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In this study, concrete canvas (CC) layers were used as a novel method to strengthen reinforced concrete (RC) beams because of their flexibility, rapid installation, fast curing, and rapid strengthening. Due to the importance of the CC mechanical properties, various combinations of cement including ordinary (OPC) and High Alumina (HAC), as well as silica fume, were investigated to determine the optimal mixture for strengthening RC beams. The results indicate that substituting 75% of HAC with OPC significantly boosted flexural strength by 33%, and increased tensile strength in the warp and weft directions by 25% and 21%, respectively. The study examined six RC beam specimens in a four‐point flexural test, assessing their flexural properties, ductility, cracking behavior, and energy dissipation. The number of CC layers and the bonding method, which involved either the conventional externally bonded reinforcement (EBR) technique or the externally bonded reinforcement on grooves (EBROG) technique were studied. The experimental results revealed the superiority of the EBR method over the EBROG technique due to the uniform bond between CC and the concrete surface. Using the EBR technique, improvements of 35% and 51% were observed in the load‐carrying capacity of the beams strengthened with one and two CC layers, respectively. It is while for the beam with an improved loading capacity of 51%, the crack width decreased from 5.3 to 2.1 mm, and the energy dissipation increased by three times compared to the control specimen. Theoretical analysis also was performed to calculate the load‐carrying capacity of the RC beams strengthened with CC layers. [ABSTRACT FROM AUTHOR]

Many studies have suggested that engineered cementitious composite (ECC) could be a highly efficient and cost‐effective material for enhancing the flexural strength of reinforced concrete (RC) beams. Recently two effective retrofitting configurations using steel and polyvinyl‐alcohol hybrid fiber reinforced engineered cementitious composite (SPH‐ECC) were proposed (Qasim et al., Eng Struct, 2023, 284, p. 115992) and their high effectiveness for enhancing the flexural strength of RC beam was verified experimentally. However, to examine the performance of these strengthening configurations thoroughly by conducting experiments to cover practical ranges of design parameters is deemed to be too expensive and time consuming. In this study, a numerical parametric study of SPH‐ECC strengthened RC beams was conducted by employing a validated finite element (FE) modeling procedure developed by the authors. The effects of four key design parameters including the compressive strength of concrete and SPH‐ECC, the thickness of SPH‐ECC strengthening layer and the area of reinforcement bars embedded in SPH‐ECC layers on the flexural performance of the strengthened beams were studied. Parametric study results showed that the area of reinforcement bars in the SPH‐ECC layers could significantly affect the flexural strength of the strengthened beams. Furthermore, in order to allow engineers to predict the flexural strength of the strengthened beams quickly, two simple but accurate analytical models were also developed for the two strengthening configurations considered. Their reliability and accuracy were then verified and confirmed by comparing with the parametric study results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cement has historically been a major contributor to carbon dioxide emissions, and substituting cement in concrete with alternative cementitious materials will lead to a decrease in carbon footprints. A vast amount of literature focuses on the mechanical properties and performance of concrete partially replaced with different cementitious materials. However, the literature on the structural performance of concrete with different cementitious materials is very limited. Therefore, the main aim of the current experimental study is to evaluate the flexural and shear performance of reinforced concrete (RC) beams cast with various replacement percentages of ordinary Portland cement (OPC) with supplementary cementitious materials (SCM) such as ground granulated blast furnace slag (GGBS) and fly ash. A total of 33 RC beams were cast with 50% and 70% replacement of cement with GGBS and fly ash. In addition, the tensile and compressive strengths of the different mixes with GGBS and fly ash were also compared with the 100% OPC mix at 28 and 56 days. All beams were subjected to monotonic four-point bending tests and load-deflection response curves along with failure modes were presented. The experimental results showed that the average compressive and tensile strength of mixes with GGBS and fly ash replacement were comparable with OPC. The mixes with 50% replacement and higher usage of GGBS showed higher compressive strengths compared to mixes with 70% replacement. In addition, the flexural performance of beams with GGBS and fly ash were comparable to the specimen with 100% OPC. Even GGBS and fly ash replacement increased the stiffness and yield strength of the beam specimens by 36 and 16% compared to the control specimen. The specimens tested at 56 days with higher usage of fly ash and 50% replacement showed the highest flexural load as compared with other specimens. In the case of the shear specimens, the normalized ultimate shear capacity of RC beams is not significantly affected when OPC is replaced with 50% and 70% of GGBS and fly ash, respectively. Therefore, it can be concluded that the overall behavior of SCM beams was comparable to that of the control OPC beams. The ACI 318-19 design guidelines were also used to predict the flexural and shear capacity of RC beams cast with GGBS and fly ash. The aforementioned experiments indicate the viability and effectiveness of cement replacements in concrete with SCM, which in return, contribute to lower carbon footprints. [ABSTRACT FROM AUTHOR]

The objective of this research is to experimentally study the flexural behavior of hybrid reinforced concrete beams. Three test beams, each with dimensions of (2200 X 150 X 240) mm, were fabricated for this purpose. The first beam was constructed using ordinary concrete, while the second beam consisted of two layers of high-strength concrete in the compression zone and normal concrete in the tension zone. The third beam was entirely cast using high-strength concrete. In terms of reinforcement, all beams were equipped with 2φ12 steel bars in the tension zone and 2φ12 steel bars in the compression zone. Additionally, φ12 steel bars were employed to resist shear forces, distributed along the length of the beams with a spacing of 125 mm c/c. Two-point loading was applied to all beams until failure occurred. The results obtained from the experimental tests reveal that the use of hybrid concrete beams enhances the ultimate load capacity by approximately 20.93%. On the other hand, beams constructed entirely from highstrength concrete exhibited an increase in failure load capacity by approximately 28.68%. [ABSTRACT FROM AUTHOR]

