Tensile Behavior Of Concrete Research Articles

Numerical Modeling of Four-Pile Caps Using the Concrete Damaged Plasticity Model

Four-pile caps made from concrete are essential elements for the force transfer from the superstructure to piles or pipes. Due to the difficulties in carrying out full-scale tests and all the instrumentation involved, the use of numerical models as a way to study the mechanical behavior of these elements presents itself as a good alternative. Such numerical studies usually provide useful information for the update and improvement of normative standards and codes. The concrete damaged plasticity (CDP) constitutive model, which combines damage and plasticity with smeared-crack propagation, stands out in the simulation of reinforced concrete. This model is composed of five parameters: dilatation angle (ψ), eccentricity (ϵ), ratio between biaxial and uniaxial compressive strength (σbo/σco), failure surface in the deviator plane normal to the hydrostatic axis (Kc), and viscosity (μ). For unidimensional elements, the values of the CDP parameters are well defined, but for volumetric elements, such as concrete pile caps, there is a gap in the literature regarding the definition of these values. This fact ends up limiting the use of the CDP on these structural elements due to the uncertainties involved. Therefore, the aim of this research was to calibrate two numerical models of concrete four-pile caps with different failure modes for the evaluation of the sensitivity of the CDP parameters, except for ϵ, which remained constant. As a result, the parameters σbo/σco and Kc did not significantly influence the calibration of the force × displacement curves of the simulated structures. Values of ψ and μ equal to 36° and 1 × 10−4, respectively, are recommended for “static” analysis, while for “quasi-static” analysis, ψ values ranging between 45° and 50° are suggested according to the failure mode. The results also showed to be sensitive to the constitutive relation of concrete tensile behavior in both modes of analysis. For geometric parameterization, the “static” analysis is recommended due to the lower coefficient of variation (3.29%) compared to the “quasi-static” analysis (19.18%). This conclusion is supported by the evaluation of the ultimate load of the numerical models from the geometrically parametric study compared to the results estimated by an analytical model.

Finite Element for the Analysis of Massive Reinforced Concrete Structures with Cracking

The solid finite element has been developed for the calculation of massive reinforced concrete structures with cracks. When constructing a finite element in the compression-compression-compression mode, the Willam Warnke failure criterion was used. The tensile behavior of concrete was assumed to be linear before the crack initiation. Modern building codes require non-linear calculations of concrete and reinforced concrete structures, taking into account the real properties of concrete and reinforcement. In this regard, a technique has been developed and a solid finite element has been built, adapted to the PRINS software, which makes it possible to perform calculations of massive reinforced concrete structures, taking into account their actual work. Development of a method for calculating reinforced concrete structures under conditions of a three-dimensional stress state, taking into account the brittle fracture of compressed concrete and cracking in tensile concrete. Based on this technique, the implementation of a solid finite element in the PRINS software. To verify the developed finite element, a series of test calculations of a beam under three-point bending conditions was carried out. Comparison of the calculation results with the data of experiments by the authors confirmed the high accuracy and reliability of the results obtained. The developed solid finite element included in the PRINS software can be effectively used by engineers of design and scientific organizations to solve a wide class of engineering problems related to the calculations of massive reinforced concrete structures.

The Effects of Stochastic Circular Pores on Splitting Tensile Behavior of Concrete Based on the Multifractal Theory

Concrete naturally contains a large number of circular-like stochastic pores which weaken the tensile strength of concrete and change the crack propagation path. This study investigates the influences of the size distribution and the spatial distribution of stochastic pores on the fracture behavior of concrete based on the splitting tensile test. The mesoscale model of concrete containing coarse aggregate, mortar, interface transition zone (ITZ), and circular pores is established to simulate the crack initiation, propagation, and coalescence of concrete. Concrete samples with a single hole are prepared to verify the effectiveness of the numerical simulation method. Numerical tests are conducted on numerous mesoscale concrete samples with various porosities, pore size distributions, and pore spatial distributions. The numerical simulation results indicate that the tensile strength decreases with the increase of pore size at the same porosity. Based on multifractal theory, a quantitative indicator to describe the spatial distribution uniformity of concrete stochastic pores is proposed. There is a positive correlation between the spatial distribution uniformity of stochastic pores and the tensile strength. The stochastic circular pores can have a profound effect on the concrete’s fracture pattern, which results in three typical macro-crack patterns in the numerical simulation of the splitting tensile test. The presented results deepen the understanding of the influence of stochastic circular pores on the tensile mechanical properties of concrete and provide a reference for the design of concrete structures.

