Flexural Performance Of RC Beams Research Articles

Flexural Performance of Reinforced Concrete Beams Strengthened with a Novel High-Strength and High-Toughness Epoxy Mortar Thin Layer

The flexural performance of RC beams strengthened with a novel high-strength and high-toughness epoxy mortar thin layer was investigated through four-point flexural tests on two contrast beams and two strengthened beams. The effects of this strengthening method on the failure modes, crack distribution, load–deflection curves, and bearing capacity of the RC beams with two reinforcement ratios were studied. The experimental results revealed that the contrast beams exhibited the typical bending failure modes where the failure mode of the reinforced beam is the yielding of the tensile reinforcement of the original beam and then fracture damage of the new epoxy mortar-reinforced thin layer. No debonding phenomenon was observed between the reinforced thin layer and the original concrete, and no visible cracks appeared before the tensile failure occurred in the thin layer. The cracks in the reinforced beams developed slowly, increased in number, and decreased significantly in width and spacing. The stiffness of the strengthened beam increased significantly, while its deformation ductility coefficient noticeably decreased. Compared to the corresponding contrast beams, the cracking load for strengthened beams A1 and B1 increased by 14% and 23%, respectively; the yield load increased by 32% and 40%, respectively; and the peak load increased by 18% and 17%, respectively. Finally, a calculation method for the flexural bearing capacity of RC beams strengthened with the novel epoxy mortar thin layer based on the flat section assumption was proposed. The calculated values showed a good agreement with the experimental values (with errors at −11.73% and 4.14%, respectively), providing a valuable reference for further research and application related to this kind of reinforcement method.

Theoretical Calculation of Flexural Load Capacity of RC Beams Reinforced with Aluminum Alloy -ECC Composites

In order to study the flexural performance of RC beams reinforced with aluminum alloy-ECC composites under different damage modes and to improve the theoretical method of calculating their flexural ultimate bearing capacity, the formula for the ultimate flexural bearing capacity of concrete beams reinforced with aluminum alloy tendons under two different damage modes of aluminum alloy tendons pulling off and concrete crushing in the compression zone was derived based on the intrinsic relationship of concrete in the compression zone, and the formula for the ultimate bending bearing capacity of concrete beams reinforced with aluminum alloy tendons and ECC composites under different reinforcing modes was calculated. The ultimate bearing capacity of concrete beams under different reinforcement modes was calculated, and the finite element analysis of the flexural performance of the reinforced beams was carried out at the same time, and the theoretical values were compared with the results of finite element simulation and the existing test values to verify the correctness of the formulae. The results show that the theoretical calculated values of RC beams reinforced with aluminum alloy -ECC composites are in good agreement with the results of finite element analysis and test values, and the accuracy of the theoretical calculations is high, and the formulae derived can effectively avoid the problems that are unfavorable to the practical application of engineering due to the excessive complexity of theoretical calculations, and the relevant calculation methods are of certain reference value for guiding the design of RC beams reinforced in actual projects.

Investigation on influence of corrosion and protective coating on steel rebars on flexural performance of RC beams

Investigation on influence of corrosion and protective coating on steel rebars on flexural performance of RC beams

An Assessment of the Structural Performance of Rebar-Corroded Reinforced Concrete Beam Members

This paper aims to determine the effects of local corrosion at three different corrosion areas, the (1) entire area, (2) the constant moment area, and (3) the constant shear area, on the flexural performance of RC beams. To analyze this, an experimental study was carried out to prepare two series of RC beams (200 × 300 × 2800 mm) created with three different degrees of corrosion, inducing local rebar corrosion. Furthermore, two series of experimental tests were conducted under different loading types: monotonic and cyclic loading. It was observed that the strength capacity reduction grew in the RC specimens with induced corrosion in the order of the (1) entire area > (2) the constant moment area > (3) the constant shear area, as the average corrosion rate increased. Our test results further showed that the yield and ultimate strength were kept nearly equivalent to the uncorroded RC specimen, with average corrosion rates of 10% and 15%, respectively. Over these corrosion rates, the yield strength and ultimate strength dropped significantly. Compared to the test results under a monotonic loading condition, the structural capacity under a cyclic loading condition decreased, with a more pronounced tendency for each corrosion case as the corrosion rate increased. Longitudinal cracks developed throughout and adjacent to the corrosion areas as the corrosion rate increased. Thus, we can infer that strength reductions may be strongly influenced by these longitudinal cracks.

