High Strength Reinforced Concrete Beams Research Articles

Bending Capacity Analysis of High-strength Reinforced Concrete Beams Using Environmentally Friendly Synthetic Fiber Composites

The research was conducted to determine the bending capacity of high-strength reinforced concrete beams with the addition of three environmentally friendly synthetic fibers i.e., polypropylene fiber, tie wire fiber, and used rubber tires fiber. Four beams with a dimension of 15 x 30 x 220cm were tested, including a beam for specimen without fiber as comparison. Specimens were designed to experience bending failure. Yield point of steel (fy) used for flexural and shear reinforcement was 407.43MPa. The diameter of flexural tensile reinforcement was 15.8mm, 11.9mm for the compressive reinforcement, as well as 11.9mm for the shear reinforcement. Concrete proportion incorporated 8% silica fume and 1.5% polycarboxylate ethers based superplasticizer ViscoCrete 10 from the cement weight. The maximum diameter of split was 15.9mm, having 550kg/m3 cement content and w/c-ratio 0.30. The target compressive strength was 70MPa for cylinder 15/30cm. The results showed that all beams experienced flexural failure as planned. Addition of fibers enhanced the bending behavior significantly, especially in flexural capacity, deflection and ductility. In comparison with high-strength reinforced concrete beam without fibers, the beam with polypropylene fiber had the increase of flexural strength of 115.24%, deflection of 306.56% and ductility of 298.9%; with tie wire fibers resulted in the increase of flexural strength of 117.39%, deflection of 160.52% and ductility of 148.0%; as well as with used rubber tires fiber produced the enhance of flexural strength of 112.13%, deflection of 184.56% and ductility of 178.3%. It can be concluded that the use of such environmentally friendly synthetic fibers can reduce the brittleness of high strength concrete, in which polypropylene fiber had delivered the best value and can be used very effectively than the other two types of fibers.

Repair of shear-deficient normal weight concrete beams damaged by thermal shock using advanced composite materials

The use of advanced composite materials such as Fiber Reinforced Polymers (FRPs) in repairing and strengthening reinforced concrete structural elements has been increased in the last two decades. Repairing and strengthening damage structures is a relatively new technique. The aims of this study was to investigate the efficiency and effectiveness of using Carbon Fiber Reinforced Polymer (CFRP) to regain shear capacity of shear-deficient normal weight high strength RC beams after being damaged by thermal shock. Sixteen high strength normal weight RC beams (100×150×1400mm) were cast, heated at 500°C for 2h and then cooled rapidly by immersion in water, repaired, and then tested under four-point loading until failure. The composite materials used are carbon fiber reinforced polymer plates and sheets. The experimental results indicated that upon heating then cooling rapidly, the reinforced concrete (RC) beams exhibited extensive map cracking without spalling. Load carrying capacity and stiffness of RC beams decreased about 68% and 64%, respectively, as compared with reference beams. Repairing the thermal damaged RC beams allowed recovering the original load carrying without achieving the original stiffness. Repaired beams with CFRP plates with 90° and 45° regained from 90% to 99% of the original load capacity with a corresponding stiffness from 79% to 95%, whereas those repaired with CFRP sheet on the web sides and a combination of CFRP plates and sheet regained from 102% to 107% of the original load capacity with a corresponding stiffness from 81% to 93%, respectively. Finally, finite element analysis model is developed and validated with the experimental results. The finite element analysis showed good agreement as compared with the experimental results in terms of load–deflection and load–CFRP strain curves.

