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Showing 30 results for Shi

A. ArdeShir,
Volume 2, Issue 1 (March 2004)
Abstract

In this research a mathematical model was developed to study bed elevation variation of alluvial rivers. It utilizes two principal modules of hydraulics and sediment transport for simulation purposes. SDAR (Scour and Deposition model of Alluvial Rivers) is a new model with both one and semi-two dimensional (S-2D) computational schemes. It is regarded S-2D in a sence that lateral variation of velocity, hydraulic stresses, and geometrical specifications are achieved by dividing the main channel into serveral stream tubes. In order to overcome the existing limitations, a new idea of reachwise stream tube concept was also introduced. This allows to include branch connections and withdrawal points across the tube barriers. Sediment routing and bed variation calculations are accomplished along each river strip desigated by virtual interfaces of the tubes. Presently, quasi-steady gradually varied flows are processed by the model. It should also be emphasised that this version is only valid for alluvial rivers composed of noncohesive bed material. To assess the model, several river cases and laboratory data base were used. During calibration runs, the ability of model in longitudinal and transversal bed profile simulation and armor layer development predection were especially detected. Results of simulation are also compared with the results of well-known models, e.g. HEC-6, GSTARS-2, and FLUVIAL-I2. It was found that the ability of model in simulating bed variation is noticeably increased when S-2D concept is introduced. Indeed, the comparative validity tests confirm SDAR"s promising functioning in facing with complex real engineering cases. Obviously more article discussions would bring oppurtunities to demonestrate it"s technical cappabilities profoundaly.
S.n. Moghaddas TafreShi, Gh. Tavakoli Mehrjardi, S.m. Moghaddas TafreShi,
Volume 5, Issue 2 (June 2007)
Abstract

The safety of buried pipes under repeated load has been a challenging task in geotechnical engineering. In this paper artificial neural network and regression model for predicting the vertical deformation of high-density polyethylene (HDPE), small diameter flexible pipes buried in reinforced trenches, which were subjected to repeated loadings to simulate the heavy vehicle loads, are proposed. The experimental data from tests show that the vertical diametric strain (VDS) of pipe embedded in reinforced sand depends on relative density of sand, number of reinforced layers and height of embedment depth of pipe significantly. Therefore in this investigation, the value of VDS is related to above pointed parameters. A database of 72 experiments from laboratory tests were utilized to train, validate and test the developed neural network and regression model. The results show that the predicted of the vertical diametric strain (VDS) using the trained neural network and regression model are in good agreement with the experimental results but the predictions obtained from the neural network are better than regression model as the maximum percentage of error for training data is less than 1.56% and 27.4%, for neural network and regression model, respectively. Also the additional set of 24 data was used for validation of the model as 90% of predicted results have less than 7% and 21.5% error for neural network and regression model, respectively. A parametric study has been conducted using the trained neural network to study the important parameters on the vertical diametric strain.
S.n. Moghaddas TafreShi, A. Asakereh,
Volume 5, Issue 4 (December 2007)
Abstract

Conventional investigations on the behavior of reinforced and unreinforced soils are often investigated at the failure point. In this paper, a new concept of comparison of the behavior of reinforced and unreinforced soil by estimating the strength and strength ratio (deviatoric stress of reinforced sample to unreinforced sample) at various strain levels is proposed. A comprehensive set of laboratory triaxial compression tests was carried out on wet (natural water content) non-plastic beach silty sand with and without geotextile. The layer configurations used are one, two, three and four horizontal reinforcing layers in a triaxial test sample. The influences of the number of geotextile layers and confining pressure at 3%, 6%, 9%, 12% and 15% of the imposed strain levels on sample were studied and described. The results show that the trend and magnitude of strength ratio is different for various strain level. It implies that using failure strength from peak point or strength corresponding to the axial-strain approximately 15% to evaluate the enhancement of strength or strength ratio due to reinforcement may cause hazard and uncertainty in practical design. Hence, it is necessary to consider the strength of reinforced sample compared with unreinforced sample at the imposed strain level. Only one type of soil and one type of geotextile were used in all tests.
Kourosh Behzadian, Abdollah ArdeShir, Zoran Kapelan, Dragan Savic,
Volume 6, Issue 1 (March 2008)
Abstract

