Behavior Of High-strength Concrete Beams Research Articles

Effects of amount and geometrical properties of steel fiber on shear behavior of high-strength concrete beams without shear reinforcement

This study aims to investigate the effects of the geometrical properties and volume content of steel fibers on the shear resistance of reinforced high-strength concrete (HSC) beams without stirrups. Hooked-end and twisted steel fibers with different aspect ratios ranging from 60 to 100 were used at volume fractions of 0.5%–1.0%. The shear strength of HSC beams without stirrups significantly increased due to the addition of steel fibers and by increasing their volume fraction by up to 1.0%, resulting in approximately 1.7 times higher shear resistance. A higher fiber aspect ratio was effective in improving the resistance to shear failure of HSC beams without stirrups and in enhancing beam deformability relative to the increase in shear strength. Using twisted steel fibers led to better shear resistance than hooked-end steel fibers, resulting in 1.11- and 3.34-times higher shear strength and ductility at the same fiber volume fraction on average. The shear strength of steel fiber-reinforced concrete (SFRC) beams was also predicted using eight different models. Narayanan's model most precisely predicted the shear strengths of reinforced SFRC beams without shear reinforcement, with an average vu,exp/vu,pred ratio of 1.16. The shear strength increased with the decrease in shear span-to-depth (a/d) ratio and the increase in the fiber factor. The contribution of steel fibers to shear strength was greater for deep beams than slender beams. The predicted shear strengths of deep beams and high-strength SFRC showed a significant deviation from the actual value and required careful consideration.

Effects of stainless steel reinforcement and fibers on the flexural behaviour of high-strength concrete beams subjected to static and blast loading

This research has investigated the effects of stainless steel (SS) reinforcement on the flexural behaviour of high-strength reinforced concrete beams subjected to static and blast loading. As part of the tests, beams built with high-strength concrete (HSC) and Grade 520 MPa stainless steel bars were tested under blast loads using a shock-tube. Companion beams were also tested under quasi-static conditions. The effects of steel fibers on shear and flexural response were also investigated. In the beams with stirrups, the use of SS bars improved blast behaviour by increasing blast capacity and reducing displacements when compared to identical beams designed with ordinary steel. The use of fibers further improved blast performance by reducing displacements and increasing damage tolerance. In beams without stirrups, the use of fibers was unable to completely substitute for transverse steel and prevent failure, however the shear capacity was increased. As part of the numerical study, the behaviour of the test beams was simulated using 2D finite element (FE) modelling. The FE results show reliable predictions of the beams under static and blast conditions.

Effect of Concrete Strength on Shear Capacity of Reinforced High-Strength Concrete Continuous Beams without Web Reinforcements

In order to evaluate the shear strength and behavior of high-strength concrete beams without web reinforcing, eight high-strength continuous concrete beams with cross sections of 200 mm by 300 mm were cast and tested to failure. The ultimate load-carrying capability and shear behavior are presented. The applicability of the Sudheer et al. equations and ACI 318M-14 is examined. In addition, the effects of the compressive strength ( f c ′ ) and shear span to effective depth ratio (a/d) on the shear strength and behavior of HSRC beams without stirrups are also studied. 63 MPa, 78.8 MPa, 85.9 MPa, and 92 MPa were the concrete’s compressive strengths, while 2.41 and 3.33 were its shear span to effective depth ratios. There were two equal spans of continuous beams, and at each span, they were evaluated under a single-point load. It was found that with increasing compressive strength, the failure load was increased. But the deflection did not affect it significantly. While increasing, (a/d) led to a decrease in failure load but increased deflection. It was also found that both ACI 318 M-14 and Sudheer et al. equation were more conservative.

Effect of UHPC jacketing on the shear and flexural behaviour of high-strength concrete beams

Ultra-high performance concrete (UHPC) is an advanced material which shows high compressive strength, tensile resistance, toughness and durability when compared to conventional concrete. One of the potential applications of UHPC is in the retrofit of ageing or deteriorated reinforced concrete structures. However, limited research exists on the use of UHPC to strengthen higher strength concrete members (with compressive strength exceeding 80 MPa). This paper examines the ability of UHPC to improve the shear and flexural performance of high-strength concrete (HSC) beams. As part of the tests two shear-deficient HSC beams built without stirrups, and having 15M or 20M bars (steel ratios of 1.6% and 2.4%), were retrofitted with a thin UHPC jacket and tested under four-point bending. The results are compared to a control set of HSC beams built with and without stirrups. The effect of steel ratio in the retrofitted beams was also investigated. The results show that the UHPC jacketing significantly increased the shear capacity by 40–125% in the shear-deficient HSC beams, allowing the beams to reach their full flexural resistance. The UHPC retrofit also allowed for improved flexural performance, with increases of 80–85% in stiffness, 20–35% in flexural strength and 40–180% in ductility when compared to the control beams built with stirrups. The failure mode and ductility in the UHPC retrofitted beams was affected by the longitudinal steel ratio, with the failure transitioning from bar fracture to concrete crushing as the steel ratio in the reference HSC beams was increased from 1.6% to 2.4%. To supplement the engineering case, finite element modelling is used to study the influence of other retrofit types, as well as the shear-span-to-depth ratio.

