Fundamental Problems of Modeling the Fracture Processes in Concrete II: Size Effect and Selection of the Solution Approach

AbstractTheory of concrete fracture, despite all the efforts of numerous researchers, still did not provide the clear answer to the problem of modeling the fracture processes of concrete. Three well known theories are at hand: fracture mechanics, plasticity theory and mechanics of continuous damages. The fundamental assumptions, those theories are based on, do not completely correspond to the nature of concrete. They all are confronted with numerous problems, out of which the four are fundamental: damages micromechanics, damages localization, size effects and the dilemma when to apply the phenomenological and when the micromechanical approach to considering this problem. In this paper are considered the last two of those problems: size effect (scaling laws) and decision making what would be the best way in solving problems of modeling the fracture processes in concrete and concrete structures

Some Aspects of the Three-Dimensional Interface Cracks Analysis

Many problems of interfacial cracks are three dimensional in nature. Three-dimensional cracks at an interface of the two materials are analysed in this paper. For a crack at an interface, the stress intensity factors, load phase angle and energy release rate depend on elastic characteristics of two bonded materials and on geometry and the load conditions of a bimaterial sample. Influence of Dundurs\u27 parameters on stress intensity factors, load phase angle and energy release rate for different bi-material combinations and for the quarter-circular corner crack are discussed in this paper. Results show that elastic properties of materials constituting the interface have significant influence on behaviour of the 3D interface crack. Mode I stress intensity factor KI increases when the crack front approaches the free surface, while KII remains almost constant having the highest values between 10° and 80°, what results in high values of the load phase angle. The KIII stress intensity factor is zero in the symmetry plane, while its value increases as the crack front approaches free surfaces. The energy release rate diagrams show that the crack of a quarter circular front propagates faster closer to free surfaces than in the middle what means that the crack front would have the tendency of straightening

Punching shear tests on compact footings with uniform soil pressure

Punching shear is usually the governing failure criterion for the select ion of the depth of reinforced concrete footings. Despite the fact that large experimental programmes have been performed in the past aimed at the punching strength of slender flat slabs, only a few experimental campaigns on full-scale compact reinforced concrete footings can be found in the literature. In this paper, the results of an experimental programme including 8 reinforced concrete footings with a nominal thickness of 550 mm is presented. These experiments investigated the influence of the column size, member slenderness and the presence of compression and shear reinforcement. The test s were performed using an innovative test setup to ensure a uniform soil pressure. The experimental results show that the slenderness influences the punching shear strength as well as the effectiveness of the shear reinforcement. It is also experimentally shown that an important interaction amongst bending and shear occurs for high levels of shear forces near the column (typical case of compact footings or members with large amounts of shear reinforcement). Different continuous measurements recorded during the experimental tests allow a complete description of the kinematics and strains at failure. On that basis, experimental evidence is obtained showing that crushing of the concrete struts near the column is the phenomenon that triggers the punching failure of compact footings

Analyse globale de poutres mixtes acier béton : approche analytique et modélisation non-linéaire

Two types of models applicable to the overall analysis of steel concrete composite beams are presented and analyzed in the thesis. The analytical model based on elastic theory of beams, allows the calculation of the shift and its influence on the arrows of simple and continuous composite beams. The nonlinear behavior of the composite beam is studied using a finite element modeling. A formulation by shell elements is used to represent the slab and the metal beam. The Connextion is made ​​by short beam elements. The three-dimensional finite element model is validated by comparing with experimental results from different sources. It proves to be effective to represent the influence of creep and concrete cracking on the stiffness of the composite beam. Numerical examples illustrate the application of models to the overall analysis of simple beams, continuous and composite floorsDeux types de modèles applicables à l'analyse globale de poutres mixtes acier béton sont présentés et analysés dans le mémoire de thèse. Le modèle analytique, basé sur la théorie élastique des poutres, permet le calcul du glissement et de son influence sur les flèches de poutres mixtes simples et continues. Le comportement non linéaire de la poutre mixte est étudié au moyen d'une modélisation par éléments finis. Une formulation par éléments de coque est utilisée pour représenter la dalle et la poutre métallique. La connextion est formulée par des éléments de poutre courts. Le modèle éléments finis tridimensionnel est validé par la confrontation à des résultats expérimentaux de différentes sources. Il s'avère être efficace pour représenter l'influence du glissement et de la fissuration du béton sur la raideur de la poutre mixte. Des exemples numériques illustrent l'application des modèles à l'analyse globale de poutres simples, continues et planchers mixte

Research on Shear Connection Design in Composite Beams

The paper deals with a way of determining concrete pressure strength when calculating load carrying capacity of steel perfobond strip connectors. This type of strip connectors has been used in composite bridges only recently and no precise methods of calculating them have been worked out so far. The effect of axial forces on bearing capacity of classical stud shear connectors is also given in the paper as a result of research

Investigation on Cracks Creation and Propagation in Concrete Slab of Composite Beams

Analytical and experimental research have illustrated initiation of cracks in concrete deck immediately after its casting and placing on the upper flange of steel beams, especially prior to application of additional permanent load on composite element. Not only value of concrete shrinkage strain may influence creation and propagation of cracks in concrete. However ratio of deck reinforcement, cross-sectional area of reinforcement steel and strength of concrete can modify the process. Moreover, the ratio of steel beam flexural stiffness and flexural stiffness of concrete deck can be significant. Important shrinkage strains can occur at the lower concrete surface in the steel and concrete interface. Parametrical studies have provided the relationships illustrating impact of above parameters on crack aspect. The aim of the paper is to provide further details

Analyse globale de poutres mixtes acier béton (approche analytique et modélisation non-linéaire)

Deux types de modèles applicables à l'analyse globale de poutres mixtes acier béton sont présentés et analysés dans le mémoire de thèse. Le modèle analytique, basé sur la théorie élastique des poutres, permet le calcul du glissement et de son influence sur les flèches de poutres mixtes simples et continues. Le comportement non linéaire de la poutre mixte est étudié au moyen d'une modélisation par éléments finis. Une formulation par éléments de coque est utilisée pour représenter la dalle et la poutre métallique. La connextion est formulée par des éléments de poutre courts. Le modèle éléments finis tridimensionnel est validé par la confrontation à des résultats expérimentaux de différentes sources. Il s'avère être efficace pour représenter l'influence du glissement et de la fissuration du béton sur la raideur de la poutre mixte. Des exemples numériques illustrent l'application des modèles à l'analyse globale de poutres simples, continues et planchers mixtesCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF