Effect Of Concrete Strength Research Articles

On the Effective Concrete Compressive Strength in the Theory of Plasticity

In his fundamental book Nielsen (1984) summarized the basics of application of plastic theories to the design of concrete structures. Since that time extended experimental and theoretical works were carried out. Models based on plastic theories were developed for bending, shear, for beams, plates, etc. The strut-andtie-, the stress field models and the Modified Compression Field Theory perform further developments of application of the theory of plasticity. Crucial point (the governing material characteristic) of these models is the effective concrete compressive strength. This paper critically reviews its different theoretical origins and despairs of its existence. It reveals that the main source of plastic behavior of structural concrete structures is the reinforcement. In design for shear instead of a preposterous effective concrete strength the effective web thickness and (a maybe slightly reduced) concrete compressive strength should be taken into account. Neither the concrete compressive strength nor any reduced (effective) value of it are applicable as governing material characteristic of any plasticity model for structural concrete structures.

Effect of hygrothermal acid rain environment on the shear bonding performance of CFRP-concrete interface

In this study, forty-five carbon fiber-reinforced polymer (CFRP)-concrete single shear specimens were designed to investigate the effect of hygrothermal acid rain environment. At first, the hygrothermal acid rain environment was simulated through a mechanical high-temperature dry-wet cycle and by artificially preparing acid rain solution with a pH value of 1.5. Subsequently, the effects of concrete strength and corrosion times on the interface failure mode, bond shear capacity, ultimate displacement, load–displacement behavior, and strain distribution in bonding interval were studied through the single shear test of CFRP-concrete. Then, the interface constitutive relation model was built based on the influence coefficient of hygrothermal acid rain. Finally, a reference method was proposed to divide the corrosion degree in hygrothermal acid rain environment, and the interface failure mechanism was expounded using a scanning electron microscope (SEM) for detection. The results indicated that the interface bonding performance was enhanced with the increase of the concrete strength, and the interface peeling position tended to change to the adhesive layer. The interfacial bonding performance increased first and then decreased with the increase of the corrosion times. When the corrosion number reaches ten cycles, the interfacial bond performance gets the best, the interfacial peel load and ultimate displacement of the three types of strength concrete(C30\\C40\\C50) were examined as 3.04 %, 3.50 %, 5.78 %, and 0.50 %, 0.49 %, 0.95 % higher than those of the uncorroded specimens, respectively. The SO42- ions in the acid rain invaded the surface of the concrete to synthesize an expansive substance CaSO4·2H2O, thus temporarily enhancing the interfacial bonding performance at the early corrosion stage. The load–displacement curve comprised four stages, including rising, oscillating, strengthening, and falling. In this study, an interface constitutive model was proposed based on the influence coefficient of hygrothermal acid rain, which is well consistent with the existing experimental data and exhibits high accuracy and safety. The relevant research results can provide theoretical support and design guidance for CFRP reinforcement projects in high-humidity and high-heat acid rain areas.

Bond-slip behavior between high-strength steel tube and Ultra-high Performance Concrete

To satisfy the requirement of super high-rise buildings and large-span structures, an Ultra-high Performance Concrete Filled High-Strength Steel Tube (UHPC-FHSST) is presented. The effects of concrete strength, length-to-diameter ratio, and diameter-to-thickness ratio on interfacial bond-slip performance are investigated through push-out tests of 12 UHPC-FHSST specimens. The bond-slip process of the UHPC-FHSST is revealed and its strain evolution is analyzed. The research results show that the bond strength between the high-strength steel tube (HSST) and the UHPC core increases with the decrease of the diameter-to-thickness ratio and the length-to-diameter ratio, and the increase of concrete strength will lead to the decrease of bond strength. The longitudinal strain increases with the growth of the axial load. Based on the experimental results, the shear transfer length is determined and computed, and the mathematical model to reflect the bond-slip behavior of UHPC-FHSST is developed, which can provide valuable instruction for the engineering application of UHPC-FHSST.

Characteristics of Concrete With Rice Husk Ash Local Kutai Kartanegara

Abstract. Concrete material made from natural waste was developed to balance the use of concrete materials resulting from natural exploration with an impact on environmental damage, rice husk is a waste material from rice mills and contains reactive silica and has the benefit of reducing energy consumption in cement production. Laboratory test method in the form of testing the compressive characteristics used standard cube concrete 150 mm x 150 mm x 150 mm with a total sample of 24 samples. The effect of concrete strength on the amount of cement replacement is 0%; 5%; 10% ; and 15% which could be compared with concrete without using husk ash. The compressive strength obtained in terms of the age of the concrete is 28 days. The mechanical properties of husk ash at the age of 28 days gave optimal compressive strength results with the addition of 5% husk ash.

