Journal of Materials and Engineering Structures
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Comportement d’un matériau sablo-graveleux sur chemin cyclique
Full text linkThis article has the results of the cyclic triaxial compression tests to study the potential of liquefaction of a gravel-sand material. The last part is devoted to the not drained cyclic tests and their analyses. Many articles are devoted to the tests on the standard sand of laboratory Hostun in particular for the study of liquefaction or on reconstituted clays but few tests are carried out on a natural material. The scarcity of cyclic tests on such rough natural materials shows the difficulty of assessing the seismic risk. Faced with these difficulties, the use of tests such as the CPT provides a different but very practical approach. The overall results show a trend of relatively high liquefaction of the material, even under conditions of moderate stress (qc / 2s'3 = 0.2). This trend is growing very strongly when the rate of cyclic loading reached 0.3. The CPT test also shows a great tendency to liquefaction with a safety factor of well below 1. Cet article présente les résultats des essais triaxiaux cycliques pour étudier le potentiel de liquéfaction d’un matériau sablo-graveleux. De nombreux articles sont consacrés aux essais sur le sable de laboratoire type Hostun notamment pour l’étude de la liquéfaction ou sur des argiles reconstituées mais peu d’essais sont effectués sur un matériau naturel. La rareté des essais cycliques sur les matériaux naturels notamment grossiers, montre la difficulté d’évaluer le risque sismique. Devant ces difficultés, l’utilisation des essais comme le CPT permet une approche différente mais très pratique. L’ensemble des résultats montre une tendance à la liquéfaction relativement importante du matériau, même dans des conditions de sollicitation modérées (qc/2s’3 = 0.2). Cette tendance s’accroît très fortement quand le taux de sollicitation cyclique atteint 0.3. L’essai au CPT montre également une grande tendance à la liquéfaction avec un coefficient de sécurité largement inférieure à 1.
Cylindrical bending of orthotropic plate strip based on nth-order plate theory
Full text linkIn this paper, cylindrical bending of orthotropic plates is presented using nth-order plate theory. Classical plate theory and parabolic shear deformation theory of Reddy can be considered as special cases of present theory. The theory accounts for realistic variation of the transverse shear stress through the thickness of plate and satisfy the traction free conditions at top and bottom surfaces of the plate. The number of unknown variables in the present theory is same as that of first order shear deformation theory. The theory is variationally consistent. The use of shear correction factors which are problem dependent and are normally associated with first order shear deformation theory is avoided in the present theory. The governing equations and associated boundary conditions are derived by the principle of virtual work. Navier solution technique is employed for the simply supported plates. The program has been developed in FORTRAN. The displacement and stresses of a simply supported plate infinitely long in y-direction under sinusoidally distributed load are calculated to demonstrate the accuracy and efficiency of the present theory
Coupling Neumann development and component mode synthesis methods for stochastic analysis of random structures
Full text linkDans ce papier, on propose une méthode pour calculer les deux premiers moments (moyenne et variance) de la réponse dynamique d’une structure comportant des variables incertaines et soumise à une excitation aléatoire. Pour cela la méthode de Newmark est utilisée pour transformer l’équation de mouvement de la structure en une équation d’équilibre quasi-statique dans le domaine temporel. La méthode de développement de Neumann a été couplée aux simulations de Monte Carlo pour calculer les valeurs statistiques de la réponse aléatoire. L’utilisation des méthodes de synthèse modale permet de réduire les dimensions du modèle avant intégration de l’équation de mouvement. Des applications numériques ont été élaborées pour monter l’efficacité de la méthode développée pour analyser la réponse stochastique des structures de grande taille.In this paper, we propose a method to calculate the first two moments (mean and variance) of the structural dynamics response of a structure with uncertain variables and subjected to random excitation. For this, Newmark method is used to transform the equation of motion of the structure into a quasistatic equilibrium equation in the time domain. The Neumann development method was coupled with Monte Carlo simulations to calculate the statistical values of the random response. The use of modal synthesis methods can reduce the dimensions of the model before integration of the equation of motion. Numerical applications have been developed to highlight effectiveness of the method developed to analyze the stochastic response of large structures.
Design Fatigue Lives of Polypropylene Fibre Reinforced Polymer Concrete Composites
Full text linkFlexural fatigue behavior of Poly-propylene fibre reinforced polymer concrete composites (PFRPCC) has been investigated at various stress levels and the statistical analysis of the data thus obtained has been carried out. Polymer Concrete Composite (PCC) samples without addition of any type of fibres were also tested for flexural fatigue. Forty specimens of PCC and One hundred and Forty One specimens of PFRPCC containing 0.5%, 1.0% and 2.0% polypropylene fibres were tested in fatigue using a MTS servo controlled test system. Fatigue life distributions of PCC as well as PFRPCC are observed to approximately follow a two parameter Weibull distribution with correlation coefficient exceeding 0.9. The parameters of the Weibull distribution have been obtained by various methods. Failure probability, which is an important parameter in the fatigue design of materials, has been used to obtain the design fatigue lives for the material. Comparison of design fatigue life of PCC and PFRPCC has been carried out and it is observed that addition of fibres enhances the design fatigue life of PCC
Structural characteristics of simply connected planar sections with application to airfoils
Full text linkThe presented work is to develop a numerical computation program to determine the geometrical characteristics of arbitrary simply connected planar sections and applications to airfoils. In the literature, there are exact analytical solutions only for some simples’ geometries, such as circular, rectangular and elliptical sections. Hence our interest is focused on the search of approximate numerical solutions for more complex sections used in aeronautics. The used method is to subdivide the section in the infinitesimal triangular sections with a single observer within the area having a suitable position. The characteristics of any triangle, given by the positions of these three nodes are known in the literature. Using the principle of compound surfaces, one can determine the geometric characteristics of the airfoil surface. The analytic function of the airfoil boundary is obtained by using the cubic spline interpolation because the airfoil is given in the form of tabulated points. Error estimation is done to determine the accuracy of the numerical computation
Buckling Response of Thick Functionally Graded Plates
Full text linkIn this paper, the buckling of a functionally graded plate is studied by using first order shear deformation theory (FSDT). The material properties of the plate are assumed to be graded continuously in the direction of thickness. The variation of the material properties follows a simple power-law distribution in terms of the volume fractions of constituents. The von Karman strains are used to construct the equilibrium equations of the plates subjected to two types of thermal loading, linear temperature rise and gradient through the thickness are considered. The governing equations are reduced to linear differential equation with boundary conditions yielding a simple solution procedure. In addition, the effects of temperature field, volume fraction distributions, and system geometric parameters are investigated. The results are compared with the results of the no shear deformation theory (classic plate theory, CPT)