Showing 1–12 of 628 results
3D & three phase’s micromechanical constitutive model for the Uniaxial compression test of concrete
The mechanical behav...رایگان!
The mechanical behavior of concrete materials is strongly influenced by its microstructure. The macroscopic properties of concrete materials such as strength and stiffness are dependent on the properties micromechanics. The advance of composite mechanics and advanced computing technologies has made possible the micromechanical analysis of concrete materials.. In the first status of micromechanical modeling with special emphasis on the advantage and disadvantage of each model is presented. The current paper focuses on the geometrical description and numerical simulation of normalweight concrete at the mesoscale. In the first part the numerical representation of concrete at the mesoscale is introduced. The internal structure of concrete is considered at the micro level, and is treated as a three phase material comprised of aggregate particle, matrix, and the aggregatematrix interfaces The generation of the mesoscale geometry, the finite element discretisation and the applied material laws Whit micro plane theory are described. The main objective of this paper is to investigate the macroscopic behavior and Progressive failure of concrete materials under static loading, as influenced by the properties of its constituents at the meso level.
A beam–column joint element for analysis of reinforced concrete frame structures
Earthquake reconnaissance and laboratory tests reveal that the beam–column joints of existing RC frame structures in China are susceptible to failure, leading to severe structural damage. However, the inelastic response of joint elements is rarely considered in structural analysis or design. A new joint element considering shear deformation and bar-slip behaviour was proposed and verified using an extensive experimental data set. Two RC frame specimens with different details were modelled with the joint element and their simulated seismic responses were compared with experimental results in terms of global and local performance. Based on the simulation, the joint element proved to be reliable and suitable for 2D structural modelling. Finally, two reinforced concrete frame structures with the same dimensions and reinforcement ratios but different ductility are modelled with and without the proposed joint elements. The proposed joint element was shown to accurately predict the mechanical behaviour of such structures and their components, especially the hysteresis behaviour. Analysis shows that joint failure tends to happen in low- ductility structures and will reduce the ductility and the energy dissipation ability of the structure, even cause structural collapse. Compared with the new designed structures, seismic performance of the low-ductility ones is worse, with poor energy dissipation, weak collapse resistance and brittle failure modes
A comparison of sophisticated neural network and Finite Element Method in estimating of variations in permeability of earth-dam body in leakage phenomenon
Leakage is one of thرایگان!
Leakage is one of the most important problems in earth dam construction. Lake of leakage phenomenon analysis for earth dams can lead to destructive problems like increase in leakage forces, increase in pore water pressure and instability of the earth dam. In this study, leakage in two sections of an earth dam are modeled and analyzed by Finite Element Method (FEM), Multilayer Pereceptron network (MLP) and Radial Basis Function network (RBF) and the results are compared. Based on the results, it can be concluded that FEM prediction are not compatible with actual data, whereas sophisticated neural network give acceptable results.
A Level Set Method for Structural Shape and Topology Optimization Using Radial Basis Functions
In this paper, the cرایگان!
In this paper, the conventional level set method is extended as an effective approach for shape and topology optimization by the introduction of the radial basis functions (RBFs). We apply the RBFs to represent the implicit level set modeling to reconstruct the shape and topology of an admissible design in a parametric way. This scheme converts the original PDE based level set method into a set of much easier ODE system and makes the level set method more efficient to implement. Numerical examples show the convergence speed and insensitivity to initial designs of proposed method in shape and topology optimization of 2D problems.
A model for concurrent maintenance of bridge elements
Maintenance activities on existing bridges are important for bridge safety and management. However, maintenance activities cause traffic jams and detours, and thus increase user costs. To reduce user costs resulting from maintenance activities while maintaining bridge elements in good condition, we introduce the concept of “concurrent element maintenance.” The concurrent maintenance concept attempts to integrate maintenance timings of different elements of a bridge to reduce user costs over the bridge’s life cycle. The proposed model adopts constraint programming as the search algorithm for optimizing the maintenance strategy of any bridge .An example using real data for a reinforced concrete highway bridge is presented. Sensitivity analysis of the discount rate investigates its influence on the life-cycle cost. The results demonstrate that the proposed model is effective for reducing the user costs as well as the total life-cycle costs.
A new wavelet-based method for determination of mode shapes: Experimental Results
In this article a neرایگان!
In this article a new method is proposed to determine the mode shapes of linear dynamic systems from the results of wavelet analysis. A previously proposed method based on a modified Morlet wavelet function with an adjusting parameter is used to identify the natural frequencies and damping ratios of system. The mode shapes are obtained from the time signal of responses and the extracted natural frequencies from wavelet transform of response signals. The method is applied to a steel real beam excited by an impact force. It is shown that the extracted mode shapes are not scaled. Therefore, the mass change method is used for scaling of the mode shapes.
A Robust Approach to Estimate the Uniaxial Compressive Strength of Intact Rocks
The uniaxial compres...رایگان!
The uniaxial compressive strength of intact rocks is extensively used in many rock engineering projects. High-quality core samples are required for the uniaxial compressive strength determinations. However, such core samples cannot always be obtained from weak rocks. For this reason, the predictive models are often employed to estimate indirectly. In present study, various models have been developed in order to predict uniaxial compressive strength. For this purpose different tests were accomplished. The root mean square error index was calculated as 6.1 from the neuro-fuzzy model and 13.63 from the multiple regression model. As a result, performance index reveled that the neuro-fuzzy exhibited a very high prediction capacity
A simplified Nonlinear Sway-Rocking model for evaluation of seismic response of structures on shallow foundations
This paper presentsرایگان!