Study of Post-Cracking Torsional Behaviour of High-Strength Reinforced Concrete Beams with a Ferrocement Wrap

Abstract The post-cracking behaviour of structures subjected to torsion can be well predicted by Hsu’s softened truss model. The softened truss model is applicable to structures having symmetry in their material properties on all four sides. Wrapping on three faces is a common phenomenon when the top face is provided with a flange or slab. Such a wrapping on three faces of a beam is referred to as a “U” wrap. “U” wraps are better wrapping strategies for distressed structures, as their top face is not accessible for many structures. The material property of an unwrapped face differs from the rest of wrapped faces. For the effective use of wrapping, the unwrapped face needs to be provided with a material having a higher resistance to tension and shear. For this, high-strength concrete in the core is a better option. Here, an attempt is made to predict the torsional capacity of “U” wrapped high-strength concrete beams having an asymmetry in the material using a softened truss model with suitable modifications of the material properties. Efficient algorithms are proposed for the solution of simultaneous equations. The predictions are found to be in good agreement with the experimental test results

Experimental Investigation on the Shear Crack Development of Shear-Critical High-Strength Reinforced Concrete Beams

The main propose of this work is to investigate the shear crack development and suggest the design formulas that can ensure serviceability and reparability for shear-critical high-strength reinforced concrete (HSRC) beam members based on the experimental data of ten full-size simple-supported beam specimens. According to the experimental results, the design formulas that can ensure the serviceability and reparability are recommended for shear-critical HSRC beam members. Additionally, relationship between shear stresses of member and widths of shear cracks are also built for the quantitative analysis of shear crack development. Based on the crack development of each specimen, the average ratio of the residual total shear crack widths to the residual maximum shear crack width for the HSRC beam specimens is approximately 4.5; then, in the crack-based assessment, this work recommends setting the ratio as 4.0 to estimate residual maximum shear cracking. Additionally, the ratio of maximum peak shear crack width to residual maximum crack width, it can be increased by shortening stirrup spacing and increasing stirrup strength, and its overall average value is 2.44. This work suggests the applicable value of a HSRC shear-critical beam to be 2.5. Besides of the post-earthquake damage assessment, these results can also be used to build the performance-based design for HSRC structures.

Shear strength of high-strength concrete beams: Modeling and design recommendations

In the present paper, the flexural and the shear resistance of high strength reinforced concrete (HSC) beams with longitudinal bars, in the presence of transverse stirrups is analyzed both theoretically and experimentally. The experimental researches here presented are parts of previous researches carried out by the author. Researches refer to HSC beams with high percentages of steel bars failing in shear and in flexure. From the analytical point of view, a model based on the evaluation of the resistance contribution due to beam and arch actions including bond splitting and concrete crushing failure modes is developed and presented. The model was verified against available experimental results and those recently obtained by the author. Some of the more recent analytical expressions able to predict the shear and the flexural resistance of concrete beams were mentioned and design considerations are made referring to a ductile design of HSC beams. Finally, design recommendations were derived with the proposed model and compared with expressions given in most common codes.

순환굵은골재 치환율에 따른 고강도 철근콘크리트 보의 휨 거동

순환굵은골재 치환율에 따른 고강도 철근콘크리트 보의 휨 거동

Ductility and strength assessment of HSC beams with varying of tensile reinforcement ratios

Nine rectangular-section of High Strength Concrete(HSC) beams were designed and casted based on the American Concrete Institute (ACI) code provisons with varying of tensile reinforcement ratio as (pmin, 0.2pb, 0.3pb, 0.4pb, 0.5pb, 0.75pb, 0.85pb, pb, 1.2pb). Steel and concrete strains and deflections were measured at different points of the beam\'s length for every incremental load up to failure. The ductility ratios were calculated and the moment-curvature and load-deflection curves were drawn. The results showed that the ductility ratio reduced to less than 2 when the tensile reinforcement ratio increased to 0.5pb. Comparison of the theoretical ductility coefficient from CSA94, NZS95 and ACI with the experimental ones shows that the three mentioned codes exhibit conservative values for low reinforced HSC beams. For over-reinforced HSC beams, only the CSA94 provision is more valid. ACI bending provision is 10 percent conservative for assessing of ultimate bending moment in low-reinforced HSC section while its results are valid for overreinforced HSC sections. The ACI code provision is non-conservative for the modulus of rupture and needs to be reviewed.