Theoretical and Experimental Research of Ultra-High-Performance Concrete Tensile Behaviour Based on Micro-Analysis

The cracking resistance and durability of the ultra-high-performance concrete (UHPC) structure are directly affected by its tensile behaviour. A micro-analysis method was established to study the tensile behaviour of the UHPC before the appearance of visible cracks. The cooperative characteristic of the steel fibre and the cement matrix was taken as a research focus of the micro-analysis method. The random distribution of steel fibre was considered as normal distribution. Based on the micro-analysis method, the tensile behaviour of UHPC was divided into the elastic stage and micro-damage development stage. Other data sourced elsewhere were used to verify the feasibility of the micro-analysis method and the necessary data were tested using pure bending specimens to verify the theoretical model. The results show that the working mechanism of inner steel fibre can be described by the micro-analysis method. The bending test results of the UHPC at the elastic and the micro-damage development stage match the theoretical model. The tensile behaviour of the UHPC is dominated by the inner steel fibre and the contribution of the cement matrix can be ignored. A bilinear model is proposed to describe the tensile constitutive of UHPC before the appearance of visible cracks, and the limitations of each stage are 8.85 MPa and 12.36 MPa.

Local bond-slip behaviour of reinforcing bars in fibre reinforced lightweight aggregate concrete at ambient and elevated temperatures

This paper presents an experimental investigation of the bond-slip behaviour of reinforcing bars in fibre-reinforced lightweight aggregate concrete (FRLWAC) at ambient and elevated temperatures. Sixty-four bond-slip specimens with four target temperature exposures, two concrete covers and four steel fibre contents were tested to failure. The experimental results showed that exposure to elevated temperature shifted failure pattern from more ductile pull-out to brittle splitting modes, and reduced the peak bond strength and toughness of bond-slip behaviour. Scanning electron microscope (SEM) images of the concrete-steel interface showed that thermal mismatch induced microcracks contributed to degradation of bond strength, in addition to temperature induced degradation of concrete materials. The temperature exposure also negated beneficial effect of concrete cover in enhancing bond behaviour. Addition of steel fibre helped in preventing brittle failure mode, enhancing bond strength in specimens with small concrete cover and improving the post-peak bond-slip behaviour at all target temperatures. A simple semi-analytical bond-slip model that considers different failure modes and incorporates fibre-reinforced concrete tensile behaviour from Swedish Code SS 812310 was proposed and validated based on the test results in this study.

Mode I Crack Propagation in Concrete Structures under Impact Loadings

This paper proposes a new analysis of previous works related to the concrete tensile behaviour under impact loadings.

Dynamic Splitting Tensile Behaviour of Concrete Confined by Natural Flax and Glass FRP.

Flax fibre has been used to reinforce concrete composite, but its dynamic properties have not been thoroughly studied. This study investigates the dynamic splitting tensile properties of plain concrete (PC) confined by flax-fibre-reinforced polymer (FFRP) and glass-fibre-reinforced polymer (GFRP). The dynamic splitting tensile tests were carried out on PC, FFRP-PC, and GFRP-PC cylinder specimens by the high-speed servo-hydraulic machine, with the impact-induced strain rates ranging from 0.1 to 58 s−1. The effect of the FRP confinement, FRP thickness and strain rate on the dynamic splitting tensile behaviour were assessed. The results indicated that similar confinement effectiveness of FFRP and GFRP is observed. The dynamic tensile strength of 1- and 2-layer FFRP-PC increased by 29% and 67%, and the one- and two-layer GFRP-PC increased by 32% and 84%, respectively. FFRP-PC and GFRP-PC cylinders showed less sensitivity to the strain rate compared with PC. The empirical relationship between the tensile DIF and strain rate for PC, FFRP-PC and GFRP-PC was proposed based on experimental data. The proposed model was developed to predict the dynamic splitting tensile strength. The results suggested the potential of FFRP composites applied into concrete structures under extreme dynamic loadings.

