High Strength Concrete Beams Research Articles

Experimental Research of Ratio between Residual and Elastic Strains εres/εE in High-Strength Concrete Beams Subjected to Bending.

In the mechanics of concrete constructions, one distinguishes between residual and elastic strains. Cyclic loadings evoke changes mainly in the elastic strains; however, the total strains are decided by the sum of the residual and elastic strains. The knowledge of the ratio between the residual and total strains allows to predict the total deformations of a construction assuming it is made from an ideally elastic material. This paper presents the effect of the load level at the values of the residual strains for beams made of high-strength concretes and subjected to bending. The investigations showed that the share of residual strains for these concretes differed from the share of residual strains for concretes of lower classes. The investigations were made for cyclically loaded concrete samples and ferroconcrete beams for various relative load levels. The ratio between the residual and total strains was presented in the form of a dependence on the relative load level of the element. An important conclusion was that, after the crack formation, the share of residual stresses reduced, along with the increase in the concrete strength and elastic features of the construction which started to predominate.

Shear behavior of headed stud connectors in steel-MPC based high strength concrete composite beams

In this paper, magnesium phosphate cement (MPC) based high strength concrete (HSC) was first introduced into steel–concrete composite beams due to its better durability, good antirust performance, high early strength and eco-friendly. Twenty-four push-out specimens were conducted to examine the static behavior of headed stud connector in steel-MPC based HSC composite beams, including 21 MPC based concrete specimens and 3 normal concrete specimens. The failure modes, load-slip behavior, ductility, shear stiffness and shear capacity of stud connector were investigated. The effect of stud height, stud diameter, concrete strength and concrete type were also discussed. The test results showed that the shear behavior was greatly improved with the increase of the stud diameter. The aspect ratio, concrete strength and type had minor effect on the shear capacity of stud embedded in MPC based HSC concrete, while the shear stiffness and ductility were obviously affected. Furthermore, according to the existing equations and current design codes, the test results and calculated results of shear stiffness, load-slip behavior and shear capacity were compared and analyzed. Finally, an empirical equation considering stud diameter was put forward to assess the load-slip relationship of headed stud embedded in MPC based HSC.

Numerical study on the flexural behaviour of normal- and high-strength concrete beams reinforced with GFRP bar, using different amounts of transverse reinforcement

This study was numerically focused on the non-linear behaviour of glass fibre reinforced polymer (GFRP) reinforced concrete beams with different amounts of transverse reinforcement. The mid-span deflection of concrete beam cannot effectively be restricted using higher amount of flexural GFRP bars, owing to their low deformability factor. So, the use of high transverse reinforcement ratio is proposed to decrease the mid-span deflection and crack widths. Following this, the effect of reinforcement is required to carefully assess to better understand the flexural behaviour of concrete beams. The main goal of this study was to numerically evaluate the mid-span deflection, stress distribution and failure mechanism of normal- and high-strength concrete beams with low and high flexural reinforcement ratios (GFRP bar) and different amounts of transverse reinforcement using finite element (FE) analysis. The results revealed a fair agreement between the developed FE models and experimental beams. Besides, the mean value of experimental-to-predicted load ratio was 0.96, with average coefficient of variation of 2.69 %. Moreover, the truss action mechanism generated the diagonal compression in the cracked concrete and tension in the transverse reinforcement, resulted in decreasing the mid-span deflection. In addition, for all specimens with and without transverse reinforcement, the highest stress intensities were observed in the bottom of concrete component at service load. However, by increasing the load from service to ultimate, the use of transverse reinforcement caused to propagate some parts of high stress intensities near to the sides of concrete component. Furthermore, the presence of the transverse reinforcement resulted in distributing the stress intensity in the normal-strength concrete beams more than that in the high-strength concrete beams either at service load or at ultimate load.

