Abstract in English:This work intends to introduce a probabilistic approach for the crack propagation analysis. It presents a methodology that is based on the distribution of the initial flaw size a0. Departing from fatigue test results for specific structural components, an estimation of the initial flaw distribution is obtained, and from this distribution it becomes possible to establish the appropriate initial flaw size for crack propagation analysis for the chosen statistical distribution, such as Weibull or Log-normal. The methodology allows to apply different values of a0 for different components or structural details, reflecting the quality of the manufacturing process for the item evaluated. Two examples of practical applications of the EIFS concept are presented, corresponding to lugs and shear joints usually used for aerospace applications.
Abstract in English:Three-dimensional bending and stress analyses of the rotating two-directional functionally graded annular/circular plates or disks have not been accomplished so far. This task is performed in the present paper, employing a finite element formulation with a C¹-continuity. Therefore, both transversely graded and radiallygraded plates may be analyzed as special cases of the present research. Distribution of the transverse loads as well as coefficients of the elastic foundation may be non-uniform. Mixed stress-based and displacement-based edge conditions are considered to cover many practical applications. Compatible Hermitian elements are employed to develop a consistent formulation and avoid jumps in the stress components at the elements interfaces. In contrast to the very limited works presented for the rotating functionally graded circular plates so far, the transverse flexibility and the transverse stress components are also considered in the present research. Finally, influences of the material properties distribution, angular speed, geometric parameters, and the elastic foundation on distributions of the stress and displacement components are investigated for a variety of edge and boundary conditions and some design criteria are extracted.
Abstract in English:Static analysis of skew composite shells is presented by developing a C0 finite element (FE) model based on higher order shear deformation theory (HSDT). In this theory the transverse shear stresses are taken as zero at the shell top and bottom. A realistic parabolic variation of transverse shear strains through the shell thickness is assumed and the use of shear correction factor is avoided. Sander's approximations are considered to include the effect of three curvature terms in the strain components of composite shells. The C0 finite element formulation has been done quite efficiently to overcome the problem of C1 continuity associated with the HSDT. The isoparametric FE used in the present model consists of nine nodes with seven nodal unknowns per node. Since there is no result available in the literature on the problem of skew composite shell based on HSDT, present results are validated with few results available on composite plates/shells. Many new results are presented on the static response of laminated composite skew shells considering different geometry, boundary conditions, ply orientation, loadings and skew angles. Shell forms considered in this study include spherical, conical, cylindrical and hypar shells.
Abstract in English:Pounding of neighbouring construction of structures due to seismic excitation increases the damage of structural components or even causes collapse of structures. Among the possible building damages, earthquake induced pounding has been commonly observed in several earthquakes. Therefore it is imperative to consider pounding effect for structures. This study aims to understand the response behaviour of adjacent buildings with dissimilar heights under earthquake induced pounding. Effects of different separation distances between structures are also investigated. Nonlinear finite element analysis in time domain has been carried out for pounding of neighbouring structures having varying heights. To show the importance of avoiding pounding in structures the results obtained were compared with model having no pounding phenomena. The results were obtained in the form of storey shear, pounding force, storey drift, point displacement and acceleration. The acceleration at pounding level significantly increases during collision of building. The generated extra pounding force may cause severe damage to structural members of structures. Pounding produces shear at various story levels, which are greater than those obtained from no pounding case. Building with more height suffers greater damage than shorter building when pounding occurs. Increasing gap distance tends to reduce story shear in consistent manner. The results also show that the conventional modelling of building considering only beams and columns underestimates pounding effects. More realistic modelling such as beams, columns and slabs shall be adopted to accurately understand the pounding phenomenon.