An experimental study on the failure modes of high strength concrete beams with particular references to variation of the tensile reinforcement ratio

For many years, high-strength concrete (HSC) has been used in high-rise buildings and bridges. The primary reasons for selecting HSC are to produce a more economical product, provide a feasible technical solution, or a combination of both. Despite a lot of advantages in the usage of HSC, it exhibits a brittle failure in comparison with normal strength concrete (NSC). For a comprehensive discussion on the failure of HSC beams, a total of six full scale reinforced HSC beams have been designed based on ACI code provisions and cast with compressive strength in the range of 65MPa⩽fc′⩽75MPa and tested under two-point top loading. The general behaviour of tested beams has been investigated with observation on mid span deflection, failure mode and crack growth. Increase of the tensile reinforcement ratio results in more cracks but with lower height and width. The linear graphs between the applied load and corresponding deflection or curvature in reinforced HSC beams showed that the behaviour of these beams is elastic and any increase in the tensile reinforcement ratio results in an increase in the ultimate load too. The moment–curvature graph and load–deflection curve started with an initial elastic response followed by an inelastic behaviour that appears with a gradual decrease in stiffness till the ultimate moment is reached.

Flexural Behavior of High Strength Reinforced Concrete Beams by Replacement Ratio of Recycled Coarse Aggregate

Recently, many structures which were built about 30 years ago are watched by reconstruction. Demolished concrete is occurred in the process and these quantity increase about 10% more than the preceding year. Fortunately, recycled aggregates are produced from demolished concrete, whereas the recycled aggregates are not used often because there are not many researches which have been verified by experts or researchers about strength when reinforced concrete is made with recycled aggregates. In this paper, high strength reinforced concrete is valued with potential applications and check change of strength when it made by recycled aggregates. For this, flexural tests of 4 high strength reinforced concrete beams with recycled aggregates were performed, and the high strength reinforced concrete beams were tested within the limits such as compressive strength, flexural strength, ductility, strain, and curvature. The current test data were examined in terms of flexural strength, along with the data from previously tested reinforced concrete beams with recycled aggregates.

Optimum Position of Shear Reinforcement of High-Strength Reinforced Concrete Beams

This paper reports experimental data on the behavior and strength of high-strength concrete slender beams reinforced with vertical shear reinforcement. Tests were conducted on ten reinforced concrete beams with stirrups in different positions using high-strength concrete (compressive strength about 85.0 MPa). The beams measured 2000 mm long, 100 mm wide and 200 mm deep, and were tested under two point loads. The test variables were position and amount of web reinforcement; conventional steel bars were used as longitudinal reinforcement in this investigation. The test results indicated that beams with shear reinforcement (vfy = 1.65 to 4.24MPa) within the shear span (G1) and along the beam length (G2), were failed in flexure, while beams with shear reinforcement (vfy = 1.65 to 4.24MPa) between two point loads (G3) and the beam without shear reinforcement (G4) were failed in shear. The optimum position of stirrups is the shear span for high strength concrete beams and for different amounts

Shear Behavior of Reinforced High-Strength Concrete Beams

This paper describes the shear behavior of reinforced high-strength concrete (RHSC) beams without web reinforcement. The use of high-strength concrete (HSC) has led to some concerns about its shear strength because of its brittleness, smooth fracture surface, and high early-age shrinkage. Test results indicated that the ratio of uniaxial compressive strength to tensile strength (the ductility number) of the concrete relative to that of the aggregate governs the shear strength of HSC. When the ductility number of the concrete coincided with that of the aggregate, the shear strength remained constant, irrespective of concrete strength. When the ductility number of the concrete was higher than that of the aggregate, however, shear strength started to decrease due to the smooth fracture surface and brittleness. By introducing early-age shrinkage and a suitable aggregate size, the modified compression field theory was found to accurately predict the shear strength of RHSC beams.

