel bars. The influences of exposure temperatures (room temperature, 200, 400, 600, 800, and 1000 °C), holding times (0, 1, and 2 h), yield strength grades of steel bars (600 and 500 MPa), and the number of heating sides (2 and 3 sides) on the flexural behavior of beams, including failure mode, load–deflection response, flexural bearing capacity, ductility, and concrete strain, were investigated. The results showed that all beam specimens presented flexural failure mode. When the exposure temperatures were below 600 °C, the flexural capacities changed negligibly, decreasing significantly when the exposure temperatures exceeded 800 °C. The peak loads of specimens with HRB600 bars after exposure to 800 and 1000 °C decreased by 12.9% and 38.7% relative to that under room temperature. The flexural capacities decreased more significantly when the holding time was 2 h relative to that was 0 h and 1 h, of which peak load decreased by 2.4% and 9.4%, respectively. The number of heating sides had no obvious effects on the load - deflection response of the specimens. The load - deflection curves were similar in the elastic stage and yield stage between the specimens were heated on two and three heating sides. At last, combining the temperature distribution on the cross-section obtained by the elevated temperature tests, the calculation methods on the flexural capacities of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures were proposed based on the equivalent section reduction method and the material reduction method, respectively. Comparing the calculated results with test results, a good agreement could be noted.

Study on flexural behavior of concrete beams reinforced with hybrid high-strength and high-toughness (HSHT) and ordinary steel bars

To study the flexural behavior of high-strength and high-toughness (HSHT) reinforced concrete beams with negative Poisson’s ratio and special spiral grooves on the surface, fifteen beams of 250 mm × 450 mm × 3200 mm were designed and manufactured to conduct bending tests. The effects of different parameters, including the reinforcement ratio, compressive strength of concrete, loading mode, the number of HSHT steel bars in hybrid reinforcement, and longitudinal steel bars type, were studied on failure modes, crack patterns, flexural stiffness, flexural strength, ductility, and energy absorption capacity. The load versus mid-span deflection curves for concrete beams reinforced with HSHT steel bars can be divided into five stages. The concrete beams reinforced with HSHT steel bars can also bear higher residual strength (approximately 0.9 Fp) and exhibit superior crack width control ability. The peak load increases by a maximum of 22.9 % with the reinforcement ratio of HSHT steel bars increasing from 0.86 % to 1.08 %. Hybrid reinforcement can improve the service performance of concrete beams, take full advantage of HSHT steel bars, and increase the energy absorption capacity of beams. Based on strain analysis of cross-section, the flexural strength model of concrete beams reinforced with hybrid reinforcement was proposed by considering the ultimate compression strain. The calculation results show that the proposed model can accurately calculate the flexural strength of concrete beams reinforced with HSHT steel bars.

Experimental and numerical investigation on flexural behavior of concrete beams strengthened by different NSM tendons

To comprehensively study the flexural behavior of RC beams strengthened by means of near-surface mounted (NSM) technology, 142 simply supported concrete beams strengthened in flexure with a wide variety of NSM materials, including fiber reinforced polymers (FRPs) and metallic materials were collected from previous experimental studies. The effects of the material properties and number of NSM reinforcements on the failure modes of beams strengthened with the NSM system were analyzed. The enhancements in the load-bearing capacity, ductility, and energy consumption capacity of beams were discussed. By classifying the NSM strengthening materials into brittle reinforcement and ductile reinforcement, the results demonstrated that beams strengthened with brittle NSM reinforcement were prone to premature brittle failure modes, as beams strengthened with only one FRP tendon easily failed through rupture of FRP, and those with more than one tendon were prone to debonding failure. Whereas beams using ductile materials were more likely to fail in a ductile manner. A numerical analysis was performed to predict the maximum strength of beams strengthened with different materials and prestress levels. Conservative prediction was observed for beams that failed by concrete crushing, and overestimated prediction was observed for beams governed by debonding failure or rupture of NSM tendons.