A Numerical Study to Investigate Shear Behavior of High-strength Concrete Beams Externally Retrofitted with Carbon Fiber Reinforced Polymer Sheets

A Numerical Study to Investigate Shear Behavior of High-strength Concrete Beams Externally Retrofitted with Carbon Fiber Reinforced Polymer Sheets

Shear capacity and behavior of high-strength concrete beams with openings

Transverse openings alter the structural behavior and undermine the integrity of concrete beams, resulting in stiffness degradation, shear strength reduction, stress concentration, premature cracking, and force-flow disturbances. Consequently, they require special attention during the design and construction of concrete beams with openings. Owing to the abrupt change in the beam's cross-sectional area, the strain distribution in the region around an opening is disturbed and nonlinear, making conventional bending and shear theories irrelevant. Few studies have investigated the impact of openings on concrete beams, especially that of openings on high-strength concrete (HSC) beams. Therefore, in this study, we perform tests on 12 reinforced concrete beam specimens to investigate the influence of depth, length, and location of openings on the ultimate shear strength of HSC beams with openings. The results revealed that the opening depth and length of HSC beams are negatively and almost linearly correlated to the ultimate shear strength; furthermore, based on their size and location, the shear capacity reduces by 2–53%. Similarly, the opening location along the shear span had a substantial impact on the capacity and behavior of the beam. Subsequently, finite element models of the tested beams were developed in ABAQUS software package and validated in compliance with the experimental results. The simulations exhibited good performance in predicting the ultimate strength, load–deflection relationship, and crack propagation in the beams. Accordingly, the developed models can be utilized to conduct further parametric studies and develop strut-and-tie models.

Flexural Performance of Concrete Beams Reinforced with Continuous FRP Bars and Discrete Steel Fibers under Cyclic Loads.

This research investigated the flexural behavior of high-strength concrete beams reinforced with continuous basalt fiber-reinforced polymer (BFRP) bars and discrete steel fibers. Five concrete beams with the dimensions of 150 × 300 × 2100 mm3 were constructed and tested to failure under four-point bending cyclic loading. The specimens consisted of four BFRP-reinforced concrete beams with various reinforcement ratios (ρf), namely, 0.56%, 0.77%, 1.15%, and 1.65%, and one conventional steel-reinforced concrete beam for comparison purposes. The cracking behavior, failure modes, load-deflection behavior, residual deformation, and stiffness degradation of the beams were studied. Additionally, a deformation-based approach was used to analyze the deformability of the beams. The results show that an increase in the ρf effectively restrained the crack widths, deflections, and residual deformation while also enhancing the flexural bearing capacity of the beams. In comparison to the first displacement cycle, the bearing capacity dropped by 10% on average in the third cycle. The stiffness exhibited a fast to slow degradation trend until failure. The residual stiffnesses were higher in beams with a higher ρf. The over-reinforced beams had superior deformability than the under-reinforced beams, according to the deformability factors.

Torsional behaviour of high strength concrete beams with spiral reinforcement

ABSTRACT The torsional behaviour of high-strength concrete beams that are transversely reinforced with continuous spiral reinforcement is experimentally investigated in this research. Seventeen specimens are divided into four groups according to their concrete strength: 25, 50, 60, and 70 MPa. Two types of transverse reinforcement, including closed and spiral stirrups, are used at a transverse spacing of 75 and 125 mm for each group. Test results are compared to the analytical values predicted using the ACI equation. Test results have shown an enhancement in the ultimate torsional capacity for the specimens made with high strength concrete compared to those made using normal strength concrete. The enhancement percentage ranges from 1.4% to 46.3%. In addition, results have shown an enhancement in the ultimate torsional capacity for specimens reinforced with spiral reinforcement compared to specimens made with conventional closed stirrups. The enhancement percentage varies from 8.3% to 34.6%. The study concluded that utilising continuous spiral reinforcement would result in higher ultimate torsional capacity than traditional closed stirrups for the same strength of concrete and that the torsion equations of ACI-318 M-19 are applicable and conservative for high strength concrete with a continuous spiral reinforcement.

The combined effect of crumb rubber aggregates and steel fibers on shear behavior of GFRP bar-reinforced high-strength concrete beams

To reduce reinforcement congestion in locations of high rebar concentration in a structure, fiber-reinforced polymer (FRP) rebar (replacing steel rebar) can be used in combination with steel fiber (replacing stirrups). Here, an extensive investigation was conducted for the first time in literature on the effect of steel fibers and crumb rubber (CR) aggregate on the shear behavior of high-strength concrete beams reinforced with glass FRP (GFRP) bars. Thirty beam specimens were manufactured and the effect of the key variables including the GFRP reinforcement ratio, shear span-to-depth ratio, CR content, and fiber content in volume on the shear performance of the beams was investigated. Parameters under investigation were the cracking pattern, manner of failure, load-midspan deflection performance, shear capacity, toughness, and post-cracking strength of the beams. The results indicate that when the fiber volume fraction, concrete compressive strength, and GFRP reinforcement ratio increased, the beam shear capacity increased. Conversely, increasing the shear span-to-depth ratio and CR content led to a decrease in the shear capacity. It was also found that the steel fibers were more efficient in improving the beam shear behavior at higher content of CR, such that they changed the cracking type and failure mode from shear to flexural. Finally, the analysis of variance (ANOVA) technique was used to perform statistical analysis of experimental data and calculate the contribution of different parameters to the experimental results.

Ability of steel fibers to enhance the shear and flexural behavior of high-strength concrete beams subjected to blast loads

The provision of steel fibers improves many of the properties of high-strength concrete (HSC), including its tensile capacity, ductility, toughness and fragmentation resistance. These enhanced features also make high-strength fiber reinforced concrete (HSFRC) an ideal material for the blast resistant design of structures. One of the established applications of fiber-reinforced concrete is in beams, where fibers can be used to increase shear capacity and replace transverse reinforcement. While extensive research exists on the behavior of FRC and HSFRC beams under static loads, studies examining the blast behavior of such beams is scarce. Accordingly, this paper presents the results of an experimental program which studies the effect of steel fibers on the blast performance of high-strength concrete beams. As part of the study, ten HSFRC beams are tested under either static loads or simulated blast loads using a shock-tube. Test variables include the effects of fibers, fiber content, fiber type, longitudinal steel ratio and combined use of fibers and transverse reinforcement. The results show that the use of fibers in HSC beams increases blast resistance, improves control of displacements and results in superior damage tolerance. In addition, the results show that steel fibers can substitute for transverse reinforcement and prevent blast-induced shear failures. The analytical investigation shows that the use of SDOF analysis, with development of non-linear resistant functions, can be used to predict the blast response of HSFRC beams with good accuracy.

Torsional Behavior of High-Strength Concrete Beams with Minimum Reinforcement Ratio

Although there is a growing trend to use higher strength for concrete and steel in reinforced concrete structures due to the lightness and slenderness of these members together with the simplified arrangement of their reinforcement, there is still the necessity to inspect the reduction of ductility resulting from the gain in strength. Taking into account that this also concerns the design for torsion, this study intends to investigate the regulations related to the torsional minimum reinforcement ratio in view of the minimum ductility requirement with focus on Eurocode 2. To that goal, the relation between the torsional cracking moment and the ductile behavior is discussed for the beam reinforced with the minimum torsional reinforcement ratio to examine the eventual properness of the minimum torsional reinforcement ratio recommended by Eurocode 2. Moreover, a pure torsion test is performed on 18 beams made of 80 MPa concrete reinforced by high-strength bars with rectangular section and various test variables involving the minimum torsional reinforcement ratio, the transverse-to-longitudinal reinforcement ratio, and the total reinforcement ratio. As a result, for the high-strength concrete beams, the minimum torsional reinforcement ratio recommended by Eurocode 2 was insufficient to prevent the sudden loss of strength after the initiation of the torsional cracking. But with regard to the compatibility torsion of statically indeterminate structure, the adoption of the minimum torsional reinforcement ratio recommended by Eurocode 2 might secure enough deformability under displacement-controlled mode to allow the redistribution of the torsional moment.

