Showing 296 results for An
A. Shamsai, R. Soleymanzadeh,
Volume 4, Issue 1 (March 2006)
Abstract
Flow regime in dam's bottom outlet is divided in pressurized flow and free surface flow by
the gate located for discharge control. Down stream tunnel involves high velocity Multi component
Air –water flow studied by mathematical model. In this research work, we used Finite volume
mixture two phase flow model. Because of high Reynolds number, standard two equations k-e
turbulence model was used. Model was verified by backward-facing step flow and results have been
compared with experiments founded by Durst and Schmitt. Air demand ratio has been determined
as function of Froude number at contracted section. Flow patterns have been compared at two
categories of slug & stratified flows, Air mean concentration profile has been obtained at down
stream tunnel. Comparison of flow pattern at two case with and without of aeration was
investigated. Pressure drop behind of the gate and formation of vortex flow after the gate section
have been discussed. Measurement of flow discharge and determination of contraction coefficient
of the gate was outlined.
B. Saghafian, A.r. Shokoohi,
Volume 4, Issue 1 (March 2006)
Abstract
Time–Area method is one of the most widely applied techniques of watershed routing, and
can be potentially used as a distributed model. In this paper, a fundamental flaw in the arrangement
of subareas in the original time-area histogram is identified for one-dimensional flow. This is
conducted on the basis of comparing time-area hydrograph with that of the kinematic wave theorem.
Accordingly, a revised time-area algorithm is developed as a substitute for the original time-area.
It is proved that in the revised approach, subareas must be reversely arranged. It is also shown that
the revised time-area hydrograph is in perfect agreement with the hydrograph derived by the
kinematics wave theory.
H. Behbahani, S.m. Elahi,
Volume 4, Issue 1 (March 2006)
Abstract
To properly plan for construction, repair, maintenance, and reconstruction of highways the
minimum acceptable roadway condition is needed information. This, along with other pavement
management tools, will help select the most desirable roadway alternatives. In this research the
minimum acceptable conditions are developed based on an opinion survey of non-technical but
high-level decision makers. Roadway roughness, expressed as international roughness index (IRI),
is used as the measurement criteria. Because IRI is a widely known, acceptable, and a uniformly
measurable index, it is used for the purpose of this research. The minimum IRI values developed
here will help managers, planners, and engineers in prioritizing their plans and projects. Iran has
a central planning system, hence having a minimum acceptable IRI will help in producing
homogeneity in decision making. A questionnaire is sent to top level and influential managementlevel
officials who have a decisive input in highway matters. The officials are asked to choose the
minimum acceptable service level of different types of roadways and classifications. Naturally,
roadways with higher levels of importance would require higher service levels. The answers to the
survey questionnaires are investigated to determine a preferred minimum acceptable roadway
condition. The IRI is computed using a mechanical device enabling a more uniform data collection.
The IRI was first proposed by The World Bank as a standard roughness statistic. Extensive research
has proven that the IRI can be related to pavement condition. The result of the opinion survey is
investigated to determine the minimum levels acceptable for each category. The responses show
distinct preference patterns for most of the roadway types. Survey results are investigated by plotting
and analyzing them. Based on road user’s perception of roadway condition using guidelines from
AASHTO, the Corp of Engineers, and related research work. The appropriate IRI limits and ranges
are determined for Iran’s highways. These values are adjusted to obtain final values for Iran. The
result, shown in a table, gives upper and lower IRI values accepted and recommended for Iran’s
highways. The result of this research work is specifically useful in developing specifications for new
pavement design, accepting new pavement from contractors, pavement management, highway
planning, and in roadway life cycle cost analysis decision making. The results are subject to
refinement over time.
A.r. Khoei, S. Yadegari, M. Anahid,
Volume 4, Issue 3 (September 2006)
Abstract
In this paper, a higher order continuum model is presented based on the Cosserat
continuum theory in 3D numerical simulation of shear band localization. As the classical
continuum models suffer from the pathological mesh-dependence in strain softening models, the
governing equations are regularized by adding the rotational degrees-of-freedom to conventional
degrees-of-freedom. The fundamental relations in three-dimensional Cosserat continuum are
presented and the internal length parameters are introduced in the elasto-plastic constitutive matrix
to control the shear bandwidth. Finally, the efficiency of proposed model and computational
algorithm is demonstrated by a 3D strip in tensile. A comparison is performed between the classical
and Cosserat theories and the effect of internal length parameter is demonstrated. Clearly, a finite
shear bandwidth is achieved and the load-displacement curves are uniformly converged upon
different mesh sizes.
