Flexural Behavior Of Reinforced Concrete Beams Research Articles

Flexural behavior of RC beams incorporating recycled concrete aggregate and reclaimed asphalt pavement exposed to elevated temperatures

Reducing the environmental footprint of concrete is one of the most effective methods to mitigate climate change since cement production contributes to about 8 % of global CO2 emissions. This paper presents an experimental investigation into the strength and flexural performance of reinforced concrete (RC) beams incorporating natural aggregate (NA), recycled concrete aggregate (RCA), and reclaimed asphalt pavement concrete (RAP) at normal and elevated temperatures. The NA was replaced by RAP at three replacement ratios of 40 %, 60 % and 80 %. Additionally, there were four mixes of 80 % RCA-20 % RAP, 60 % RCA-40 % RAP, 40 % RCA-60 % RAP, and 20 % RCA-80 % RAP. A total of 16 beams (L: 1400 mm, W: 150 mm, H: 250 mm) and 128 cylinders (H: 200 m, D: 100 mm) were tested to evaluate the flexural capacity and material strength. Eight RC beams were tested after exposure to a temperature of 600 °C for 3 h. The compressive strength, ultimate flexural load, and mid-span deflection were measured. The results showed that temperature has an adverse effect on the s compressive strength, flexural load capacity, and deflection of RC beams. Specimens made with the RAP and RCA combination showed a significant loss in their load-carrying capacity under elevated temperature by (55 %–65 %), while the temperature effect was relatively less severe in specimens made with high RAP replacement of NA. Increasing the RAP percentage increased the reduction of flexural capacity in RCA-RAP mixes by (3 %–10 %), while in NA-RAP mixes, the effect is similar except for 60 % RAP, which has a smaller reduction compared to 40 % and 80 % RAP.

An Experimental Study Incorporating Carbon Fiber Composite Bars and Wraps for Concrete Performance and Failure Insight

Corrosion of conventional steel reinforcement is responsible for numerous structurally deficient bridges, which is a multi-billion-dollar challenge that creates a vicious cycle of maintenance, repair, and replacement of infrastructure. Repair of existing structures with fiber-reinforced polymer (FRP) has become widespread due to multiple advantages. Carbon FRP’s superior tensile strength and stiffness make it particularly effective in shear and flexural strengthening of reinforced concrete (RC) beams. This experimental study incorporates carbon fiber polymer composite bars and wraps to study and report on the flexural behavior of RC beams. By employing a combination of CFRP bar and wrap for strengthening RC beams, this study observed an approximate 95% improvement in flexural load capacity relative to control RC beams without strengthening. This substantial enhancement highlights the effectiveness of integrating CFRP in structural applications. Nevertheless, the key observation is the failure mode due to this combination providing significant insights into the changes facilitated by this combination approach.

Flexural behavior of RC beams externally reinforced with CFRP composites using various strategies

Abstract The external composite material bonding is an effective and practical method for flexural strengthening of reinforced concrete (RC) beams, providing a large opportunity to develop high-performance and cost-effective structures. Numerous uses exist for carbon fiber-reinforced polymer (CFRP) materials as RC-member strengthening methods. However, issues with bonding and de-bonding continue to be a barrier to this technique's accomplishment. In this research, the CFRP sheets were integrated as an external strengthening material to evaluate their contribution to the flexural performance and so determine how well the CFRP sheets are being used. The experimental work includes one control beam and ten RC beams with CFRP sheets as external strengthening. All beams have the same dimensions: a length of 1.7 m and a sectional area of 20 cm × 25 cm. Experimental tests were carried out with varying CFRP types, lengths, numbers, and arrangements. Each beam’s performance was evaluated in terms of failure mode, ultimate load capacity, ultimate deflection, and a load–deflection curve. The findings demonstrate the effectiveness of CFRP strengthening by demonstrating a considerable improvement in the majority of the study variables. Furthermore, the CFRP strengthening offered an exterior crack-arresting mechanism.

