Showing 1–12 of 726 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 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 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
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.
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.
Assessment of Equivalent Static Earthquake Analysis Procedure for Structures with Mass Irregularity in Height
Sudden changes in st...رایگان!
Sudden changes in structural dimensions and mass irregularities are inevitable in urban buildings. Most building codes have different analysis and design previsions for such buildings. In this article, such provisions based on the Iranian seismic code of practice (Standard No. 2800), which is to a great extent similar to UBC-97 model code, are verified in order to assess the provisions for different types of structures. Thus, four two-dimensional residential type steel structures with 4, 8, 12 and 16 stories and with different forms of mass irregularities in height are designed using the standard equivalent static procedure per the Iranian Seismic Code of practice. The designed structures, then, were subjected to different nonlinear static (pushover) and dynamic analyses. Two levels of irregularities, i.e. 150 and 300 percents, located at the heights equal to 50% and 75% of the overall height of the structures, have been considered. The results show that the static procedure adapted in the code results in much higher internal forces, story shears and overturning moments in various parts of the structures compared to the dynamic results. Also, this study shows that lateral inter-story drifts obtained using the equivalent static procedure and dynamic analyses are quite comparable for short buildings. For taller buildings, in contrast, dynamic analyses showed less inter-story drifts. It is also observed that mass irregularities in height could be responsible for more contribution of higher modes in seismic response of such structures
Bee Colony Optimization of Tuned Mass Dampers for Earthquake Vibrations of High-rise Buildings Including Soil Structure Interaction
This paper investigaرایگان!
This paper investigates the optimization of Tuned Mass Dampers (TMDs) for high-rise buildings. The model is assumed as a 40 story building with 160m height considering the translation and rotation of foundation. The Soil Structure Interaction (SSI) is considered for the better prediction of building’s response. To illustrate the results, Bam earthquake data is applied to the model. The three soil types, i.e. soft, medium and dense soil are utilized, and the results are compared with the fixed based model. The model is based on time domain analysis, and Newmark method is used to obtain the displacement, velocity and acceleration of different elements. The Artificial Bee Colony (ABC), a heuristic method based on the behavior of bees forage for food, is employed to obtain the best parameters for TMD device. The design variables are assumed as mass, damping and spring stiffness quantity. The objective is to decrease both the maximum displacement and acceleration of the building. The results show that the presented model can be effectively applied to evaluate the response of high-rise buildings including SSI effects. It is indicated that the results obtained by this model is more accurate than the results of fixed based model. The effects of TMD on the oscillations of structures including different soil characteristics are also investigated. It is shown that the TMD is more effective for soft soil foundations. It is also shown that how the bee colony optimization technique can be employed to design the optimum TMD for the minimum displacement and acceleration. This study leads the researchers to the better understanding of earthquake oscillations of the high-rise buildings, and helps the designers to achieve the optimized TMD for the structures.
Comparison between Seismic Behavior of Suspended Zipper Braced Frames and Various EBF Systems
Zipper frames are in...رایگان!
Zipper frames are intended to improve on the behavior of conventional inverted-V-braced frames, which show poor performance taking place from the early buckling of braces in the lower story. A zipper frame affords better performance by forcing simultaneous buckling of all braces. In this article, seismic behaviors of zipper braced frames and three types of eccentrically braced frames are evaluated using finite element simulation. Two dimensional finite element models have been created for three-story onebay frames for various bay lengths and different arrangement of braces. Seismic response of frames subjected to near-fault ground motions (LA21) has been studied through dynamic analysis, considering no nlinearity of geometry and materials. For this purpose, SAP2000 has been used. Results have been ompared and structural response of steel frames and some other parameters such as ductility of frames, maximum base shear and optimized link length have been investigated. Against other researches, in this article, the ratio of maximum shear over the weight of structure and its relation to behavior of structure has also been studied. It was found that optimized link length in EBF systems which caused to maximum du ctility of frame is about 30 percent of the bay length. Moreover, the results showed that zipper frames provide desirable post buckling behavior and exhibit more ductility.
Compliance of Rigid Arbitrary Shape Foundations Using 1 DOF BEM
In this study the reرایگان!
In this study the relationship between the dynamic force and displacement (impedance or compliance) is evaluated for rigid foundations with arbitrary shape resting on a half-space medium, consisting of homogeneous, isotropic, linear elastic materials with constant Boundary Element Method, (1 DOF). Green’s function is computed for half-space and presented in explicit form. By using BEM formulation the stress beneath foundations and compliance of them are obtained. The vertical compliance of a rigid circular disc which is calculated by this method is compared by semi-closed form solution and verifies the accuracy and efficiency of this method. the vertical and rocking compliance functions for rigid rectangular and some arbitrary shape foundations are obtained. And also, the variation of stress distribution pattern beneath square and circular foundations with frequency is studied and these results are compared with the results of the other methods.