Effects of Steel Fibers on Shear Behavior of High-Strength Reinforced Concrete Beams

The paper describes an experimental study that consisted of beam specimens made of Normal Strength Concrete (NSC) and of High Strength Concrete (HSC), with and without steel fibers that were subjected to predominant shear in four-point loading tests. HSC specimens included the four combinations of beams with and without fibers, with and without stirrups. The experimental program included study of the effects of concrete strength and inclusion of steel fibers on the load capacity, load-deflection curve and mode of failure. The results show that the effect on the shear capacity of the hooked-end steel fibers that were used in the tests was more pronounced when no shear reinforcement was used and that in the presence of stirrups fibers affected mainly the structural ductility and mode of failure. The results from the current study are also compared with the predictions of various theoretical models and of the American and European design codes. Examination of the results also shows that a required contribution of the shear reinforcement, which is determined according to the concrete capacity, leads to an increased amount of minimum shear reinforcement. However, the overall response of the beams that were tested shows otherwise.

Experimental Study on Fatigue Behavior of Low-Strength Concrete Beams

Reinforced concrete (RC) structures taking full advantages of concrete and reinforcing steel bars are widely applied in civil engineering. Concrete bridges are subjected to alternate loads as well as static loads, much importance should be attached to their fatigue. Reinforced concrete beams are the elementary members of concrete bridges. Fatigue failure mode and fatigue life prediction of normal or high-strength RC beams were the research focus at home. The fatigue behavior of low-strength RC beams was studied through four-point bending fatigue test in the paper. The test results indicated that all beams fractured for concrete shear failure, which made the fatigue life of low-strength concrete beams drop greatly compared to that of normal or high-strength concrete beams, because the fatigue failure of normal or high-strength concrete beams were caused by the fracture of one or more reinforcing steel bars; the mid-span deflection development of low-strength RC beams had three phases, and the middle phase occupied about 90% of whole fatigue life, also in the second phase the mid-span deflection developed linearly with the increasing of cycle numbers. This research work provides necessary basis for the fatigue life deterioration of low-strength RC beams.

Calculation of Flexural Capacity of High-Strength Reinforced Concrete Beams Strengthened with FRP

The mechanical properties of high-strength reinforced concrete beams strengthened with FRP ( fiber reinforce polymer) are further investigated theoretically including it s failure mechanism and loadability,based on earlier theoretical works on RC beams. And the correlation equation of flexural capacity on the cross section of high-strength reinforced concrete beams strengthened with FRP is deduced according to different types of failure.The correlation equation is shown to be in good agreement with the experimental results, which can be referred to engineering application.

Prediction of Diagonal Crack Widths of High-Strength Reinforced Concrete Beam by Artificial Neural Network

Based on influencing factors of the diagonal crack widths of high-strength reinforced concrete beam, the paper presents a model for predict the diagonal crack width of high-strength reinforced concrete beam by artificial neural network. The model is verified using experimental data; it indicates that the neural network model has a good effect on the forecast of the diagonal crack widths. At the same time, artificial neural network provides a new way to calculate the diagonal crack widths.

BEHAVIOUR OF REINFORCED HIGH-STRENGTH CONCRETE BEAMS WITH OPENINGS SUBJECTED TO STATIC AND REPEATED LOADINGS

This paper presents the results of an experimental research on reinforced high strength concrete beams with web rectangular openings to determine their behaviour and ultimate strengths, and to compare these strengths with those predicted using the available equations. Test variables were length of openings, details of steel reinforcement around the openings, longitudinal main steel ratio, and type of loading (static-repeated). Test results showed that the ultimate load of beams with openings reduces by about 10 to 45% compared to similar solid beams. Provided that the same amount and scheme of reinforcement used, an increase in opening length, decreases both stiffness and strength of the beam. Diagonal bars at corners of openings results in spreading of cracking away from openings and reducing beam deflection, but it does not have significant influence on strength of the beam. The effects of transverse openings on overall response of reinforced concrete beams in shear becomes remarkable as main steel ratio (ρ) increases. Increasing shear reinforcement (stirrups) in the top and bottom chords of the openings increases slightly the cracking load; while increases significantly the ultimate load. Repeated load has no effect on either strength or mode of failure of the tested beams. The available equations do not produce satisfactory results for predicating the ultimate shear strength of highstrength concrete beams with openings.