Combined deterioration effects of freeze–thaw and corrosion on the cyclic flexural behavior of RC beams

Reinforced concrete (RC) stands as the predominant construction material, and with the growing prevalence of aging infrastructure, the safety assessment of deteriorating structures has emerged as a pressing and critical concern. This study presents an experimental investigation into the combined effects of freeze–thaw cycles (100, 200, and 300 cycles) and corrosion (corrosion ratio: 3% and 10%) on the cyclic behavior of RC beams. Seven RC beam specimens with varying types and levels of deterioration were fabricated, and static tests were conducted using a four-point bending method to assess the behavior of RC beams under each degradation factor. The experimental results revealed that increasing freeze–thaw cycles significantly impact RC beam behavior, leading to intensified crack formation due to cyclical frost-heaving pressure. This ultimately results in reduced yield loads ranging from 3% to 11% and peak loads reduced by 1–2% compared to the reference specimen A-0-0. Corrosion of steel bars in RC beams alters failure modes, with corroded specimens (C-0-3 and C-0-10) experiencing substantial decreases in yield load, a 15% reduction in C-0-3, and a 26% decrease in C-0-10, compared to A-0-0. Displacement at yield load and peak load also decreased, highlighting the detrimental impact of corrosion on beam mechanical properties. The combined deterioration from freeze–thaw cycles and corrosion further exacerbates these reductions, resulting in a substantial decrease in yield load (32%) and peak load (24%) in D-3-10 compared to the reference specimen A-0-0. Additionally, energy dissipation capacity and cumulative energy dissipation capacity exhibit dynamic changes influenced by the progression of freeze–thaw cycles, corrosion, and their combined effects.

Experimental and theoretical study on the flexural behaviour of RC beams strengthened with externally bonded reinforcement on grooves CFRP laminates

This paper presents a study on the flexural capacity of Reinforced Concrete (RC) beams strengthened with Externally Bonded Reinforcement on Grooves (EBROG) Carbon Fibre Reinforced Polymer (CFRP) laminates. Thirteen single-shear tests and seven RC beams strengthened with CFRP are examined, comparing Externally Bonded Reinforcement (EBR) and EBROG techniques with different groove distributions. The results showed that EBROG improved the bond and flexural performance. Comparison with existing prediction models reveals that while the literature models accurately predict EBR results, they underestimated the bending capacity for EBROG due to calibration based on EBR bond parameters. Consequently, a numerical model is developed to simulate Intermediate Crack Debonding (ICD) for various bond-slip laws, applicable to the different strengthening techniques. The proposed model is validated using experimental flexural tests and calibrated bond-slip laws obtained from single-shear tests, demonstrating accurate prediction of ICD failure for both EBR and EBROG.

A Study on the Flexural Performance of Para-aramid Fiber Reinforced Concrete Beams with Recycled Coarse Aggregates

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.

Ultimate strength behaviour of reinforced concrete beams strengthened by aluminium-alloy plates

This paper firstly proposed the new strengthening methods on reinforced concrete (RC) structures using the aluminium alloy (AA) plates. Then, the flexural behaviour of RC beams strengthened by externally bonded (EB) and mechanically fastened (MF) AA plates were studied through13 four-point bending tests. Four parameters were studied that included the strengthening method, thickness of AA plate, grade of AAs, and reinforcement ratio. Test results showed that the MF AA beams failed in flexure with concrete crushing, and the EB AA beam exhibited the bonding failure. Compared with EB AA beams, the MF AA beams exhibited larger load carrying capacity and ductility, but lower initial stiffness. Increasing the thickness of AA plate significantly improved the load carrying capacity, but slightly decreased the ductility of MF AA beams. The grade of AA plates exhibited weak influence on MF AA system since the strain of AA plate was significantly limited by the AA plate hole-anchor gap. The strengthening effect was more significant for RC beams with a relatively lower reinforcement ratio. Moreover, theoretical models were proposed to evaluate the ultimate carrying capacity of MF AA beams that considered the strengthening AA plate-concrete slips. Validations of the theoretical predictions against test results showed that they predicted reasonably on the ultimate load carrying capacity of strengthened RC beams by AA plate.

Effect of wetting/drying cycling on flexural behavior of RC beams strengthened by prestressed CFRP plate: Experimental and analytical investigations

