Showing 9 results for Ghasemi
M.h. Afshar, M.r. Ghasemi,
Volume 3, Issue 2 (June 2005)
Abstract
An efficient selection operator for use in genetic search of pipe networks optimal design
is introduced in this paper. The proposed selection scheme is the superior member of a family of
improved selection operators developed in an attempt to more closely simulate the main features of
the natural mating process which is not reflected in existing selection schemes. The mating process
occurring in the nature exhibits two distinct features. First, there is a competition between
phenotypes looking for the fittest possible mate which usually ends up with choosing a mate with
more or less the same fitness. Second, and more importantly, the search for a mate is often confined
to a community of phenotypes rather than the whole population. Four different selection operators
simulating these features in a random and pre-determined manner are developed and tested. All the
selection schemes exhibit good convergence characteristics, in particular the one in which both the
size of the sub-community and the pair of the mates in the sub-community are determined randomly.
The efficiency of the proposed selection operator is shown by applying the method for the optimal
design of three well-known benchmark networks, namely two-loop, Hanoi and New-York networks.
The proposed scheme produces results comparable to the best results presented in the literature
with much less computational effort
M. Heidarzadeh, A.a. Mirghasemi, S. Etemadzadeh,
Volume 5, Issue 1 (March 2007)
Abstract
A new chemical grouting method has been developed for conglomerate formations based
on the experimental studies. Due to the lack of chemical grouting experience of conglomerate
formations, the testing programs were performed to evaluate the performance of chemical grouting
in the water sealing of part of conglomerate foundation of Karkheh earth dam using a combination
of field and laboratory tests. First, the chemical grouts alone were examined with regard to
viscosity-time behavior, gelation time, temperature-influence, stability, and deformability. These
laboratory tests, led to the selection of the final chemical grout which was a solution of sodium
silicate, water, and ethyl acetate as reactant. The second step tested grout-soil interaction: The
injectability and permeability reduction of the selected chemical grout was examined in field
injection tests. In this step two field tests were performed including shallow test holes without
hydrostatic pressure and full scale tests under dam real hydrostatic pressure head. Based on these
two field injection tests, performed in the conglomerate foundation of Karkheh dam, a new chemical
grouting method for conglomerate formations is proposed and satisfactory results led to the
recommendation of this method for eventually successful application.
H. Shakib, A. Ghasemi,
Volume 5, Issue 4 (December 2007)
Abstract
An attempt has been made to explore the general trends in the seismic response of planasymmetric
structures when subjected to near-fault and far-fault ground motions. Systems with
structural wall elements in both orthogonal directions considering actual and common nonlinear
behavior under bi-directional excitation were studied. Idealized single-storey models with uni-axial
eccentricity were employed. The main findings are: The rotational response trend considering
actual behavior method would be different from common behavior method assumption, when the
system subjected to near-fault motions. In the former case, the minimum rotational response could
be achieved, when stiffness and strength centers are located on opposite side of the mass center. In
the latter case, stiffness eccentricity determines the minimum and maximum rotational response.
General trends in the rotational demand for far-fault motions, considering two type behavior
assumptions, are similar to the last case. Moreover, in near-fault motions, when stiffness and
strength centers are located on opposite side of the mass center, stiff side displacement demand
would be greater than that soft side which is contrary to the conventional guidelines. While, in farfault
motions similar to near-fault motions which stiffness and strength centers are located on one
side of the mass center, displacement demand would be according to conventional guidelines.
P. Ghoddousi, A.m. Raiss Ghasemi, T. Parhizkar,
Volume 5, Issue 4 (December 2007)
Abstract
Plastic shrinkage is one of the most important parameter which must be considered in hot
weather concreting. If plastic shrinkage is not prevented, cracking will be significant, especialy if
silica fume is used in the mix. In this paper, the effect of silica fume in bleeding and evaporation was
investigated in laboratory. The results showed that in restrained shrinkage, beside relative humidity,
temperature and wind velocity, sun rediation also is very important factor in evaporation rate. It is
found that under solar radition condition, the evaporation was much larger than the estimated value
in ACI 305 Nomogram. The rate of evaporaion under solar radiation was about two folds of
evaporation rate under shade condition.
The results showed that in terms of crack initiation time, crack width and total cracking area,
concrete containing silica fume is more severe than concrete with no silica fume. Reduction of water
cement ratio in concrete with silica fume makes the concrete more sensitive in cracking. The results
of this project also showed that the severity of the cracking is not related only to rate of bleeding
but all environmental factors including like sun radiation or shading and also mix compositions
have important roles.
S. Bakhtiyari, A. Allahverdi, M. Rais-Ghasemi, A. A. Ramezanianpour, T. Parhizkar, B. A. Zarrabi,
Volume 9, Issue 3 (September 2011)
Abstract
Self Compacting Concrete (SCC) specimens with limestone (L) and quartz (Q) powders were formulated. The influence of the type
of the powder on the properties of fresh and hardened concrete was evaluated. Dense packing theories were used for mix design
of samples. The equation of Fuller and Thompson for particle size distribution (PSD) of aggregates was modified with considering
fine particles and a proper PSD curve was obtained for SCC. Experimental results showed that this method needs use of less
powder content and results in higher strength/cement ratio compared to traditional mixing methods. No significant difference was
observed between the compressive strengths of specimens containing limestone (L-specimens) and quartz (Q-specimens) powders,
with similar proportions of materials. The residual compressive strength of specimens was examined at 500°C and contradictory
behaviors were observed. One Q-specimen suffered from explosive spalling, while no spalling was occurred for L-specimens. On
the other hand, the residual strength of remained Q-specimens showed considerable increase compared to L-specimens. The results
show the necessity for more detailed investigations considering different effective parameters.