Mechanical properties and durability assessment of nylon fiber reinforced self-compacting concrete

The higher paste volume in Self Compacting Concrete (SCC) makes it susceptible to have a higher creep coefficient and cracking and has brittle nature. This brittle nature of concrete is unacceptable for any construction industry. The addition of fibers is one of the most prevalent methods to enhance the ductile and tensile behavior of concrete. Fibers reduce the cracking phenomena and improve the energy absorption capacity of the structure. Conversely, the addition of fibers has a negative impact on the workability of fresh concrete. In this research work, a detailed investigation of the influence of Nylon fibers (NFs) on fresh properties, durability, and mechanical properties of SCC was carried out. NFs were added into concrete mixes in a proportion of 0.5%, 1%, 1.5%, and 2% by weight of cement to achieve the research objectives. Durability assessment of modified SCC having Nylon fibers was performed using water absorption, permeability, carbonation resistance, and acid attack resistant. Mechanical tests (compressive and tensile) were conducted for modified as well as control mix. Test results indicate that the passing and filling ability decreased while segregation and bleeding resistance increased with NFs. Furthermore, test results showed a significant increase in strength up to 1.5% addition of nylon fibers and then strength decreases gradually. Durability parameters were significantly improved with the incorporation of NFs relative to the control mix. Overall, this study demonstrated the potential of using nylon fibers in self-compacting concrete with improved durability and mechanical properties.

Mechanical properties of cracked concrete under uniaxial tensile load

Cracks have a serious impact on the safety of concrete structures, and the tensile behavior of concrete is the key to control generation and propagation of crack. To improve the safety of concrete structures, it is crucial to understand the mechanical properties of cracked concrete under uniaxial tensile load. In this article, dynamic tensile test and tensile test after different fatigue damage were conducted to investigate the mechanical properties of cracked concrete. First, the damage evolution law of cracked concrete under dynamic tensile load was investigated by means of [Formula: see text] ([Formula: see text]: crack mouth opening displacement) control mode whereupon the relationship of stress– dCMOD considering rates effect was obtained. Then, the change law of cracked concrete under uniaxial tensile load after fatigue damage was studied by analyzing four mechanical parameters including tensile strength, elastic modulus, critical displacement, and fracture toughness. The empirical formulas of the four parameters with numbers of fatigue cycles are given. Furthermore, acoustic emission technology was applied additionally.

Structural phenomenon based theoretical model of concrete tensile behavior at different stress-strain conditions

Research focused on concrete tensile strength is rather limited compared to that of compressive strength. In most cases concrete tensile strength is neglected in design, but in special cases (gas holders, tankers, nuclear plants, big diameter pipes, etc.) this strength is dominant. Although research related to concrete tensile strength has increased in the last decade, concrete tensile behavior at all stress-strain conditions has yet to be properly investigated. Therefore, additional attempts are required for proposing a methodology that enables more accurate consideration of tensile strength in structural design. In the present study, a structural phenomenon is used to develop a theoretical model of concrete tensile behavior at different stress-strain conditions. A classification of concrete tensile stress is proposed. Two groups of tension are defined – direct and indirect. The differences between indirect and direct concrete tensile strength are investigated. This study is aimed at conducting a detailed complex analysis of concrete tensile behavior that should provide concrete strength and strain characteristics for each type of tensile stress at elastic, elastic-plastic, and ultimate limit states. As a result, using empirical coefficients for analysis of concrete resistance in tension is avoided. The proposed methodology can be used for updating the existing codes for more accurate design of reinforced concrete elements.

Tensile Behaviour of Concrete with Steel Fibers Subjected To High Temperatures

The present study aims at comparing the split tensile and flexural strengths of plain concrete and steel fibre reinforced concrete subjected to high temperatures. The grade of concrete designed for investigation is M30. The fibres used for investigations are hook end steel fibres with aspect ratio 50. The dosage of fibres added was 3% by weight of cement. The specimens of size 150 mm diameter and 300 mm length cylinders and 100 x 100 x 500 mm prisms are cast for testing. The samples are cured for 3, 7, 28 and 56 days. The specimens are air dried and then exposed to 27, 100, 200, 300 and 400°C for duration of one hour and cooled to room temperature and then the cylinders are tested under 2000 kN digital compression testing machine and the prisms are tested under 1000 kN digital universal testing machine. When exposed to elevated temperatures, standard concrete with steel fibres performs better than the plain concrete without steel fibres. All the results and observations are analysed and presented in the paper.

