Mechanical Behavior Of Concrete Research Articles

Dynamic Constitutive Model of Concrete

Based on the damage and Ottosen failure criterion, a dynamic constitutive model is proposed to investigate the mechanical behavior of concrete subjected to impact loading. The model predictions fit well with experimental results. So it can be used to simulate dynamic mechanical behavior of concrete

Study of Mechanical Behavior of Concrete in Direct Tensile Fiber Chips

In this experimental study, we are interested in local fiber wavy chips derived from waste machining steel parts. This work has focused on studying the mechanical behavior of reinforced concrete, with this type of fiber, in direct tensile. Direct tensile tests were carried out on samples in free weights section and square (100x100) mm2. This test involves the design and the implementation of special mounting specimens on the tensile machine type Ibertest. Five (05) fibers percentages were retained in (W = 0.5%. W = 0.8%, W = 1%, W = 1.2%, W = 1.5% with W: volume fraction of added fiber) and two (02) concrete witness whose report on gravel sand is equal to: S / G = 0.8 and S / G = 1. The fibers have been characterized to the strength and tear by the tensile test. The interest lies in optimizing the fiber length and the number of undulations to use in a cement matrix, which will improve the mechanical properties especially tensile strength and post-cracking behavior. The comparison of different results obtained in direct tension on different percentages of fiber, as well as two reports showed that the fibers have conferred a significant ductility to the material after cracking of concrete for different percentages of fiber and a strength for improving the S / G = 0.8.

SHPB Test on Dynamical Mechanical Behavior of Concrete with High Temperature

An experimental system is designed by combining the split Hopkinson pressure bar (SHPB) with microwave heating device, based on stress wave theory, availability of the experiment technique is analyzed. Tests of concrete whose temperature changes from room temperature to 650°C and impact velocity from 5m/s to 12m/s are completed and for the first time high-temperature dynamical damaging phenomena of concrete are obtained. Based on data analysis, the dynamical mechanical behavior of concrete with high temperature is affected by not only the strain rate effect whose influence keeps on decreasing with temperature increasing, but also the high temperature weakening effect. And the strain rate hardening effect is coupled with high temperature weakening effect, but the latter has greater influence.

Mechanical Behavior of Concrete Filled Steel Tubular out Stiffener Ring Connections with Reduced Beam Section

The past study indicates that, when the space joint of concentric annular-stiffer is loaded, stress concentration may generate at corner. The destruction usually concentrates in the joint region, and then cannot generate “strong joint”. To change this unfavorable characteristic, the reduced beam section connection is adopted. Through oriented reducing beam section, the plastic region is formed, which can achieve the aim of “weak beam, strong joint”. After the simulation and analysis to space joints on outer concentric annular-stiffer which are processed by reduced beam section, the loading conditions of the joints are obviously improved in the following aspects: (1) the stress distribution on annular plate is smoothed obviously, the degree of stress concentration on corner is significantly decreased; (2) to assure plastic hinge firstly appear on the beam end but not the ring surface, we can change the size of ring plate, length of beam and the flange weaken degree; (3)the joint stiffness does not decrease during the stage of elastic loading; (4)under repeated loading, the joint region has little change and the plastic expansion on the ring surface is not obvious. Above all, reducing beam section can improve the mechanical properties of CFST-steel beam space joints with outer concentric annular-stiffer, thus the “strong joint” requirement could be fulfilled.

Mechanical Behavior and Constitutive Equation of Concrete under High-Temperature Dynamical Conditions

SPHB tests of concrete under different temperatures and various loading conditions are completed, and high-temperature dynamical behavior of concrete is obtained. Dynamical mechanical behavior of concrete with high temperature is affected by not only the strain rate effect, but also the high temperature weakening effect, and the strain rate hardening effect is coupled with high temperature weakening effect, but the latter has greater influence. Concrete failure evolution is described on basis of the damage factor, the intercoupling strain rate hardening effect and temperature weakening effect are simply set as mutually independent factors, each parameter is respectively fitted with test data, finally, concrete constitutive equation under high-temperature dynamical conditions is established, and comparative analysis with test data are conducted, indicating good coincidence with test results.