Using prestressed carbon fiber reinforced polymers (CFRPs) is a promising technique for strengthening reinforced concrete (RC) structures. This study aimed to investigate the prestress losses and flexural behavior of strengthened RC beams under wetting/drying cycling (WDC) in a chloride-containing environment. Two prestress levels (20% and 40%) and two WDC durations (90 and 180 cycles) were considered. The time-dependent prestress loss under WDC was first monitored by fiber bragg grating (FBG) for 90 days, and the composition of the prestress loss was theoretically analyzed. A four-point bending test was conducted on the strengthened beams after the WDC exposure, and the intermediate crack (IC) debonding strain and the ultimate moment of the strengthened beams were analytically evaluated. The results show that although WDC exposure aggravated the time-dependent prestress losses, the maximum time-dependent prestress losses after 90 WDCs were only 1.75%, indicating the effectiveness of the end anchorage system. After WDC exposure, the failure mode of the strengthened beams shifted from CFRP rupture to IC debonding, accompanied by the reduction of cracking and the ultimate load, CFRP utilization, and the increase of the maximum crack width. Besides, the model of Lu et al. and Said and Wu could be applied to the IC debonding strain prediction after the WDC. When the environmental reduction coefficient was incorporated, ACI 440.2 R and CECS-146 resulted in a precise IC debonding strain. The proposed method could accurately predict the ultimate moment of the prestressed FRP-strengthened RC beams with different failure modes after WDC.

Theoretical and experimental investigations into flexural behavior of existing reinforced concrete beams strengthened by CFRP bars

Strengthening existing reinforced concrete (RC) beams using carbon fiber reinforced polymer (CFRP) bars have gained greater interest and increased field applications. Theoretical and experimental investigations have been conducted in this research to learn the flexural behavior of RC beams strengthened by CFRP bars. Bending tests were performed on seven specimens to obtain the load-displacement curves of the beams with different strengthening methods. Different features of the failure modes were observed in the bending tests. Strengthened beams by CFRP bars can significantly increase the flexural bearing capacity of RC beams and retard the development of cracks, which is an effective means to improve flexural stiffness. In addition, the experimental results revealed the influences of the bar connection mode. RC beams strengthened by continue bars have a greater ultimate load than those strengthened by lapped bars. A refined finite element (FE) model was built and validated by the experimental results. This validated FE model clarified the failure mode of beams from the perspective of displacement evolution and strain development. Furthermore, theoretical formulas were established to calculate the ultimate flexural capacity of the strengthened beams, which was proved to have acceptable accuracy in predicting the flexural behavior of the CFRP-strengthened beams. This research may provide a valuable reference for strengthening the existing RC beams.

Experimental and modelling investigation on chloride transport and flexural behaviour of RC beams subjected to simultaneous deteriorating factors of carbonation, FT cycles and multi-type sustained stress

Reinforced concrete (RC) structures are often exposed to coinstantaneous deterioration effects such as carbonation, chloride corrosion, freeze–thaw cycles and external loads which causing deterioration of concrete and reinforcement. This paper discussed the effects of carbonation, freeze–thaw cycles and sustained loads on chloride ion transport and proposed a chloride ion transport model taking porosity as the main coupling variate. The attenuation law of the corroded beams under coupling corrosion factors was studied. Through chloride immersion tests, it was found that applying freezing and thawing cycles and sustained tensile stress can enhance chloride transport capacity by coarsening the pores; Carbonation and low compressive stress can repress the chloride ion transport by densifying concrete, but the compressive stress beyond about 0.7 times the compressive strength and tensile stress would enhance the penetrating capacity due to the damage of the internal microstructure of concrete. Then, a comprehensive and unified theoretical model of chloride ion transport considering the coupling of carbonation, freeze–thaw cycle, sustained loading and other factors was proposed and verified by taking porosity as the main coupling variable quantity. This model could essentially explain the effects of various factors on chloride ion transport and has good consistency with the test results. Finally, the flexural bearing capacity of the corroded beams was tested, and the failure characteristics, crack characteristics, ultimate bearing capacity, load–displacement relationship and strain distribution of the corroded beams under different corrosion conditions were researched. The results show that the flexural capacity of the corroded beams suffered the coupling effects of multiple corrosion factors degrades, and the bearing capacity decreases with the increase of the corrosion degree of carbonation-freezing thawing cycles; The continuous tensile stress applied to the test beams in the corrosion process intensifying the degradation of bending bearing capacity and ductility, the continuous compressive stress increases the flexural capacity and improves the ductility slightly, but excessive compressive stress significantly degrades the flexural capacity; When chloride ions are used as the third kind of corrosive substance for coupling corrosion, the tensioned or without-load corroded beams have obvious degradation in bending bearing capacity, while the corrosion beams bearing continuous compressive stress have no obvious degradation in bending bearing capacity.