A Comprehensive Numerical Simulation of Steel-Concrete Composite Beam Incorporating Compressive Failure of Concrete

We present a high fidelity numerical simulation technique to analyze the nonlinear behavior of a composite beam under cyclic loading. The analysis is performed by using the in-house software called E-Simulator. A constitutive model for concrete; extended Drucker–Prager model considering the compressive failure and the tensile crack has been employed and the parameters are identified so that compressive and tensile behavior of concrete can be reproduced. The relation between the bending moment and deflection angle of a composite beam has been analyzed and compared with experimental results. Damage propagation and stiffness degradation results of concrete slab are demonstrated.

Numerical Analysis of RC beam with High Strength Steel Reinforcement using CDP model

The article is based on preliminary research on use of high strength steel for RC elements. A reinforced concrete beam with a span length of 5700 mm has been subjected to four-point bending test. The bottom reinforcement of the beam was made of SAS670/800 high strength steel. This type of steel has no specific yield point. The yield limit declared by the manufacturer is specified as 670 MPa and the ultimate strength is equal to 800 MPa. The aim of the research was to establish a numerical model that would render properly the real beam behaviour. The model was created in the ABAQUS software using the CDP (Concrete Damage Plasticity) material model for concrete. The paper analyses the influence of several parameters on the results of numerical computations. The author’s aim is to define values of the dilation angle that should be implemented in the model. Generally, the value of this parameter is established a priori, without any justification. The analysis reveals that in a situation when the dilation angle is greater than or equal to 25 deg, the numerical model predicts properly the damage obtained in the experiment. For lower values of the dilation angle, the failure mode is not consistent with the actual beam behaviour in the experiment. Another issue is whether and how the results from the model are influenced by the choice of specified concrete tensile behaviour. In the CDP model, this property may be set in three ways: by giving the stress - displacement relation, stress - cracking strain relation or determining the fracture energy. All three alternatives are analysed and compared. Another aspect described in the paper, is the difference in load application through force control and displacement control as well as the influence of the amount of shear reinforcement. In order to analyse mesh size sensitivity, the results obtained for models with various mesh densities were compared.

The Effects of pH and Temperature on Compressive Strength of Synthetic Fiber-Reinforced Concrete Cylinders Exposed to Sulfuric Acid

Abstract Synthetic fibers are among the various types of fibers being used to improve the tensile behavior of concrete. They have a competitive edge over other fibers because they are resistant to most chemicals, which increases the durability. Acid attacks are one of the most threatening scenarios, especially for concrete sewer pipes and culverts. In this study, dry cast concrete cylinders, reinforced with two different volume fractions (0.52 % and 1.04 %) of polypropylene fibers, were constructed and immersed for four months in sulfuric acid solutions of two different pH and three different temperatures. The results showed that a fiber volume fraction of 1.04 % reduces the adverse effects of acid on the compressive strength of concrete, and higher temperatures and lower pH lead to extreme deterioration. The results of this study revealed that a pH of 2.5, along with the highest temperature, deteriorated the specimens more than twice as much as a pH of 4.5 at the lowest temperature.

Experimental and numerical simulating of the crack separation on the tensile strength of concrete

Effects of crack separation, bridge area, on the tensile behaviour of concrete are studied experimentally and numerically through the Brazilian tensile test. The physical data obtained from the Brazilian tests are used to calibrate the two-dimensional particle flow code based on discrete element method (DEM). Then some specially designed Brazilian disc specimens containing two parallel cracks are used to perform the physical tests in the laboratory and numerically simulated to make the suitable numerical models to be tested. The experimental and numerical results of the Brazilian disc specimens are compared to conclude the validity and applicability of these models used in this research. Validation of the simulated models can be easily checked with the results of Brazilian tests performed on non-persistent cracked physical models. The Brazilian discs used in this work have a diameter of 54 mm and contain two parallel centred cracks (90o to the horizontal) loaded indirectly under the compressive line loading. The lengths of cracks are considered as; 10 mm, 20 mm, 30 mm and 40 mm, respectively. The visually observed failure process gained through numerical Brazilian tests are found to be very similar to those obtained through the experimental tests. The fracture patterns demonstrated by DEM simulations are mostly affected by the crack separation but the tensile strength of bridge area is related to the fracture pattern and failure mechanism of the testing samples. It has also been shown that when the crack lengths are less than 30 mm, the tensile cracks may initiate from the cracks tips and propagate parallel to loading direction till coalesce with the other cracks tips while when the cracks lengths are more than 30 mm, these tensile cracks may propagate through the intact concrete itself rather than that of the bridge area.