This study intended to measure the efficiency of different strengthening techniques to advance the flexural characteristics of reinforced concrete (RC) beams using glass fiber-reinforced polymer (GFRP) laminates, including externally bonded reinforcement (EBR), externally bonded reinforcement on grooves (EBROG), externally bonded reinforcement in grooves (EBRIG), and the near-surface mounted (NSM) system. A new NSM technique was also established using an anchorage rebar. Then, the effect of the NSM method with and without externally strengthening GFRP laminates was studied. Twelve RC beams (150 × 200 × 1500 mm) were manufactured and examined under a bending system. One specimen was designated as the control with no GFRP laminate. To perform the NSM method, both steel and GFRP rebars were used. In the experiments, capability, as well as the deformation and ductileness of specimens, were evaluated, and a comparison was made between the experimental consequences and existing standards. Finally, a new regression was generated to predict the final resistance of RC beams bound with various retrofitting techniques. The findings exhibited that the NSM technique, besides preserving the strengthening materials, could enhance the load-bearing capacity and ductileness of RC beams up to 42.3% more than the EBR, EBROG, and EBRIG performances. [ABSTRACT FROM AUTHOR]

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Shear strength of a reinforced concrete (RC) member should be larger than its flexural strength, in order to prevent the shear failure, which is sudden and brittle. The reliability of a RC beam against the shear failure is closely related to the reliability of the equation determining its shear strength. In this study, the reliabilities of shear strength equations of RC beams were investigated by constructing the performance function between prediction equations and experimental results using a second-moment approach. It is assumed that the random variables are statistically independent, and the correlation effects are not taken into account. It is observed from the reliability rankings that the equation of EN 1992:2004 yields the lowest failure probability while the equation of Zsutty is the highest failure probability. [ABSTRACT FROM AUTHOR]

This research aims to conduct a comparative analysis of the first crack load, flexural strength, and shear strength in reinforced concrete beams without stirrups. The comparison is made between the conventional model developed according to the current design code (ACI building code) and an unconventional approach using Artificial Neural Networks (ANNs). To accomplish this, a dataset comprising 110 samples of reinforced concrete beams without stirrup reinforcement was collected and utilised to train a Multilayer Backpropagation Neural Network in MATLAB. The primary objective of this work is to establish a knowledge-based structural analysis model capable of accurately predicting the responses of reinforced concrete structures. The coefficient of determination obtained from this comparison yields values of 0.9404 for the first cracking load, 0.9756 for flexural strength, and 0.9787 for shear strength. Through an assessment of the coefficient of determination and linear regression coefficients, it becomes evident that the ANN model produces results that closely align with those obtained from the conventional model. This demonstrates the ANN's potential for precise prediction of the structural behaviour of reinforced concrete beams. [ABSTRACT FROM AUTHOR]

Structurally deficient bridges are commonly retrofitted using conventional methodologies, including reinforced concrete, steel jackets, and fiber-reinforced polymers. Although these retrofit methods aim to improve structural performance, exposure to aggressive environments may undermine the durability performance of the retrofit material. More recently, ultra-high-performance concrete (UHPC) has provided an alternative to conventional construction methods, with its superior material characteristics favoring its use in retrofit applications. In this study, a large-scale reinforced concrete (RC) T-beam is constructed and artificially damaged. The T-beam is then retrofitted with an external envelope of UHPC on all faces. Sandblasting is introduced to the surface, providing partially exposed reinforcement in the T-beam to simulate material deterioration. Additional reinforcement is placed in the web and flange, followed by casting the enveloping layer of UHPC around the specimen. The feasibility of this method is discussed, and the structural performance of the beam is assessed by subjecting the beam to cyclic and ultimate flexural loading. This paper presents the results of cyclic and ultimate testing on the RC-UHPC composite T-beam regarding load–displacement, failure mode, and strain responses. The retrofitted T-beam specimen is subjected to a cyclic loading range of 131 kN for 1.576 million cycles. Despite no visible cracks in the cyclic testing, the specimen experiences a 12.22% degradation in stiffness. During the ultimate flexural testing, the specimen shows no relative slip between the two concretes, and the typical flexural failure mode is observed. By increasing the longitudinal reinforcement ratio in the web, the failure mode can shift from localized cracking, predominantly observed in the UHPC shell, toward a more distributed cracking pattern along the length of the beam, which is similar to conventional reinforced concrete beams. [ABSTRACT FROM AUTHOR]

This study aims to investigate the flexural performance and design methods of flexural concrete beams reinforced with basalt fiber–reinforced polymer (BFRP) and steel bars. Eight concrete beams, which included six reinforced with a combination of BFRP and steel bars, one reinforced with only steel bars, and one reinforced with only BFRP bars, were constructed and then tested under four-point loading. For hybrid-reinforced concrete (RC) beams, two types of BFRP bars (ribbed and sand-coated) and different reinforcement ratios were considered. The test results are discussed in terms of the flexural capacity, reinforcement strain, deflection responses, and cracking behavior. Experimental results showed that the crack width of the hybrid-RC beam, obtained by adding BFRP bars in the concrete cover of the steel-RC beam, reduced by approximately 40% compared with that of the steel-RC beam, and the strength utilization of BFRP bars in hybrid-RC beams was higher than that in the BFRP-RC beam. Additionally, the cracking moment, nominal flexural strength, and midspan deflection of the hybrid-RC beams were predicted by using existing design models. The bond-dependent coefficients (kb) of the ribbed and sand-coated BFRP bars were assessed by using test data. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Near Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP) reinforcement technique to improve the flexural strength of reinforced concrete members has become increasingly attractive in recent years. In this study, the practical problem of concrete cover depth cutting limitation was investigated. Twelve specimens were tested by four-point bending until failure. Experimental parameters include concrete cover depth, CFRP reinforcement type, CFRP positioning, and stirrups status. Furthermore, a nonlinear FEA model was developed to simulate the tested beams and was able to predict the experimental behavior satisfactorily. A series of parametric studies were then performed using this model to understand the effect of various reinforcement parameters on the flexural performance of the beam. The results showed that Strengthening with CFRP resulted in a significant increase in yield and ultimate strengths, but a significant ductility loss was recorded due to CFRP strip debonding in the strengthened beams, this problem was addressed by using more efficient strengthening techniques utilizing the effective bond length and a proper groove depth and positioning for the NSM bars. [ABSTRACT FROM AUTHOR]