This paper presents a simplified Nonlinear Sway-Rocking model as a preliminary design tool for seismic soil-structure interaction analysis. The proposed model is intended to capture the nonlinear loaddisplacement response of shallow foundations during strong earthquake events where foundation bearing capacity is fully mobilised. Emphasis is given to heavily-loaded structures resting on a saturated clay half-space. The variation of soil stiffness and strength with depth, referred to as soil non-homogeneity, is considered in the model. Although independent springs are utilised for each of the swaying and rocking motions, coupling between these motions is taken into account by expressing the loaddisplacement relations as functions of the factor of safety against vertical bearing capacity failure (FSv) and the moment-to-shear ratio (M/H). The simplified model has been calibrated and validated against results from a series of static push-over and dynamic analyses performed using a more rigorous finitedifference numerical model. Despite some limitations of the current implementation, the concept of this model gives engineers more degrees of freedom in defining their own model components, providing a good balance between simplicity, flexibility and accuracy.
Active Earth Pressure of Modeled Strip Load Surcharge on Rigid Walls
In determination of ...رایگان!
In determination of the active earth pressure of strip load surcharge, we would always do elastic supposition, and for that, we used boussinesq. In this essay, by supposition of plastic environment of the earth, a new formula was presented for the effect of strip load surcharge on the wall. In this new formula, effects of gradient, and the friction angle between earth and wall, and gradient of the wall, and friction angle of earth, is considered. In this essay, by MATLAB software, a program is presented for calculation of the pressure on the wall in different situations of setting strip load surcharge. Also this essay considers the distance of the effect of strip load surcharge, and by mean of that, we can determine the length of the surcharge and the distance of surcharge from wall which has taken effects from the imported pressure. It should be pointed out that imported pressure totally consists of earth pressure and surcharge pressure. This essay expresses the considered stress distribution, under the effect of strip load surcharge on the wall having the effect of the earth behind it. And dependent on the situation of strip load surcharge, we present four kinds of distribution.
An Adaptive IHS Pan-Sharpening Method
The goal of pan-sharرایگان!
The goal of pan-sharpening is to fuse a low spatial resolution multispectral image with a higher resolution panchromatic image to obtain an image with high spectral and spatial resolution. The Intensity-Hue- Saturation (IHS) method is a popular pan-sharpening method used for its efficiency and high spatial resolution. However, the final image produced experiences spectral distortion. In this letter, we introduce two new modifications to improve the spectral quality of the image. First, we propose imageadaptive coefficients for IHS to obtain more accurate spectral resolution. Second, an edge-adaptive IHS method was proposed to enforce spectral fidelity away from the edges. Experimental results show that these two modifications improve spectral resolution compared to the original IHS and we propose an adaptive IHS that incorporates these two techniques. The adaptive IHS method produces images with higher spectral resolution while maintaining the high-quality spatial resolution of the original IHS .
Analytical solution for axisymmetric thermoelastodynamic problems in a transversely isotropic half-space under a surface loading
In the present studyرایگان!
In the present study, the theory of coupled thermoelastodynamic is applied to determine the displacement, temperature and stress (DTS) fields of a torsionless axisymmetric transversely isotropic half-space under a surface loading. The basic equations of coupled thermoelasticity consist of the equations of motion and the energy equation, which forms a set of completely coupled partial differential equations for the displacement and temperature fields. Potential method is employed for uncoupling the set of basic equations of coupled thermoelasticity. With the aid of a potential function existed in the literature, the system of equations are uncoupled, where a sixth order partial differential equation is received. Displacement components and temperature are written with respect to the potential function in cylindrical coordinate system. The Laplace and Hankel integral transforms are employed to suppress the time and radial variables, respectively. One may apply the inverse Hankel and Laplace transforms to determine the DTS fields and other quantities of interest in physical (space-time) domain. Eventually, the integrand functions of DTS components are obtained analytically.
APPLICATION OF SPECTRAL FINITE ELEMENT METHOD IN ANALYSIS OF TRANSIENT ELASTODYNAMIC PROBLEMS
Dealing with wave prرایگان!
Dealing with wave propagation phenomena using classical finite element method (FEM) results in some inefficiencies and inaccuracies in the solution. Spectral finite element method (SFEM) as a method based on FEM, presents some new features that makes it much more suitable and useful for solving wave propagation problems. The excellent characteristic of SFEM is that the mass matrix is diagonal because of the choice of the Lagrange interpolation function supported on Legendre-Gauss-Lobatto (LGL) points in conjunction with LGL integration rule. Therefore numerical calculations can be significantly efficient in comparison with the classical FEM. On the other hand choice of high order elements using specific shape functions gives us the possibility to increase the accuracy of the solution while decreasing the total number of elements used for the domain of the problem thus decreasing the analysis time. In this paper, a SFEM-based code is represented and verified, and then some wave propagation problems in elastic solid domains are solved using this code showing the capabilities of SFEM in solving elastodynamic problems.Some problems are solved using different spectral elements, and analysis time, accuracy of the solution and costs of analysis in different solutions is compared to analytical and/or numerical solutions available in the literature.