Stress-strain behavior of ECC-GFRP spiral confined concrete cylinders

This paper introduces a new confinement system that combines engineered cementitious composites (ECC) with glass fiber-reinforced polymer (GFRP) spiral as a protective cover to confine the concrete core. Meanwhile, the precast ECC-GFRP spiral cover also can serve as permanent formwork to improve construction efficiency and save construction costs. This study analyzed the confinement mechanism from the combination of ECC and GFRP spiral, and the effects of concrete strength and confinement stiffness on the stress-strain behavior of the confined concrete were investigated. The stress-strain behavior analyses confirm that the residual confining stress from ECC could enhance the ductility of the composite cylinder after GFRP rupture. Test results also indicate that an ECC-GFRP spiral layer has excellent crack control capability before peak loads, guaranteeing concrete cylinder durability. In addition, the model evaluation indicates that ultimate condition models for FRP-confined concrete are also applicable to ECC-GFRP spiral-confined concrete as long as the confining pressure from both ECC and GFRP spiral can be accurately predicted. A modified stress-strain model is proposed for this confinement form and performs well against test stress-strain curves.

A load-slip model for stud connector in steel-concrete composite structures

A new theoretical calculation method for the load-slip curve and the shear stiffness of the stud based on Winkler’s elastic foundation beam theory and deflection differential equation of the stud is proposed. Different stress characteristics of the elastic and plastic zones of the concrete are considered in the proposed method. The accuracy of the theoretical calculation method is validated by the test results. Moreover, the effect of concrete strength, stud diameter, and yield strength on the stud load-slip curve is analyzed. The results show that the proposed model can effectively reflect the change process of the load-slip curve of the test specimen stud connector. The stud diameter, stud yield strength, and concrete strength affect the peak slip, shear stiffness, and shear capacity of stud shear connectors. With an increase in stud diameter, the peak slip, shear stiffness, and shear bearing capacity of the stud are all increased. An increase in the yield strength of the stud increases its elastic slip, peak slip, and shear capacity. Lastly, with an increase in concrete strength, the elastic slip and peak slip of the stud both decrease, whereas the shear stiffness and shear bearing capacity are increased.

Experimental Evaluation of Effect Factors on Seismic Performance of Concrete Columns Reinforced with HTRB630 High-Strength Steel Bars

HTRB630 steel bar is a new type of high-strength steel bars. To study the seismic performance and promote the application of concrete columns reinforced with HTRB630 high-strength steel bars, the pseudo-static test of 10 concrete columns reinforced with HTRB630 high-strength steel bars and 3 concrete columns reinforced with HRB400 was carried out. Test specimens were divided into five categories according to concrete grade, reinforcement strength, and degree of confinement. The effect of concrete strength (C45 and C60), axial load ratio (0.1 and 0.25), equal strength substitution of longitudinal reinforcements (HTRB630 and HRB400), equal strength and volume substitution of stirrups (HTRB630 and HRB400), equal strength substitution of confined reinforcements (HTRB630 and HRB400) on the seismic performance are analyzed and discussed from the failure mode, hysteresis loops, skeleton curves, lateral strength, ductility, energy dissipation capacity, stiffness and strength degradation. The failure mode of each specimen was bending failure. Reducing of the axial lo ratio or increasing the strength of reinforcements, the seismic performance of the specimen could be improved. C60 concrete can improve the seismic performance of HTRB630 reinforced columns. The lateral strength of the concrete column specimen with HTRB630 reinforcements was slightly increased, and the ductility and energy dissipation capacity were reduced, the stiffness degradation was more gradual, the strength degradation coefficient was greater than 0.94, but still met the requirements of the code for seismic design of buildings (GB50011-2010).