Effect of Using ECC Layer on the Flexural Performance of RC Beams Previously Strengthened with EB CFRP Laminates

This paper studies the efficiency of applying an engineered cementitious composite (ECC) layer to the tensile surface of (RC) beams that were previously strengthened using externally bonded (EB) carbon fiber-reinforced polymer (CFRP) laminates. One control and ten strengthened RC beams were produced and tested utilizing a four-point loading regime. For strengthened beams, two beams were kept strengthened using only CFRP, and additional ECC layers were added to the rest of the strengthened beams. The CFRP width and overlap length and position were among the test factors. Experimental results revealed that strengthening RC beams with CFRP laminates enhanced both the stiffness and flexural capacity of beams. Additional enhancements were obtained through the application of the additional ECC layers. The existence of the ECC layer alongside the CFRP laminate improved the flexural capacity by 102% and 125% when using CFRP widths of 50 mm and 100 mm, respectively, and the stiffness was improved by an average value of 318%. Three-dimensional (3D) finite element models (FEMs) were developed using ABAQUS software and verified against the experimental results to model the response of the tested beams. The verified model was used to conduct a parametric study to consider the effect of the ECC layer thickness and the reinforcement ratio on the strengthened beam behavior. The numerical results revealed that the effect of the reinforcement ratio was more significant than the ECC layer thickness in enhancing the load-displacement response, especially after the cracking stage.

Cyclic flexural performance of RC beams with small circular openings in plastic hinge region

This paper describes the effect of a small circular web opening located in the plastic hinge region on the cyclic flexural performance of RC beams. The variable in the design of specimens is the diameter of the circular web openings installed in the plastic hinge region. Two rectangular beams scaled down to 67% of a practical RC beam were fabricated to have circular openings in the plastic hinge region with diameters 0.2 and 0.3 times the height of the beam. In another beam, in addition to the opening in the plastic hinge region, a web opening with a diameter of 0.3 times the height of the beam was installed at a location 180 mm from the center of the span. A total of four beams including a control beam were subjected to cyclic anti-symmetric moment. The cyclic flexural performance of the beams was evaluated in terms of hysteretic response, including strength, stiffness, ductility, and energy dissipation capacity. The neutral axis depth of the plastic hinge during the cyclic loading test was calculated using the linear distribution of strains of longitudinal reinforcing bars placed at the top and bottom of the openings. In addition, using the effective depth of the RC beams and the net tensile strain in the extreme tension reinforcement for tension-controlled sections, which are recommended by ACI 318–19, the maximum diameter of the circular web opening in the plastic hinge region was approximated and compared with the test results. Furthermore, with reference to the results of certain exiting studies, the ratio of the spacing between openings to the maximum diameter of the circular web opening was suggested by assuming the case of designing web openings to leap over major shear cracks expected to occur in a flexural RC beam undergoing shear-flexural failure.

Flexural performance of RC beams externally strengthened with a single-layer of basalt fiber reinforced polymer sheets

Basalt Fiber Reinforced Polymer (BFRP) is an environment friendly strengthening material that can be used in several engineering applications. In this research, an experimental program was directed to investigate the BFRP strengthening adequacy of reinforced concrete beams. Eight simple-span beams were tested under the four-point bending test and were all made from the same concrete mixture. One layer of BFRP was applied on the soffit of B1, while this layer was wrapped partially along the sides of beams B2, B3, and B4 with vertical side extensions of 25, 75, and 105 mm, respectively, to evaluate the effect of vertical extension of the bottom BFRP layer on the flexural behavior of the strengthened beams. The beams B5 and B6 were strengthened with three BFRP U-strips along the flexural span without and with a bottom layer of BFRP sheet, respectively. On the other hand, the bottom and side surfaces of B7 were fully wrapped with a layer of BFRP, while B0 was kept without strengthening as a reference beam. The test results showed that strengthening with BFRP can noticeably improve the beam load capacity at cracking, yield, and ultimate stages. The ductility of strengthened beams was less than B0 by up to 33% for partial side strengthening and 45% for full side strengthening, while the toughness of all strengthened beams was higher than that of reference beam by 8–78%. The results also showed that increasing the vertical side extension of the bottom BFRP layer leads to significant load capacity increase.

