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Showing 38 results for Finite Element

H.r. Ghafouri,
Volume 1, Issue 1 (9-2003)
Abstract

A two-dimensional mathematical model for the prediction of time-variations of river-bend displacements was developed which is particularly applicable to meandering rivers. The computational procedure consists of two stages, that is , in the first stage by utilizing depth-averaged continuity and momentum equations, velocity field as well as water surface profile in a river is determined. The well-known Finite-Element technique was applied to the governing equations. In the second stage the rate of river bank erosion is computed in terms of determined depths and velocities. The model utilizes Odgaards (1989) bank-erosion model in this stage. The procedure is then performed repeatedly over the entire time span in a staggered manner. The developed model was applied to simulate the migration of Qezel Ozan river. The fairly good match obtained indicates the applicability of the model.
Asghari K.,
Volume 1, Issue 2 (12-2003)
Abstract

The solution of shallow-water equation for a two-dimensional .simulation of overland /low for an actual watershed, is presented. The Petorv-Galerkin weighted residual method is used to overcome spurious oscillations inflow depth. For modeling overland flow over complex topography and variable surface, ct pre and postprocessor was developed to utilize the Triangulated Irregular Network (TIN) model and to generate finite element mesh. Close agreement of the model with measured data is obtained. This model can be used to better analyze the influence of varying surface roughness and topography on overland flow characteristics, including distribution of flow depth and velocity (is well as resulting hydrographs. Detailed spatial and temporal output parameters provide a basis fur further study of the patterns of soil erosion and evaluation of runoff natural slopes.
Asghari K.,
Volume 1, Issue 2 (12-2003)
Abstract

The solution of shallow-water equation for a two-dimensional .simulation of overland /low for an actual watershed, is presented. The Petorv-Galerkin weighted residual method is used to overcome spurious oscillations inflow depth. For modeling overland flow over complex topography and variable surface, ct pre and postprocessor was developed to utilize the Triangulated Irregular Network (TIN) model and to generate finite element mesh. Close agreement of the model with measured data is obtained. This model can be used to better analyze the influence of varying surface roughness and topography on overland flow characteristics, including distribution of flow depth and velocity (is well as resulting hydrographs. Detailed spatial and temporal output parameters provide a basis fur further study of the patterns of soil erosion and evaluation of runoff natural slopes.
Kheyr Aldin A., Mortezaei A.r.,
Volume 2, Issue 1 (3-2004)
Abstract

Structural walls are used extensively in moderate- and high-rise buildings to resist lateral loads induced by earthquakes. The seismic performance of many buildings is, therefore, closely linked to the behavior of the reinforced concrete walls. The analytical models used in this paper are developed to study the push-over response of T-shaped reinforced concrete walls andinvestigate the influence of the flange walls on laterally loaded walls and nonlinear behavior of shear walls, namely strength, ductility and failure mechanisms. A layered nonlinear finite element method is used to study the behavior of T-shaped and rectangular (barbell) shear walls. This paper introduces a computer program to practically study three-dimensional characteristics of reinforced concrete wall response by utilizing layered modeling. The program is first verified bysimulated and reported experimental response of 3-D reinforced concrete shear walls. Subsequently, a study considering eighteen analytical test specimens of T-shaped and barbell shear walls is carried out. Finally, based on analytical results, a new equation for minimum ratio of shear wall area to floor-plan area is proposed.
Sabouri Ghomi S., Kharazi M.h.k., Asghari A., Javidan P.,
Volume 3, Issue 1 (3-2005)
Abstract

Design and construction of efficient and economic Reinforced Concrete (R.C.) Hyperbolic Cooling Towers have driven the engineers toward the design of tall and thin-shell towers which have considerable high slenderness aspect ratio. Consequently, the shell of R.C. Cooling Towers with relative high slenderness aspect ratio is extremely prone to buckling instability due to wind loading. To increase the structural stability or buckling safety factor, one economic approach is to design and construct stiffening rings for the R.C. Hyperbolic Cooling Towers. Despite the research previously performed to determine the effect of stiffening rings on the buckling behavior of the R.C. Hyperbolic Cooling Towers, information resulting in maximum buckling stability is absent considering the optimized utilization of the quantity and dimension as well as the location of this type of stiffeners. In this paper, not only the effect of the stiffening rings on the buckling stability of the R.C. Cooling Tower is studied but also the optimized location,quantity and dimension of the stiffening rings are carried out for a sample RC Cooling Tower. The dimensions of the selected sample cooling tower are in average typical dimensions which are used in the current practice. In this study, finite element (F. E.) analyses has been carried out to define the buckling modes and resistance of this tower due to wind loading for different number of stiffening ring configurations. Based on the conducted buckling analysis, the optimized number, location and dimension of the stiffening rings that maximizes the tower.s buckling stability are defined and the methodology to achieve this information is discussed in this paper.
Ali Kheyroddin, Hosein Naderpour,
Volume 5, Issue 1 (3-2007)
Abstract

