Flexural Behavior Of RC Beams Research Articles

Bending Behavior of RC Beams with Regular Web Openings and Non-corroding GFRP Reinforcement

The present study pertains to the flexural behavior of RC beams with openings and non-metallic (GFRP) reinforcement. The main goal of preferring GFRP reinforcement over the conventional steel reinforcement was to safeguard the beams against the reinforcement corrosion. The presence of multiple regular transverse openings throughout the beam length increases the susceptibility of reinforcing bars to corrosion as the larger contact area in these beams with the outside environment increases the ingress of corrosive agents. Within the scope of the study, a total of 8 RC beams, including two reference beams without web openings, were tested under four-point bending. The test parameters were the flexural reinforcement ratio, the presence of short stirrups in the chords, and the presence of diagonal reinforcement spiraling around the openings. Since GFRP stirrups are difficult to bend, each stirrups was formed by connecting four individual FRP bars around the longitudinal bars. The opening circular geometry was adopted to avoid stress concentrations around the sharp corners of opening and to facilitate the placement and fixing of different schemes of reinforcement in the beams. The present tests depicted that the diagonal reinforcement around the openings have considerable contribution to the flexural behavior of RC beams with GFRP reinforcement and with multiple regular transverse openings. The RC beams with openings were able to approach their analytical flexural capacities in the presence of diagonal reinforcement for both moderately and heavily reinforced beam groups. The analytical deflection predictions of GFRP-RC beams with openings showed a good agreement with experimental data.

Flexural behavior of RC beams strengthened with BFRP bars and CFRP U-jackets: Experimental and numerical analysis

The strengthening of concrete structures is an inevitable requirement throughout their service life. This study proposed a hybrid strengthening method of combining near-surface mounted (NSM) basalt fiber-reinforced polymer (BFRP) bars and carbon fiber-reinforced polymer (CFRP) end anchors. To verify the proposed method, four-point bending test and corresponding numerical analysis were implemented on four reinforced concrete (RC) beams. One beam was the reference beam, while the other three were strengthened with NSM BFRP bars with or without CFRP end anchors. After validating the numerical model, it was employed to systematically investigate the impact of hybridization strengthening details on the flexural performance of RC beams. The results showed that the bearing capacity of the NSM strengthened specimens increased by more than 64 % compared to the reference beam. The addition of CFRP U-jacket end anchors significantly enhanced beam ductility. Regarding failure mode, the reference beam, BFRP strengthened beam, and the BFRP and CFRP hybrid strengthening beam were controlled by the concrete crushing, concrete cover separation, and concrete cover separation (CCS) along with CFRP-jacket rupture, respectively. Proposed numerical models by considering the effects of interfacial normal stress and shear stress on the debonding behavior of epoxy resin and concrete, which could predict theCCS of the NSM strengthened beam, and results compared between the numerical analysis and experiments verified the accuracy of the model with the errors around 2 %. Further investigations using numerical models demonstrated that the ultimate strain of BFRP bars in the presence of CFRP U-jacket is higher than that without CFRP U-jacket. It confirmed the contribution of CFRP U-jacket to improve the flexural strength of the NSM strengthened beams, while also facilitating the utilization of the tensile strength of the BFRP bars. In summary, both experimental and analytical evaluations confirm the effectiveness of the proposed strengthening technique.

Flexural behavior of RC beams strengthened with CFRP grid-reinforced engineering cementitious composite

Flexural strengthening of RC beams by replacing the tension part with carbon fiber reinforced polymer (CFRP) grid‐reinforced engineering cementitious composite (ECC) matrix has been proved to be a reliable way in the marine environments. However, few studies have been conducted on the arrangement of CFRP grids so far, which is supposed to be a possible way to deal with the premature fracture of CFRP grid and debonding of strengthening layer. In this paper, the flexural behavior of RC beams strengthened with CFRP grid‐reinforced ECC matrix is experimentally studied. The location of CFRP grid and the number of CFRP grid layers were specially discussed. Results from experiments indicated an improvement range of 66.67 %∼100 % in the peak load of strengthened RC beams, with a higher initial cracking load from 4.72 %∼20.47 % when compared to the reference beam. The generating of initial cracks was delayed with the CFRP grid close to the bottom, whereas the development of cracks was accelerated. The bearing capacity showed a nonlinear relationship with the distance from CFRP grid to the beam bottom, and a linear relationship with the number of CFRP grid layers. Finally, the formulas for the flexural capacity of strengthened beams were developed, considering the plasticity and cracking of concrete.

