Showing 192 results for Ma
A.a. Maghsoudi, H. Akbarzadeh Bengar,
Volume 5, Issue 2 (June 2007)
Abstract
Limit to the tension reinforcement ratio ( ρ) in flexural high strength reinforced concrete
(HSRC) members is based on the requirement that tension failure as sufficient rotation capacity are
ensured at ultimate limit state. However, the provisions for the total amount of longitudinal
reinforcement ratio ( ρ and ρ’) are not associated with any rational derivation. In this paper, a
quantitative measure to evaluate an upper limit to the compression reinforcement ratio ρBmax of
flexural HSRC members is proposed. The quantitative criterion to ρBmax can be derived from i) steel
congestion and ii) considerations that are related to the diagonal compression bearing capacity of
the members.
In this paper it is shown that, when shear loading is dominant, the limit to is set by the diagonal
compression criterion. Parameters that affect this limit are deeply investigated and the expressions
were derived for different end conditions, to provide an additional tool for a better design and
assessment of the flexural capacity of HSRC members.
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.
Hon.m. Asce, M.r. Jalali, A. Afshar, M.a. Mariño,
Volume 5, Issue 4 (December 2007)
Abstract
Through a collection of cooperative agents called ants, the near optimal solution to the
multi-reservoir operation problem may be effectively achieved employing Ant Colony Optimization
Algorithms (ACOAs). The problem is approached by considering a finite operating horizon,
classifying the possible releases from the reservoir(s) into pre-determined intervals, and projecting
the problem on a graph. By defining an optimality criterion, the combination of desirable releases
from the reservoirs or operating policy is determined. To minimize the possibility of premature
convergence to a local optimum, a combination of Pheromone Re-Initiation (PRI) and Partial Path
Replacement (PPR) mechanisms are presented and their effects have been tested in a benchmark,
nonlinear, and multimodal mathematical function. The finalized model is then applied to develop an
optimum operating policy for a single reservoir and a benchmark four-reservoir operation problem.
Integration of these mechanisms improves the final result, as well as initial and final rate of
convergence. In the benchmark Ackley function minimization problem, after 410 iterations, PRI
mechanism improved the final solution by 97 percent and the combination of PRI and PPR
mechanisms reduced final result to global optimum. As expected in the single-reservoir problem,
with a continuous search space, a nonlinear programming (NLP) approach performed better than
ACOAs employing a discretized search space on the decision variable (reservoir release). As the
complexity of the system increases, the definition of an appropriate heuristic function becomes more
and more difficult this may provide wrong initial sight or vision to the ants. By assigning a
minimum weight to the exploitation term in a transition rule, the best result is obtained. In a
benchmark 4-reservoir problem, a very low standard deviation is achieved for 10 different runs and
it is considered as an indication of low diversity of the results. In 2 out of 10 runs, the global optimal
solution is obtained, where in the other 8 runs results are as close as 99.8 percent of the global
solution. Results and execution time compare well with those of well developed genetic algorithms
(GAs).
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.
Abbas Afshar, S. Ali Zahraei, M. A. Marino,
Volume 6, Issue 1 (March 2008)
Abstract
In a large scale cyclic storage system ,as the number of rule parameters and/or number of operating
period increase, general purpose gradient-based NLP solvers and/or genetic algorithms may loose their
merits in finding optimally feasible solution to the problem. In these cases hybrid GA which decomposes the
main problem into two manageable sub-problems with an iterative scheme between GA and LP solvers may
be considered as a sound alternative This research develops a hybrid GA-LP algorithm to optimally design
and operate a nonlinear, non-convex, and large scale lumped cyclic storage system. For optimal operation of
the system a set of operating rules are derived for joint utilization of surface and groundwater storage
capacities to meet a predefined demand with minimal construction and operation cost over a 20 seasonal
planning period. Performance of the proposed model is compared with a non-cyclic storage system. The
management model minimizes the present value of the design and operation cost of the cyclic and non-cyclic
systems under specified and governing constraints, employing the developed GA-LP hybrid model. Results
show that cyclic storage dominates non-cyclic storage system both in cost and operation flexibility.
M.a. Khan, A. Usmani, S.s. Shah, H. Abbas,
Volume 6, Issue 2 (June 2008)
Abstract
In the present investigation, the cyclic load deformation behaviour of soil-fly ash layered system is
studied using different intensities of failure load (I = 25%, 50% and 75%) with varying number of cycles (N =
10, 50 and 100). An attempt has been made to establish the use of fly ash as a fill material for embankments of
Highways and Railways and to examine the effect of cyclic loading on the layered samples of soil and fly ash.