A parametric study is performed to assess the influence of the tension reinforcement index, ( ω = ρ fy /f Bc), and the bending moment distribution (loading type) on the ultimate deformation characteristics of reinforced concrete (RC) beams. The analytical results for 15 simply supported beams with different amounts of tension reinforcement ratio under three different loading conditions are presented and compared with the predictions of the various formulations and the experimental data, where available. The plastic hinge rotation capacity increases as the loading is changed from the concentrated load at the middle to the third-point loading, and it is a maximum for the case of the uniformly distributed load. The effect of the loading type on the plastic rotation capacity of the heavily reinforced beams is not as significant as that for the lightly reinforced beams. Based on the analytical results obtained using the nonlinear finite element method, new simple equations as a function of the tension reinforcement index, ω, and the loading type are proposed. The analytical results indicate that the proposed equations can be used for analysis of ultimate capacity and the associated deformations of RC beams with sufficient accuracy.
S.h. Ebrahimi, S. Mohammadi, A. Asadpoure,
Volume 6, Issue 3 (9-2008)
Abstract

A new approach is proposed to model a crack in orthotropic composite media using the extended finite element method (XFEM). The XFEM uses the concept of partition of unity in addition to meshless basic idea of approximating a field variable by its values at a set of surrounding nodes. As a result, higher order approximations can be designed with the same total number of degrees of freedom. In this procedure, by using meshless based ideas, elements containing a crack are not required to conform to crack edges. Therefore mesh generating is performed without any consideration of crack conformations for elements and the method has the ability of extending the crack without any remeshing. Furthermore, the type of elements around the cracktip is the same as other parts of the finite element model and the number of nodes and consequently degrees of freedom are reduced considerably in comparison to the classical finite element method. Developed orthotropic enrichment functions are further modified to enable modeling isotropic problems.
M.a. Goudarzi, S.r. Sabbagh-Yazdi,
Volume 7, Issue 3 (9-2009)
Abstract

The main objective of this article is evaluation of the simplified models which have been developed for analysis and design of liquid storage tanks. The empirical formulas of these models for predicting Maximum Sloshing Wave Height (MSWH) are obtained from Mass Spring Models (MSM). A Finite Element Modeling (FEM) tool is used for investigating the behavior the some selected liquid storage tanks under available earthquake excitations. First, the results of FEM tool are verified by analyzing a liquid storage tank for which theoretical solution and experimental measurements are readily available. Then, numerical investigations are performed on three vertical, cylindrical tanks with different ratios of Height to Radius (H/R=2.6, 1.0 and 0.3). The behaviors of the tanks are initially evaluated using modal under some available earthquake excitations with various vibration frequency characteristics. The FEM results of modal analysis, in terms of natural periods of sloshing and impulsive modes period, are compared with those obtained from the simplified MSM formulas. Using the time history of utilized earthquake excitations, the results of response-history FEM analysis (including base shear force, global overturning moment and maximum wave height) are compared with those calculated using simplified MSM formulations. For most of the cases, the MSWH results computed from the time history FEM analysis demonstrate good agreements with the simplified MSM. However, the simplified MSM doesn’t always provide accurate results for conventionally constructed tanks. In some cases, up to 30%, 35% and 70% average differences between the results of FEM and corresponding MSM are calculated for the base shear force, overturning moment and MSWH, respectively.
R. Attarnejad, F. Kalateh,
Volume 10, Issue 1 (3-2012)
Abstract