Flexural behavior of RC beams reinforced by ECC layer and steel plate: numerical simulation

PurposeThe combination of an Engineered Cementitious Composite (ECC) layer and steel plate to reinforce RC beams (ESRB) is a new strengthening method. The ESRB was proposed based on the steel plate at the bottom of RC beams, aiming to solve the problem of over-reinforced RC beams and improve the bearing capacity of RC beams without affecting their ductility.Design/methodology/approachIn this paper, the finite element model of ESRB was established by ABAQUS. The results were compared with the experimental results of ESRB in previous studies and the reliability of the finite element model was verified. On this basis, parameters such as the width of the steel plate, thickness of the ECC layer, damage degree of the original beam and cross-sectional area of longitudinal tensile rebar were analyzed by the verified finite element model. Based on the load–deflection curve of ESRB, ESRB was discussed in terms of ultimate bearing capacity and ductility.FindingsThe results demonstrate that when the width of the steel plate increases, the ultimate load of ESRB increases to 133.22 kN by 11.58% as well as the ductility index increases to 2.39. With the increase of the damage degree of the original beam, the ultimate load of ESRB decreases by 23.7%–91.09 kN and the ductility index decreases to 1.90. With the enhancement of the cross-sectional area of longitudinal tensile rebar, the ultimate bearing capacity of ESRB increases to 126.75 kN by 6.2% and the ductility index elevates to 2.30. Finally, a calculation model for predicting the flexural capacity of ESRB is proposed. The calculated results of the model are in line with the experimental results.Originality/valueBased on the comparative analysis of the test results and numerical simulation results of 11 test beams, this investigation verified the accuracy and reliability of the finite element simulation from the aspects of load–deflection curve, characteristic load and failure mode. Furthermore, based on load–deflection curve, the effects of steel plate width, ECC layer thickness, damage degree of the original beam and cross-sectional area of longitudinal tensile rebar on the ultimate bearing capacity and ductility of ESRB were discussed. Finally, a simplified method was put forward to further verify the effectiveness of ESRB through analytical calculation.

Analysing the influence of ground granulated blast furnace slag and steel fibre on RC beams flexural behaviour

This study examines the effect of Ground Granulated Blast Furnace Slag (GGBS) and steel fibers on the flexural behaviour of RC beams under monotonic loading. Various percentages of GGBS were used to substitute cement, namely 0%, 20%, 40%, 60%, and 80% and fibers were added to the concrete mix as 0%, 0.5%, 1%, and 1.5% of the volume of concrete. The load–deflection behaviour of GGBS-incorporated RC beams with fibers was compared with the control RC beam. Beams were tested under load control for 28 days and 180 days. The ultimate load of the GGBS-incorporated RC beam up to 40% cement replacement was found to higher than that of the control beam. The strength of concrete is reduced by 28% and 19% when cement was partially replaced by 80% of GGBS at 28 and 180 days, respectively, compared to control concrete without fibres. Further, the analytical load–deflection response of GGBS-incorporated RC beams was determined by using several codes of practice, namely, ACI 318-11(2011), CSA A23.3-04 (2004), EC-04 (2004), and IS 456 (2000). The Codal provisions were primarily based on the effective moment of inertia, Young’s modulus, and modulus of rupture, stiffness, and cracking. Average load–deflection plots obtained from experiments were compared with the computed load–deflection of analytical studies. It was found that the analytically predicted load–deflection behaviour is comparable with the corresponding average experimental load–deflection response. Moment curvature relations were also developed for RC beams.