A novel approach to determine optimal sampling locations under parameter uncertainty in a water distribution system (WDS) for the purpose of its hydraulic model calibration is presented. The problem is formulated as a multi-objective optimisation problem under calibration parameter uncertainty. The objectives are to maximise the calibrated model accuracy and to minimise the number of sampling devices as a surrogate of sampling design cost. Model accuracy is defined as the average of normalised traces of model prediction covariance matrices, each of which is constructed from a randomly generated sample of calibration parameter values. To resolve the computational time issue, the optimisation problem is solved using a multi-objective genetic algorithm and adaptive neural networks (MOGA-ANN). The verification of results is done by comparison of the optimal sampling locations obtained using the MOGA-ANN model to the ones obtained using the Monte Carlo Simulation (MCS) method. In the MCS method, an equivalent deterministic sampling design optimisation problem is solved for a number of randomly generated calibration model parameter samples.The results show that significant computational savings can be achieved by using MOGA-ANN compared to the MCS model or the GA model based on all full fitness evaluations without significant decrease in the final solution accuracy.
S. N. Moghaddas TafreShi,
Volume 6, Issue 4 (December 2008)
Abstract

This paper presents the numerical analysis of seismic soil-pile-superstructure interaction in soft clay using free-field soil analysis and beam on Winkler foundation approach. This model is developed to compute the nonlinear response of single piles under seismic loads, based on one-dimensional finite element formulation. The parameters of the proposed model are calibrated by fitting the experimental data of largescale seismic soil-pile-structure tests which were conducted on shaking table in UC Berkeley. A comparative evaluation of single piles shows that the results obtained from the proposed procedure are in good agreement with the experimental results.
S. A. Sadrnejad, S. A. GhoreiShian Amir,
Volume 8, Issue 2 (6-2010)
Abstract

A semi-micromechanical multilaminate model is introduced here to predict the mechanical behavior of soils.

This model is like a bridge between micro and macro scale upon the satisfaction of minimum potential energy level

during any applied stress/strain increments. The concept of this model is based on a certain number of sampling planes

which constitute the elastic-plastic behavior of the soil. The soil behavior presents as the summation of behavior on

these planes. A simple unconventional constitutive equations are used in each of the planes to describe the behavior

of these planes separately. An unconventional plasticity can predict the soil behavior as a smooth curve with

considering plastic deformation due to change of stress state inside the yield surface. The model is capable of

predicting softening behavior of the soil in a reasonable manner due to using unconventional plasticity. The influences

of induced anisotropy are included in a rational way without any additional hypotheses owing to in-nature properties

of the multilaminate framework. Results of this model are compared with test data and reasonable agreement is found.


Mr. Mehdi Mahdavi Adeli, Dr. Mehdi Banazadeh, Dr. ArdeShir Deylami,
Volume 9, Issue 3 (September 2011)
Abstract

The objective of this paper is to determine the drift demand hazard curves of steel moment-resisting frames with different number
of stories in territory of Tehran this is done through the combination of the results obtained from probabilistic seismic hazard
analysis and the demand estimated through the best probabilistic seismic demand models. To select the best demand model, in
this paper, a Bayesian regression has been used for the statistical analysis of the results obtained from incremental dynamic
analysis in order to estimate the unknown parameters of model and to select the best Intensity Measure (IM) parameter also the
probability of overall collapse of structures has been computed. Considering the efficiency and sufficiency of the models, the
results indicate that the accuracy of models with one single IM is a function of the number of stories, consequently the current
widely used model with spectral acceleration in first period as IM is not suitable for all structural heights. Furthermore,
regarding the fact that it is difficult to prepare a seismic hazard curve for a combined IM, it seems that the best model can be
found among models with two single IMs. In other words, the best model to cover all structural heights is the one with linear
combination of spectral acceleration of the first and the second period. Furthermore, using different models to calculate the
curves shows that regardless of the number of IMs, estimated demands strongly depend on the standard deviation of model.