This paper describes a numerical model and its finite element implementation that used to compute the cavitation effects on

seismic behavior of concrete dam and reservoir systems. The system is composed of two sub-systems, namely, the reservoir and

the dam. The water is considered as bilinear compressible and inviscid and the equation of motion of fluid domain is expressed

in terms of the pressure variable alone. A bilinear state equation is used to model the pressure–density relationship of a cavitated

fluid. A standard displacement finite element formulation is used for the structure. The Structural damping of the dam material

and the radiation damping of the water and damping from foundation soil and banks have been incorporated in the analysis. The

solution of the coupled system is accomplished by solving the two sub-systems separately with the interaction effects at the damreservoir

interface enforced by a developed iterative scheme. The developed method is validated by testing it against problem for

which, there is existing solution and the effects of cavitation on dynamic response of Konya gravity dam and Morrow Point arch

dam subjected to the first 6 s of the May 1940 El-Centro, California earthquake, is considered. Obtained results show that impact

forces caused by cavitation have a small effect on the dynamic response of dam-reservoir system.


A. Eslami, M. Veiskarami, M. M. Eslami,
Volume 10, Issue 2 (6-2012)
Abstract

It has been realized that the raft (mat) foundations are capable of bearing very large loads when they are assisted with a pile
group. The contribution of both raft and piles to carry the surcharge loads is taken into account, considering the stiffness and
strength of involved elements in the system, i.e. piles, raft and surrounding soil. The piles are usually required not to ensure the
overall stability of the foundation but to act as settlement reducers. There is an alternative design in which, the piles are nonconnected
from the raft to reduce the settlement, which are then known to be "settlement reducer non-connected piles" to increase
the system stiffness. In this paper, two and three dimensional finite element analysis of connected and non-connected pile-raft
systems are performed on three case studies including a 12-storey residential building in Iran, a 39-storey twin towers in
Indonesia, and the Messeturm tower, 256m high, in Frankfurt, Germany. The analyses include the investigation of the effect of
different parameters, e.g. piles spacing, embedment length, piling configuration and raft thickness to optimize the design. The role
of each parameter is also investigated. The parametric study results and comparison to a few field measurements indicate that
by concentrating the piles in the central area of the raft foundation the optimum design with the minimum total length of piles is
achieved, which is considered as control parameter for optimum design. This can be considered as a criterion for project cost
efficiency. On the other hand, non-connected piled-raft systems can significantly reduce the settlements and raft internal bending
moments by increasing the subsoil stratum stiffness. Finally, the comparison indicates that simple and faster 2D analysis has
almost similar results to the time consuming and complicated 3D analysis.


J. Jalili, M. K. Jafari, A. Shafiee, J. Koseki, T. Sato,
Volume 10, Issue 2 (6-2012)
Abstract

A series of tests and also numerical analyses were conducted to explore the mechanical behavior of a mixture of coarse gravelsize
particles floating in a matrix of silt, sand or clay. The research is a step forward in an ongoing investigation on behavior of
composite clay, which is used as the core material of some large embankment dams all over the world. After providing the reader
with an overall image about behavior of such materials through the literature, the paper focuses on a predominant feature of the
composite soil behavior: increase of non-deformable solid inclusions in a mixture leads to formation of heterogeneity of stress
field, excess pore water pressure and strain distribution along the specimens. This paper mainly probes formation of such
heterogeneity by the aid of special experiments and also numerical analyses. In addition to loading details, it is clarified through
the paper that position of inclusions relative to loading direction also affects heterogeneity of stress/strain and excess pore water
pressure distribution through the mixture. Despite the former, the latter redistributes with a rate proportional to material
hydraulic conductivity.


Seyed B. Beheshti-Aval,
Volume 10, Issue 4 (12-2012)
Abstract

A comparison between design codes i.e. ACI and AISC-LRFD in evaluation of flexural strength of concrete filled steel tubular

columns (CFTs) is examined. For this purpose an analytical study on the response of CFTs under axial-flexural loading is carried

using three-dimensional finite elements with elasto-plastic model for concrete with cracking and crushing capability and elastoplastic

kinematic hardening model for steel. The accuracy of the model is verified against previous test results. The nonlinear

modeling of CFT columns shows that the minimum thickness that recommended by ACI and AISC-LRFD to prevent local buckling

before the steel shell yielding for CFT columns could be decreased. The comparison of analytical results and codes indicates that

the accuracy of ACI method in estimation of axial-flexural strength of CFT columns is more appropriate than AISC-LRFD. The

ACI lateral strength of CFTs is located on upper bond of the AISC-LRFD’s provisions. AISC-LRFD estimates the lateral strength

conservatively but ACI in some ranges such as in short columns or under high axial load levels computes lateral strength in nonconservative

manner. Supplementary provisions for post local buckling strength of CFT columns should be incorporated in high

seismic region. This effect would be pronounced for column with high aspect ratio and short columns.