Modeling of concrete nonlinear mechanical behavior at high temperatures with different damage-based approaches

Heating of concrete leads to decrease of mechanical properties due to different damage processes: thermal strain gradients, chemical reactions, increase of vapour pressure (which is not taken and strain incompatibilities (between cement paste and aggregates, which is not taken into account explicitly here). This research project deals with comprehension of mechanical modeling (smeared cracking approach) on concrete’s behavior at high temperatures so as to be able to predict the previous mechanical damage processes and properties decreases. Two types of mechanical models are used: an isotropic elastic damage model (IED) and an orthotropic elasto-plastic damage model (OEPD). Transient thermal creep model (TTC) is also introduced. Different temperature rates are investigated and different virtual mechanical tests are performed (uniaxial tension, uniaxial compression, biaxial tension). The paper concludes, using numerical analysis and comparisons to experimental results, on relevances and performances of these different mechanical models.

Experimental Study on Dynamic Mechanical Behaviour of Concrete with High Temperature

An experimental system of high-temperature split Hopkinson pressure bar (SHPB) was developed by combination of the split Hopkinson pressure bar (SHPB) and microwave heating system, then tests of concrete whose temperature changed from room temperature to 650°С and impact velocity from 5m/s to 12m/s were completed. Based on the test results, the dynamic strength of concrete increases with increasing impact velocity whether with high temperature or room temperature, meanwhile the dynamic strength of concrete with high temperature has the strain rate effect, but the effect keeps decreasing with temperature increasing, even at temperature above 500°С , compressive strength will not have strain rate sensitive effect any longer when strain rate surpasses a certain value. In the meantime, the strain rate hardening effect is coupled with high temperature weakening effect, but the latter has greater influence.

Experimental Study of Mechanical Behavior of Concrete Filled Steel Tubular Short Columns after Fire

Mechanical behavior and bearing capacity of ordinary concrete filled steel tubular short column (NCSSC) and ceramsite concrete filled steel tubular short column (CCSSC) subjected to fire load are experimentally investigated. Effect of the parameters, such as the maximum value of fire temperatures, fire duration on the strength and ductility of the two types of specimens were especially discussed. The test results show that both of the specimens of NCSSC and CCSSC after fire have higher bearing capacity and better ductility, there was no descent segment in load-displacement curves of the most specimens after the fire load was subjected, and even the case that bearing load increased again after descent segment arose. It was concluded that the maximum response temperature of specimens and fire duration time has great effect on the axial bearing capacity of concrete-filled steel tubular short columns subjected to fire, and there is a turning point of temperature for the influence.

High Temperature Mechanical Behaviors of Concrete

Using microwave heating method to establish a set of effective technology about uniaxial compression test of concrete, and obtain the experiment phenomenon of concrete when the temperature is 16 -650 . Experiment results indicate that when concrete is damaged by high temperature, the strength of concrete decreases, the peak strain increases, and the elastic modulus decreases. Based on test data, a unified equation was putted forward to describe the relation between concrete compressive strength, the peak strain, elastic modulus and temperature. While, obtain concrete temperature stress and strain curve, and analysis shows that it gradually becomes compressed with the increase of temperature, peak point falls and moves right obviously.

Effect of Elevated Temperature on the Mechanical Behavior of Natural Aggregate Concrete

Reinforced concrete construction is very common these days and extensively used both in industrial and commercial buildings. With the gradual rise in occurrences of fire accidents in recent years, a more thorough and quantitative understanding of the damage phenomenon in natural aggregate concrete structures is required. However, little research has been done to study natural aggregate concrete behavior under high temperatures. The mechanical behavior of concrete could actually be more complex under high temperature conditions than at room temperature, for instance. Restoration and reinforcement of the structures exposed to fire may have to be based on residual strength analysis and therefore require a correlation between temperature and mechanical properties. Thus, in order to meet the modern challenges of rapid engineering advances and societal development, further research on the concrete material and its structural behavior at high temperatures becomes extremely important. The present paper deals with investigations on the effect of high temperature exposure on the compressive strength of natural aggregate concrete. Experiments were conducted to study the compressive strength variations with increasing temperatures, up to 700 °C, and the subsequent cooling modes such as natural and spray cooling. Results show that the compressive strength gradually decreases with increasing temperatures.