A database of results from 27 tests of diagonally reinforced concrete coupling beams was analyzed to develop improved force-deformation envelopes (backbone curves) for modeling and analysis of coupling beams. The database, which was selected from a larger set of 60 test results, comprises specimens that generally satisfy ACI 318-19 requirements. The analyses show that the chord rotation capacity of diagonally reinforced concrete coupling beams compliant with ACI 318-19 is closely correlated with beam clear span-to-overall depth ratio and, to a lesser extent, the ratio of hoop spacing to diagonal bar diameter. A simple expression is proposed for estimating beam chord rotation capacity. Coupling beam strength was shown to be more accurately estimated from flexural strength calculations at beam ends than other methods. Recommendations are made for obtaining more accurate backbone curves in terms of chord rotation capacity, strength, and stiffness. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effectiveness of para-aramid fiber sheet in enhancing the flexural performance of reinforced concrete (RC) beams made with Environmental-Friendly Recycled Coarse Aggregates. The experimental program examines the effect of substitution ratio of recycled aggregates (0%, 30%, and 50%), type of para-aramid fiber sheet (KN 206 RFL and KN AA070-RFL), and the method of fiber sheet attachment (bottom and bottom-side). The test results show that the ultimate load-carrying capacity of RC beams reinforced with para-aramid fiber sheet attached to the bottom and side parts increased by 23.9% compared to the unreinforced specimens. The main findings of the study include the identification of the BU-type attachment method as the most effective method for enhancing the flexural performance of reinforced concrete beams. The comparison of the experimental results with analytical predictions showed that the nominal flexural strength obtained from the experimental study was lower than the analytical predictions, but the ductile capacity of the specimens indicated the effectiveness of para-aramid fiber sheet reinforcement in EFRCA RC beams for flexural strength. The study highlights the potential of using para-aramid fiber sheet in improving the flexural behavior of RC beams made with recycled aggregates, offering a sustainable solution for the construction industry. [ABSTRACT FROM AUTHOR]

In this study, the feasibility of utilizing locally produced coarse recycled aggregate (RA) from demolition waste in the UAE for structural applications was investigated. A comprehensive literature review on the subject showed that the shear and flexural responses of reinforced beams utilizing aggregate from concrete demolition waste are greatly dependent on the aggregate replacement ratio and the quality of the recycled aggregate. The experimental program in this study consisted of three phases. Phase I focused on the evaluation of the physical and mechanical characteristics of the RA, Phase II addressed the mix design and fresh and hard properties of the concrete, and Phase III dealt with the flexural and shear behavior of structural members. The research involved twelve 150 mm × 300 mm reinforced concrete beams with a length of 1500 mm or 2000 mm that were made with 0% (control), 50%, or 100% recycled coarse aggregate, replacing natural coarse aggregate (NA). Two target concrete compressive strengths, 25 and 35 MPa, were considered in the investigation. The results showed that the recycled aggregates had lower crushing and LA abrasion values by 40% and 18–28%, respectively, whereas the absorption capacity was 40–300% higher compared to the natural aggregate. In addition, the mechanical properties of the concrete made with different replacement ratios (R%) of RA were either similar or slightly less than those of the control mix. The shear beam tests with f c ′ = 25 MPa showed that the 50%- and 100%-replacement-ratio beams demonstrated closely matched normalized shear strength values that exceeded their corresponding NA beam by 12.5%, while the shear beam tests with f c ′ = 35 MPa showed that the NA beam exhibited normalized shear strength surpassing the 50% RA and 100% RA beams by 12.5% and 17.5%, respectively. In the flexural beam tests, the flexural strength exhibited minimal disparities for the beams that shared the same RA% but differed in their compressive strength targets, and overall, the variation in the RA% had a marginal impact on the flexural strength of the beams. Further, an increase in the RA% corresponded to an increase in the shear ductility index, which was in contrast with the findings on the flexural ductility index. Furthermore, predictions of flexural strength using the ACI318-19 code and shear strength using the strut-and-tie model yielded comparable results to the experimental ones. [ABSTRACT FROM AUTHOR]

In this paper, the effectiveness of the strengthening by a wooden plate for reinforced concrete (RC) beams that incorporate waste sawdust (SD) as a partial substitute for fine aggregate (sand) has been investigated. To this end, two types of concrete mixtures were made: normal concrete (NC) and sawdust concrete (SDC), which was made by substituting 15% of the volume of sand with SD. Five RC beams (100 mm in depth, 200 mm in width, and 1500 mm in length) were experimentally tested for flexural behavior under four-point loading. Three strengthening schemes were used in this study. The first scheme used a wooden plate that was only fixed by an adhesive layer. The second and third schemes were applied by a wooden plate, which was fixed by an adhesive layer and steel angles (two and eleven angles). The findings of the study indicate that although the concrete's workability, compressive, and splitting tensile strengths were reduced with the addition of SD, the ultimate load of the beam with SD was lower than that of the control beam, with a slight variation of approximately 4%. Moreover, strengthening the RC beam with a wooden plate and two steel angles yielded the highest load capacity among all tested beams, 20% higher than the control specimen. The study's findings offered useful information for developing eco-friendly sawdust concrete beams with efficient strengthening techniques for potential future uses. [ABSTRACT FROM AUTHOR]