A. Tarighat,
Volume 11, Issue 3 (9-2013)
Abstract

Concrete bridge deck damage detection by measurement and monitoring variables related to vibration signatures is one of the main tasks of any Bridge Health Monitoring System (BHMS). Generally damage puts some detectable/discoverable signs in the parameters of bridge vibration behavior. However, differences between frequency and mode shape before and after damage are not remarkable as vibration signatures. Therefore most of the introduced methods of damage detection cannot be used practically. Among many methods it seems that models based on artificial intelligence which apply soft computing methods are more attractive for specific structures. In this paper an Adaptive Neuro-Fuzzy Inference System (ANFIS) is used to detect the damage location in a concrete bridge deck modeled by finite element method. Some damage scenarios are simulated in different locations of the deck and accelerations as representatives of response at some specific points are calculated. Excitement is done by applying an impact load at the center of the deck. In the proposed ANFIS damage detection model accelerations are inputs and location of the damage is output. Trained model by simulated data can show the location of the damage very well with a few training data and scenarios which are not used in training stage. This system is capable to be included in real-time damage detection systems as well.
A. R. Rahai, S. Fallah Nafari,
Volume 11, Issue 4 (12-2013)
Abstract

The seismic behavior of frame bridges is generally evaluated using nonlinear static analysis with different plasticity models hence this paper tends to focus on the effectiveness of the two most common nonlinear modeling approaches comprising of concentrated and distributed plasticity models. A three-span prestressed concrete frame bridge in Tehran, Iran, including a pair of independent parallel bridge structures was selected as the model of the study. The parallel bridges were composed of identical decks with the total length of 215 meters supported on different regular and irregular substructures with non-prismatic piers. To calibrate the analytical modeling, a large-scale experimental and analytical seismic study on a two-span reinforced concrete bridge system carried out at the University of Nevada Reno was used. The comparison of the results shows the accuracy of analytical studies. In addition, close correlation between results obtained from two nonlinear modeling methods depicts that the lumped plasticity approach can be decisively considered as the useful tool for the nonlinear modeling of non-prismatic bridge piers with hollow sections due to its simple modeling assumption and less computational time.
M. B. Esfandiari Sowmehsaraei, R. Jamshidi Chenari,
Volume 12, Issue 1 (1-2014)
Abstract

Soil reinforced with fiber shows characteristics of a composite material, in which fiber inclusion has a significant effect on soil permeability. Concerning to the higher void ratio of carpet fibers, at first stages it may be expected that an increase in fiber content of the reinforced soil would result in an increase in permeability of the mixture. However, the present article demonstrates that fiber inclusion will decrease the permeability of sand-fiber composite.A series of constant head permeability tests have been carried out to show the effects and consequently, a new system of phase relationships was introduced to calculate the dry mass for the sand portion of the composite. Monte Carlo simulation technique adopted with finite element theory was employed to back calculate the hydraulic conductivity of individual porous fibers from the laboratory test results. It was observed that the permeability coefficient of the porous fibers are orders of magnitude less than the skeletal sand portion due to the fine sand particle entrapment and also the fiber volume change characteristics.
E. Lotfi, S. Delfan, A. Hamidi, H. Shahir, Gh. Fardi,
Volume 12, Issue 1 (1-2014)
Abstract

In saturated soils, heating induces thermal expansion of both grains and the pore fluid. Lower thermal expansion coefficient of aggregates results in the increase of pore pressure and reduction of the effective stress besides subsequent volume changes due to the dissipation of pore pressure and heat transfer. Dissipation of thermally induced pore pressure with time is a coupled thermo-hydro-mechanical (THM) phenomenon, involving gradients of pore pressure and temperature, hydraulic and thermal flows within the mass of soil and changes in the mechanical properties with temperature. The objective of this paper is presentation of a numerical method to determine the effect of temperature on consolidation of clays. In this regard, the finite element code, PISA is used for one dimensional THM analysis of porous media. The analysis performed using both linear elastic and elastoplastic Cam clay models. Modified Cam clay model was applied in elastoplastic analysis. Variation of temperature, displacements and pore pressure determined with time and compared with numerical solutions of other researchers. Also it was indicated that implementation of coupled THM analysis yields better results for displacements compared to the hydro mechanical (HM) one. Application of elastoplastic constitutive model instead of linear elastic one indicated that preconsolidation pressure has an important effect on results of analysis.
Kaustav Bakshi, Dipankar Chakravorty,
Volume 12, Issue 2 (6-2014)
Abstract