Flexural behavior of RC beams with multiple parallelogram openings

On account of the detrimental effects of the post-drilling holes in hardened RC beams, designing the beams with transverse openings before construction is becoming more popular in the last decades. The contribution of the transverse openings to the overall economy and efficiency of construction by reducing the unusable dead space in the floor height is a rather significant motivation behind the vast number of studies on this topic. In search for the opening geometries and reinforcement schemes with the least negative effects on the beam behavior, the present study focused on the parallelogram (diamond) opening geometry, which is thought to facilitate the transmission of diagonal compression forces in the beam web thanks to the inclination of the posts. Within this scope, a total of 12 beams, including two reference beams without openings, were tested under four-point bending. Circular, square and parallelogram (45°−60°−75°) opening geometries were adopted and the test results were evaluated based on the opening geometry and the longitudinal reinforcement ratio. In order to avoid various shear failure modes of beams with openings, different special reinforcement schemes were employed around the web openings. Two different longitudinal reinforcement ratios were used to understand if pure flexural failure can be reached in RC beams with openings without being affected by different shear failure modes (beam- and frame-type diagonal tension and diagonal compression). The inclination angle of the posts between the openings in parallelogram opening geometry was found to be the most crucial parameter in the final beam failure and beam ductility. The use of diagonal cables surrounding the openings and connecting the posts and chords was established to be obligatory in square and parallelogram opening geometries to reach a ductile beam behavior without being affected by Vierendeel panel action and different shear failure modes.

Flexural behavior of RC beam using industrial copper slag as a sustainable substitute for fine aggregate

Flexural behavior of RC beam using industrial copper slag as a sustainable substitute for fine aggregate

Flexural behavior of RC beams strengthened with CFRP sheets and ECC material

Premature debonding is a common failure mode of externally bonded fiber reinforced polymer (EB-FRP) strengthened reinforced concrete (RC) members, which leads to inefficient use of FRP. In this paper, engineered cementitious composite (ECC) with multiple fine cracks was introduced as a transition layer in FRP-concrete interface to delay CFRP sheet debonding. Four strengthened beams with CFRP sheet and ECC layer and one reference RC beam were tested under four-point bending. The effects of the type of strengthened scheme and CFRP sheet layers were investigated. The results showed that the beams strengthened with CFRP sheet and ECC layer had a significant improvement in crack load (71.8–105.1%), yield load (39.5–86.1%) and ultimate load (59.5–84.6%) relative to the reference beam. The introduction of the ECC layer could effectively delay CFRP debonding and had positive effect on the crack resistance. Fracture of CFRP sheet occurred when the beam was strengthened with one CFRP sheet layer. These findings are expected to provide better understanding on the FRP-ECC repair system.

Flexural Behavior of RC Beam According to the Change in Adhesion Between Rebar and Concrete Due to Complex Deterioration

Flexural Behavior of RC Beam According to the Change in Adhesion Between Rebar and Concrete Due to Complex Deterioration

A regularized higher-order beam elements for damage analysis of reinforced concrete beams

This work presents a numerical method for damage analysis of reinforced concrete beams using the higher-order beam theory based on Carrera unified formulation. The component-wise approach is employed to model the concrete and steel reinforcing bars as two independent one-dimensional finite elements. A modified Mazars damage model with tensile and compressive damage propagation laws is utilized for concrete, and an elastic-perfectly plastic law is used for steel rebars. To address the instability and mesh dependence caused by the strain-softening behavior of concrete, a fracture energy regularization technique based on the crack band model is developed, especially for the higher-order beam theory. The proposed method is validated by comparing its numerical results with three experimental benchmark results. The comparison indicates that the method accurately predicts the damage distribution of concrete and the flexural behavior of RC beams under quasi-static loading conditions while remaining computationally efficient.

Shear and Bending Performances of Reinforced Concrete Beams with Different Sizes of Circular Openings

The present study pertains to the effects of transverse opening diameters and shear reinforcement ratios on the shear and flexural behavior of RC beams with two web openings across different spans, i.e., a single opening in each half-span. Within the scope of the study, a total of 12 RC beams with five different opening diameter-to-beam depth ratios (0, 0.20, 0.27, 0.33, 0.40, and 0.47) and two shear reinforcement ratios were tested to failure under four-point bending. The load capacities, ductilities, rigidities and energy dissipation capacities in the elastic and plastic ranges of beam behavior were compared. Furthermore, the load capacities of the beams were compared to the existing analytical shear strength formulations in the literature. The test results indicated that whether an RC beam with openings has adequate or inadequate amounts of shear reinforcement, the frame-type shear failure becomes much more pronounced with increasing opening diameter. The reductions in the load capacity and modulus of toughness with increasing opening diameter are more considerable in the presence of inadequate amounts of shear reinforcement, while the beam ductility is less affected in shear-deficient RC beams with openings as compared to the ones with adequate shear reinforcement.