Flexural behavior of prestressed concrete-filled steel tubular flange beams

This research presents a numerical and analytical investigation on the structural characteristics of concrete-filled steel tubular flange beams (CFSTFBs) prestressed using steel strands under bending. CFSTFBs are found to benefit from higher flexural and shear strength compared to those of I-section beams with flat flanges. The geometrical configurations of these sections provide them with higher web local buckling resistance due to a larger flange depth-to-width ratio. A large number of existing structures, constructed with steel–concrete composite beams, need to be retrofitted due to many factors such as loss of strength as a result of service loads and environmental conditions. A potentially economical and feasible approach to strengthening these beams is upgrading them using steel prestressing strands. The finite element (FE) approach was utilized to develop a three-dimensional numerical model considering both material and geometrical nonlinearity. Accordingly, the effects of concrete strength, tubular flange shape and dimension, steel yield stress, and quantity and eccentricity of strands were included in the analysis. A simplified model, on the basis of the plastic stress distribution method (PSDM), was used to estimate the ultimate moment capacity. In order to visualize the influence of steel and concrete strength and tubular flange size on the moment capacity of CFSTFBs, several artificial intelligence (AI) algorithms were employed and a partial dependence analysis was also conducted accordingly. The ultimate capacities obtained by analytical and FE models, considering the effect of confinement, were verified by comparing the predictions with the results from experimental studies. Both analytical and FE results indicated that the prestressing strands are significantly capable of enhancing the stiffness and strength of CFSTFBs under flexural loading. It was demonstrated that the tube geometric properties can significantly control the overall performance of prestressed CFSTFBs. The results also indicated a negligible effect of the concrete compressive strength.

The bond strength of reinforced concrete with confinement of recycled steel strap

The potential use of recycled steel strap from packaging industry to strengthen bond between reinforcement steel and concrete was investigated. Through a series of pull-out experimental tests, this technique was shown to improve the bond properties between reinforcement steel and concrete. This research found that concrete strength and amount of steel straps provided for confinement affect the improvements on the bond between reinforcement steel and concrete. The analysis conducted in this research found that higher concrete strength and less amount of steel strap confinement would result in lower improvement in the bond strength. Subsequently, the effects of concrete strength and amount of steel strap confinement provided were considered into a newly developed equation to estimate bond strength. This research also conducted a model assessment on the proposed equation and the equation was found to be in good agreement with the experimental test results.

Investigation on shear behavior of studs and PBL shear connectors in steel-concrete hybrid bridge girder

Due to the excellent properties of concrete and steel, steel–concrete composite structures have a wide range of applications in civil engineering. The most common shear connectors are the stud and perfobond rib (PBL) shear connectors, and there are a lot of studies on the shear behavior of stud and PBL shear connectors, respectively. But fewer studies were conducted on the combined shear behavior of both. This research presents experimental and numerical studies on the shear behavior of stud and PBL shear connectors. Test results show that the primary failure of the specimens is that the studs were sheared off, accompanied by concrete damage. The number of rows of shear connectors and the diameter of the transverse rebar can significantly affect the shear capacity. In contrast, the concrete dowel diameter has a limited impact on the shear capacity. Based on the validated finite element (FE) analysis, the effects of concrete strength, perforated plate thickness, and stud diameter on the shear capacity were parametrically investigated. The test and FE analysis results are compared with the existing equations of stud and PBL shear connectors. A combination most consistent with test and FE analysis results with discrepancies less than 5% is suggested for predicting the shear capacity of stud and PBL shear connectors.

Experimental Research on Flexural Mechanical Properties of Ultrahigh Strength Concrete Filled Steel Tubes

Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength (fcu) of the core concrete reached 80.3–115.2 MPa. The effects of concrete strength on flexural bearing capacity, deformation characteristics, and failure modes of UHSCFST specimens were discussed. Test results showed that the bending failure modes of UHSCFST specimens were the same as those of ordinary ones. The failure of UHSCFST specimens was attributed to excessive deflection, and local buckling occurred in the compression zone. Moreover, the bending capacity of the specimens did not decrease, even if they had yielded. Although ultrahigh strength concrete was poured, all of the specimens displayed outstanding bending ductility. The main function of core concrete was to provide radial restraint for the steel tube to avoid premature buckling. When the steel content of the specimen section was constant, the strength increases of core concrete had a slight impact on the bending failure mode, bearing capacity and ductility of UHSCFST specimen. The research results can deepen the understanding of the mechanical behaviors of the UHSCFST composite truss structure.

Using the Simplified Concrete Damage Plasticity Model in Studying the Penetration Depth in Concrete

This paper, with the simplified concrete damage plasticity (SCDP) model, studying the penetration depth of steel projectile in the concrete block by Abaqus software. Comparing the results calculated by Abaqus software with the Modified NDRC formula to check the reliability of the computational model and material model. From there, studying the effect of concrete strength on penetration depth in concrete B20, B30, B40, B50.