Microscopic Analysis and Experimental Research on Thermal Mechanical Behavior of Natural Aggregate Concrete

Reinforced concrete construction is very common recently and extensively used both in industrial and commercial buildings. With the gradual rise in occurrences of fire accidents in recent years, a more thorough and quantitative understanding of the damage phenomenon in concrete structures is required. However, the mechanical behavior of concrete could actually be more complex under high temperature conditions than at room temperature. Restoration and reinforcement of the structures exposed to fire may have to be based on residual strength analysis and therefore require a correlation between temperature and mechanical properties. Thus, in order to meet the modern challenges of rapid engineering advances and societal development, further research on the concrete material and its structural behavior at high temperatures becomes extremely important. The present paper deals with investigations on the effect of high temperature exposure on the compressive strength of natural aggregate concrete. Experiments were conducted to study the compressive strength variations with increasing temperatures, up to 700 °C, and the subsequent cooling modes such as natural and spray cooling. Results show that the compressive strength gradually decreases with increasing temperatures. And micro-structural observations of the concrete specimens by means of scanning electron microscopy (SEM) were obtained. These test methods and results can be used for analyzing and investigating the behavior of recycled aggregate concrete with increasing temperatures.

A mesoscopic model for a better understanding of the transition from diffuse damage to localized damage

ABSTRACT The aim of this paper is to present a modelling of mechanical behaviour of concrete on a mesoscopic scale. Concrete is considered as a bi-phasic material where the cement paste and the aggregates are described with their own mechanical characteristics. Firstly, the model is studied in two dimensions in order to optimize the geometrical model of the inner structure of concrete in terms of the meshing strategy and the smallest size of the aggregate to be taken into account. The model shows interesting results on the transition from diffuse to localized damage and is able to reproduce dilatancy in compression. Finally, results of the three-dimensional model are shown in tension.

An experimental study on the tensile strength of steel fiber reinforced concrete

This paper deals with steel fiber reinforced concrete mechanical static behaviour and with its classification with respect to fibers content and mix-design variations. A number of experimental tests were conducted to investigate uniaxial compressive strength and tensile strength. Different mixtures were prepared varying both mix-design and fiber length. Fibers content in volume was of 1% and 2%. Mechanical characterization was performed by means of uniaxial compression tests with the aim of deriving the ultimate compressive strength of fiber concrete. Four-point bending tests on notched specimens were carried out to derive the first crack strength and the ductility indexes. The tensile strength of steel fiber reinforced concrete (SFRC) was obtained both from an experimental procedure and by using an analytical modelling. The experimental tests showed the different behaviour of SFRC with respect of the different fiber content and length. Based on the experimental results, an analytical model, reported in literature and used for the theoretical determination of direct tensile strength, was applied with the aim of making a comparison with experimental results. The comparison showed good overall agreement.

Vers une modélisation simple et unifiée du fluage propre, du retrait et du fluage en dessiccation du béton

ABSTRACT A three-dimensional rheological modelling is proposed for the long term concrete mechanical behaviour. Concrete is supposed to have a non-linear visco-elastic behaviour. The non-linearity used first allows conferring a realistic non asymptotic strain to the basic creep, based on a consolidation theory. Moreover, for the non-saturated concrete, a dependence of the capillary pressure effects on the stress state is postulated. It assumed that a damage state exists around microcavities in depression, this damage depends also on the applied stresses whose can led to a closing or opening of the micro-cracking and consequently to a best or to a worst transmission of capillary effects to the solid skeleton. This dependency is highlighted using a simple numerical analysis of a composite material including in an elastic matrix both cavities in depression and rigid inclusions. The linear dependence of capillary effect on the applied stress confers to the model the capability to simulate shrinkage and drying creep strains.