The number of cycles, confining pressures and the intensity of loads at which loading unloading has been
performed were varied. The resilient modulus, permanent strain and cyclic strength factor are evaluated from
the test results and compared to show their variation with varying stress levels. The nature of stress-strain
relationship is initially linear for low stress levels and then turns non-linear for high stress levels. The test
results reveal two types of failure mechanisms that demonstrate the dependency of consolidated undrained
shear strength tests of soil-fly ash matrix on the interface characteristics of the layered soils under cyclic
loading conditions. Data trends indicate greater stability of layered samples of soil-fly ash matrix in terms of
failure load (i) at higher number of loading-unloading cycles, performed at lower intensity of deviatoric stress,
and (ii) at lower number of cycles but at higher intensity of deviatoric stress.
Mahmoud Hassanlourad, Hosein Salehzadeh, Habib Shahnazari,
Volume 6, Issue 2 (June 2008)
Abstract
In this paper shear behavior of two calcareous sands having different physical properties are
investigated using drained and undrained triaxial tests. The investigated sands are obtained from two different
zones located in Persian Gulf, Kish Island and Tonbak region. Analysis based on energy aspects show that
friction angle in these soils, having crushable particles, is formed of three components: substantial internal
friction angle, dilation and particle breakage angle. Dilation component is available in the two investigated
sand. Particle breakage component is a function of grains hardness, structure and geometry shape. Particles
breakage decreases the volume of sample during drained tests and creates positive pore water pressure during
undrained tests. Two investigated sands show different amount of dilation and particle breakage under similar
conditions. Simultaneous dilation and particles crushing and different amount of them result in different shear
behavior of the two studied sands. Energy aspects are used to determine the effect of particle crushing on the
shear strength. There is a suitable compatibility between relative breakage of grains and consumed energy
ratio for particle breakage.
Kourosh Shahverdiani, Ali Reza Rahai, Faramarz Khoshnoudian,
Volume 6, Issue 2 (June 2008)
Abstract
Large capacity cylindrical tanks are used to store a variety of liquids. Their Satisfactory
performance during earthquake is crucial for modern facilities. In present paper, the behavior of cylindrical
concrete tanks under harmonic excitation is studied using the finite element method. Liquid sloshing, liquid
viscosity and wall flexibility are considered and additionally excitation frequency, liquid level and tank
geometry is investigated. The results show a value for wall thickness to tank diameter ratio which may be used
as a guide in the consideration of wall flexibility effects.
Mehdi Poursha, Faramarz Khoshnoudian, Abdoreza S. Moghadam,
Volume 6, Issue 2 (June 2008)
Abstract
The nonlinear static pushover analysis technique is mostly used in the performance-based design of
structures and it is favored over nonlinear response history analysis. However, the pushover analysis with
FEMA load distributions losses its accuracy in estimating seismic responses of long period structures when
higher mode effects are important. Some procedures have been offered to consider this effect. FEMA and
Modal pushover analysis (MPA) are addressed in the current study and compared with inelastic response
history analysis. These procedures are applied to medium high-rise (10 and 15 storey) and high-rise (20 and
30 storey) frames efficiency and limitations of them are elaborated. MPA procedure present significant
advantage over FEMA load distributions in predicting storey drifts, but the both are thoroughly unsuccessful
to predict hinge plastic rotations with acceptable accuracy. It is demonstrated that the seismic demands
determined with MPA procedure will be unsatisfactory in nonlinear systems subjected to individual ground
motions which inelastic SDF systems related to significant modes of the buildings respond beyond the elastic
limit. Therefore, it’s inevitable to avoid evaluating seismic demands of the buildings based on individual
ground motion with MPA procedure.
Mohammad Reza Kavian Pour, H.r. Masoumi ,
Volume 6, Issue 3 (September 2008)
Abstract
Hydraulics of stepped spillway is a very complicated phenomenon, as it consists of a two phase flow passing through a set of designed steps. The steps increase the rate of energy dissipation taking place on the spillway face. Turbulence, flow aeration and energy dissipation are the main tasks in the design of such structures. This study consists of the experimental investigation to determine the energy dissipation over stepped spillways. Experiments conducted at Water Research Institute on two physical models of the Siyah Bisheh stepped spillways in Iran. To develop a more generalized expression, the results of previous investigations were also considered in our study. Therefore, a wide range of variables were taken into account to estimate the energy dissipation along the non-uniform flow regime. Assuming the energy dissipation along the uniform flow regime to be equal to the vertical displacement of the jet, the total energy lost was calculated. A comparison of the results with those of measurements showed a regression of 0.92 for the total energy dissipation, which is one of the features of the present method for estimating of the energy dissipation, compared with the previous investigation.