Abstract in English:In this paper, a scaled 3D ship under shock loading is modeled and analyzed by finite element method. By using of shock factor, there is no need to have different tests or even numerical simulation. Shock factor is an important parameter which clarifies shock severity. It was found that although the new shock factor introduced by Yao et al. (2009), when constant, predict the response better than older shock factor, but for varying values of shock factors, the older would predict better. It is also found that costly and time-consuming experiments can be avoided by proper finite element modeling, yet the errors can remain within an acceptable range. The results of the present work can be used as benchmarks for future works.
Abstract in English:A mechanical model for the analysis of reinforced concrete frame structures based on the Finite Element Method (FEM) is proposed in this paper. The nonlinear behavior of the steel and concrete is modeled by plasticity and damage models, respectively. In addition, geometric nonlinearity is considered by an updated lagrangian description, which allows writing the structure equilibrium in the last balanced configuration. To improve the modeling of the shear influence, concrete strength complementary mechanisms, such as aggregate interlock and dowel action are taken into account. A simplified model to compute the shear reinforcement contribution is also proposed. The main advantage of such a model is that it incorporates all these effects in a one-dimensional finite element formulation. Two tests were performed to compare the provided numerical solutions with experimental results and other one- and bi-dimensional numerical approaches. The tests have shown a good agreement between the proposed model and experimental results, especially when the shear complementary mechanisms are considered. All the numerical applications were performed considering monotonic loading.
Abstract in English:As a seismic wave travels along the separate supports of an extended structure, the structure is subjected to multiple-support excitation due to seismic wave propagation. Considering the seismic wave passage effect, this paper describes seismic analysis of a maglev vehicle moving on a multiply supported gudieway. The guideway system is modeled as a series of simple beams and the vehicle as a four degrees-of-freedom (DOFs) rigid bar equipped with multiple onboard PI+LQR hybrid controllers. The controller is used to regulate control voltage for tuning both magnetic forces of uplift levitation and lateral guidance in the maglev system. Numerical studies show that as a maglev vehicle is equipped with more supported magnets then they can provide more control gains for tuning the guidance forces of the moving vehicle, and mitigate seismic-induced lateral vibration of a maglev vehicle running a guideway.
Abstract in English:Thermal stresses and displacements for orthotropic, two-layer antisymmetric, and three-layer symmetric square cross-ply laminated plates subjected to nonlinear thermal load through the thickness of laminated plates are presented by using trigonometric shear deformation theory. The in-plane displacement field uses sinusoidal function in terms of thickness co-ordinate to include the shear deformation effect. The theory satisfies the shear stress free boundary conditions on the top and bottom surfaces of the plate. The present theory obviates the need of shear correction factor. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. The validity of present theory is verified by comparing the results with those of classical plate theory and first order shear deformation theory and higher order shear deformation theory.
Abstract in English:This paper attempts to present a new analysis for dynamical behavior of two-layer beams with frictional interface which held together in a pressurized environment, including stick-slip nonlinear phenomenon. To achieve a proper outlook of two-layer beam structures behavior, it is essential to realize the mechanisms of motion precisely. Coupled equation of transversal and longitudinal vibration of two-layers in the presence of dry friction is derived and nondimensionalized. Furthermore, free and forced vibration of the mentioned system is investigated and the system dynamics is monitored via Poincare maps and Lyapunov exponent analysis. A comparative study with ANSYS is developed to show the accuracy of the proposed approach.
Abstract in English:Optimisation of stacking sequence for composite panels under slamming impact loads using a genetic algorithm method is studied in this paper. For this purpose, slamming load is assumed to have a uniform distribution with a triangular-pulse type of intensity function. In order to perform optimisation based on a genetic algorithm, a special code is written in MATLAB software environment. The optimiser is coupled with the commercial software ANSYS in order to analyse the composite panel under study and calculate the central deflection. After validation, different cases of stacking sequence optimisation are investigated for a variety of composite panels. The investigations include symmetric as well as asymmetric conditions of stacking sequence. Results obtained from these analyses reveal the fact that the adopted approach based on a genetic algorithm is highly capable of performing such optimisations.