Experimental and finite element analysis of flexural performance of RC beams retrofitted using near-surface mounted with CFRP composites and cement adhesive

Fiber reinforced polymer (FRP) composite has been used effectively for the rehabilitation of concrete and steel structures in the last decades due to its excellent properties compared with conventional reinforcing materials such as steel. Despite the major role of epoxy resins as a bonding material between fibre and substrate, the rapid deterioration of the mechanical properties at elevated temperature is the critical issue for the epoxy matrix. Therefore, substitution of epoxy adhesive with cementitious bonding agent will be beneficial in order to provide more resistant systems at elevated temperatures. Near-surface mounted (NSM) strengthening technique with cement adhesives has only been investigated for torsion. Flexural performance is a significant factor in the strengthening of different structures. This paper reports the experimental study on the behavior of small scale retrofitted beams using Near-Surface Mounted strengthening system with carbon fiber reinforced polymer (CFRP) textile and laminate and cement-base adhesives for flexure. The beams retrofitted with modified cement-based adhesive achieved 98% to 100% ultimate loads of that beams strengthened with epoxy adhesives. Numerical analyses is utilized to evaluate the experimental results, and comparable results were observed between the experimental results and finite element analysis.

Enhancement of flexural performance of RC beams with steel wire rope by external strengthening technique

ABSTRACT Reinforced concrete structures around the world need repairing or strengthening at some stage in their lifetimes for different reasons. Steel wire rope is one of the potential materials to strengthen reinforced concrete structures do to its high strength, lightweight, and high flexibility properties. This research was, therefore, conducted to investigate a relatively new technique to strengthen reinforced concrete beams using external steel wire ropes. This involved testing five beam specimens under a four-point bending configuration for failure, and the strengthening effects of external wire ropes on their performance were also studied. The results showed the ultimate load capacity was also significantly enhanced up to 250% compared to the control specimen. Moreover, the stiffness and energy absorption capacity of the strengthened specimens were improved due to the external strengthening technique. This means reinforced concrete beams strengthened with external steel wire rope are capable of fulfilling the flexural performance required for reinforced concrete structures.

Study on the flexural performance of RC beams anchored with CFRP plates under secondary load

In order to explore the influence of length and width of CFRP as well as anchor spacing on the reinforcement effectiveness of CFRP plates on reinforcement concrete beams (RC beams) under secondary load, 7 anchored damaged FRP reinforced concrete beams are used as test beams, 1 unanchored beam is used as a control beam, and structural indicators such as ultimate load and bending strength are analyzed in the result. The conclusion is that composite CFRP plate can effectively prevent the early peeling and failure of carbon plates and improve the ultimate bearing capacity of the beam. When the width of the CFRP plate decreases, the thickness increases and the steel plate anchor spacing increases appropriately, the ultimate bearing capacity and ductility of the beam are significantly improved.

An Experimental Study on Flexural Performance of RC Beams Reinforced With Hybrid Prefabricated Retrofit Method

An Experimental Study on Flexural Performance of RC Beams Reinforced With Hybrid Prefabricated Retrofit Method

Analytical and experimental study on shear performance of RCC beam elements reinforced with PSWC rebars: a comparative study