Finite element modelling and analysis of brass coated steel fibre reinforced concrete beams

The study's objective was to use brass-coated micro steel fibre to improve the strength and flexibility of beams. Steel fibres with a brass coating are resistant to corrosion and improve the fracture resistance and tensile strength of the concrete, making them appropriate for use in the building and construction industry, refractory industry, rocket launch pads, airport runways and highway pavements etc. In this work analytical research on the flexural behaviour of RC beams with brass-coated steel fibre reinforcements is presented. The beams were modelled and analysed using the Abaqus FEA software. Five beams total with various fibre volume percentages (Vf = 0, 0.5, 1, 1.5, 2) were examined for this purpose. The beam cross sections were 1000 mm in length, 100 mm broad, and 150 mm deep. The analytical results show that addition of 2.0% volume of fibres exhibited better performance. When compared to the reference beam, the increase in maximum load and deflection was found to be 36.3% and 61.84%, respectively. The load–deflection and fracture patterns of different beams were compared with the experimental and analytical responses. Amongst the two approaches, it demonstrates good agreement across the whole range of loading. Thus, the deflections obtained from both the methods are ‘very close to each other’ and within ‘generally acceptable limits (say10%)’. Modeling and evaluating the structural parts can be done much more quickly and affordably using the Finite Element Analysis (FEA).

Effect of different load levels on the flexure performance of RC beams exposed to fire

The paper presents the effect of different load ratios on the thermal and flexural behaviour of RC beams during and after fire. Full scale beam specimens of normal strength concrete of dimensions 230 mm × 400 mm × 4000 mm were exposed to design fire curves for the same duration under load ratios of 0.0, 0.20 and 0.40 of the ultimate load. Finally the beams were mechanically loaded till failure to estimate the residual capacity after cooling. The results showed that with the increase in the pre-load during fire alters (a) the thermal profile of the specimens (b) The performance of the beam specimens and (c) The ultimate capacity and flexural stiffness of the beam specimens after fire. A numerical model was also proposed to validate the experimentally obtained results..

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

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

Structural behavior of RC beams strengthened using fiber‐reinforced polymer U‐jackets

AbstractThe study aims to identify flexural behavior of RC beams strengthened using three different fiber‐reinforced polymers (FRPs) with differential cross‐sections configuration (i.e., middle and support sections). The experimental and calculations results of strengthening methods for RC beams were investigated utilizing FRPs under flexural loading. The strengthening FRP materials (CFRP, AFRP, and GFRP) were externally attached to the surface of the samples with U‐wrapped shape at the three different regions of the beams. The experimental results were compared with the fiber polymer systems of the American Concrete Institute according to the ACI 440.2R‐08 standards. The results demonstrated that RC‐9 specimen reinforced using AFRP exhibited higher load capacity performance than the others. The RC beams strengthened at both middle and support area exhibited more ductile behavior, which depends on the failure mode. Less crack formation was seen in the RC‐10 beams reinforced with AFRP, both in the middle and in the support area, compared with reference sample. The experiment revealed that FRP U‐jackets could be a promotive alternative to improve structural performance greatly and provide reliable and suitable solutions for sustainable buildings.

Effect of the outer UHDC layer on shear and flexural behavior of RC beams produced with low binder concrete

Composite beams with a cement distribution along the cross-section more efficient can be used to increase their durability and simultaneously decrease the ecological footprint related with cement production. The higher dosages are used only on the cover layer, to provide a higher protection of the steel reinforcement, and the core of the beams is produced with a low cement concrete, using in this case 125 kg of cement per m3. In addition, the core is not subjected to such higher normal stresses as on both bottom and top of the cross section, so the mechanical performance of this concrete is not so challenging and, consequently, the cement dosage can be thus reduced.This experimental study aims to analyze how the strength capacity and stiffness of beams are affected using the ‘superskin’ concept, particularly the influence of how the external layer made with an ultra-high durability concrete (UHDC) is applied, being the core produced with a low binder concrete (LBC).Nine different beams were tested, until bending or shear-controlled failure occur, varying the longitudinal tensile reinforcement ratio and the way how the UHDC layer is applied: i) one single layer with a ‘U’ shape around cross-section and, ii) three separated thin plates, cast against the core concrete. The followings parameters were analyzed: load–displacement relation, flexural strength, shear strength, ductility, crack pattern and failure mode. The results show that this type of beams present a better structural behavior relatively to the reference beams, beyond the two benefits already identified, the durability and eco-efficiency increase. In certain beams the flexural strength increased around 70% and the shear strength almost 90%. The results also reveal the advantages of using a monolithic UHDC layer, namely, in terms of cracking.