Chloride diffusion behavior and microstructure of basalt-polypropylene hybrid fiber reinforced concrete in salt spray environment

The chloride diffusion performances of basalt-polypropylene hybrid fiber reinforced concrete (BPHFRC) in salt spray environment were investigated. The effects of concrete strength, fiber addition form and content on the pore solution pH and chloride concentration were evaluated. The results showed that the stable depth of pore solution pH of BPHFRC increased with the increase of exposure time.The greater the strength of concrete, the slower the decrease rate of pore solution pH with exposure time. The effects of addition form and content of basalt fiber (BF) and polypropylene fiber (PF) on chloride concentration were different. When the fiber content was 0.1%, the addition of BF, PF or hybrid BF-PF could improve the chloride corrosion resistance of concrete.However, addition of 0.2% hybrid BF-PF increased the chloride concentration in the concrete. The apparent chloride diffusion coefficient of BPHFRC decreased with an increase of salt spray erosion time, and exhibited a power function with erosion time. The calculation model of BPHFRC apparent chloride diffusion coefficient was established, and its effectiveness was verified. In addition, the pore structure, phase composition and micromorphology of BPHFRC before and after erosion were performed using RapidAir-457 porosity analyzer, X-ray diffraction and field emission scanning electron microscope, and the influence rules of BF and PF on chloride diffusion properties of concrete was discussed.

Influence of concrete strength and aggregate size on the size effect of shear capacity of RC beam-column joints under monotonic loading: Mesoscale numerical tests

In this research, the influence of width on mechanical performance of joints is studied by numerical tests based on 2D mesoscale models. Meanwhile, the effects of concrete strength and aggregate particle size on size effect of joints are analyzed. Firstly, the proposed 2D mesoscale model, which is reflective of the heterogeneity of concrete and damage development within joints, is validated based on existing experimental results. Secondly, based on the proposed 2D mesoscale model, a range of numerical tests about size effect are conducted. It turns out that, the size effect of shear capacity becomes more remarkable with the increasing concrete strength and the decreasing aggregate size. Thirdly, the size effect of joints is discussed based on different SELs (size effect laws). The Type-II SEL proposed by Bažant (1984) is initially adopted to evaluate the size effect of joints. Although it can give generally adequate trends on size effect, the nominal shear strength of joints considering the effect of concrete strength and aggregate size cannot be calculated quantitatively. Therefore, the authors present a new SEL that considers concrete strength and aggregate size, which is able to give concise shear capacity of joints.

NLFE modeling of bond between NSM CFRP strips and heat-damaged concrete

A nonlinear finite element (NLFE) model was developed to describe bond behavior between heat-damaged concrete and near-surface mounted (NSM) fiber-reinforced polymer (FRP) strips. The different components of near-end pullout specimens were represented using proper elements in ABAQUS software with the cohesive element adopted to consider bond behavior. The model is calibrated using data from two published experimental works, before its predictions were extrapolated to consider the effect of temperatures (23–550 °C), along with the effects of concrete strength (25–55 MPa), bond length (100–350 mm), spacing (50–200 mm) and fiber type of NSM CFRP strips. Elevated temperatures, in excess of 300 °C, caused a reduction in residual pullout force, yet an increase in bond ductility. The degradation in bond was more pronounced for specimens with higher-grade concrete and lower spacing between strips. Exposing concrete blocks to 450 °C and above undermined the contribution of NSM CFRP strips (100–350 mm) to bond strength. The type of composite had a minor (if any) impact upon bond behavior between heat-damaged concrete and FRP strips for temperatures higher than 300 °C. The NLFE cracking patterns indicated that bond failure mode in the pullout specimens is dictated by the spacing between strips with minimal impact of exposure temperature or bond length.

Fire resistance of ultra-high performance concrete columns subjected to axial and eccentric loading

This paper experimentally investigated fire resistance of UHPC and HPC columns under the ISO 834 fire curve. Effects of concrete strength, inclusion of fibers, and load eccentricity were investigated. Spalling behavior, failure mode, temperature distribution, axial deformation, mid-height column deflection, and fire resistance were measured and analyzed. From the results, columns with plain UHPC matrix were highly susceptible to explosive spalling due to its dense microstructure and low permeability, which led to premature failure and low fire resistance. Although the addition of 3 kg/m3 of PP fibers was higher than the dosage recommended in Eurocode 2, it did not eliminate spalling for the axially-loaded UHPC columns. With the addition of hybrid PP and steel fibers, the UHPC columns only showed marginal spalling under axial loading, which significantly improved the fire resistance. However, load eccentricity promotes explosive spalling of UHPC columns especially on the compression side of bending, which reduced the fire resistance.