Numerical analysis of inelastic reinforced high-strength concrete beams with low reinforcement ratio

Numerical modelling of flexural behavior of the reinforced highstrength concrete beams with low reinforcement ratio is discussed in this paper. Modelling mechanism of failure reinforced concrete beams under static load, static deformation processes of the reinforced high-strength concrete beams with regard to the physical nonlinearities of the structural materials (i.e. concrete and reinforcement steel) were developed using finite element analysis. The comparison of the numerical and experimental results as well as theoretical solutions, were presented. The compared results indicate correctness of the constitutive models of the structural materials: concrete and reinforcing steel and effectiveness of the solution method.

Flexural ductility of reinforced HSC beams strengthened with CFRP sheets

Externally bonding fiber reinforced polymer (FRP) sheets with an epoxy resin is an effective technique for strengthening and repairing reinforced concrete (RC) beams under flexural loads. Their resistance to electro-chemical corrosion, high strength-to-weight ratio, larger creep strain, fatigue resistance, and nonmagnetic and nonmetallic properties make carbon fiber reinforced polymer (CFRP) composites a viable alternative to bonding of steel plates in repair and rehabilitation of RC structures. The objective of this investigation is to study the effectiveness of CFRP sheets on ductility and flexural strength of reinforced high strength concrete (HSC) beams. This objective is achieved by conducting the following tasks: (1) flexural four-point testing of reinforced HSC beams strengthened with different amounts of cross-ply of CFRP sheets with different amount of tensile reinforcement up to failure; (2) calculating the effect of different layouts of CFRP sheets on the flexural strength; (3) Evaluating the failure modes; (4) developing an analytical procedure based on compatibility of deformations and equilibrium of forces to calculate the flexural strength of reinforced HSC beams strengthened with CFRP composites; and (5) comparing the analytical calculations with experimental results.

Nonlinear Models and Experimental Investigation of Lifetime History of HSC Flexural Beams

The nature of fracture in high strength concrete is brittle and therefore, the investigation behavior of flexural high strength concrete (HSC) members is important. This paper describes the deflection, strain and energy ductility and the lifetime history of experimental and theoretical analysis of six caste reinforced HSC beams with different percentage of I and I×³. The beams were loaded incrementally by a two point loads and the vertical deflection and concrete strain were measured at mid span, at 20cm from mid span and under load point up to failure. Based on the experimental results, load-deflection, load-strain and energy observed diagrams of each beam for mentioned sections plotted. In the theoretically phase, a 3-D model i.e., ANSYS nonlinear software was used and the load-deflection, load-strain and energy observed diagrams were also plotted and the comparison of experimental and theoretical results for lifetime history of HSC beams is performed. The obtained results by two methods are indicated that a reasonably good agreement is achieved.

Reinforced High-Strength Concrete Beams in Flexure

An important design issue is the ductility or the ability of a reinforced concrete (RC) member to deform at or near the ultimate load without significant strength loss. This article reports on a study of reinforced high-strength concrete (HSC) beams in flexure. The study included flexural test results generated on 16 reinforced concrete beams. Test parameters considered include concrete compressive strength, ratios of tensile and compressive reinforcements, and spacing of lateral ties. The authors found that the current code provisions for serviceability requirements of maximum crack width and ultimate strength are adequate up to a concrete strength of approximately 130 MPa. The authors express concerns regarding the adequacy of current code provisions, however, for cracking moment and service load deflection. They show that stresses generated by shrinkage of concrete and the creep associated with it can significantly affect the cracking moment and service load deflection of reinforced HSC beams. The authors recommend that the ACI Code specification for maximum spacing of ties in RC flexural members need to be reduced to d/4, particularly at critical sections. This will prevent premature disintegration of the confined concrete core in the compression zone due to buckling of compression reinforcement.