Despite having many advantages, using rubber to produce reinforced concrete members like beams is still restricted. When there is more waste tire rubber in concrete structures, rubber concrete's flexural and compressive strengths gradually decrease. However, this study used steel fibers to improve compressive strength and externally bonded carbon fiber-reinforced polymer (CFRP) sheets to increase flexural strength. Four groups of three reinforced concrete beams each were established for the study's use. The first and third groups of concrete beams used a volumetric replacement of fine and coarse aggregates with 5% and 10% waste tire rubber. However, steel fibers were added to the second and third groups at a rate of 1.25% of the concrete volume. Waste tire rubber and steel fibers were not replaced or added to the fourth group, the main reference group. The dimensions of each beam were 2.1×0.2×0.3 m. A concrete beam's first member is always free of external reinforcement, followed by its second member, which has one layer, and its third member, which has two layers of CFRP sheet. ABAQUS, a finite element analysis program, was used numerically to represent the third strengthening layer. The results showed that strengthening the reinforced rubberized concrete beams with a single layer of CFRP sheets increased the load at first crack and failure by 8.57% and 17.64%, respectively, compared to the unreinforced reference beam, compensating for the loss caused by the production of rubberized concrete and adding additional flexural strength. These loads increased by 31.43% and 26.45%, respectively, due to the steel fibers added to the beams containing these waste tire rubber. Strengthening with two layers of CFRP sheets increased the load at first crack and failure by 17.14 and 34.27, respectively. The steel fibers added to the beams that contained these amounts of waste tire rubber, on the other hand, caused these loads to increase by 42.86 and 49.23%, respectively. Strengthening with three layers numerically results in an exponential increase in load at the first crack and the failure by 8.03 and 52.88%, respectively. On the other hand, the loads on the beams that contained these quantities of waste tire rubber increased by 50.49% and 104.47%, respectively, when steel fibers were added to them. [ABSTRACT FROM AUTHOR]

The study of damage processes in concrete and their effects on the residual properties represents a key point related to the service life of reinforced concrete (RC) structures. The use of steel fibers in RC beams mainly improves the cracking control and the shear bearing capacity. Considering the shear behavior, the presence of fibers not only leads to partial or total substitution of secondary reinforcement, but they can also result in a modification of the failure behavior from a shear failure (brittle) to a bending (ductile) one. The contribution of fibers on flexural and shear behavior of sound and damaged RC beams was investigated using alkali‐silica reaction as a damaging tool. First, the evolution of deformations and cracks were measured on creep tests of RC beams with and without fibers and reactive aggregates. Second, the flexural and shear behavior of damaged and undamaged beams incorporating steel fibers were compared. Results showed that alkali‐silica reaction damage can provoke a reduction of RC beam ductility, while the flexural strength is preserved. Regarding shear, it was observed that even in damaged concrete, fibers were able to control the crack propagation and increase the bearing capacity. [ABSTRACT FROM AUTHOR]

This study aimed to assess the feasibility of utilizing geopolymer for repairing reinforced concrete beams. Three types of beam specimens were fabricated: benchmark specimens without any grooves, rectangular-grooved beams, and square-grooved beams. The repair materials employed included geopolymer material, and epoxy resin mortar, while carbon fiber sheets were used as reinforcement in select cases. The repair materials were applied to the rectangular and square-grooved specimens, with the carbon fiber sheets attached to the tension side of the specimens. To evaluate the flexural strength of the concrete specimens, a third-point loading test was conducted. The test results indicated that the geopolymer exhibited higher compressive strength and shrinkage rate compared to the epoxy resin mortar. Furthermore, the specimens reinforced with carbon fiber sheets demonstrated even greater strength than the benchmark specimens. In terms of flexural strength under cyclic third-point loading tests, the carbon fiber-reinforced specimens exhibited the ability to withstand over 200 cycles of repeated loading at 0.8 times the ultimate load. In contrast, the benchmark specimens could only withstand seven cycles. These findings highlight that the use of carbon fiber sheets not only enhances compressive strength but also improves resistance to cyclic loading. [ABSTRACT FROM AUTHOR]

The present study investigates the flexural behavior of reinforced concrete (RC) beams; the longitudinal reinforcing rebars of the beams were corroded and then strengthened with carbon fiber-reinforced polymer (CFRP). The corrosion of the longitudinal tension reinforcing rebars in eleven beam specimens was accelerated in order to obtain different corrosion levels. Afterwards, the beam specimens were strengthened by bonding one layer of CFRP sheets to the tension side to restore the strength loss due to the corrosion. The failure modes, flexural capacity, and midspan deflection of the specimens with different corrosion levels of the longitudinal tension reinforcing rebars were obtained by the four-point bending test. It was found that the flexural capacity of the beam specimens decreased with the increase in the corrosion level of the longitudinal tension reinforcing rebars and that the relative flexural strength was only 52.5% when the corrosion level was 25.6%. The stiffness of the beam specimens decreased significantly when the corrosion level was higher than 20%. Through a regression analysis of the test results, a model for the flexural bearing capacity of the corroded RC beams strengthened with CFRP was proposed in the study. [ABSTRACT FROM AUTHOR]