A. R. Majidi, A.a. Mirghasemi, M. Arabshahi,
Volume 9, Issue 4 (December 2011)
Abstract
In the current study, an effort is made to determine three dimensional bearing capacity of rectangular foundations using Discrete
Element Method. The soil mass is modeled as discrete blocks connected with Winkler springs. Different factors affect the geometry
of failure surface. Six independent angles are used to define the failure surface. By trial and error, the optimum shape of failure
surface beneath the foundation can be found. The paper includes the derivation of the governing equations for this DEM based
formulation in three dimensional state as well as parametric sensitivity analyses and comparison with other methods. Moreover,
using the current method, bearing capacity coefficients are presented for various friction angles and foundation aspect ratios.
M. Heidarzadeh, A.a. Mirghasemi, S. M. Sadr Lahijani, F. Eslamian,
Volume 11, Issue 1 (Transaction B: Geotechnical Engineering, May 2013)
Abstract
In a rare engineering experience throughout the world, we successfully stabilized relatively coarse materials of drain using
cement grouting. The grouting work was performed at the Karkheh earth dam, southwest Iran, and was part of the efforts to
extend the dam’s cut-off wall. Since the dam was completed, the execution of the new cut-off wall from the dam crest was
inevitable. Hence, one of the main difficulties associated with the development of the new cut-off wall was trenching and execution
of plastic-concrete wall through the relatively coarse materials of drain in the dam body. Due to high permeability of drain, the
work was associated with the possible risk of excessive slurry loss which could result in the collapse of the trench. In order to
achieve an appropriate grouting plan and to determine the mix ratio for the grouting material, a full-scale test platform consisting
of actual drain materials was constructed and underwent various tests. Results of the testing program revealed that a grouting
plan with at least 2 grouting rows and a Water/Cement mix ratio of 1/ (1.5-2) can successfully stabilize the drain materials. After
finalizing the technical characteristics of the grouting work, the method was applied on the drain materials of the Karkheh dam
body. The results were satisfactory and the drain materials were stabilized successfully so that the cut-off wall was executed
without any technical problem.
A. Ardeshir, M. Amiri, Y. Ghasemi, M. Errington,
Volume 12, Issue 4 (Transaction A: Civil Engineering December 2014)
Abstract
In the water industry tunnels can be used to transfer water from a basin to other areas over varying distances. The construction of such tunnels is inherently risky and can result in unpredicted events and incidents. It is therefore necessary that thorough risk assessments are carried out as a priority of the owner, contractor and consultant organization. This is so that, through a systematic and logical plan, they can risk posed by these unforeseen events and incidents. In this paper, the risks and their main causes which are often encountered in such projects are identified and assessed. A fault tree method is applied in order to identify the main causes of events and incidents. By its nature a Risk assessment cannot be defined by absolute values and so fuzzy data must be used in order to calculate the probability of incidence and the severity of the risk. This is done on the four main criteria of time, cost, quality and safety. In order to estimate the significance of each criterion and to calculate the significance of the total influence of risk Analytic Hierarchy Process (AHP) is applied. In this paper the case study of Dasht-e Zahab water conveyance tunnel has been selected for discussion as it was subjected to severe and multiple hazards. The results obtained using the method were validated by conducting different interviews with the field experts. It was concluded that by applying the proposed methodology on the case study the risks of the project can be evaluated in a more methodical and accurate way than could be done without using the method. This approach is therefore recommended for similar types of projects where there are complicated risks that must be thoroughly investigated and understood.
M. Heidarzadeh, A. A. Mirghasemi, H. Niroomand,
Volume 13, Issue 1 (Transaction B: Geotechnical Engineering March 2015)
Abstract
We report engineering experiences from the critical task of relief well installation under high artesian flow conditions at the downstream toe of the Karkheh earth dam, Iran. Due to the establishment of excessive uplift pressure at the downstream toe of the Karkheh dam, installation of a series of new relief wells was considered to permanently relieve part of these pressures. The mentioned uplift pressure, as high as around 30 m above the ground level, was produced in a confined conglomerate aquifer bounded above and below by relatively impervious mudstone layers which reduced the safety factor of the dam toe to below 1.0. Investigations on the shortcomings of the old relief wells installed at the dam site showed that the main problems were: insufficient well numbers, insufficient well diameters, irregular well screens causing their blockage by time passing, and insufficient total opening area. Despite engineering difficulties and associated risk of downstream toe instability, installation of new relief wells was successfully completed under high artesian flow conditions” was successfully completed. The employed technique for the construction of the new relief wells under flowing artesian conditions was based on: 1) cement grouting and casing of the well, 2) telescopic drilling, 3) application of appropriate drilling fluid, and 4) controlling the artesian flow by adding a long vertical pipe to the top of the relief wells. Numerical modeling of seepage for the Karkheh dam foundation showed that, as a result of the installation of the new relief wells, the safety factor of the downstream toe increased to the safe value of 1.3 for the normal reservoir water level.