Shahram Feizee Masouleh, Kazem Fakharian,
Volume 6, Issue 3 (September 2008)
Abstract
A finite-difference based continuum numerical model is developed for the pile-soil dynamic response
during pile driving. The model is capable of simulating the wave propagation analysis along the pile shaft and
through the soil media. The pile-soil media, loading and boundary conditions are such that axisymmetric
assumption seems to be an optimized choice to substantially reduce the analysis time and effort. The
hydrostatic effect of water is also considered on the effective stresses throughout the soil media and at the pilesoil
interface. The developed model is used for signal matching analysis of a well-documented driven pile. The
results showed very good agreement with field measurements. It is found that the effect of radiation damping
significantly changes the pile-soil stiffness due to the hammer blow. The pile tip response shows substantial
increase in soil stiffness below and around the pile tip due to driving efforts.
G. Ghodrati Amiri, F. Manouchehri Dana, S. Sedighi,
Volume 6, Issue 3 (September 2008)
Abstract
By application of design spectra in seismic analyses, determination of design spectra for different
site conditions, magnitudes, safety levels and damping ratios will improve the accuracy of seismic analysis
results. The result of this research provides different design acceleration spectra based on Iran earthquakes
database for different conditions. For this purpose first a set of 146 records was selected according to
causative earthquake specifications, device error modification and site conditions. Then the design
acceleration spectra are determined for 4 different site conditions presented in Iranian code of practice for
seismic resistant design of buildings (Standard No. 2800), different magnitudes (MsO5.5 & Ms>5.5), different
damping ratios (0, 2, 5, 10, 20 percent) and also various safety levels (50% & 84%). Also this research
compares the determined design spectra with those in Standard No. 2800.
S.h. Ebrahimi, S. Mohammadi, A. Asadpoure,
Volume 6, Issue 3 (September 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.
Mahmood R. Abdi, Ali Parsapajouh, Mohammad A. Arjomand,
Volume 6, Issue 4 (December 2008)
Abstract
Clay soils and their related abnormal behavior such as excessive shrinkage, swelling, consolidation settlement and cracking on drying has been the subject of many investigations. Previous studies mainly evaluated the effects of additives such as lime, cement and sand on these characteristics. Initial results indicated that the soil characteristics were improved. However, reportedly in many cases, these additives resulted in a decrease in plasticity and increase in hydraulic conductivity. As a result, there has been a growing interest in soil/fiber reinforcement. The present investigation has focused on the impact of short random fiber inclusion on consolidation settlement, swelling, hydraulic conductivity, shrinkage limit and the development of desiccation cracks in compacted clays. To examine the possible improvements in the soil characteristics, samples consisting of 75% kaolinite and 25% montmorillonite were reinforced with 1, 2, 4 and 8 percent fibers as dry weight of soil with 5, 10 and 15mm lengths. Results indicated that consolidation settlements and swelling of fiber reinforced samples reduced substantially whereas hydraulic conductivities increased slightly by increasing fiber content and length. Shrinkage limits also showed an increase with increasing fiber content and length. This meant that samples experienced much less volumetric changes due to desiccation, and the extent of crack formation was significantly reduced.
A. Hamidi, M. Alizadeh, S.m. Soleimani,
Volume 7, Issue 1 (March 2009)
Abstract
There are limitations in experimental studies on sand-gravel mixtures due to the small size of testing
specimens. Due to this problem, many researchers have worked on prediction of the shear strength of mixture by testing
the sandy fraction of soil alone and developed empirical relationships. Most of the previous relationships have been
determined for low surcharge pressures in which particle breakage does not affect the shear strength parameters.
However, the particle breakage affects the relationships in higher confinements. At the present study, the results of
large scale direct shear tests on sand and sand-gravel mixtures was used to investigate the shear behavior and
dilatancy characteristics in a wider range of surcharge pressures. The gravel content, relative density, surcharge
pressure and gravel grain size were considered as variables in testing program. The relationships between shear
strength characteristics of sand and sand-gravel mixtures were determined considering dilation characteristics of the
soil. In this regard, the minimum void ratio was found as a useful indirect index that relates uniquely to the critical
state friction angle independent of soil gradation. The relations between critical state or peak friction angles of the
mixture with minimum void ratio were determined as a function of surcharge pressure. The correlations could be useful
for determination of the strength parameters of sand-gravel composites by testing sandy fraction of mixture.