Experimental study on flexural behavior of RC beams strengthened with FRP/SMA composites

Fiber reinforced polymer (FRP)/shape memory alloy (SMA) composites are disclosed that can be used to repair cracked members and improve the mechanical behavior of concrete structures. This work aims to synthetically investigate the flexural behavior of reinforced concrete (RC) beams strengthened with FRP/SMA composites through both experimental study and finite element analysis. Five beam specimens are prepared to investigate the effect of important parameters on the flexural behavior of RC beams strengthened with FRP/SMA composites, including the different strengthened materials (i.e., SMA wires, CFRP sheets, and FRP/SMA composites) and different types of FRP/SMA composites (i.e., CFRP/SMA composites and BFRP/SMA composites). The test results showed that the flexural stiffness and capacity improvement of the beam strengthened with only SMA wires were not significant, but the ductility was not reduced. The flexural capacity of the beam strengthened with CFRP sheets was effectively improved, but the stiffness improvement was limited. However, the flexural stiffness and capacity of the beam strengthened with FRP/SMA composites significantly increased. At the same time, the service performance was also improved, FRP/SMA composites could effectively reduce the strain of longitudinal rebars and constrain crack development. Compared to the control beam, the capacity of the beam strengthened with the FRP/SMA composites improved from 17.52% to 40.23%, and the stiffness improved from 9.95% to 17.65%. In addition, the CFRP/SMA composites could more effectively improve the capacity and stiffness of strengthened beams than the BFRP/SMA composites because of the higher elastic modulus of CFRP sheets. The strength of BFRP sheets of the BFRP/SMA composites can be fully utilized after reinforcement. Finally, an iterative method for calculating the recovery stress of SMA wires for reinforcement was proposed and incorporated with finite element method for simulation, which was verified by experimental results.

Flexural behavior of RC beams enhanced with carbon textile and fiber reinforced concrete

Concrete cracking is the major cause of steel corrosion and performance degradation of reinforced concrete (RC) members. To significantly enhance the crack resistance and flexural performance of RC beams, textile and fiber-reinforced concrete (FRC) were used in this study, and a simple anchoring method of textile was proposed to prevent debonding failure. Eight RC beams were designed and tested, and the test variables included carbon textile, anchoring method and pouring thickness of FRC. The test results revealed that the proposed anchoring method can effectively avoid the debonding phenomenon; both carbon textile and FRC can improve the crack resistance, improve the flexural capacity and reduce the damage of specimens. Among, the combination of carbon textile and FRC is the most effective method to improve the mechanical properties of specimens. Compared with the ordinary RC beam, the crack resistance and flexural capacity of textile-FRC composite beams can be increased by 79.56% and 39.04% respectively under specific conditions. With the increase of the pouring thickness of FRC, the mechanical properties of the specimens gradually enhanced, while the growth rate gradually slowed down. Through sectional analysis, the calculation methods of the load-midspan deflection curve and flexural capacity of textile-FRC composite beams were established. The accuracy and applicability of the calculation methods were verified by test and finite element analysis. In addition, theoretical calculation results show that the enhancing effect is not significant in the case that the pouring thickness of FRC is beyond 64% of the section height.

Experimental and numerical investigation of flexural behavior of RC beams retrofitted with reinforced UHPFRC layer in tension surface

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has recently been used in reinforced concrete (RC) full-cast or strengthened beams because it has better mechanical properties and durability. However, the main parameters that affect the flexure behavior of retrofitted RC beams with a UHPFRC layer need more study. This paper investigates experimentally and numerically the major parameters that control the effectiveness of retrofitting RC beams with an additional reinforced UHPFRC layer applied to the tensile surface. One non-strengthened RC beam and seven retrofitted RC beams (divided into three groups) were experimentally tested under a four-point loading test. The effects of different parameters, such as the length (0.50, 0.60, and 0.80 times the length of the strengthened beams), the thickness of the UHPFRC layer (30 and 40 mm), and the retrofitting technique (with or without the concrete cover), on the crack patterns and failure modes, load–deflection behavior, load carrying capacity, energy absorption, and stiffness, were studied. The results showed that retrofitted beams exhibited significantly improved ultimate load, stiffness, and energy absorption ability compared to the control beam. UHPFRC layer length and thickness were the most significant parameters; moreover, increasing the UHPFRC layer thickness can compensate for the reduction in its length. Lastly, the validated finite element (FE) model was used to study the effect of different parameters, such as the length (0.40, 0.70, and 0.90 times the length of the strengthened beams), the thickness of the UHPFRC layer (50 mm), and the reinforced bar diameter (12 and 16 mm) in the UHPFRC layer, on the flexural behavior of the strengthened RC beams.