A review of literature reveals that although singly curved conical shells applicable in many fields of mechanical engineering have been studied by many researchers but doubly curved conoidal shells which are very popular as civil engineering roofing units have not received due attention. Hence relative performances of composite conoidal shells in terms of displacements and stress resultants are studied in this paper under static and dynamic loadings. Free vibration frequencies are also reported. A curved quadratic isoparametric eight noded element is used to model the shell surface. Clamped and simply supported boundary conditions are considered. Results obtained from the present study are compared with established ones to check the correctness of the present approach. A number of additional problems of composite conoidal shells are solved for eight different stacking sequences of graphite-epoxy composite for each of the edge conditions. Uniformly distributed load for static bending analysis and step load of infinite duration for solution of forced vibration problem are considered. The results are interpreted from practical application standpoints and findings that are important for a designer to note, before he decides on the shell combination he will finally adopt among a number of possible options, are highlighted.
A. Kaveh, M.s. Massoudi ,
Volume 12, Issue 2 (6-2014)
Abstract

Formation of a suitable null basis is the main problem of finite elements analysis via force method. For an optimal analysis, the selected null basis matrices should be sparse and banded corresponding to sparse, banded and well-conditioned flexibility matrices. In this paper, an efficient method is developed for the formation of the null bases of finite element models (FEMs) consisting of tetrahedron elements, corresponding to highly sparse and banded flexibility matrices. This is achieved by associating special graphs with the FEM and selecting appropriate subgraphs and forming the self-equilibrating systems (SESs) on these subgraphs. Two examples are presented to illustrate the simplicity and effectiveness of the presented graph-algebraic method.
Wen-Chao Huang,
Volume 12, Issue 3 (7-2014)
Abstract

When geogrid reinforcement is used as a treatment method for improving soft subgrade as a roadway foundation, a top layer of subgrade is usually excavated and backfilled with geogrid-reinforced aggregates. This treatment method produces an adequate platform for the planned roadway construction site, where heavy traffic loading is constantly moving. This paper presents a quantitative assessment of subgrade improvement by geogrid reinforcement based on numerical modelling and parametric studies. First of all, the preliminary numerical models were verified by comparing the analysis results with previous studies. Secondly, the major numerical models in this study were assumed to be a simplified simulation of a geogrid-reinforced two-layer system with an aggregate layer above a subgrade layer. The numerical models were applied a quasi-static loading and unloading cycle, in order to monitor the permanent deformation at the surface of the models. Afterwards, thickness of aggregate layer, and subgrade CBR values were varied in order to summarize the outcomes of each case. This approach makes it possible to quantify the effects of geogrid reinforcement and aggregate material in terms of an enhanced California Bearing Ratio (CBR) of a single subgrade clay layer. Results have shown that when the aggregate thickness is up to 450mm, the contribution of enhanced CBR is mostly from aggregate material. However, when the aggregate thickness is about 150mm with a relatively weak subgrade material, the inclusion of geogrid material can contribute about 50% of the enhanced value.
Khaled Farah, Mounir Ltifi, Tarek Abichou, Hedi Hassis,
Volume 12, Issue 3 (7-2014)
Abstract

The purpose of this study is to compare the results of different probabilistic methods such as the perturbation method, Stochastic Finite Element Method (SFEM) and Monte Carlo Method. These methods were used to study the convergence of direct approach for slope stability analysis and are developed for a linear soil behavior. In this study, two dimensional random fields are used and both the First Order Reliability Method (FORM) and Limited Step Length Iteration Method (LSLIM) have been adopted to evaluate the reliability index. The study found that the perturbation method of the second order is easy to apply using the field’s theory because accuracy is reached even with different coefficients of variation of input variables, while the spectral finite element method yields accurate results only for high levels of solution development.

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