Mohammad Naisipour, Mohammad Hadi Afshar, Behrooz Hassani, Ali Rahmani Firoozjaee,
Volume 7, Issue 1 (March 2009)
Abstract
A meshless approach, collocation discrete least square (CDLS) method, is extended in this paper, for solving
elasticity problems. In the present CDLS method, the problem domain is discretized by distributed field nodes. The field
nodes are used to construct the trial functions. The moving least-squares interpolant is employed to construct the trial
functions. Some collocation points that are independent of the field nodes are used to form the total residuals of the
problem. The least-squares technique is used to obtain the solution of the problem by minimizing the summation of the
residuals for the collocation points. The final stiffness matrix is symmetric and therefore can be solved via efficient
solvers. The boundary conditions are easily enforced by the penalty method. The present method does not require any
mesh so it is a truly meshless method. Numerical examples are studied in detail, which show that the present method
is stable and possesses good accuracy, high convergence rate and high efficiency.
A.a. Maghsoudi, H. Akbarzadeh Bengar,
Volume 7, Issue 1 (March 2009)
Abstract
Limit to the tension reinforcement ratio in flexural high strength reinforced concrete (HSRC) members is
based on the requirement that tension failure as sufficient rotation capacity are ensured at ultimate limit state.
However, the provisions for the total amount of longitudinal reinforcement ratio ( and ) are not associated with
any rational derivation. In this paper, a quantitative measure to evaluate an upper limit to the compression
reinforcement ratio of flexural HSRC members is proposed. The quantitative criterion to can be derived
from i) steel congestion and ii) considerations that are related to the diagonal compression bearing capacity of the
members. In this paper it is shown that, when shear loading is dominant, the limit to is set by the diagonal
compression criterion. Parameters that affect this limit are deeply investigated and the expressions were derived for
different end conditions, to provide an additional tool for a better design and assessment of the flexural capacity of
HSRC members.
A.a. Ramezanianpour, M. Mahdi Khani, Gh. Ahmadibeni,
Volume 7, Issue 2 (June 2009)
Abstract
Rice Husk Ash (RHA) is a by-product of the agricultural industry which contains high amount of silicon dioxide (SiO2). In this research, for the first time in the Middle East, in order to supply typical RHA, a special furnace was designed and constructed in Amirkabir University of Technology. Afterwards, XRD and XRF techniques were used to determine the amorphous silica content of the burnt rice husk. Attempts were made to determine the optimum temperature and duration of burning. Results show that temperature of 650 degrees centigrade and 60 minutes burning time are the best combination. Then various experiments were carried out to determine properties of concretes incorporating optimum RHA. Tests include compressive strength, splitting tensile strength, modules of elasticity, water permeability and rapid chloride permeability test. Results show that concrete incorporating RHA had higher compressive strength, splitting tensile strength and modulus of elasticity at various ages compared with that of the control concrete. In addition, results show that RHA as an artificial pozzolanic material has enhanced the durability of RHA concretes and reduced the chloride diffusion.
R. Abbasnia, M. Kanzadi, M. Shekarchi Zadeh, J. Ahmadi,
Volume 7, Issue 2 (June 2009)
Abstract
Drying shrinkage in concrete, which is caused by drying and the associated decrease in moisture content, is
one of the most important parameters which affects the performance of concrete structures. Therefore, it is necessary
to develop experimental and mathematical models that describe the mechanisms of drying shrinkage and damage build
up in concrete. The main objective of this research is the development of a computational model and an experimental
method for evaluation of concrete free shrinkage strain based on the internal moisture changes. For this purpose and
for modeling of moisture losses in concrete members a computational program based on finite element approach and
the modified version of Fick's second law in which the process of diffusion and convection due to water movement are
taken into account, is developed. Also the modified SDB moisture meter was used to measure the internal moisture
changes in concrete. Based on the obtained results, calculated humidity is in good agreement with measured data when
modified Fick's second law with diffusion coefficient from Bazant method were used, and are very reasonable for
determining the moisture gradient. Also, the predicted value of shrinkage strain from the proposed method is in good
agreement with measured data and also the established relationship can be used for determine the distribution of
shrinkage strains in concrete members.
M. Givehchi, M.f. Maghrebi, K. Kawanisi,
Volume 7, Issue 2 (June 2009)
Abstract
Maghrebi has previously introduced a model for the production of isovel contours in a normalized form,
which can be used for estimation of discharge in artificial and natural channels. The model is applied to a tidal river
with partially reverse flow, which is caused by opening a sluice gate located asymmetrically close to the right bank of
the Ohta floodway in Hiroshima, Japan. An acoustic Doppler current profiler (aDcp) was used to measure the velocity
profiles at different verticals and then discharge was calculated. In addition, the estimated discharge based on each
measured point and the predicted isovels of flow cross section was obtained. The results show that the corresponding
errors for the measured points away from the solid boundaries and the imaginary boundary of the flow between the
two adjacent regions with opposite directions, which are associated with lower absolute values of isovels, are
reasonable.