The motive of building sustainable structures and strengthening the structural members is important to overcome the problems associated with poor initial design and/or construction, accidental events, and degradation related to the environment. This paper aims to assess the flexural behavior of a prestressed basaltic fiber-reinforced polymer- (FRP-) strengthened reinforced concrete (RC) beam under static load through the finite-element method using ABAQUS CAE that is validated with experimental results from relevant literature. To achieve the desired objective, 18 models were prepared based on prestressing level, thickness of basalt FRP (BFRP), width of BFRP, length of BFRP, bond between concrete and BFRP, and type of FRP as study parameters. The results indicate that the use of prestressed BFRP is efficient in strengthening the flexural strength of the RC beam. Compared to nonstrengthened specimens, the flexural capacity of the specimens strengthened with BFRP at prestressing levels of 0%, 15%, 35%, and 45% show enhancement of 6.09%, 9.17%, 13.89%, and 17.57%, respectively. While increasing the width, length, and thickness of the prestressed BFRP section, increased yielding and ultimate load capacity of the specimen have been obtained; however, the ductility has been reduced up to 13.87% with increasing the BFRP thickness. The result also shows that the specimen strengthened with prestressed BFRP has better ductility than the prestressed carbon FRP (CFRP)-strengthened specimen; however, the model strengthened with prestressed CFRP has shown higher load-carrying capacity. It is also noticed that a cohesive bond better suited the experimental specimen than the fixed interference of the concrete surface, and relative to the cohesive bond, the fixed interference has shown a 17.4% higher ultimate load carrying capacity. [ABSTRACT FROM AUTHOR]

The growing concern to reduce global warming has necessitated the use of more eco-friendly materials in construction. The study is focused on the utilization of cassava peel ash as supplementary cementitious material and bamboo as reinforcement in concrete beams. The response surface methodology approach was explored to determine the effect of simultaneously varying the cassava peel ash content, bamboo size, beam length, and beam depth on the flexural strength and strain of beams. An analysis of variance was carried out on experimentally obtained results to determine the accuracy of the obtained models and the contributions made by the linear interaction and quadratic terms on flexural strength and flexural strain. The coefficient of determination obtained for RSM models showed a good correlation between all predicted and experimentally obtained results. The optimum conditions obtained for bamboo-reinforced concrete containing cassava peel ash were 3% cassava peel ash, 16 mm bamboo diameter, 500 mm beam length, and 150 mm beam depth. The predicted flexural strengths were 11.85, 14.34, and 14.95 N/mm2 and flexural strains of 0.64, 0.67, and 0.91 for 28 days, 56 days, and 90 days, respectively. To validate the model prediction, a laboratory experiment was conducted using the optimum mix design proportion. From the results obtained, it was observed that the experimental results were close to those predicted by the models. These models can be efficiently used for simulating the flexural behavior of bamboo-reinforced concrete beams. [ABSTRACT FROM AUTHOR]

Overlaying a reinforced concrete beam (RCB) with polymer cement mortar (PCM) is a strengthening method that improves flexural stiffness by the increasing sectional force. However, the reduction between bond strength and the reinforcement in PCM overlay at high temperatures results in an increase in flexural crack spacing. Therefore, the pullout force must be taken into account when estimating the flexural capacity of PCM-overlay RCBs. The experimental study aims to assess the flexural performance of PCM-overlay RCBs under three different environmental temperature conditions: 20, 40, and 60°C. Seventeen beams with varying reinforcement ratios in PCM are tested at the mentioned temperature levels. Experimental results indicate a decrease of approximately 6 to 13% in strength at elevated temperatures, which can be attributed to the reduction in bond strength of the reinforcement caused by the degradation of the PCM. Analytically, the strength reduction is calculated by determining the average crack spacing in the flexural zone. Therefore, the proposed average crack spacing method (CSM) predicts that the flexural strength is within ±10% limits of experimental observations. This method is more conservative than the conventional sectional analysis method (SAM). The average CSM can contribute to a safer design of PCM-overlay RCBs by preventing overestimated prediction of the ultimate strength at high environmental temperatures. [ABSTRACT FROM AUTHOR]

In this study, an experimental program was developed to investigate the flexural behavior of pre-damaged reinforced concrete (RC) beams that had been repaired and strengthened using carbon fiber-reinforced polymer (CFRP) laminates under a monotonic load. Two techniques were used: externally bonded reinforcement (EBR) and near-surface-mounted (NSM) reinforcement, to repair and strengthen the tested beams. The experimental program involved casting and testing nine simply supported RC rectangular beams; one beam was considered as the reference beam and did not undergo additional strengthening, and the remaining beams were strengthened using CFRP laminates. These eight beams were divided into two main groups for the purposes of strengthening: beams for which the EBR technique was used, and beams for which the NSM technique was used. The primary variables observed in the EBR and NSM groups included four damage percentages obtained according to the preload (20, 40, 60, and 80%) from the ultimate load carried by the reference beam. The experimental results show that decreasing the damage percentage leads to an increase in ultimate strength from about 3.6% to 17.2% for the beams repaired using the EBR technique and from 27.6% to 57% for the beams repaired using the NSM technique; additionally, the NSM method was more effective than the EBR method in terms of the flexural strength and mode of failure. However, using CFRP laminates enhances the flexure capacity of strengthened RC beams. [ABSTRACT FROM AUTHOR]

