Modélisation numérique des structures à non linéarité de contact local

Le traitement de nombreux problèmes de mécanique rencontrés en structure, nécessite la modélisation de la surface de discontinuité à diverses échelles comme par exemple la surface de contact dans les assemblages, la surface d’interaction sol-structure et le contact entre béton et massifs rocheux. Pour cela, la surface de contact est représentée par une série d’éléments de contact qui prennent en compte la géométrie réelle de la discontinuité et ses caractéristiques mécaniques, afin de déterminer l’état final en tout point de la discontinuité à partir d’un état initial donné et suivant les conditions de chargements sans oublier les critères et lois de contact (critère de glissement et décollement).Dans ce but un modèle 2D de calcul des contraintes de contact été  développé. Ce dernier permet d’utiliser deux types d’éléments à savoir l’élément de contact à  deux noeuds type ressort et l’élément quadrilatère à neuf noeuds pour la modélisation des deux solides en contact.Mots-clés : Modélisation, contact, discontinuité, frottement, glissement, interface, structur

Durability of self-compacting concretes made with the natural pozzolan and siliceous fines

The effect of natural pozzolan and local waste siliceous fines on the durability of SCC was studied in this paper. Three self-compacting concretes were made with the following three additions, namely limestone fillers (SCC LF), pozzolanic fillers (SCC NP) and siliceous fillers (SCC SF). Durability tests, such as the porosity accessible to water, capillarity, carbonation, permeability to oxygen gas and diffusion of chloride ions, were carried out on these concretes in order to study the influence of these fillers on the transfer properties and durability of SCCs. The results obtained indicate that the SCC LF and SCC NP generally have the same transfer properties; these properties are significantly influenced by porosity and carbonation. In addition, the capillarity is nearly similar for all three SCCs. Moreover, it is worth noting that SCC NP gives permeability and diffusion coefficients of chloride ions slightly lower in comparison with those of the other SCCs. These finding suggest that the incorporation of Algerian natural fines and industrial waste as mineral additions into the SCC may have a positive environmental impact and can promote the development of local materials that are available in large quantities and whose production cost is low

Influence des additions minérales sur la résistance mécanique des mortiers

Les grands ouvrages tels que les tunnels sont de gros consommateurs du matériau béton dans lequel des millions de tonnes de ciment sont utilisés pour leur réalisation. La fabrication du ciment ternaire en utilisantdes additions minérales (Fines Siliceuses : FS) représente double intérêt lorsque le ciment Portland n’est pas largement disponible ; d’une part cela permet de diminuer les émissions de CO2 et d’autre part d’obtenir unliant moins coûteux. Cet article présente les résultats des résistances à la compression du mortier contenant différents pourcentages de FS. Le ciment a été partiellement remplacé par 0, 5, 10, 15 et 20 % de FS. Aussinous avons utilisé les dosages recommandés par le fabricant à savoir 15 et 30 Kg/m3. Le rapport liant -sable et liant - eau ont été maintenu respectivement constant à des valeurs 1/3 et 0,52. Les échantillonsont été mis à la cure dans l’eau jusqu’aux échéances de l’écrasement. Des essais de résistance à la compression ont été effectués à différentes échéances 7, 28, 60 et 90 jours. Un mortier témoin (CPA + 15 % de pouzzolane naturelle) a été confectionné pour les besoins de comparaison.Mots-clés : grands ouvrages-tunnels, ciment ternaire, addition minérale, mortier, résistance mécanique

Durability of self-compacting concretes made with the natural pozzolan and siliceous fines

The effect of natural pozzolan and local waste siliceous fines on the durability of SCC was studied in this paper. Three self-compacting concretes were made with the following three additions, namely limestone fillers (SCC LF), pozzolanic fillers (SCC NP) and siliceous fillers (SCC SF). Durability tests, such as the porosity accessible to water, capillarity, carbonation, permeability to oxygen gas and diffusion of chloride ions, were carried out on these concretes in order to study the influence of these fillers on the transfer properties and durability of SCCs. The results obtained indicate that the SCC LF and SCC NP generally have the same transfer properties; these properties are significantly influenced by porosity and carbonation. In addition, the capillarity is nearly similar for all three SCCs. Moreover, it is worth noting that SCC NP gives permeability and diffusion coefficients of chloride ions slightly lower in comparison with those of the other SCCs. These finding suggest that the incorporation of Algerian natural fines and industrial waste as mineral additions into the SCC may have a positive environmental impact and can promote the development of local materials that are available in large quantities and whose production cost is low

Influence of thermal activation of natural pozzolan on the mechanical behavior of cement pastes

This experimental work focused on the thermal activation of natural pozzolan (NP) from the town of Beni-Saf, in order to improveits reactivity. The present study consists of using natural pozzolan as partial replacement of ordinary Portland cement, with 10 to 40% by weight of cement. Various curing temperatures were used to assess the influence of thermal treatment on the mechanical properties of the pozzolan pastes. For this purpose, three curing modes were chosen, namely the normal curing at the temperature T = (20 ± 2) °C, taken as a reference, the curing at 40 °C, and another one at 60 °C. The experimental results obtained showed that the 40% natural pozzolan paste, which was stored at 40 °C, exhibited much better strengths than those of ordinary cement (CEM I), which was kept at room temperature. This finding leads us to consider that the replacement rate of 40% of NP, stored at the temperature of 40 °C, constitutes the best conditions for preparing an efficient eco-material. Natural pozzolan pastes thermally treated at 60°C gives better mechanical strengths with larger amounts of natural pozzolan