EVALUATION OF FLEXURAL CAPACITY AND DUCTILITY ON HIGH-STRENGTH CONCRETE BEAMS REINFORCED WITH FRP REBAR AND STEEL FIBER

C60 class of concrete is produced with addition of hooked-end steel fibres at dosages of 0kg/m3, 39kg/m3, 78kg/m3, 117kg/m3, and its compressive strength and split tensile strength are measured. The flexural behaviour of high-strength concrete beams containing basalt fibre reinforced polymer (BFRP) rebars and steel fibres is investigated in the present study. An experimental program was set up and seven reinforced concrete beams have been tested, including one series with steel fibres content of 0%, 0.5%, 1.0%, and 1.5% in volume, and one series with ratio of BFRP rebars from 0.38%, 0.57% to 0.76%, 0.95% and tested under four-point flexural loading condition. The result revealed that with the addition of steel fibre, crucial properties of working performance, ductility, and bearing capacity is improved. By increasing BFRP rebar reinforcement ratio, desired ultimate strength is anticipated. Considering the deformability and energy dissipation, a synthesis ductility index for FRP and steel fibre reinforced beams was proposed; while a synthesis ductility index for FRP reinforced flexural structure was also advised. The model of the synthetic ductility index coefficient is verified by relevant experimental data, and was expected to give an insight into the problem of deformability and ductility for the FRP rebar (and steel fibre) reinforced flexural concrete member.

Effects of stirrup, steel fiber, and beam size on shear behavior of high-strength concrete beams

This study investigates the effectiveness of steel fibers and minimum amount of stirrups on the shear response of various sized reinforced high-strength concrete (HSC) beams. For this, six large reinforced HSC beams with a shear span-to-depth ratio (a/d) of 3.2 were manufactured. Three of them contained 0.75% (by volume) steel fibers without stirrups as per ACI Committee 318, while the rest were reinforced with the minimum amount of stirrups without fibers. Test results indicate that, with increasing beam size, significantly lower shear strength was obtained for steel fiber-reinforced high-strength concrete (SFR-HSC) beams without stirrups, than for the plain HSC beams with stirrups. The inclusion of steel fibers effectively limited crack propagation, produced more diffused initial flexural cracks, and led to higher post-cracking stiffness, compared to plain HSC. On the other hand, the use of minimum stirrups gave better shear cracking behaviors than that of steel fibers, and effectively mitigated the size effect on shear strength. Therefore, a large decrease in shear strength, with an increase in the beam size, was only obtained for SFR-HSC beams without stirrups. A shear strength decrease of 129% was obtained by increasing the effective depth from 181 mm to 887 mm. The shear strengths of reinforced steel fiber-reinforced concrete beams were not accurately predicted by most previous prediction models. Therefore, a new shear strength formula, based on a larger dataset, that considers the size effect, is required.

Influence of steel fibers on the shear and flexural performance of high-strength concrete beams tested under blast loads

This paper presents the results of a study examining the effect of steel fibres on the blast behaviour of high-strength concrete beams. As part of the study, a series of three large-scale beams built with high-strength concrete and steel fibres are tested under simulated blast loading using the shock-tube testing facility at the University of Ottawa. The specimens include two beams built with conventional high-strength concrete (HSC) and one beam built with high-strength concrete and steel fibres (HSFRC). The effect of steel fibres on the blast behaviour is examined by comparing the failure mode, mid-span displacements and, overall blast resistance of the specimens. The results show that the addition of steel fibres in high-strength concrete beams can prevent shear failure and substitute for shear reinforcement if added in sufficient quantity. Moreover, the use of steel fibres improves flexural response under blast loading by reducing displacements and increasing blast capacity. Finally, the provision of steel fibres is found to improve the fragmentation resistance of high-strength concrete under blast loads.

Flexural behavior of high-strength concrete beams reinforced with a strain hardening cement-based composite layer

High-strength concrete (HSC) is often used in construction. High-strength concrete exhibits high compressive strength, but the flexural strength and cracking are problems for this material. Strain-hardening cement-based composites were recently developed as a repair material for improving crack control and flexural strength. This paper details the behavior of high-strength concrete beams reinforced with a strain hardening cement-based composite (SHCC) and steel fibers. A new method for improving concrete beam flexural behavior was explored by laying a layer of SHCC in the concrete beam in situ. The flexural behavior of HSC beams containing steel fibers was also studied using a high fiber content. Three types of beams were cast, and a series of tests were conducted. The flexural results indicated that the added SHCC layer increased the load-bearing capacity of the beams. Adding steel fibers significantly increased the load-bearing capacity of the beam.