The concrete cover is a part of the concrete that provides the required protection for the reinforcing steel within the required element from external effects. This concrete cover can be damaged for an assortment of reasons, one of which is environmental factors. As a result, this research focused on the effect of worn concrete covering on the structural response of beams. Moreover, the possibility of repairing or replacing this concrete cover with a cement material was done by testing seven beams with the exact dimensions (2700 mm long, 250 mm deep, and 140 mm wide). The first specimen was a control specimen, while in the remaining specimens, a part of the concrete cover was removed in the midspan region with a length of 600 mm and in different formats. The part below the neutral axis (tension zone) was removed in the first two specimens. The part above the neutral axis (the compression zone) was removed in the second two specimens. The whole cover was removed within the specified distance for the other two specimens. In one out of every two of these six specimens, the removed concrete cover was replaced with cementitious material. A flexural test was performed for all specimens, and the conclusion was reached that damaging or removing the concrete cover from the tensile region (below the neutral axis) is less harmful than from the compression region since the beam is often designed as a cracked section. Also, removing the concrete cover from the compression region gives cracks a greater width than removing the concrete cover from the tension region at the same loading level. In the case of replacing the concrete cover with a cementitious one, if the replacement is in the compression zone, it will result in cracks when loading with a width greater than that of the rest of the cases. For specimens that removed their concrete covers from the tension zone, compression zone, and the whole section, the failure loads decreased by 39%, 20%, and 23%, respectively, concerning the control beam. In contrast, all these specimens were repaired with cementitious materials, with an ultimate load capacity approximately equal to the control beams. From these results, any damaged concrete cover for beams in any zone with cementitious materials having high strength and a good bond with old concrete sections can be repaired. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) structures can experience damage due to material degradation, overloading, and other circumstances. Damage can take the form of spalling and delamination. One of the straightforward techniques to repair those localized damages is patching. Several types of materials can be used as patching material, one of which is Unsaturated Polyester Mortar (UPR)-Mortar. The UPR-mortar possesses low elastic modulus, high early strength, and adequate bond strength. However, only a few studies investigate the efficacy of employing the UPR-mortar patching to rehabilitate reinforced concrete structures. The current study uses experimental and numerical methods to examine how patching with UPR-mortar affects the flexural performance of reinforced concrete beams. Loading tests on RC beams with and without patching repair were carried out in the laboratory. During the loading test, the load and midspan deflection, strain development of the flexural reinforcements, and flexure crack evolution were monitored. Numerical simulations were also performed to validate the experimental results and further investigate the beam behavior with varying patching lengths. The results indicate that the remediation of RC beam with UPR-mortar patching can restore and boost flexural strength. Furthermore, when the patching length exceeds the maximum beam moment zone's length, the beam's flexural capacity increase becomes more apparent. [ABSTRACT FROM AUTHOR]

Previous studies have shown that the use of calcium stearate in concrete can increase the impermeability of concrete, the corrosion resistance, the reduce chloride ion infiltration and reduce drying shrinkage in concrete. Unfortunately, its effect on the mechanical properties of reinforced concrete has not been well studied. This study aims to determine the effect of calcium stearate on the bond of steel reinforcement with concrete and the flexural strength capacity of reinforced concrete. The study has been conducted on concrete with a quality of 30 and 40 MPa. The doses of calcium stearate used in this study have been 0, 1, 5 and 10 kg per cubic meter of concrete. The specimen for the bond strength of steel bar is a concrete cylinder with a diameter of 15 cm and a height of 30 cm, and a steel bar with a diameter of 16 mm and a length of 42 cm. Reinforced concrete beams measuring 10 cm × 10 cm × 100 cm are used as flexural specimens. The number of specimens used is 2 pieces for each concrete code. The results have showed that the addition of calcium stearate to the concrete has slightly decreased the bond and the flexural strength of the concrete at both grade 30 MPa and 40 MPa. [ABSTRACT FROM AUTHOR]

This paper is an experimental study of the effectiveness of using internal and external alkali-resistant glass fabric textile (AR-GT) layers for flexural strengthening of reinforced concrete (RC) beams. The experimental work compares internal single and triple layers of AR-GT as supplemental flexural reinforcement with textile-reinforced mortar (TRM) in RC beams subjected to four-point bending loading. In addition, a control beam specimen is cast with no AR-GT fabric. Monitoring the load–deflection curves, crack patterns, and strengthening layer performance showed that using AR-GT for internal and external layers increased the load-carrying capacity of RC beams. The failure patterns of beams with one external AR-GT layer and three internal AR-GT layers showed a similar trend, with higher loading capacity and lower deflections than the other beams. Three internal textile AR-GT layers recorded higher flexural strength (52%) than one internal layer (6.3%), compared to the control beam specimen. Moreover, using one layer of external AR-GT fabric exhibited higher flexural strength than using one or three internal layers (56.8%). [ABSTRACT FROM AUTHOR]

Fibers that are used to enhance the residual flexural and tensile strength of fiber reinforced concrete (FRC) are reinforcing materials possessing good mechanical characteristics and properties. The effect of fiber on the flexural strength of FRC at elevated temperatures is limited and hence the present paper studies the influence of fibers (basalt, carbon, glass, polypropylene, polyvinyl alcohol) on strength grades M20, M30, M40 and M50 concrete specimens exposed to elevated temperature for a duration of 30, 60, 90 and 120 min, respectively, with an ISO 834 fire-curve. The objective of the study is to determine the effect of temperature on the flexural strength of fiber reinforced concrete prism and reinforced concrete beam specimens. Past studies have revealed that concrete's tensile strength is one of the primary factors affected by exposure to higher temperatures, more so than its compressive strength. The residual strength of the specimens was determined after cooling in air, and it was found that carbon fiber reinforced concrete specimens retained more residual flexural strength than the other specimens. The residual energy absorption capacity was analyzed and an empirical relationship was established to find the residual flexural strength in terms of the grade of concrete, the type of fiber and the duration of heating. [ABSTRACT FROM AUTHOR]