 


AfShin Firouzi, Ali Reza Rahai,
Volume 9, Issue 3 (September 2011)
Abstract

Corrosion of reinforcement due to frequently applied deicing salts is the major source of deterioration of concrete bridge decks, e.g. severe cracking and spalling of the concrete cover. Since crack width is easily recordable in routine visual inspections there is a motivation to use it as an appropriate indicator of condition of RC bridge elements in decision making process of bridge management. While few existing research in literature dealing with spatial variation of corrosion-induced cracking of RC structures is based on empirical models, in this paper the extent and likelihood of severe cracking of a hypothetical bridge deck during its lifetime is calculated based on a recently proposed analytical model for corrosion-induced crack width. Random field theory has been utilized to account for spatial variations of surface chloride concentration, as environmental parameter, and concrete compressive strength and cover depth as design parameters. This analysis enables to track evolution of cracking process, spatially and temporally, and predict the time for the first repair of bridge deck based on acceptable extent of cracked area. Furthermore based on a sensitivity analysis it is concluded that increasing cover depth has a very promising effect in delaying corrosion phenomenon and extension of the service life of bridge decks.


S. N. Moghaddas TafreShi, Gh. Tavakoli Mehrjardi, M. Ahmadi,
Volume 9, Issue 4 (December 2011)
Abstract

The results of laboratory model tests and numerical analysis on circular footings supported on sand bed under incremental

cyclic loads are presented. The incremental values of intensity of cyclic loads (loading, unloading and reloading) were applied

on the footing to evaluate the response of footing and also to obtain the value of elastic rebound of the footing corresponding

to each cycle of load. The effect of sand relative density of 42%, 62%, and 72% and different circular footing area of 25, 50,

and 100cm2 were investigated on the value of coefficient of elastic uniform compression of sand (CEUC). The results show that

the value of coefficient of elastic uniform compression of sand was increased by increasing the sand relative density while with

increase the footing area the value of coefficient of elastic uniform compression of sand was decreases. The responses of footing

and the quantitative variations of CEUC with footing area and soil relative density obtained from experimental results show a

good consistency with the obtained numerical result using “FLAC-3D”.


K. Behzadian, M. Alimohammadnejad, A. ArdeShir, H. Vasheghani, F. Jalilsani,
Volume 10, Issue 1 (March 2012)
Abstract

Compared to conventional chlorination methods which apply chlorine at water treatment plant, booster chlorination has almost

solved the problems of high dosages of chlorine residuals near water sources and lack of chlorine residuals in the remote points

of a water distribution system (WDS). However, control of trihalomethane (THM) formation as a potentially carcinogenic

disinfection by-product (DBP) within a WDS has still remained as a water quality problem. This paper presents a two-phase

approach of multi-objective booster disinfection in which both chlorine residuals and THM formation are concurrently optimized

in a WDS. In the first phase, a booster disinfection system is formulated as a multi-objective optimization problem in which the

location of booster stations is determined. The objectives are defined as to maximize the volumetric discharge with appropriate

levels of disinfectant residuals throughout all demand nodes and to minimize the total mass of disinfectant applied with a specified

number of booster stations. The most frequently selected locations for installing booster disinfection stations are selected for the

second phase, in which another two-objective optimization problem is defined. The objectives in the second problem are to

minimize the volumetric discharge avoiding THM maximum levels and to maximize the volumetric discharge with standard levels

of disinfectant residuals. For each point on the resulted trade-off curve between the water quality objectives optimal scheduling of

chlorination injected at each booster station is obtained. Both optimization problems used NSGA-II algorithm as a multi-objective

genetic algorithm, coupled with EPANET as a hydraulic simulation model. The optimization problems are tested for different

numbers of booster chlorination stations in a real case WDS. As a result, this type of multi-objective optimization model can

explicitly give the decision makers the optimal location and scheduling of booster disinfection systems with respect to the tradeoff

between maximum safe drinking water with allowable chlorine residual levels and minimum adverse DBP levels.