H. Soltani-Jigheh, A. Soroush,
Volume 4, Issue 3 (September 2006)
Abstract
This paper presents the results of a series of monotonic and post-cyclic triaxial tests
carried out on a clay specimen and three types of clay-sand mixed specimens. The focus of the paper
is on the post-cyclic mechanical behavior of the mixed specimens, as compared to their monotonic
behavior. Analyses of the tests results show that cyclic loading degrade undrained shear strength
and deformation modulus of the specimens during the post-cyclic monotonic loading. The
degradation depends on the sand content, the cyclic strain level and to some degrees to the
consolidation pressure.
Sh. Afandizadeh Zargari, R. Taromi,
Volume 4, Issue 3 (September 2006)
Abstract
Optimization is an important methodology for activities in planning and design. The
transportation designers are able to introduce better projects when they can save time and cost of
travel for project by optimization methods. Most of the optimization problems in engineering are
more complicated than they can be solved by custom optimization methods. The most common and
available methods are heuristic methods. In these methods, the answer will be close to the optimum
answer but it isn’t the exact one. For achieving more accuracy, more time has been spent. In fact,
the accuracy of response will vary based on the time spent.
In this research, using the generic algorithms, one of the most effective heuristic algorithms, a
method of optimization for urban streets direction will be introduced. Therefore model of decision
making in considered one way – two way streets is developed. The efficiency of model in Qazvin
network is shown and the results compared whit the current situation as case study. The objective
function of the research is to minimize the total travel time for all users, which is one of the most
used in urban networks objectives.
F.m. Wegian, M.t. Alkhamis, S.r. Sabbagh Yazdi,
Volume 4, Issue 4 (December 2006)
Abstract
This study evaluates two different types of techniques for concrete hollow-block sections
reinforced with traditional steel rebars and wire meshes, and compares their structural behaviour
to that of an ordinary reinforced concrete beam section. The comparisons are based on the
responses both before and after they were repaired with glass fibre reinforced polymers (GFRP).
The specimens were subjected to concentrated loading up to initial failure. After failure, the
specimens were repaired and loaded once again until ultimate failure. It was shown that the
success of the repair by GFRP depended on the mode of failure of the hollow-block concrete
beams.
M. Mazloom, A.a. Mehrabian,
Volume 4, Issue 4 (December 2006)
Abstract
The objective of this paper is to present a new method for protecting the lives of residents
in catastrophic earthquake failures of unreinforced masonry buildings by introducing some safe
rooms within the buildings. The main idea is that occupants can seek refuge within the safe rooms
as soon as the earthquake ground motions are felt. The information obtained from the historical
ground motions happened in seismic zones around the globe expresses the lack of enough safety of
masonry buildings against earthquake. For this potentially important reason, an attempt has been
made to create some cost-effective seismic-resistant areas in some parts of the existing masonry
buildings, which are called safe rooms. The practical method for creating these areas and
increasing the occupant safety of the buildings is to install some prefabricated steel frames in some
of their rooms or in their halls. These frames do not carry any service loads before earthquake.
However, if a near field seismic event happens and the load bearing walls of the building destroy,
some parts of its floors, which are in the safe areas, will fall on the roof of the installed frames
consequently, the occupants who have sheltered in the safe rooms will survive. This paper expresses
the experimental and theoretical work executed on the steel structures of the safe rooms for bearing
the shock and impact loads. Finally, it was concluded that both the strength and displacement
capacity of the steel frames were adequate to accommodate the distortions generated by seismic
loads and aftershocks properly.
M.b. Javanbarg, A.r. Zarrati, M.r. Jalili, Kh. Safavi,
Volume 5, Issue 1 (March 2007)
Abstract
In the present study a quasi 2-D numerical model is developed for calculating air concentration distribution in rapid flows. The model solves air continuity equation (convection diffusion equation) in the whole flow domain. This solution is then coupled with calculations of the free surface in which air content in the flow is also considered. To verify the model, its results are compared with an analytical solution as well as a 2-D, numerical model and close agreement was achieved. The model results were also compared with experimental data. This comparison showed that the decrease in air concentration near the channel bed in an aerated flow could be well predicted by the model. The present simple numerical model could therefore be used for engineering purposes.
M. Khanzadi, G. Ghodrati Amiri, G. Abdollahzadeh Darzi,
Volume 5, Issue 1 (March 2007)
Abstract
According to performance-based seismic design method by using energy concept, in this
paper it is tried to investigate the duration and damping effects on elastic input energy due to strong
ground motions. Based on reliable Iranian earthquake records in four types of soils, structures were
analyzed and equivalent velocity spectra were computed by using input energy. These spectra were
normalized with respect to PGA and were drawn for different durations, damping ratios and soil
types and then effects of these parameters were investigated on these spectra. Finally it was
concluded that in average for different soil types when the duration of ground motions increases,
the input energy to structure increases too. Also it was observed that input energy to structures in
soft soils is larger than that for stiff soils and with increasing the stiffness of the earthquake record
soil type, the input energy decreases. But damping effect on input energy is not very considerable
and input energy to structure with damping ratio about 5% has the minimum value.