Flexural behaviour of concrete beams reinforced with steel-FRP composite bars

Corrosion of steel reinforcement affects the durability of concrete structures. This led researchers to look forward to alternatives for steel reinforcement. One of these alternatives is Fiber Reinforced Polymer (FRP) reinforcement, which has high tensile strength as well as excellent corrosion resistance. However, the use of FRP reinforcement always comes at the expense of ductility. Thus, Steel Fiber Composite Bars (SFCBs), which consist of a steel core and FRP protective coating, could be a suitable alternative to conventional steel/FRP reinforcement. In the current work, fourteen concrete beams were tested to investigate the flexural performance of concrete beams reinforced with manually produced SFCBs. All beams had similar dimensions of 200 mm width, 300 mm height, and a clear span of 1700 mm. The main parameters were the reinforcement type (steel/SFCB) and the concrete compressive strength (30, 40, and 50 MPa). The experimental results were presented in terms of; crack pattern, failure modes, cracking load, ultimate load, load-crack width response, load-deflection curves, and the reinforcing bars' strain curves. The test results showed that, at the same load level, using SFCBs as tensile reinforcement increased the beams' mid-span deflection and crack width compared with those reinforced with steel bars. Finally, an analytical study was performed to predict the ultimate loads, maximum crack width and maximum deflection at service load of SFCBs reinforced beams. The results from the analytical study were very close to the test results, validating the accuracy of the suggested formulas for usage in practice.

Linear Concrete Tension Stiffening Model for Reinforced Concrete Elements

Linear expressions for tension stiffening of concrete are nowadays widely used in software packages of structural analysis. Nevertheless, more elaborated expressions of tension stiffening available in the literature have been used successfully in the past. The use of linear approximations is justified since the influence of the tension stiffening effect in the deformation of the structure is small but not negligible. In this sense, linear approximations are simpler and can be accurate enough. However, this linear approximation, in its present form, does not provide good results in terms of deformations at the element level. This paper proposes a linear expression of the tension stiffening supported by the experimental formulation used to predict the flexural behavior of concrete beams. A detailed example is presented.

Investigation of the effect of using geogrid, short glass, and steel fiber on the flexural failure of concrete beams

This research studies the flexural behavior of concrete beams reinforced with biaxial geogrids, distributed short glass and steel fibers. No longitudinal steel reinforcement bars were used. Therefore, an amount of short glass and steel fibers was used to improve the concrete beam behavior against flexural failure. Eleven specimens of single reinforced (flexural reinforcement) concrete beams and double reinforced (compression and flexural reinforced) concrete beams using two biaxial geogrids sheet layers, with randomly distributed short glass and steel fibers were cast. The samples were tested using two points of load along the beam specimen span with an increment of loading by 5 KN to evaluate several parameters. The studied parameters are using geogrids as a main flexural reinforcement, using geogrid sheet layers as a flexural and compression reinforcement, using short glass and steel fibers as an additional reinforcement of concrete with various ratios 0.25 %, and 0.75 %. The test results indicated that the use of geogrid layers as the main flexural reinforcement improved the behavior of the concrete beam specimens at failure. As well as; more enhancement of beam specimens at failure was observed when using short glass and steel fibers with geogrid reinforcement in concrete beams. The tested beam specimens which were reinforced by geogrids in the flexural and compression zone using 0.75 % of steel fibers gave better results due to modes of failure, toughness, failure load capacity, crack width, and post cracking stiffness.

Experimental and Theoretical Research on Flexural Behaviour of Concrete Beams Reinforced with High-Strength Steel Bars after Exposure to Elevated Temperatures

Experimental and Theoretical Research on Flexural Behaviour of Concrete Beams Reinforced with High-Strength Steel Bars after Exposure to Elevated Temperatures