In this study, the efficacy of strengthening of reinforced concrete (RC) beams in shear by utilizing high-performance fiber-reinforced concrete (HPFRC) was explored. The shear strengthening was achieved by epoxy bonding of prefabricated HPFRC strips or plates onto the beams. The beams were strengthened utilizing two different strengthening schemes: (i) plates side strengthening (ii) vertical strips applied at shear critical sections. The behavior of the two configurations was compared to the behavior of non-shear reinforced and shear-reinforced RC beams. The high-performance concrete (HPC) utilized contains 1.5% of steel fibers per volume of HPC mortar and is known as HPFRC. Parameters determined were the flexural strength and compressive strength of HPFRC mortar. The obtained results revealed that HPFRC realized a 28-day flexural strength of 20 MPa and a compressive strength of 108 MPa. Moreover, HPFRC strengthened RC beams experienced an increased in strength capacity of about 50% for plates and 36% for vertical strips compared to the RC beams with no stirrups. The results for HPFRC strengthened beams with plates were superior compared to those of the stirrup-reinforced beams, whereas the results of HPFRC strips strengthened beams were almost identical to the stirrup-reinforced beams. Also observed, was an improvement in the ductility of the beams with the best results achieved when employing HPFRC plates and strips. Highlights: Shear Strengthening of RC beams by HPFRC plates utilizing two methods. Precast HPFRC plates bonded by epoxy adhesive and anchored. Continuous shear strengthening resulted in high-capacity enhancement and ductility. [ABSTRACT FROM AUTHOR]

This paper develops reliability-based design provisions for flexural strength of reinforced concrete (RC) beams with hybrid arrangements of fiber-reinforced polymer (FRP) and steel reinforcements. Firstly, three flexural failure modes of the hybrid RC beams were distinguished through balanced reinforcement ratios, and closedform solutions for the flexural strength were proposed. Based on the Monte Carlo simulation technique, probabilistic analyses of flexural failure modes were conducted to determine the minimum and maximum flexural reinforcement ratios for the hybrid beams. The first-order second-moment method was then applied to calibrate strength reduction factors to meet uniform target reliability level, βT = 3.5. Sensitivity analyses were performed to identify the most important parameters that influence the reliability indexes, indicating that the reliability of the hybrid FRP-steel RC beam decreased with the increase of the reinforcing index χ. As a result, this study recommended flexural strength reduction factors of (0.9 to 0.15χ) for the hybrid reinforced beam to achieve the target reliability index of 3.5. [ABSTRACT FROM AUTHOR]

Four‐point bending tests were conducted to investigate the flexural properties of fly‐ash‐based geopolymer concrete beams. Although geopolymer concrete has a stress–strain relationship with brittle compressive softening behavior, it can be used as a flexural member because it exhibits ductile bending moment–deflection relationships when used with compression reinforcing bars and transverse reinforcement. The test results revealed that the conventional design method can be used to estimate the bending moment–deflection relationship of geopolymer concrete beams. However, the stiffness reduction ratio for yielding must be modified to consider the difference in the modulus of elasticity between geopolymer concrete and ordinary Portland cement concrete. [ABSTRACT FROM AUTHOR]

The significant CO2 emissions that can be associated with cement manufacture is the primary cause of global warming. Thus, the authors and research groups are motivated by many factors to find long-term solutions to this problem. Geopolymer concrete is such type of concrete in which the primary binder is resulted from alkali activation of some source materials like fly ash, metakaoline, rice husk ash, and ground granulated blast furnace slag. Commonly, geopolymer concrete gives comparable mechanical strength properties to conventional concrete. The use of this type of concrete is restricted by the properties of the used source materials and the molar concentrations of the alkali activator. As a consequence, making investigations to the relevant structural behavior as a result of these variables are rich sources of scientific research. The goal of this work is to provide a brief overview to the recent contributions that have dealt with the structural behavior of geopolymer concrete. The context of this paper was obtained to illustrate the main findings as well as the used source materials and some additional considerations. [ABSTRACT FROM AUTHOR]

This paper describes a study on finite element modeling (FEM) carried out on the ABAQUS platform for the prediction of flexural strength of corrosion-damaged reinforced concrete (RC) beams strengthened using layers of ultra-high-performance concrete (UHPC). Considering different combinations of the degree of reinforcement corrosion and thickness and configuration of UHPC layers, a total of twenty-two corroded, un-strengthened, and strengthened RC beam specimens were tested to record their flexural behavior. Following the flexural testing, the FEM was carried out considering the degradation in the diameter and the yielding strength of the corroded reinforcing bars. The cohesive surface bonding approach was used to simulate the interfacial bond stress slip between the corroded bars and surrounding concrete. The results of the FEM were validated using the experimental test results of the respective beam specimens. The FEM results (including crack pattern, flexural strength, stiffness, and linear and nonlinear behavior of the strengthened RC beams) were found to be in close agreement with the corresponding experimental test results. This indicates that the proposed FEMs can capture the flexural behavior of the corroded RC beams strengthened using layers of UHPC with high accuracy. Furthermore, a parametric study was carried out using the validated FEMs to investigate the effects of varying the compressive strength and thickness of UHPC layers on the flexural strength of the corroded strengthened RC beams. [ABSTRACT FROM AUTHOR]

The durability of reinforced concrete structures has always been an important problem in civil engineering because steel rebars rust easily. Therefore, fiber-reinforced polymer (FRP) rebars possessing good corrosion resistance, low weight, and easy construction has become a substitute for reinforcement. However, since FRP rebar has a low elastic modulus and is a brittle failure material, large deflections and cracks occur in the FRP concrete beam with no obvious warning before failure. A hybrid reinforced concrete beam that combines the advantages of steel rebar and FRP rebar is a good structural form. The reliability of hybrid reinforced beams must be analyzed to ensure their safety. A flexural performance test of the hybrid basalt FRP (BFRP)–steel-reinforced beam was performed, the failure mode was explored, and the numerical models were established. The accuracy of the models was verified by comparing them with the test results. The numerical models were used to establish a database (630 cases) that was combined with existing research results (33 cases), to obtain the statistics of the uncertainty of the prediction model. Reliability analysis of a large-scale design space was conducted to calibrate the BFRP. Finally, the average deviation from the target reliability index suggested that the values of the partial coefficient of the materials range from 1.2 to 1.4. [ABSTRACT FROM AUTHOR]