EVALUATION THE SHEAR STRENGTH OF FIBROUS REACTIVE POWDER CONCRETE BEAMS STRENGTHENED WITH CFRP STRIPS

A new expression for estimating the ultimate shear strength of steel fibers reinforced high strength concrete (SFRHSC) beams strengthened with CFRP strips based on previous researches is proposed in this research. The proposed expression covers different characteristics and principal parameters such as concrete compressive strength, shear span to effective depth ratio, volume fraction of steel fibers, CFRP amount and distribution, CFRP stiffness, deep beam effect, as well as the end anchorage state of the CFRP strips with the beam. A comparison between computed values and experimentally observed values (with a low COV of about 3.58 %) shows the validation of the proposed theoretical treatment.

Flexural Behavior of Ultra-High-Performance Fiber-Reinforced Concrete Beams after Exposure to High Temperatures.

Due to the dense structure of ultra-high-performance concrete (UHPC), it is prone to explosive spalling at high temperatures. In this paper, flexural testing of UHPC and high-strength concrete (HSC) beams was carried out at room temperature and after being subjected to different levels of thermal exposure (300–500 °C). The cross-section of the beam specimen was 150 (width) × 200 (depth) mm, and its length was 1500 mm. The flexural and shear design of the beam specimens were carried out in accordance with the ACI 318M-14 code. All of the beams were singly reinforced with two #4 rebars (minimum reinforcement ratio) as a longitudinal tensile reinforcement at the bottom of the specimen and at an effective depth of 165 mm. The flexural load was applied using the three-point load method. The results show that, at room temperature and after being subjected to different thermal exposures, compared with the HSC specimens, the stiffness of the UHPC specimens in the post-cracking stage was relatively larger and the deflection under a given load was smaller. Moreover, whether at room temperature or after exposure to different thermal exposures, the ductility of the UHPC specimens was better than that of the HSC specimens.

Flexural shear behavior of FRHSC beams with fibers only in shear span

As per Code of Indian Standards, a concrete having a compressive strength greater than or equal to 65 N/mm2 is referred to as a high strength concrete. High strength concrete has many favorable properties, but it is a brittle material and has a low rate of increase of tensile strength due to which it is not of great use in earthquake-prone areas. The best method to improve the flexural shear behavior is to incorporate fibers in concrete at the required proportions. This paper investigates the flexural shear behavior of high strength concrete beams by replacing traditional shear reinforcements with steel fibers only in the shear span. The effect of varying volume fractions of fibers (0%, 0.5%, and 0.75%) is also studied. It was found that the brittle failure was converted to ductile failure by fiber addition only in shear span. The load carrying capacity, compressive strength and split tensile of high strength concrete increased with increase in fiber volume.

Cyclic response of high strength fibre reinforced concrete beams with fibre reinforced polymer (FRP) laminates

This paper assesses the cyclic response of high strength concrete beams with externally bonded GFRP laminates reinforced by steel fibre. For the current research work a total of six rectangular beams have been casted. In the preliminary we are used three different percentage of steel fibre 0.5%, 1% and 1.5% from the different tests are conducted in laboratory we were find out the optimum as 1%. One of the beam was worked as control beam as well as the other five have been provided with the steel fibres of having 1% in volume fraction in that 4 beams laminated of 3 mm and 5 mm thickness of CSMGFRP and UDCGFRP. The beams in the cross-section were 150 mm × 250 mm, and 3000 mm long. The beams were tested over a span of 2800 mm, in four-point bending. Under monotonically increasing loading, one beam has been tested and manual readings have been recorded directly in a spreadsheet programme from that load range was fixed from the static ultimate load of the control beam fmin 20% and fmax 60%.The test specimens were subjected to sinusoidal loading at a frequency of 2 Hz. The remaining five beams are test under cyclic loading have been tested and readings have been recorded directly by using MTS793 Flextest software. Adequate data has been collected upon its deformation, strength, fatigue life and failure properties of high-strength concrete beams reinforced with GFRP laminates, and also high-strength concrete beams reinforced with steel fibre. The analysis approaches adopted with this research work comprised sufficient information on deflection, number of cycles, rigidity, number of cracks, crack duration, average crack spacing, energy absorption and failure characteristics for high-strength concrete beams reinforced with externally bonded GFRP laminates under cyclic loading. The findings of the tests performed are thoroughly explained and analyzed.

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.