Influence of thermal activation of natural pozzolan on the mechanical behavior of cement pastes

This experimental work focused on the thermal activation of natural pozzolan (NP) from the town of Beni-Saf, in order to improveits reactivity. The present study consists of using natural pozzolan as partial replacement of ordinary Portland cement, with 10 to 40% by weight of cement. Various curing temperatures were used to assess the influence of thermal treatment on the mechanical properties of the pozzolan pastes. For this purpose, three curing modes were chosen, namely the normal curing at the temperature T = (20 ± 2) °C, taken as a reference, the curing at 40 °C, and another one at 60 °C. The experimental results obtained showed that the 40% natural pozzolan paste, which was stored at 40 °C, exhibited much better strengths than those of ordinary cement (CEM I), which was kept at room temperature. This finding leads us to consider that the replacement rate of 40% of NP, stored at the temperature of 40 °C, constitutes the best conditions for preparing an efficient eco-material. Natural pozzolan pastes thermally treated at 60°C gives better mechanical strengths with larger amounts of natural pozzolan

Finite element modelling of composite castellated beam

Nowadays, castellated beam becomes popular in building structural as beam members. This is due to several advantages of castellated beam such as increased depth without any additional mass, passing the underfloor service ducts without changing of story elevation. However, the presence of holes can develop various local effects such as local buckling, lateral torsional buckling caused by compression force at the flange section of the steel beam. Many studies have investigated the failure mechanism of castellated beam and one technique which can prevent the beam fall into local failure is the use of reinforced concrete slab as lateral support on castellated beam, so called composite castellated beam. Besides of preventing the local failure of castellated beam, the concrete slab can increase the plasticity moment of the composite castellated beam section which can deliver into increasing the ultimate load of the beam. The aim of this numerical studies of composite castellated beam on certain loading condition (monotonic quasi-static loading). ABAQUS was used for finite element modelling purpose and compared with the experimental test for checking the reliability of the model. The result shows that the ultimate load of the composite castellated beam reached 6.24 times than the ultimate load of the solid I beam and 1.2 times compared the composite beam

Influence of thermal activation of natural pozzolan on the mechanical behavior of cement pastes

This experimental work focused on the thermal activation of natural pozzolan (NP) from the town of Beni-Saf, in order to improveits reactivity. The present study consists of using natural pozzolan as partial replacement of ordinary Portland cement, with 10 to 40% by weight of cement. Various curing temperatures were used to assess the influence of thermal treatment on the mechanical properties of the pozzolan pastes. For this purpose, three curing modes were chosen, namely the normal curing at the temperature T = (20 ± 2) °C, taken as a reference, the curing at 40 °C, and another one at 60 °C. The experimental results obtained showed that the 40% natural pozzolan paste, which was stored at 40 °C, exhibited much better strengths than those of ordinary cement (CEM I), which was kept at room temperature. This finding leads us to consider that the replacement rate of 40% of NP, stored at the temperature of 40 °C, constitutes the best conditions for preparing an efficient eco-material. Natural pozzolan pastes thermally treated at 60°C gives better mechanical strengths with larger amounts of natural pozzolan

Effects of rubber aggregates on the physical-mechanical, thermal and durability properties of self-compacting sand concrete

The aim of this research was to study the effect of incorporating waste rubber aggregates on the physical, mechanical, thermal and durability performance of Self-Compacting Sand Concrete SCSC mixtures. For this purpose, the separately developed Rubberized Self-Compacting Sand Concrete RSCSC were prepared with three fractions of rubber grains where the natural aggregates were replaced with powder rubber, sand rubber and gravel rubber and four addition ratios (5, 10, 15 and 20%) as volume rates. The performed fresh properties using slump-flow, spreading, t500, sieve stability and air-entrained content tests proved better results for the RSCSC in comparison with reference concretes. Hardened state characterization of the concretes exhibited decreases in the mechanical properties of the RSCSC but the thermal conductivity and the dynamic elastic modulus were improved. Assessment of the concrete’s durability was accomplished through determination of apparent porosity, capillary absorption. Therefore, RSCSC to be can used in structural elements of dense reinforcement and complex formwork. Furthermore, this allows promising solution to reduce the impact of waste tyres on the environment and fight pollution

Elastic and inelastic buckling of steel cellular beams under strong-axis bending

This paper presents an extensive parametric study of elastic and inelastic buckling of cellular beams subjected to strong axis bending in order to investigate the effect of a variety of geometric parameters, and further generate mass data to validate and train a neural network-based formula. Python was employed to automate mass finite element (FE) analyses and reliably examine the influence of the parameters. Overall, 102,060 FE analyses were performed. The effects of the initial geometric imperfection, material nonlinearity, manufacture-introduced residual stresses, web opening diameter, web-post width, web height, flange width, web and flange thickness, end web-post width, and span of the beams and their combinations were thoroughly examined. The results are also compared with the current state-of-the-art design guidelines used in the UK. It was concluded that the critical elastic buckling load of perforated beams corresponds to the lateral movement of the compression flange while the most critical parameters are the web thickness and the geometry of the flange. However, from the inelastic analysis, the geometry and position of the web opening influence the collapse load capacity in a similar fashion to the geometry of the flange and thickness of the web. It was also concluded that the effect of the initial conditions was insignificant