A. Yeganeh Bakhtiary, A. Ghaheri, R. Valipour,
Volume 5, Issue 1 (March 2007)
Abstract
Determination of allowable free span length plays a crucial role in design of offshore
pipelines. The seabed intervention cost and safety of an offshore pipelines project are largely
influenced by pipelines free spanning during the project life time. Different criteria are proposed by
both the current designing guidelines and researchers there is however lack of comprehensive
assessment of independent parameters affects the design length of free span. In this note, it is
intended to investigate the effects of seabed formation along with axial force on Natural Frequency
of offshore pipelines. Based on this assessment a new simple formula is proposed. Finally, to
evaluate the result of this study, the allowable free span length of Qeshem Island pipelines is
calculated as a case study and compared with those of the DNV (1998) and ABS (2001) guidelines
and the modal analysis.
A. Rahmani Firoozjaee, M.h. Afshar,
Volume 5, Issue 2 (June 2007)
Abstract
A meshless method namely, discrete least square method (DLSM), is presented in the
paper for the solution of free surface seepage problem. In this method computational domain is
discredited by some nodes and then the set of simultaneous equations are built using moving least
square (MLS) shape functions and least square technique. The proposed method does not need any
background mesh therefore it is a truly meshless method. Several numerical two dimensional
examples of Poisson partial differential equations (PDEs) are presented to illustrate the
performance of the present DLSM. And finally a free surface seepage problem in a porous media is
solved and results are presented.
H.r. Ashrafi, A.a. Ramezanianpour,
Volume 5, Issue 3 (September 2007)
Abstract
Deterioration of concrete structures in the Gulf region is a serious problem. Penetration
of Chloride ion into concrete is responsible for such early deterioration. Determination of chloride
diffusion coefficient is an effective way to predict the service life of concrete structures.
In order to investigate the performance of concrete mixtures in such environments, ordinary and
silica fume concrete mixtures containing various water to cementitious materials ratios were used.
Rapid chloride permeability test and determination of diffusion coefficient of chloride ion
penetration in accordance with bulk diffusion test under laboratory conditons simulated to Persian
Gulf climate, and site investigation were performed. Concentration of chloride ions in various
depths of concrete specimens was measured using acid soluble chloride test method.
Test results show that silica fume reduces the chloride penetration and the diffusion coefficient in
concrete mixtures. Different models were made for rapid chloride test results, and diffusion
coefficient, of concretes maintained in the hot and corrosive environments of the Persian Gulf. The
models which were calibrated with real data obtained from the concrete structures are capable to
predict the penetration and service life of concrete structures in such corrosive environments.
F. Amini, R. Vahdani,
Volume 5, Issue 3 (September 2007)
Abstract
In this research, an innovative numerical simulating approach for time domain analysis
of multi degrees of freedom structures with uncertainty in dynamic properties is presented. A full
scale finite element model of multi-story and multi bays of three sample structures has been
constructed. The reduced order model of structure with holding the dominant and effective
Gramians in the balanced state-space realization has been achieved for easy and safe design of the
optimal control forces applied to the structure. Some easy selective control algorithms based on the
Optimal-Stochastic control theories such as LQG, DLQRY and modified sliding mode control has
been programmed with the simulation control sequences. Some real features of accurate control
system such as time delay and noise signals in earthquake time histories and also measurement
sensors are considered in illustrative simulation models. These models can be analyzed under either
various intensity of corresponding earthquakes or desired random excitations passed through the
suitable filters providing stochastic parameters of earthquake disturbances. This control procedure
will be shown to be very efficient suppressing all the severities and difficulties may arise in design
of a multi-objective optimal control system. The obtained results illustrate the feasibility and
applicability of the proposed stochastic optimal control design of active control force providing a
stable and energy-saving control strategy for tall building structures.
S. Eshghi, V. Zanjanizadeh,
Volume 5, Issue 3 (September 2007)
Abstract
This paper presents an experimental study on seismic repair of damaged square reinforced
concrete columns with poor lap splices, 90-degree hooks and widely spaced transverse bars in
plastic hinge regions according to ACI detailing (pre.1971) and (318-02) using GFRP wraps. Three
specimens were tested in “as built” condition and retested after they were repaired by glass fiberreinforced
plastic sheets. They were tested under numerous reversed lateral cyclic loading with a
constant axial load ratio. FRP composite wraps were used for repairing of concrete columns in
critically stressed areas near the column footings. Physical and mechanical properties of composite
wraps are described. Seismic performance and ductility of the repaired columns in terms of the
hysteretic response are evaluated and compared with those of the original columns. The results
indicated that GFRP wraps can be an effective repair measure for poorly confined R/C columns
due to short splice length and widely spaced ties with 90-degree anchorage hooks. Both flexural
strength and ductility of repaired columns were improved by increasing the existing confinement in
critical regions of them.