Flexural Strengthening of Large-Scale RC Beams with Nonprestressed and Prestressed CFRP Using Different Anchorages.

Externally bonded carbon-fiber-reinforced polymer (CFRP) technology can be used by different methods based on the anchorage device, CFRP type, and prestressing/nonprestressing. However, a direct comparison between the strengthening efficacies of different methods is still lacking. Seven large-scale RC beams were tested in this study to investigate the influences of the anchorage method, CFRP type, prestress, and prestressing system on the flexural strengthening efficacy of RC beams. The test results showed that the ultimate load increased by 38.3%, whereas the cracking and yielding loads were slightly affected when the anchorage method was enhanced from CFRP U-wraps to wedge-clamp anchors. The CFRP plate and CFRP sheet could provide a rather close flexural strengthening efficacy under the same CFRP strengthening amount. Compared to the nonprestressed CFRP plate, the prestressed CFRP plate was highly superior in improving the flexural behavior of RC beams. The cracking, yielding, and ultimate loads of the prestressed CFRP-strengthened specimens were 57.1%, 22.9%, and 5.9%, respectively, higher than those of the nonprestressed CFRP-strengthened specimen with an effective anchorage. The two types of prestressing systems based on the adhesive-friction anchor and wedge-clamp anchor were proven to be effective for flexural strengthening of RC beams with prestressed CFRP plates, and they could provide almost the same strengthening effect.

Numerical analysis of high-strength reinforcing steel with conventional strength in reinforced concrete beams under monotonic loading

Abstract This work presents finite element (FE) modeling using the ABAQUS program to investigate the effect of steel reinforcement with three different types of high-strength steels, grades 420, A1035, and SD685 on the flexural behavior of RC beams under monotonic loading. Experimental findings from the literature have been used to validate the proposed model. The numerical load, deflection, mode of failure, failure concrete strain, and bottom steel strain at failure of 24 numerical specimens with collapsed conditions of tension-controlled, balanced, and compression-controlled are recorded. Also, the effect of compression reinforcement is being investigated. The results reveal that the flexural behavior of the experimental test for the three steel grades is well validated by FE analysis. The ductile and brittle behavior features of yield strength (YS) larger than 420 can be predicted for specimens designed according to current standards ACI-318M-19. Also, the compression reinforcement improves load capacity while reducing displacement. It may be argued that when YS decreases, tensile stress and strain of flexural rebar rise, causing the beam to become more ductile. When the YS increased, the brittle behavior was induced.

Flexural behavior of RC beams strengthened by enlarging the member size using cementitious grout: experimental and theoretical study

Flexural behavior of RC beams strengthened by enlarging the member size using cementitious grout: experimental and theoretical study

The efficiency of CFRP strengthening and repair system on the flexural behavior of RC beams constructed with different concrete compressive strength

This paper presents experimental investigation on the effectiveness of CFRP strengthening and repair system on the load carrying capacity, stiffness, flexural behavior, and failure mode mechanism of RC beams constructed with different concrete compressive strength (fc′). Eight RC simply supported beams were strengthened and repaired with one layer of CFRP composite and tested experimentally under flexural load. The beams were built with varying the concrete compressive strength (fc′) value of (21.1, 36.1, 48.2, and 68.5) MPa, to demonstrate low, normal, and high strength. The results obtained in this work revealed that the performance of the CFRP composite material was inversely correlated to the concrete compressive strength in repaired beams while a proportion relation was observed in strengthened beams only with low to normal concrete strength. Finally, reasonable agreement between the estimated bending moment capacities for strengthened beams (based on the ACI 440.2R-17 provision) and the experimental results within ±16% were obtained.