Mechanical properties and flexural behaviour of reinforced concrete beams containing recycled concrete aggregate

Increasing waste recycling has become an essential process in the construction industry due to the environmental and economic advantages, such as minimizing waste in landfills, saving natural resources, and decreasing pollution. Crushing and sieving waste from standard compression test cubes is used to produce the recycled concrete aggregate (RCA). A set of standard concrete cylinders, cubes, and beam specimens were made by utilizing coarse aggregate replacement ratios of 0%, 30%, 50% and 70%. At the day 28 stage, the specimens were tested to determine compressive strength, stress–strain relationship, splitting tensile strength, and flexural strength. In addition, four reinforced concrete (RC) beams were cast and tested under a four-point load to evaluate the flexural behaviour of RC beams with partial replacement of the natural aggregate with RCA. One was a natural aggregate (NA) control beam, while the others had varying RCA ratios (30%, 50% and 70%). The results show that the compressive strength of RCA concrete with the replacement by 30%, 50% and 70% decreased by 9.10%, 18.88% and 22.57% respectively, in comparison to the compressive strength of normal concrete (NC). The RCA concrete showed a high strain capacity, which indicated high ductility. The maximum RCA type strains ranged from 0.0056 to 0.0072. Concrete flexural strength showed a slight decrease in comparison to NC (18.83% decrease), where the tensile strength showed a 10.61% decrease in comparison to NC. As for RC beams, the load-carrying capacity decreased by 10.5% with increases in the replacement ratio.

Flexural Behavior of RC Beams with an Abrupt Change in Depth: Experimental Work

The most crucial components in the case of roofs with two levels or a variable floor height are variable depth beams. In order to investigate the flexural behavior of reinforced concrete (RC) beams with varying depths under static loads, experimental research was conducted. Under the four-point bending flexural test, two reference beams with constant depth, six dapped beams at the soffit, and four dapped beams at the top were tested. For all beams with a 150 mm depth, a 100 mm increase in depth occurred at the middle span of the beams. The primary characteristics included the impact of increasing depth, the impact of stirrups’ absence and their various ratios, and the characteristics of the longitudinal bars at the locations of sudden depth changes in either the top or bottom bars. Both the cracks’ progression and the load-deflection relationship along the beam’s length were observed. The ultimate carrying load (Pu) was reduced by 23.56% and 27.35% as a result of the 100 mm increase in the half-span of the beam over the constant depth in case of changes at the top and soffit, respectively. The Pu was increased by a ratio ranging from 20.9% to 31.35% for the bottom dapped beams and by a ratio of 29.79% for the top dapped beams due to the various stirrup ratios in the dapped area. The ductility was significantly impacted by the elevated stirrup ratios in the dapped area. The predicted results and the experimental results matched when the Pu of the tested beams was evaluated using the strut and tie model.

Parametric analysis on the flexural behaviour of RC beams strengthened with prestressed FRP laminates

In this paper, the effectiveness of reinforced concrete (RC) beams strengthened with prestressed basalt fibre-reinforced polymer (BFRP) laminates was parametrically studied through discrete displacement-coordinated finite element (FE) method. Three dimensional (3D) FE models were established based on experiments, and the reliability of the FE model was verified. The influences of material properties, prestress load level, reinforcement ratio, and shear span on the overall behavior were investigated. The results demonstrated that the optimal capacity of strengthened beam can be achieved in large shear span with low reinforcement ratio and high-strength concrete. The cracking load of RC beams was also significantly increased by strengthening with prestressed BFRP laminates. Then, polynomial equations were fitted to quantify the influences of different parameters on capacity enhancement. The shear span ratio was found to be the most important factor. In addition, the utilisation efficiency of BFRP is much higher than that of carbon FRP (CFRP) with the same section and prestress level due to the strong deformation ability.