Analysis on the Seismic Performance of Steel Fiber-Reinforced High-Strength Concrete Beam-Column Joints.

The present research study aims to investigate numerically the behavior of steel fiber-reinforced high-strength concrete (SFRHC) beam–column joints (BCJs) under seismic action. Based on the plastic damage constitutive model of concrete and elastic–plastic mixed-strengthen constitutive model of steel material, the finite element software ABAQUS was utilized to establish the 3D finite element (FE) model of BCJs. Additionally, the feasibility and accuracy of the numerical simulation were verified by comparing the computed results and experimental observations in terms of the hysteresis curves, skeleton curves, and failure mode. Furthermore, based on the validated FE modeling approach, load vs. displacement hysteresis curves of SFRHC–BCJs during the loading process were analyzed in detail; the failure process was also investigated. Furthermore, the effect of various parameters on the seismic behavior of BCJs was analyzed comprehensively, including the concrete strength, the volume ratio of steel fiber, and the stirrup ratio in the core area. Finally, parametric studies illustrated that increasing the concrete strength helps in enhancing the ultimate load, while the ductility decreased noticeably. Both adding the steel fiber and increasing the stirrup ratio can significantly improve the seismic performance of BCJs.

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.

Torsional Behavior of High Strength Concrete Members Strengthened by Mixed Steel Fibers

Twelve mixing steel fibers-reinforced high strength concrete beams were experimentally tested under pure torsion to investigating the concrete member torsional behavior. The first cracking torque, ultimate torsional resistance, crack patterns, effect of steel fiber ratio, effects of shape and size of hollow cross-section, and effect of stirrups reinforcement were discussed. The ratio of mixing steel fiber, different shape and size of hollow cross-section, and ratio of stirrups reinforcement were considers as major parameters. The results are shown that the width of cracks decreases and the cracks number increases with mixing steel fibers ratio increased. The first cracking torque and ultimate torsion load increased with decrease in the hollow cross-section area of high strength concrete members strengthened by steel fibers.

Flexural behavior of high strength concrete deep beams reinforced with GFRP bars

This paper presents an experimental and numerical study of the flexural behavior of high concrete deep beams reinforced with locally produced glass fiber reinforced polymers (GFRP) bars using high strength concrete (HSC). Both studies were carried out to study the effect of using (GFRP) bars with different ratios of reinforcement and concrete compressive strengths on the behavior of these beams.A total of eight beams, measuring 150 mm wide 500 mm depth and 1800 mm length, were cast, and tested up to failure under two-point loading. The main parameters were the types of reinforcement used, whether steel or GFRP bars. Also, concrete compressive strengths of 50 MPa and 60 MPa were used. In addition, different reinforcement ratios of 0.0033 for steel reinforcement and ratios (0.8, 1.0 and 1.2) of the balanced condition were used. The mid-span deflections, failure loads and GFRP reinforcement strains of the examined deep beams were recorded and compared with each other.The test results revealed that the crack widths and mid-span deflections significantly decreased when using 1.2μb of GFRP reinforcement ratio compared with beams reinforced with steel bars where μb is balanced reinforcement ratio of beam. The decrease in deflection varied between 20%–39.0% for specimens having 50 and 60 MPa respectively, with a significant decrease in the concrete cracks’ widths. Also, the ultimate load slightly increased by 2.5 % and 4.0 % as the concrete strengths increased.A Non-Linear finite element analysis (NLFEA) using ANSYS 2019-R1 was constructed to simulate the flexural behavior of the tested deep beams, in terms of failure load, crack pattern and load deflection behavior. Comparison between the experimental and numerical methods showed good agreement between both results.