The use of steel- and carbon-fiber-reinforced polymer (CFRP) bars as combined reinforcement within concrete members promises strength enhancement and ductility improvement. To verify this and to assist the design of concrete members with combined reinforcement, experimental and theoretical investigations were conducted on 17 one-way concrete slabs, including six control slabs reinforced exclusively with steel or CFRP bars. Flexural strength, failure modes, cracking loads, load–deflection behavior, moment–curvature relationship, and ductility evaluation were investigated. Amount of reinforcement and combination ratio of steel to CFRP were the key parameters. Test results indicated the effectiveness of combined reinforcement in terms of increasing the flexural strength of steel RC slabs from one hand and ductility improvement of CFRP RC slabs from the other hand. Theoretical analysis successfully predicted the ultimate flexural capacity and modes of failure. Two terms were defined: effective reinforcement ratio and critical reinforcement ratio, which can be used to effectively select a favorable mode of failure when designing concrete slabs reinforced with combined reinforcement. It was found that increasing ratio of steel to CFRP in combined reinforced slabs resulted in stiffer load–deflection and moment–curvature curves. Ductility evaluation showed the critical role of deformability factor in comparison with conventional ductility index and curvature ductility in determining the ductility of combined reinforced slabs. It was found that a combination ratio of steel to CFRP amount in the range of 2.54–3.38 can achieve a satisfactory ductility index and curvature ductility, as well as a low deformability factor in under-reinforced concrete slabs with combined reinforcement. [ABSTRACT FROM AUTHOR]

This research studies the effect of glass fiber-reinforced polymer (GFRP) bars as compressive reinforcement in reinforced concrete (RC) beam members. Three singly and six doubly reinforced GFRP-RC beams were tested under a four-point loading configuration. The effect of compressive reinforcement on the load-bearing capacity, ductility, stiffness, and failure mode is determined. Also, the compressive performance of GFRP bars is evaluated by testing GFRP-RC cylinders. According to the results, GFRP bars in compression had a limited contribution to enhancing flexural strength, and the maximum increment in the flexural capacity of doubly reinforced beams compared to singly reinforced specimens was 5%. GFRP-RC cylinders demonstrated a similar pattern, as the maximum strength increase compared to control specimens was 8%. Based on the evaluation of GFRP behavior, the contribution of bars in compression is limited due to the maximum strain that concrete withstands under compression. Considering the singly reinforced specimens, due to the presence of compressive GFRP bars, the stiffness of the doubly reinforced beams was reduced (up to 16%); however, the curvature and ductility were increased (up to 10% and 35%, respectively). In the end, a method based on deformations at the near-peak and peak load capacity was proposed to calculate the ductility of beams. The method predicts ductility enhancement due to compressive bars, as was observed in experiments, and also makes a distinction on failure modes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Textile-reinforced mortar (TRM) is used to strengthen reinforced concrete (RC) structures using a textile and inorganic matrix. TRM is a part of textile-based composites; the basic structural behaviors, application methods, and methodologies for the extension of actual structures in TRM were studied. However, structural behavior and performance verification which depict the long-term service situation and fatigue is limited. Therefore, this study, verified the flexural behavior of TRM-strengthened beams and their fatigue performances using carbon- and alkali-resistant (AR) glass textiles through 200,000 load cycles. TRM-strengthened beams were applied to an optimization strengthening method which consisted of whether the textile was straightened. According to the test results, the strengthening efficiency of TRM-strengthened beams when subjected to cyclic loading was lower than that of the monotonic loading, except for the straightened carbon textile specimen. The average efficiency of the AR-glass textile (straightened and non-straightened) and carbon (non-straightened) was 0.86 compared to the TRM-strengthened beam subjected to monotonic loading in terms of flexural strength. In the case of deflection, the average efficiency of the AR-glass textile type was similar to the monotonic loading test results, while that of the non-straightened carbon textile was improved. The Ca-S specimen that was used to straighten the carbon textile showed a reliable structural performance with a strength efficiency of 0.99 and a deflection efficiency of 0.97 compared to the monotonic load test. Therefore, TRM strengthening using a straightened carbon textile is expected to be sufficient for the fatigue design of TRM-strengthened beams. [ABSTRACT FROM AUTHOR]

Experimental study of the flexural implementation of high-strength reinforced recycled aggregate mixture is investigated for 100x150x1000 mm beams of reinforced concrete with different coarse recycled aggregate ratios plus three steel reinforcement ratio (ρ) casting and testing at 28 days. The aim of this research is to use coarse recycled aggregate ratios as a natural coarse aggregate replacement by (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100%) in high strength concrete. Former investigations experiments have been carried out and provided on the characteristics of the mixture prepared with recycled aggregates, such as strength in compressive, workability, flexural tensile strength, and splitting tensile strength. Prism and cylinders have been prepared, and specimens have been tested at ages 7, 14, 28 days of curing. This investigation considers the flexural efficiency of reinforced recycled aggregate mixture beams in describe as cracking and ultimate flexural strength, and load-deflection correlation, the moment at mid-span, and ductility and failure modes. Results show that 100% recycled coarse aggregate degrades the concrete strength relevant to 18.0, 18.9, and 19.3%, 16.2, 16.6, and 19.4% and 16.0, 16.2, and 18.2% in expression of compressive, splitting and flexural strength with tensile for 7, 14 and 28 days, reduces the workability by 33.3% and decreases the cracking and ultimate load with the improved rate of recycled coarse aggregate regarding of 39.4 and 45.1% and 10.9% for ductility for the beams with ratio of reinforcement of ρ=0.0157%. Decreasing the reinforcement ratios with ρ=0.0105 and 0.0067% while keeping the strength of concrete constant 100% recycled coarse aggregate decreases the cracking and ultimate load of about 11.3 and 20.8% and 15.6 and 24.4% respectively and 2.0 and 4.3% for ductility. [ABSTRACT FROM AUTHOR]