Today's concretes exposed to fire—test results and sectional analysis

The well-known capacity of concrete to withstand high temperature and fire is put to the test by the most recent, high-and ultra high-performance cementitious composites, since their more closed pore structure favours pressure build-ups in the pores filled with water, turning to vapour at high temperature. The ensuing spalling phenomena can be prevented by adding polymeric fibres to the mix, while material toughness can be improved – at any temperature – by adding metallic fibres. However, concrete mechanical behaviour depends on the thermal field, which is strictly related to the type of fire and to the thermal properties of the material. Hence, special concretes for special structural applications should be thoroughly characterised at high temperature and after cooling, to evaluate their thermal and mechanical properties. These properties are recalled in the first part of this paper, with reference to thermal diffusivity, compressive and tensile strength, elastic modulus and fracture energy. Furthermore, to maximise the benefits coming from the use of better materials, a parallel rethinking of some aspects of structural analysis is needed. With regard to this point, in the second part of the paper some suggestions and proposals are formulated with reference to the analysis of reinforced concrete sections subjected to combined bending and axial force, and some considerations are made on two rather underrated aspects of the analysis: the role of the thermal self-stresses and the increasing slenderness of fire-exposed columns.

Approche mésoscopique du comportement du béton

ABSTRACT The macroscopic modeling of the mechanical behavior of concrete has much evolved, and the current models enable us to take into account increasingly complex phenomena. In spite of that, and particularly when coupled phenomena are concerned, the various scales present in the structure of material are badly represented by this kind of approach. The modeling of the material structure at the scale of the sand grain (mesoscopic) coupled with nonlinear computation methods makes it possible to take into account complex phenomena. The mesoscopic models for the concrete often idealize the geometry of inclusions by spheres or discs. This study is focused on the role of the acuracy of the geometrical representation of inclusions or aggregates on the results provided by the model.

Concrete mechanical behaviour and calcium leaching weak coupling

Concrete mechanical behaviour and calcium leaching weak coupling

Concrete mechanical behaviour and calcium leaching weak coupling

ABSTRACT A rheological model with orthotropic short-time and long-time damage is developed in order to model leached concrete behaviour. Coupling with calcium leaching is obtained by affine attenuation of model parameters according to a microhardness profile measured on leached cement pastes. Calibration shows that most model parameters managing mechanical behaviour have the microhardness law as their attenuation law.

Effects of desiccation on mechanical behaviour of concrete

The objective of this work is experimental characterisation and numerical modelling of coupled behaviours between drying shrinkage and plastic damage in concrete. In the first part, we present an original experimental study on an ordinary concrete in order to determine material damage induced by drying shrinkage. Uniaxial compression tests are performed on samples dried for different periods. It is shown that material damage can be caused by drying process. Mechanical behaviour becomes more brittle with higher damage kinetics when concrete is dried. In the second part, a constitutive model is proposed in order to describe coupled hydro-mechanical behaviour of partially saturated concrete. This model takes into account induced damage, mechanical and capillary plastic deformations. Numerical simulations of experimental tests are presented, and show a qualitatively good agreement with experimental data. The results are relevant with respect to the importance of drying process in the durability study of concrete structures.

Application of softened truss model with plastic approach to reinforced concrete beams in torsion

The present paper discusses the behavior of the reinforced concrete beams subjected to torsion by applying the endochronic plastic model in conjunction with the softened truss model. The endochronic constitutive equations are developed to describe the behavior of concrete. The mechanical behavior of concrete is decomposed into hydrostatic part and deviatoric part. New definition of the bulk modulus and the shear modulus are defined in terms of compressive strength of concrete. Also, new deviatoric hardening function is developed. Then, the endochronic constitutive equations of concrete are applied with the softened truss model for the behavior of the reinforced concrete beams subjected to torsion. The theoretical results obtained based on the present model are compared with the experimental data. The present model has shown the ability to describe the behavior of reinforced concrete beams subjected to torsion.