Early distress in RCC (Reinforced Cement Concrete) structures in the recent times poses a major problem for the construction industry. It is found that in most of cases, distresses in reinforced concrete structures are caused by corrosion of rebar embedded in the concrete. The HYSD (High Yield Strength Deformed) rebars which are used to offer excellent strength properties is detrimental to durability due to action of ribs as stress concentrators. Nowadays, concept of PSWC rebars (plain surface with wave type configuration rebars, formerly known as C-bars/mild steel rebar with curvy profile) is emerging to have a compromise between strength and durability. This investigation assesses the flexural behaviour of RCC elements reinforced with PSWC rebars. The flexural performance of RC beams of size 1000mm x 150mm x 150mm reinforced with PSWC rebars at 4mm and 6mm deformation level was studied by conducting test as per IS 516-1959 under four point loading. The performance of PSWC bar reinforced elements are compared with beams reinforced with mild steel rebars, HYSD rebars with spiral and diamond rib configuration to assess the viability of PSWC rebars to replace conventional reinforcement. The test results are validated by numerical analysis with the help of ANSYS software. Totally 15 beams are subjected to flexure test and the performance evaluators are first crack load, deflection at first crack load, ultimate load carrying capacity, deflection at ultimate load, load-deflection behaviour, load-strain behaviour and failure pattern. It is found that PSWC rebars as reinforcement in concrete beams enhanced the ductile behaviour of beams as compared to conventional HYSD and mild steel rebar beams. The energy absorbing capacity has increased significantly for beams reinforced with PSWC rebars when compared with conventional HYSD and mild steel rebar beams. The load-deflection behaviour and failure mode of PSWC rebars reinforced concrete beams were found to be similar to that of high yield strength rebars irrespective of deformation level. The analytical investigation from ANSYS software gave good agreement with the experimental results. It is concluded that PSWC bar has the potential to replace conventional HYSD rebar. Further study needs to be done to optimize the profile level and stirrup locations; and usage with high concrete grade for effective exploitation.

Flexural Performance of RC Beams Strengthened by Carbon Fiber Reinforced Polymer (CFRP) Laminates

Flexural Performance of RC Beams Strengthened by Carbon Fiber Reinforced Polymer (CFRP) Laminates

Experimental assessment of the performance of reinforced concrete beams strengthened with carbon fiber reinforced polymer laminates

In this study, experimental research is carried out to assess the flexural performance of RC beams strengthened with different amount of CFRP laminates at the tension face. Twelve rectangular RC beams were fabricated and three are un-strengthened and used as reference beams and the remaining nine are strengthened with different amount of CFRP varying from single to triple layers and all are tested to failure under three points bending test. The increase of ultimate strength provided by the bonded CFRP laminates is assessed and failure modes is identified and compared to the un-strengthened RC beams. The results indicated that the flexural capacity of the beams was significantly improved as the amount of the laminates increases that ranged from 20% to 52% increased for single to triple layers laminates. It is concluded that the attachment of CFRP laminates has substantial influence on the performance of CFRP strengthened RC beams. Based on the observed results, recommendations are made that externally application of CFRP laminates can be used for a significant enhancement of the strength deficient RC beams in increasing the ultimate load carrying capacity.
 Keywords: CPRP laminate, Reinforced concrete, ductility, index, epoxy resin, flexural strengthening

Effectiveness of Various Techniques Using FRP for the Strengthening of R. C. Beams with Tension Lap Splices

This paper presents an experimental program conducted to investigate the flexural performance of RC beams with tension reinforcement lap splice strengthened using externally bonded FRP different techniques in splice region. The specimens were reinforced on the tension side with four deformed bars spliced at mid span. The tested beams are of 3200 mm total length and 250*120 mm cross section, tested in positive bending. The considered parameters were splice length, type of FRP (glass or carbon), strengthening techniques in splice region (externally confine strips around cross section, Near Surface Mounted technique "NSM" stirrups, externally bonded sheets or bars on the tension face, number of GFRP strips layers (one layer, two layers, and three layers), and shape of NSM stirrups (Box or U shape). No additional anchorage mechanism or bonding methodology was applied for the FRP strips on the concrete except the epoxy adhesive. The effect of these factors on the failure of modes, the ultimate load, the bond strength and that the ductility were investigated. The results indicated that all applied strengthening techniques were efficient in improving the bond strength of the lap splices, the ductility, and the load-deflection behavior of the tested beams, especially when strips were installed over the splice region. This study approved that NSM technique gave more prominent simplicity of employ.

The performance of lap splices in RC beams under inelastic reversed cyclic loading

A number of design codes such as ACI 318-14 have prohibited the use of lap splices in critical zones of special moment frames where flexural yielding is anticipated. This restriction is due to the unreliable performance of lap splices under cyclic loading. This article is concerned with the flexural performance of RC beams with lap splices under reversed quasi-static cyclic loading. For the calculation of lap splice length two procedures were adopted here; i.e. conventional design procedure recommended in ACI 318-14 and modified splice length which assumes 1.25fy in design relations instead of the nominal yield strength. For this purpose, a total of nine full-scale RC beams with different splice and reinforcement configurations for two grades of steel were designed and fabricated. Four-point bending tests were carried out on test specimens to evaluate the performance of lap splices under pure bending. Test results indicated that the specimen with splice designed according to ACI318-14 provisions could not survive reverse cyclic loading up to flexural failure. However, the specimens with a modified splice length were able to survive cyclic loading with adequate flexural ductility.