Flexural Behavior of Concrete Beams Reinforced with Recycled Plastic Mesh

The production of plastic material continues to increase around the world. Consequently, large amount of waste plastic is generated. This will lead to environmental concern due to its disposal. In order to reduce the environment effects and cost, waste plastic can be recycled and utilized in other applications including construction. This paper investigated the flexural behavior of non-structural concrete beams containing waste plastic meshes as a replacement of traditional steel reinforcement. To achieve this objective, beams with steel reinforcing bars and waste plastic sheets with different effective widths and patterns were prepared. After 28 days of curing, the beams were subjected to an increasing load until failure and the central deflection was measured at each load increment. Furthermore, a numerical analysis was performed on the specimens using ABAQUS software. This will allow the comparison between the experimental and numerical results. The experimental data indicated that using plastic sheets improved the flexural toughness and ductility of concrete beams. Additionally, correlations were carried out between the ultimate capacity of the beams, the flexural toughness and the effective width of the plastic meshes. As the effective mesh width increased, the flexural toughness and ultimate capacity of the concrete beams increased. The results of this investigation will allow greater utilization of waste plastic in construction activities.

Flexural behavior of concrete beams reinforced by partially unbonded steel-FRP composite bars

Fiber-reinforced polymers (FRPs) are linear elastic materials that are widely used to reinforce newly built bridges and strengthen existing structures due to its high strength and good durability. To avoid brittle failure, the strength utilization of FRPs in practical applications is relatively low. A steel-FRP composite bar (SFCB) is a composite bar compound of an inner steel bar and outer longitudinal FRPs; its advantages include a good initial modulus, high durability and controllable postyield stiffness. When a concrete structure is reinforced by SFCBs, due to the limited rupture strain of the SFCB’s outer FRP, the deformability of the corresponding member is often controlled by the rupture of the FRP. To improve the deformability of an SFCB beam, an experimental study on concrete beams with partially unbonded SFCBs was conducted, and the failure modes, load–deflection curves and strain distribution were investigated. The test results showed that with partial unbonding treatment of the SFCB, the failure mode involving rupture of the SFCB’s outer FRP during SFCB reinforced concrete failure can be delayed or transferred into failure due to concrete crushing after the SFCB’s inner steel bar yielded, and the corresponding deformability and energy ductility can be improved. Then, a numerical 3D model was built and validated with the test results, and a parametric study of partially unbonded SFCB beams with different parameters was carried out. The simulation results show that the partial unbonding treatment can increase the deformability of the SFCB beam (with rupture of FRP) by two times while maintaining the stability of the load carrying capacity. When the unbonded length lub is between 0.5D and 1.0D (D is the height of the concrete beam), balanced failure of the SFCB beam is more likely to occur (the postyield stiffness is between 0.20 and 0.25). An excessive unbonded length lub will prematurely lower the depth of the compression zone, and the corresponding bearing capacity will decrease. As a result, when designing an SFCB reinforced concrete beam, the postyield stiffness ratio, reinforcement ratio and unbonded length should be comprehensively considered.

Flexural and Serviceability Behavior of Concrete Beams Reinforced with Ribbed GFRP Bars

Glass fiber-reinforced polymer (GFRP) bars are used as internal reinforcement in many structural applications. The structural performance of GFRP-reinforced concrete elements is dependent on the physical and mechanical properties of GFRP reinforcement. There is a lack of experimental data on the flexural behavior of concrete beams reinforced with ribbed GFRP bars. This study evaluates the flexural strength and serviceability performance of concrete beams reinforced with ribbed GFRP bars. A total of 11 GFRP-reinforced concrete beams with dimensions of 4,350 × 400 × 200 mm (length × height × width) were constructed and tested under a four-point loading test setup. The main test parameters were the concrete cover, reinforcement ratio, bar spacing, and confinement due to the transverse reinforcement in the bending zone. The results uantify the effect of increasing the reinforcement ratio on the increase in the ultimate capacity and the reduction in deflection at the service and ultimate stages. In addition, the results showed that the increase in the confinement in the bending zone due to closely spaced stirrups resulted in a higher ductility index and ultimate capacity with no considerable effect on the postcracking stiffness of the beams. Moreover, based on the experimental results, the accuracy of deflection equations available in design codes and guidelines is evaluated and discussed.