A. Asakereh, S.n. Moghaddas TafreShi, M. Ghazavi,
Volume 10, Issue 2 (June 2012)
Abstract

This paper describes a series of laboratory model tests on strip footings supported on unreinforced and geogrid-reinforced sand
with an inside void. The footing is subjected to a combination of static and cyclic loading. The influence of various parameters
including the embedment depth of the void, the number of reinforcement layers, and the amplitude of cyclic load were studied.
The results show that the footing settlement due to repeated loading increased when the void existed in the failure zone of the
footing and decreased with increasing the void vertical distance from the footing bottom and with increasing the reinforcement
layers beneath the footing. For a specified amplitude of repeated load, the footing settlement is comparable for reinforced sand,
thicker soil layer over the void and much improved the settlement of unreinforced sand without void. In general, the results
indicate that, the reinforced soil-footing system with sufficient geogride-reinforcement and void embedment depth behaves much
stiffer and thus carries greater loading with lower settlement compared with unreinforced soil in the absent of void and can
eliminate the adverse effect of the void on the footing behavior. The final footing settlement under repeated cyclic loading becomes
about 4 times with respect to the footing settlement under static loading at the same magnitude of load applied.


A. Eslami Kenarsari, R. JamShidi Chenari, A. Eslami,
Volume 11, Issue 1 (Transaction B: Geotechnical Engineering, May 2013)
Abstract

Among the different ways of in-situ soil investigation, cone penetration test data are selected to evaluate the spatial variability

of geomaterials and the scale of fluctuations is chosen to evaluate the correlation structure of CPT data. In this regard six case

studies in sandy materials from Australia, U.S.A. and Iraq are selected. Various techniques for the calculation of the scale of

fluctuation of geotechnical parameters are suggested in literature e.g. VXP, SAI, AMF, BLM and VRF without any preference or

privilege for any specific procedure. In order to isolate the stochastic portion of cone tip resistance, deterministic trend was first

removed by regression analysis. This study suggests that quadratic trend removal is more suitable for selected CPT data

soundings. The closeness of the estimated scale of fluctuation using different approaches is assessed too. Mean value of the scale

of fluctuation by five established methods ranges between 0.44 to 1.52 meter for six different cases and the coefficient of

variation for the scale of fluctuation calculated by these methods varies between 12 to 27 % showing that available established

methods produce almost compatible and comparable results.


P. VahabkaShi, A. R. Rahai, A. Amirshahkarami,
Volume 12, Issue 1 (Transaction A: Civil Engineering March 2014)
Abstract

Piles or drilled shafts used in bridge foundation, waterfronts, and high rise buildings are generally subjected to lateral loads. In order to study the effect of concrete pile geometry on the structural behavior in layered soils, several models with different shapes and dimensions for piles and different properties for two soil layers with variable thickness were selected and analyzed using the finite difference method. The performance of piles situated in layered granular soil with different compaction and thicknesses were studied in two cycles of lateral loading and unloading. The applied finite difference procedure is also validated based on experimental and published results. The pile head displacement of different models due to their overall deformation and rotation were calculated under maximum loading. For a comparison of pile head displacement due to their overall deformation and rotation in different models, the "performance index” is defined as the ratio of “displacement due to deformation” to the “total displacement”.
M. B. Esfandiari Sowmehsaraei, R. JamShidi Chenari,
Volume 12, Issue 1 (Transaction B: Geotechnical Engineering, January 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.
S. N. Moghaddas TafreShi, T. Nouri. A,
Volume 12, Issue 2 (Transaction B: Geotechnical Engineering April 2014)
Abstract

This paper presents a simple solution based on the limit equilibrium of sliding soil wedge of reinforced backfill subjected to the horizontal acceleration in the framework of the pseudo-static method. In particular, contrary to most studies on the reinforced retaining wall, the solution proposed in this study, takes into account the effect of the uniform surcharge on the reinforced backfill soil and of its distance from the face of the wall. The results are investigated in dimensionless form of the maximum reinforcement required strength (Kmax), the dimension of the sliding wedge (Lc/H), and the factor of safety (FS). Compared to the reinforced backfill without surcharge, the presence of surcharge over the reinforced backfill and of its distance from the top of the backfill have significant effects on the stability of the system. For a fixed surcharge, a minimum distance of surcharge exists for which the presence of the surcharge does not affect the solution and the failure mechanism is that corresponding to the case of system with no surcharge. A detailed design example is included to illustrate usage of proposed procedures. Comparisons of the present results with available results show a favorable agreement.
R. JamShidi Chenari, P. Pishgah ,
Volume 12, Issue 2 (Transaction B: Geotechnical Engineering April 2014)
Abstract