Research on the Fatigue Flexural Performance of RC Beams Attacked by Salt Spray

The fatigue flexural performance of RC beams attacked by salt spray was studied. A testing method involving electro osmosis, electrical accelerated corrosion and salt spray was proposed. This corrosion process method effectively simulates real-world salt spray and fatigue loading exerted by RC components on sea bridges. Four RC beams that have different stress amplitudes were tested. It is found that deterioration by corrosion and fatigue loading reduces the fatigue life of the RC and decreases the ability of deformation. The fatigue life and deflection ability could be reduced by increasing the stress amplitude and the corrosion duration time. The test result demonstrates that this experimental method can couple corrosion deterioration and fatigue loading reasonably. This procedure may be applied to evaluate the fatigue life and concrete durability of RC components located in a natural salt spray environment.

Flexural performance of RC beams made with recycled brick aggregate

An investigation on the flexural performance of reinforced concrete beams made with recycled brick aggregate was conducted. For this, 24 reinforced concrete beam specimens of width 200mm, height 250mm and length 2100mm were made with recycled brick aggregate, picket brick aggregate, and brick aggregate. Other variables include steel ratio, doubly reinforced, and singly reinforced concrete beams. Flexural tests of the beams were performed by four-point loading test. During loading, deflections of the beams at the middle and middle-third locations were recorded. Crack widths and crack spacing were also recorded. The beams were loaded gradually till failure. The results of beams made with recycled brick aggregate were compared with the same results of beams made with virgin brick aggregates, i.e. picket brick aggregate and brick aggregate. It is revealed that the design equations proposed in ACI 318-14 for design of reinforced concrete beams can be used for design of beams made with recycled brick aggregate.

Research on the flexural performance of RC beams strengthened with TRC under the coupling action of load and marine environment

Textile reinforced concrete (TRC) possesses an excellent bearing capacity and anti-crack and corrosion resistance abilities, making it suitable for reinforcing concrete structures under a harsh marine environment. However, the performance of concrete structures strengthened with TRC under a corrosion environment requires further research. Therefore, the coupling action of loads with a chloride wet-dry cycle and freeze-thaw cycle, on the flexural performance of RC beams strengthened with TRC was studied. The results indicated that under the coupling action of loads and the chloride wet-dry cycle, when the sustained load ratio of beams exceeded 0.2, the larger the sustained load, the wider the initial cracks that appeared in the beams, resulting in chloride ions easily invading the internal concrete. Therefore, the stiffness and bearing capacity of the beams decreased. Moreover, under repeated loading and unloading, the bearing capacity of the beam decreased significantly. The damage of the beams would be serious with the increase of the sustained load under the coupling action of load and the freeze-thaw cycle. Thus, there was a significant decrease in the bearing capacity and stiffness of the beam. In summary, the coupling action of loads and the corrosion environment have a substantial influence on the TRC-strengthened beam, causing a change of the failure mode, bearing capacity and deflection of beams.

Effect of adhesive replacement with cement mortar on NSM strengthened RC Beam

This paper presents the experimental behavior of reinforcement concrete beams strengthened with near surface mounted (NSM) steel bar. Several researchers have used NSM fiber reinforced polymer (FPR) bar or strip for strengthening reinforced concrete beams. Though FRP has a number advantages like high strength, light weight and corrosion resistance it doesn’t show any ductile behavior, still highly expensive and not easily available in market. On the other hand, steel bar is less expensive, readily available in the market and shows good ductility. In order to get rapid and economic strengthening solution, strengthening with near surface mounted steel bar may become a potential alternative to retrofit reinforced concrete members. Therefore, the main purpose of this paper to investigate the experimental behavior of reinforced concrete beam strengthened with near surface mounted steel bar. Seven full-size beams (one control beams and six strengthened beams) were tested. Steel bars were used for strengthening. The failure load, mode of failure, deflection, and strain behavior are discussed. The study reveals that the near surface mounted technique with steel bars and cement mortar is the most economical strengthening solution to increase the flexural performance of RC beams.