Effects of novel multiple hooked-end steel fibres on flexural tensile behaviour of notched concrete beams with various strength grades

3-point bending tests were carried out on notched low, normal and high strength concrete beams containing single or novel multiple hooked-end steel fibres, ranging 0 ~ 110 kg/m3 in dosage, 35 ~ 60 mm in length, and 0.55 ~ 0.90 mm in diameter. The experimental results suggest that the Limit of Proportionality (LOP), which is related to initial concrete cracking, largely depends on concrete strength rather than fibre properties. Increasing fibre dosage, length, aspect ratio and number of hooked-end are beneficial for enhancing residual flexural tensile strength of steel fibre reinforced concrete (SFRC). New empirical equations, which can explicitly characterise the effects of concrete strength and fibre properties, were proposed to predict the LOP and residual flexural tensile strength of SFRC. By using the proposed equations, the effects of concrete strength and fibre properties on LOP and residual flexural tensile strength were discussed in depth. It was concluded that the LOP is mainly governed by concrete strength, while the residual flexural tensile strength is mainly dictated by fibre properties.

Flexural behavior of ultra-high performance geopolymer RC beams reinforced with GFRP bars

Geopolymer concrete (GPC) reinforced with glass fiber reinforced polymer (GFRP) bars can give a good structure system with high durability and strength. So, this research was described the flexural behavior of the geopolymer Ultra-high-performance concrete (UHPC) beams. Also, the impact of UHPC reinforced with glass fiber reinforced polymer (GFRP) bars was studied. For this purpose, (eight) UHP geopolymer RC beams was studied. Four High Strength Concrete (HSC) beams and another four in UHPC were reinforced using GFRP with different ratios. The Results exhibited increasing the first crack load and ultimate load carrying capacity. GPC beams showed a smaller deflection increase at the same ultimate load. GPC beams reinforced with GFRP bars documented a higher crack width compared with control. Using GFRP bars in reinforcement improved the concrete defection, the patterns of cracks, cracks number of and the failure mode. A non-linear analysis using Ansys 2019-R1 was conducted to validate the experimental results for each beam. Results showed well agreement between experimental results and analytical ones.

Seismic Performance of Steel Fiber Reinforced High-Strength Concrete Beam-Column Joints.

In high–strength concrete, the reinforcement concentration will cause some problems in the beam–column joints (BCJs) due to a large amount of transverse reinforcement. Hence, the main object of this paper is to prevent the reinforcement concentration and reduce the amount of transverse reinforcement in the BCJs through the ideal usage of steel fibers and reinforced high–strength concrete. Pseudo–static tests on seven specimens were carried out to investigate and evaluate the seismic performance of beam–column joints in steel fiber reinforced high–strength concrete (SFRHC). Test variables were steel fiber volume ratio, concrete strength, the stirrup ratio in the core area, and an axial compression ratio of the column end. During the test, the hysteresis curves and failure mode were recorded. The seismic indicators, such as energy dissipation, ductility, strength, and stiffness degradation, were determined. The experimental results indicated that the failure modes of SFRHC beam–column joints mainly included the core area failure and the beam end bending failure. With the increase in stirrup ratio, volume ratio of steel fiber, and axial compression ratio in the core area, both the ductility and energy consumption of beam–column joints increased, while the opposite was true for concrete strength.

Analytical Study on Moment-Curvature of Normal and High Strength Concrete Beams

In the present study, reinforced concrete beams areconsidered for the calculation of minimum flexuralreinforcement, Moment-Curvature relationship and ductilityindex using fracture energy. Normal strength concrete i.e. M20,M30, M40, M50 and high strength concrete i.e. M60, M70, M80, M90,M100 are considered in this experiment with the varying grade ofsteel from Fe250, Fe415, Fe500. In a particular grade ofconcrete, minimum flexural reinforcement is decreased with theincrease in grade of steel. In a particular grade of steel,minimum flexural reinforcement is increased with the increasein the grade of concrete. Ductility Index is decreased with theincrease in grade of concrete. Similar trend is observed whenfracture energy is not considered in calculation of minimumpercentage of reinforcement.