In this technical note, a methodology is introduced for reliability calculation of consolidation settlement based on cone penetration test (CPT) data. The present study considers inherent soil variability which influences consolidation settlements results. To proceed reliability analysis, the measured data of a sample corrected cone tip resistance (􀝍􀯧) is detrended using a quadratic trend and the residuals are assumed to be lognormally distributed random field. Realizations of 􀝍􀯧 is generated by using spatial variability of residuals including standard deviation and the scale of fluctuation. The quadratic trend and the generated residuals are then combined to correlate shear and bulk modulus as input consolidation properties for coupled analysis and subsequently consolidation settlement was calculated by using finite difference method adopted in Monte Carlo simulations. The results of reliability analysis are presented describing the range of possible settlements by considering characteristics of uncertainties involved at the particular site. Number of realizations rendering settlements smaller than the allowable settlement must be such that guarantee proper performance or acceptable reliability index.
Jui-Chao Kuo, Teng-Yi Kuo, Cheng-Han Wu, Shih-Heng Tung, Ming-Hsiang Shih , Wen-Pei Sung, Weng-Sing Hwang,
Volume 12, Issue 2 (Transaction A: Civil Engineering, June 2014)
Abstract

In this study digital image correlation (DIC) technique combined with a high speed video system was used to predict movement of particles in a water model. Comparing with Particle-image velocimetry (PIV) technique, it provides a low cost alternative approach to visualize flow fields and was successfully employed to predict the movement of particles in a water model at different submergence depth using gas injection. As the submergence depth increases, the number of the exposed eye is reduced accordingly. At 26.4 cm submergence depth, an exposed eye was found at 1/3 of the submergence depth, whereas two exposed eyes were observed at 1/2 depth and near the bottom wall at 24 cm submergence depth.
Kaustav BakShi, Dipankar Chakravorty,
Volume 12, Issue 2 (Transaction A: Civil Engineering, June 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.
Ali Kavand, S.mohsen Haeri, Arian Asefzadeh, Iraj Rahmani, Abbas Ghalandarzadeh, Ali BakhShi,
Volume 12, Issue 3 (Transaction B: Geotechnical Engineering, July 2014)
Abstract

In this paper, different aspects of the behavior of 2×2 pile groups under liquefaction-induced lateral spreading in a 3-layer soil profile is investigated using large scale 1-g shake table test. Different parameters of the response of soil and piles including time-histories of accelerations, pore water pressures, displacements and bending moments are presented and discussed in the paper. In addition, distribution of lateral forces due to lateral spreading on individual piles of the groups is investigated in detail. The results show that total lateral forces on the piles are influenced by the shadow effect as well as the superstructure mass attached to the pile cap. It was also found that lateral forces exerted on the piles in the lower half of the liquefied layer are significantly larger than those recommended by the design code. Based on the numerical analyses performed, it is shown that the displacement based method is more capable of predicting the pile group behavior in this experiment comparing to the force based method provided that the model parameters are tuned.
Nader Shariatmadari, Amir Hossein Sadeghpour, FarShid Razaghian,
Volume 12, Issue 3 (Transaction B: Geotechnical Engineering, July 2014)
Abstract

This research shows the results of studies carried out to define and analyze the effect of aging on MSW behavior of Kahrizak Landfill, the biggest landfill in Iran. Studied samples consisted of fresh samples and also aged ones with 5.5, 14 and 21 years of age which were obtained by mechanical excavators in aged burial locations. Analyzing variation in MSW components illustrates that paste fraction of MSW decreases due to aging process while fibers show a rising trend. Also the moisture content and the organic content of MSW reduce below half of the initial values while the degree of decomposition (DOD) increase up to almost 60% after 14 years. These variations over the time are significantly related to the burying methods and environmental condition of burying location. Shear strength behavior of MSW material was analyzed by some CU tests using large scale triaxial apparatus (D=150mm, H=300mm) on remolded MSW specimens. General observations depict that with an increase in strain level, loading rises without any peak point on stress-strain curves. Fresh samples represent the lowest shear strength followed by 21, 14 and 5.5 year-old samples respectively. There is a direct relationship between fiber content and shear strength. Internal friction angle of aged samples decreases in comparison with fresh ones while cohesion has an inverse trend and rises over the time. According to the effect of burying condition on MSW characteristics, it seems that DOD factor is a more appropriate factor than age in order to analyze long-term behavior of MSW.

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