M. Rezaiee-Pajand, M. Riyazi-Mazloomi,
Volume 5, Issue 3 (September 2007)
Abstract
In this research a new approach is proposed for elasto-plastic analysis of structures with
truss elements. This method covers both perfectly plastic and hardening properties. The Proposed
technique uses substituting virtual loads instead of modifying the stiffness matrix. To solve this kind
of problems, complementary programming is utilized. Numerical examples demonstrate that elastoplastic
analysis by this approach has very good convergence, rapidity, and accuracy.
H. Behbahani, S.a. Sahaf,
Volume 5, Issue 3 (September 2007)
Abstract
The available methods for predicting mechanical characteristics of pavement layers are
categorized into two general groups, Destructive and Non-destructive. In destructive method, using
coring and pavement subgrade and performing necessary experiments on them, the quantities of
layers properties will be identified. In Non-destructive method, the attained deflection is measured
by applying the loading on pavement surface using equipments such as FWD which charges the
impact dynamic load, and the mechanical characteristics of pavement layers are determined using
back calculations. The procedure of conducting these calculations is that by knowing the thickness
of the pavement layers and assuming the initial amounts for mechanical characteristics of the layer,
the attained deflection at the desired points on the pavement surface will be calculated. Then, new
figures are assumed for the characteristics of layers in a reattempt and calculations are repeated
again. This trial and error is continued until the produced basin deformations from the calculations
with true value, differs in an acceptable range. Using this method may have no accurate and single
answer, since the various compositions of layers characteristics can produce similar deformations
in different points of pavement surface. In this article, using an innovative method, a measurement
is taken in constructing and introducing a mathematical model for determining the elastic module
of surface layer using deflections attained from FWD loading equipment. The procedure is such that
by using dynamic analysis software of finite elements like ABAQUS and ANSYS, the deformation of
corresponding points on the surface of the pavement will be attained by FWD loading equipment.
This analysis will be performed on a number of pavements with different thicknesses and different
layers properties. The susceptibility analysis of different points deformations show, which will be
performed as a result of the change of properties and layers thicknesses. Using this artificial data
base as well as deflection basin parameters (DBP), a measurement will be taken toward
constructing a regression model for determination of asphalt layer model, i.e. Eac =f(DBP) function
shall be attained. To achieve the maximum correlation coefficient, an attempt is made to use the
parameters of deformations basin which has the most susceptibility in changing asphalt layer
module.
Faradjollah Askari, Orang Farzaneh,
Volume 6, Issue 1 (March 2008)
Abstract
Although some 3D slope stability algorithms have been proposed in recent three decades, still role
of pore pressures in three dimensional slope stability analyses and considering the effects of pore water
pressure in 3D slope stability studies needs to be investigated. In this paper, a limit analysis formulation for
investigation of role of the pore water pressure in three dimensional slope stability problems is presented. A
rigid-block translational collapse mechanism is used, with energy dissipation taking place along planar
velocity discontinuities. Results are compared with those obtained by others. It was found that water pressure
causes the three-dimensional effects to be more significant, especially in gentle slopes. This may be related to
the larger volume of the failure mass in gentle slopes resulting in more end effects. Dimensionless stability
factors for three dimensional slope stability analyses are presented - including the 3D effect of the pore water
pressure – for different values of the slope angle in cohesive and noncohesive soils.
A. Foroughi-Asl, S. Dilmaghani, H. Famili,
Volume 6, Issue 1 (March 2008)
Abstract
Self-Compacting Concrete (SCC) is a highly fluid yet stable concrete that can flow consistently under
its own weight, pass between bars, and fill in formwork without the need of compaction. The application of
SCC effectively resolves the difficulties of concreting in situations with complicated formwork and congested
reinforcements. In this paper, the bond between SCC and steel reinforcement was investigated. The bonding
strengths of reinforcing bars were measured using cubic specimens of SCC and of normal concrete. The SCC
specimens were cast without applying compaction, whereas the specimens of normal concrete were cast by
conventional practice with substantial compaction and vibration. The results showed that SCC specimens
generated higher bond to reinforcing bars than normal concrete specimens and the correlation between bond
strength and compressive strength of NC is more consistent.
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.