ENVIRONMENTAL BENEFIT OF TWO-LAYER STEEL FIBERED HIGH-PERFORMANCE CONCRETE BEAMS

ABSTRACT This study evaluated Life-Cycle Assessment (LCA) of two different designs of high-performance concrete beam: (1) a single-layer beam (SLB) that consisted of steel fibered high-strength concrete in both the compression and tensile zones and (2) a two-layer beam (TLB) that consisted of steel fibered high-strength concrete and normal-strength concrete in the compression and tensile zones, respectively. The SLB and steel fibered high-strength concrete layer of the TLB were of the same concrete class C70/85. LCAs of the SLB and TLB were conducted using the ReCiPe2016 midpoint and endpoint-single-score methods. The difference between the two endpoint-single-score results was evaluated using a two-stage nested analysis of variance. The ReCiPe2016 midpoint results showed that replacing the SLB with the TLB reduces the environmental impact of global warming potential, terrestrial ecotoxicity, water consumption, and scarcity of fossil resources by 15%, 17%, 11%, and 17%, respectively. The ReCiPe2016 endpoint-single-score results showed that the environmental damage from the TLB compared to the SLB was statistically reduced (p = 0.0256). Therefore, considering two different designs of steel fibered high-strength concrete beams, the TLB design was found environmentally preferable to SLB design on both, midpoint and endpoint-single-score evaluations.

Experimental and analytical study on flexural behavior of reinforced concrete beams using nano silica

Nano technology is an emerging field in material science. Hence this research has been conducted to examine the flexural behaviour of the Reinforced concrete beam with Nano Silica and the same is compared analytically using ABAQUS. The structural behaviour of Reinforced concrete beam which has been strengthened using nano silica of various proportion 1%, 2%, 3%, 4%, 5% along with various proportion of 25%,40%, 50%,75%,100% Manufactured sand (Msand) is investigated. Mix proportion of M40 and M50 grade of concrete was used for concrete mix design. This flexural behaviour of nano concrete is compared with the conventional concrete. Nano silica which has a large surface area eventually, strengthens the reinforced concrete beam which behaves as micro filler improving the microstructure and makes it more homogeneous, the pozzalonic reaction improves the microstructure and makes it more homogeneous. The effect of concrete strain, the cracking patterns, the mode of failure and deflection was examined. To verify the experimental results a non-linear finite element analysis of three dimensional high strength concrete beam was conducted using ABAQUS. It was found that analytical and the Experimental results are agreeable.

Effect of Anchorage Length on the Shear Capacity of High Strength Concrete Deep Beams

Ten simply supported deep beams with high strength concrete (C55 MPa) have been casted and subjected to a four-point loading test. Different parameters were examined for their influence on specimen behavior. These parameters were the shear span to overall depth ratio (a/h), the overall depth of deep beams (h), and additional anchorage length beyond the centerline of support (la). The experimental results show that the beam capacity decreases as the shear span to the overall depth ratio increases, and the overall depth and embedment length decrease. The major effect of anchorage length on the shear strength is studied. Different failure modes were observed which do not match strut-and-tie failure modes. The shear compression and anchorage failures were con-trolled in the high compressive concrete deep beams due to bottom steel yielding. Finally, the ex-perimental test results are compared with predictions of the strut-and-tie method according to the ACI 318-14 and a good agreement was found.

Investigations on Mechanical Characteristics and Microstructural Behavior of Laterized High Strength Concrete Mix

The present research focuses on the varying proportion of lateritic fine aggregates in High strength concrete (HSC). Concrete mixes of M60 grade were produced by replacing manufactured sand with laterite in the ratio of 25 to 100 percent (by weight), and properties of the mixes are studied. To attain high strength mix, 10% micro silica and 10% of fly ash (FA) were added to all mixes. Mechanical properties were studied after 7, 28, 56, and 90 days of curing, and laterized specimens achieved approximately 12 percent higher compressive strength than control specimens, whereas the split-tensile and flexural strengths increased up to 11.14% and 12.83%, respectively. The results indicated that 25% substitution of laterite was the optimum percentage in HSC concrete. Microstructural studies of optimum mix and reference mix were conducted at 28 days to better morphological and mineralogical understanding of the laterized HSC. Durability parameters such as water penetration depth, chloride ion permeability, and sorptivity exhibited higher values for laterite mixes than the control mixes. The flexural behavior of Reinforced HSC beams using lateritic aggregates was investigated, and the load-carrying capacity of laterized beams was reported to be 11.3 percent higher than control beams. The study results indicate that HSC can be achieved with partial substitution with lateritic fine aggregates and proves that laterite can replace conventional aggregates.