An experimental study on the flexural behavior of heavily steel reinforced beams with high-strength concrete

In recent years, an emerging technology termed high-strength concrete (HSC) has become popular in construction industry. Present study describes an experimental research on the behavior of high-strength concrete beams in ultimate and service state. Six simply supported beams were tested, by applying comprising two symmetric concentrated loads. Tests are reported in this study on the flexural behavior of high-strength reinforced concrete (HSRC) beams made with coarse and fine aggregate together with Microsilica. Test parameter considered includes effect of being compressive reinforcement. Based on the obtained results, the behavior of such members is more deeply reviewed. Also a comparison between theoretical and experimental results is reported here. The beams were made from concrete having compressive strength of 66.81-77.72 N/mm2 and percentage reinforcement ratio (ρ/ρb) in the range of 0.56%–1.20%. The ultimate moment for the tested beams was found to be in a good agreement with that of the predicted ultimate moment based on ACI 318-11, ACI 363 and CSA-04 provisions. The predicted deflection based classical formulation based on code provisions for serviceability requirements is found to underestimate the maximum deflection of HSC reinforced beams at service load.

고강도 콘크리트의 인장강성을 고려한 철근 콘크리트 보의 비틀림 해석

고강도 콘크리트 보의 극한상태의 거동을 강도에 따라 연구하였다. 13개의 보를 해석하고 그 결과를 제시하였다. 변수는 콘크리트의 압축강도로 범위는 57~184 MPa이며, 횡방향 철근비로 범위는 0.35~1.49%이다. 실험에서 측정한 극한 비틀림 강도를 본 논문에서 제안한 값과 ACI 기준에 따른 값을 비교하였다. 그 결과 본 논문에서 제안한 이론에 의한 극한 비틀림 강도가 ACI 기준에 따른 값보다 더 좋은 결과를 보였다. The ultimate behavior of high-strength concrete beams is studied with respect to their strength. Thirteen beams were analyzed and the results are presented herein. The variable parameters were the concrete's compressive strength, from 57 to 184 MPa and the amount of lateral torsional reinforcement, from 0.35 to 1.49%. The ultimate torsional strengths from tests were compared with those by this proposed theory and by the ACI code. As a consequence, The ultimate torsional strengths by this proposed theory show the better results than those by the ACI code.

Nonlinear Numerical Simulation Analysis on Mechanical Behavior of High-Strength Concrete Beams Reinforced by HRBF500 Steel

Mechanical Behavior of 3 high-strength concrete simply supported beams reinforced by HRBF500 steel with different stirrup ratio are simulated by software OpenSees .In order to establish the constitutive relationship of high-strength concrete more accurately, some parameters of modified Kent-Park were adjusted partly. Furthermore, the restraining effect of different stirrup ratio to the core concrete is considered by the concrete strength rasied coefficient k. The analysis results matched the test ones well, indicating that the OpenSees program is effective to simulate the mechanical behavior of high-strength concrete members reinforced by high-strength steel.

Effect of Member Depth on Shear Strength of High-Strength Fiber-Reinforced Polymer–Reinforced Concrete Beams

AbstractThis paper examines the effect of depth on the shear strength and behavior of high-strength concrete beams reinforced with glass-fiber-reinforced polymer (GFRP) and carbon-fiber-reinforced polymer (CFRP) bars in the longitudinal direction only without stirrups. Three beams, for each reinforcement type, with depths approximately equal to 300, 450, and 600 mm were tested to determine their shear strength and behavior before and after cracking. The targeted concrete strength was 70 MPa. The tests were carried out using two-point monotonic loading. The test results are presented in terms of crack patterns, load-deflection behavior, and failure modes. It was observed that the shear strength decreased with the increase in the depth of the beams. These results were compared with Bažant size-effect law and a good agreement was observed. The test results were also compared with the predictions using the Canadian Standard Association (CSA) and American Concrete Institute (ACI) shear design equations. The pr...

Effect of anchorage and strength of stirrups on shear behavior of high-strength concrete beams

This study investigated possible ways to replace conventional stirrups used on high-strength concrete members with improved reinforcing materials. Headed bar and high-strength steel were chosen to substitute for conventional stirrups, and an experimental comparison between the shear behavior of high-strength concrete large beams reinforced with conventional stirrups and the chosen stirrup substitutes was made. Test results indicated that the headed bar and the high-strength steel led to a significant reserve of shear strength and a good redistribution of shear between stirrups after shear cracking. This is due to the headed bar providing excellent end anchorage and the high-strength steel successfully resisting higher and sudden shear transmission from the concrete to the shear reinforcement. Experimental results presented in this paper were also compared with various prediction models for shear strength of concrete members.