Experimental Study on Cyclic Tensile Behavior of Concrete under High Stress Level

Experimental Study on Cyclic Tensile Behavior of Concrete under High Stress Level

Experimental Study on Direct Tensile Behavior of Concrete under Various Loading Regimes

An experimental study of the stress-strain behavior of concrete under monotonic and cyclic uniaxial tensile loading is carried out. Complete monotonic and cyclic stress-strain curves are obtained by six various loading regimes. The uniqueness of envelope curve is validated for the concrete subjected to monotonic and cyclic tensile loading. Residual strain accumulation and the change of initial elastic modulus were used to evaluate damage accumulation and stiffness change with the increasing of cyclic loads. The stress drop versus number of cycles to specified maximum strain is investigated and the result shows that the rate of stress drop decreases as the cycling continues and finally tends to stable. The proposed semi-empirical mathematical expression model to simulate the stress-strain curve for unloading and reloading has been developed by fitting the experimental stress-strain curves. The analytical results show a good agreement with the experimental results for all loading regimes.

콘크리트 재료의 동적 물성 변화를 모사하기 위한 유변학적(Rheological)모델 개발 및 평가

In this study, the rheological models were introduced and developed to reflect rate dependent tensile behaviour of concrete. In general, mechanical properties(e.g. strength, elasticity, and fracture energy) of concrete are increased under high loading rates. The strength of concrete shows high rate dependency among its mechanical properties, and the tensile strength has higher rate dependency than the compressional strength. To simulate the rate dependency of concrete, original spring set of RBSN(Rigid-Body- Spring-Network) model was adjusted with viscous and friction units(e.g. dashpot and Coulomb friction component). Three types of models( 1) visco-elastic, 2) visco-plastic, and 3) visco-elasto- plastic damage models) are considered, and the constitutive relationships for the models are derived. For validation purpose, direct tensile test were simulated, and characteristics of the three different rheological models were compared with experimental stress-strain responses. Simulation result of the developed visco-elasto-plastic damage(VEPD) model demonstrated well describing and fitting with experimental results.

Tensile behavior of concrete under high loading rates

The experimental and theoretical studies show that the influence of loading rate on tensile behavior of concrete is relatively strong. Dynamic tensile resistance of concrete is difficult to measure by direct tensile test. Therefore, the indirect tensile tests such as split Hopkinson bar tests are used. The evaluation of experimental measurements shows that after reaching a certain critical strain rate, tensile resistance progressively increases with increasing strain rate. In this paper, the authors attempt to investigate and discuss: (i) the reason for progressive increase of tensile resistance beyond a certain strain rate and (ii) whether the dynamic resistance can be attributed only to material strength or whether some other factors also contribute towards the same. To answer these questions, numerical analysis on two different types of examples is carried out: (i) Simple elastic-cohesive finite element (FE) model subjected to direct tension and (ii) FE model of indirect tension test on modified split Hopkinson bar. The results are evaluated in terms of apparent and true strength and compared with experimental results. It is found that under static loads, the true and apparent strengths are always equal, while under dynamic loads they are different. The true strength is controlled by the rate dependent constitutive law and the apparent strength is significantly influenced by the size of the fracture process zone and the size of the specimen. Evaluation of numerical results shows that concrete fracture energy is approximately a linear function of strain rate (semi-log scale) and is controlled by the rate dependent constitutive law. It is concluded that the results of any indirect tension test such as split Hopkinson bar test need careful interpretation, i.e. due to the fact that concrete specimen is damaged, and not elastic, the results of measurement need to be corrected.

Effect of Testing Method and Strain Rate on Stress-Strain Behavior of Concrete

The flexural behavior of concrete is often different from its behavior under direct tension. This paper presents an experimental program aimed at the testing method and strain rate effects on the tensile behavior of concrete. Concrete specimens were tested with different testing methods (direct tension and four-point loading) and four strain rates (10(−6), 10(–5), 10(–4), and 10(−3) s(−1)). The results show that the peak stresses increase with an increase in the strain rate; the strain rate dependence of the peak stress is stronger for direct tensile specimens than for four-point loading specimens. The dynamic increase factor is expressed as a function of the strain rate and highly stressed volume method. The continuous damage model is also used to predict the strain rate effects on the ascending stress-strain behavior of concrete. Using the model parameters for the stress-strain curve of concrete at a static strain rate, the stress-strain curves of concrete for dynamic strain rates in four-point loading and direct tension are satisfactorily predicted.