The effect of longitudinal hole shape and size on the flexural behavior of RC beams

The building's electro-mechanical piping systems can pass through transverse or longitudinal holes inside the reinforced concrete (RC) secondary beams, thus increasing the available floor height. These holes induced a reduction in the beam stiffness and strength. This work analytically and experimentally investigates the impact of longitudinal hole shape on the flexural behavior of RC beams. The interaction between hole shape and hole location has also been studied. The test program includes nine beams with the same cross section dimensions and steel reinforcement. Holes have been made using two circular PVC pipes (50 and 75 mm in diameter), and wooden medium-density fiberboard (MDF) square tubes (50×50 mm) and rectangular tubes (50×100 mm). Each hole shape was installed at two locations (90 and 160 mm) from the top of the beam. All beams were tested to failure using a four-point bending test. The results show that the hole shape and size up to half the beam width does not affect the failure mode compared to the solid control beam. The reduction in the ultimate strength of hollow beams compared to the control beam depends on the hole shape and size, with a maximum reduction of 20%. The developed analytical models were validated using experimental test results and can be employed to accurately predict the full flexural behavior of hollow RC beams, including cracking, yielding, and ultimate moments/loads.

Flexural Behavior of RC Beams Strengthened with GFRP Laminate and Retrofitting with Novelty of Adhesive Material

Two unique approaches were proposed to strengthen the bond between the glass fiber reinforcement polymer (GFRP) and the RC concrete surfaces. The two bonding materials are epoxy (EP) and geopolymer (GPP) with different ratios of short glass fibers (SGF). The experimental program includes seven reinforced concrete (RC) beams that have the same cross-section (150 mm × 200 mm) and are 1500 mm in length. The first beam is the control beam (B0-Control). The next three beams B1-0-GPP, B2-0.6-GPP, and B3-1.2-GPP have GPP with SGF ratios of 0%, 0.6%, and 1.2%, respectively. The last three beams B4-0-EP, B5-0.6-EP, and B6-1.2-EP have EP with SGF ratios of 0%, 0.6%, and 1.2%, respectively. The results show that the failure loads of beams B1-0-GPP, B2-0.60-GPP, and B3-1.2-GPP are greater than the control beam B0-Control by approximately 20.80%, 25.60%, and 31.40%, respectively, whereas the failure loads of beams B4-0-EP, B5-0.6-EP, and B6-1.2-EP are greater than the B0-Control by approximately 16.90%, 26.90%, and 26.10%, respectively; it is also noted that debonding occurs. In addition to the adhesive material, GPP has a great effect on increasing the beam’s failure load capacity due to the enhanced interfacial bond shear strength. Additionally, a finite-element program ABAQUS is performed to verify the experimental results.

Flexural Response of Axially Restricted RC Beams: Numerical and Theoretical Study.

Reinforced concrete (RC) frame beams are subject to axial restriction at the ends, which plays an important role in the nonlinear behavior of these beams. This paper presents a numerical and theoretical investigation into the flexural behavior of RC beams axially restricted with external steel or fiber reinforced polymer (FRP) reinforcement. A numerical procedure for RC beams axially restricted with external reinforcement has been developed and it is verified against available experimental results. A numerical parametric study is then performed on axially restricted RC beams, focusing on the effect of type, area, and depth of external reinforcement. The results show that axial restriction increases the post-cracking stiffness and ultimate load-carrying capacity but reduces the flexural ductility. The ultimate stress in external reinforcement is substantially impacted by reinforcement type, area, and depth. A simplified model is developed to predict the ultimate load of RC beams axially restricted with external steel/FRP reinforcement. The predictions of the proposed simplified model agree favorably with the numerical results. The correlation coefficient for the ultimate load is 0.984, and the mean difference is −2.11% with a standard deviation of 3.62%.

Time-dependent behavior of NSM CFRP-strengthened RC beams under different service temperatures

The use of fiber reinforced polymer (FRP) for flexural strengthening of reinforced concrete (RC) beams has become a popular strengthening technique. Significant amount of work is available on the short-term flexural behavior of RC beams strengthened with near-surface mounted (NSM) technique. However, their time-dependent flexural behavior, specifically under high service temperature, has not yet been addressed. This paper presents an experimental work to evaluate the time-dependent behavior of NSM carbon FRP (CFRP)-strengthened RC beams. The experimental program included 23 beams, where the effect of different parameters such as strengthening (CFRP) area, steel reinforcement ratio and applied temperature (20 and 50 °C) have been considered. Experimental results show that the effect of strengthening area is significant on the flexural short-term response of the beams, while minor effects are found on the time-dependent deflections. On the other hand, increasing the service temperature has no significant effect on the short-term tests, but it produces a large increase in the time-dependent deflection of the specimens. Finally, an analytical procedure for the prediction of time-dependent deflections, which is based on the age-adjusted effective modulus method (AEMM), is presented. Good agreement between the experimental results and analytical predictions on time-dependent deflections is shown.