Design of ductile H-anchorage for strengthening reinforced concrete beams with prestressed FRP

Most FRP strengthening methods increased load capacity at the cost of decreased ductility. A review of 551 specimens from 64 literatures shows that the ductility of FRP strengthened RC beams experienced an average decrease of ductility by 37.2%. To achieve balanced improvement of ductility and load capacity, a previously proposed H-anchorage is adopted to prestress FRP laminates and to strengthen reinforced concrete (RC) beams in flexure. A total of ten specimens were cast and tested under four-point bending, the test results are presented and discussed. The effects of concrete strength, bond scheme, and prestress level of FRP were investigated. The H-anchorage was found to improve the utilization of FRP in tension, achieve great increase of load capacity, and maintain satisfactory ductility. Partial bonding of prestressed FRP effectively improved the flexural performance within the elastic range, and the load capacity generally increased with increasing prestress level of FRP laminates. The increase of ductility was more prominent in the specimens using high-strength concrete than those using low-strength concrete. During the loading process, the deformed concrete section remained planar. Based on this observation, an analytical model is proposed to estimate the load capacity, reaching good agreement with the experimental results. Finally, a design method is proposed for optimizing the configuration of H-anchorage to ensure optimum performance in terms of load capacity and ductility.

Axial compression performance of coral concrete-filled aluminium tube (CCFAT) square stub columns

Coral materials have been used as concrete aggregate for decades to achieve self-sufficiency of materials and reduce costs of island construction. Considering the aggressive environment of islands, filling concrete into steel tube to produce coral concrete-filled steel tube (CCFST) columns is impractical. The combination of concrete and aluminium tube is proposed to avoid steel corrosion and optimize concrete performance in island construction. This study experimentally investigated the axial compression performance of nine coral concrete-filled aluminium tube (CCFAT) square stub columns. The failure mode, load-carrying capacity, and load-deformation relations were obtained, and the effects of concrete strength (fc), aluminium ratio (α), and confinement factor (ξ) on the strength, stiffness, and ductility performance were discussed. Moreover, the adaptability of concrete-filled steel tube (CFST) design codes in the load-carrying capacity prediction of CCFAT square stub columns was assessed. The results show that the increase in α mostly improves the strength index (SI) and stiffness index (KI) while the effects of fc is less significant. The ductility index (DI) and composite action are closely correlated to ξ. Using the design equation in AIJ code to predict the load-carrying capacity of CCFAT square stub columns is acceptable.

Investigation of crack growth in CFRP-concrete interface under fatigue loading

In this paper, the fatigue crack growth behavior along the interface between carbon fiber reinforced polymer (CFRP) sheets and concrete induced by intermediate flexural crack in CFRP-sheet strengthened concrete beams was studied, both experimentally and theoretically. The fatigue crack growth behavior of the intermediate crack-induced debonding was investigated by modified beam tests. The major variables considered in the test were loading amplitude, concrete strength, and the width ratio of CFRP-sheet to concrete. Test results indicated that three stages were observed in the evolution of CFRP-concrete interfacial crack propagation under cyclic loading, including debonding initiation, steady propagation, and instability propagation. Furthermore, the fatigue crack propagation rate grew with the increase of the load level, concrete strength, or the width ratio of CFRP-sheet to concrete, and was reduced as load cycles increased in the steady propagation stage due to the interfacial friction existed in the debonding zone. Based on the test results and fracture mechanic method, a crack growth prediction model, which considered the effects of concrete strength and width ratio of CFRP-sheet to concrete, was proposed for predicting the whole crack growth process and fatigue life of intermediate crack-induced debonding of CFRP-concrete interface under cyclic loading. The predicting results using this proposed model agreed well with test results.

A mechanical bond model for reinforcing bar in concrete subjected to monotonic and reversed cyclic loading

The reinforcing bar with diameters of 10 mm and 12 mm are widely used in shear walls, whose bond-slip performance has great influence on the seismic performance of the shear walls. Besides, the bond stress-slip model plays an important role in the theoretical analysis of the seismic performance of shear walls. Therefore, an analytical solution for the maximum bond stress was carried out and modified based on the thick-walled cylinder model and the tensile stress-strain model of concrete. The bond-slip tests of reinforcing bars in concrete were conducted on 48 specimens under monotonic and reversed cyclic loading. The effects of concrete strength, diameter of bar and bonding length on the bond-slip performance were examined and analyzed. The test results showed both the maximum bond stress and residual bond stress increased with increasing concrete strength, but decreased with increasing diameter of bar or bonding length. The reversed cyclic loading can cause the degeneration of the maximum bond stress and the bond stiffness. According to the bond-slip performance, the bond stress-slip model was established based on the analytical solution for the maximum bond stress, which is suitable for calculating both monotonic and reversed cyclic loading. A good agreement was observed by comparing the proposed models with the test curves in the study.