Experimental and Numerical Study of Three Dimensional
Flow Structure at Lateral Intake
M. A.
Omidbeigi
author
S. A.
Ayyoubzadeh
author
A.
Safarzadeh Gendeshmin
author
text
article
2012
per
The flow at a channel bifurcation is turbulent, highly three-dimensional (3D) and has many complex
features. There is transverse motion accompanying the main flow and an extensive separation zone
that develops in the branch channel. There are two complex flow regions along the intake channel: one
is the separation zone and the other is the region in which helical motion of water particles forms. This
separation occurs because the flow entering the branch channel has considerable momentum in the
direction of the main channel flow. This zone causes hydraulic and sedimentation problems that must
be known before designing the system. This necessitates a deeper insight into the flow patterns and
shear stress distributions near the solid boundaries. In this research, 3D flow patterns at lateral
diversion were investigated experimentally and numerically. The experimental investigation was
carried out at a T-junction, formed by two channels with rectangular cross-sections. The width of
lateral intake to the main channel was 0.4. 3D velocity measurements were obtained using Acoustic
Doppler Velocimeter at junction region for 11%, 16% and 21% discharge ratios. Fluent mathematical
model was then used to investigate the dividing open-channel flow characteristics. Turbulence was
modeled by Two Equation (k-ε, k-ω) and Reynolds Stress (RSM) turbulence models. The predicted
flow characteristics were validated using experimental data and the proper model was selected for
hydrodynamic and parametric studies. Within the main channel, good agreement was obtained
between all models prediction and the experimental measurements, but within the lateral channel, the
RSM predictions were in better agreement with the measured data, and k-ω predictions was better than
those of k-ε. The comparison of experimental and numerical streamlines at different elevations
showed that the selected model is capable to simulate the most important features of flow at
diversions. The study of the velocity contours at different elevations showed that the velocity
magnitude decreases at main channel, just downstream corner of lateral intake at the near bed levels
and this causes the sedimentation in movable beds. The results showed that the width of separation
zone at lateral intake will decrease and the distance of dividing stream surface from left bank of the
main channel will increase by increasing of the discharge ratio. Investigation of the flow pattern at the
entrance of the lateral intake showed that the secondary flow will form at this section. The dimension
of the secondary flow at near bed elevation will increase by increasing of the discharge ratio and this
causes entering of more bed load into the lateral channel.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1817_f07ad97ffa54f12f5f8070ad84b9b531.pdf
Investigation of Steel Welded Moment Connections
Performance under Column Collapse
A.R.
Jalali
author
Y.
Yasrebinia
author
text
article
2012
per
Progressive collapse of buildings has raised questions on adequacy of the existing regulations
to prevent local and, in turn, global collapses. The present study mostly focuses on the
performance of welded moment connections against progressive collapse. The performance of
moment connections suggested in the FEMA 350, which are proper for seismic forces,
Welded Flange Plate (WFP), Reduced Beam Seaction (RBS), Welded Unreinforced Flange-
Welded Web (WUF-W) and Free Flange (FF), has been studied. The models used include
non-linear behavior of materials and geometrical nonlinear behavior. The behavior of steel
materials used in the structure is the true behavior of steel was stress-strain, which has been
considered in the model completely. The nonlinear stress-strain behavior of steel selected for
modeling the real behavior of beam and column members in the structure. The material
properties of all steel components were modeled using elastic-plastic material model from
ABAQUS. For connection region porous material plasticity was used. The diagram of vertical
force against vertical displacement for each connection was drawn, and the state of each
connection failure was investigated. Making the large scale experimental models to study the
progressive collapse of structures seems too difficult. Using finite element models to study the
behavior of structures are relatively appropriate option with regard to time and cost. In all of
the numerical models, shell (S4) element has been used to simulate the beams, columns and
connections. This is a four-node element, which contains four integration points on the
element. During the calculations, full integration method with more precision was used. For
analysis of the models, dynamic explicit method was used. This method is suitable to analyze
the models with more members having nonlinear characteristics of materials and large
deformations. In this method, the central difference integrating is used to solve the dynamic
equations. In every time step, this method performs simpler than other methods in solving
dynamic equations since there is no need to inverse stiffness matrix in any time stage. The
used numerical method has compared using the laboratorial results, which have tested in 2010
by NIST. The analytical results showed a good agreement with laboratory models. The results
of numerical analyses illustrated that RBS connection has less strength in comparison with
other connections and this connection reaches maximum vertical displacement with less force.
Performance of FF and WUF-W connections is similar to each other. These connections more
resistant in comparison with RBS. WFP connection is more resistant as compared with the
WUF-W, FF and RBS connections against the failure of the column. Failure load in WFPconnection is twice of other connection, and according to the analytical results, this
connection is suitable for HLOP structures. In all connections, rotation capacity
corresponding to collapse prevention against column removal scenario is about twice of the
accepted criteria that FEMA 350 has suggested for seismic loads.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1818_92ba33e5b86102a7d1adae07d0416146.pdf
Investigation of Element Size Effect on the Nonlinear
Behavior of Flanged Shear Walls
S.M.
Khatami
author
A.
Kheyroddin
author
text
article
2012
per
Completion and development of reliable analytical models using finite element method could
help investigation and prediction of the actual structure response results. Analysis of each
model in finite element software needs meshing, in which computer results are dependent
specifically to geometry and dimensions of the elements, called "mesh dependence". Finding
a strategy for independency of the results to meshing is tangible. For the mentioned purpose
and also to investigate the role of finite elements meshing in flanged shear walls, finite
element software was used. Different meshings of shear walls (tested by Vecchio and
Palermo) were analyzed and studied. The results of analyses with different meshs showed
different ultimate strengthes and lateral displacementes. Different shapes of mesh create
various results, which are indicated in the finite element model. By increasing of the size of
mesh, the final force was increased and the lateral displacement was decreased, which
presents a rigid model. On the other hand, by decreasing of the dimension of mesh, a stiff
model was seen. So, it is a need to create well proses to analyze and evaluate the flanged
section of shear walls with finite element model. Getting suitable accuracy of finite element
model, the mentioned concrete shear wall (vecchio and Palermo) was modeled by ANSYS.
3D SOLID65 element was employed for modeling of shear wall structures. This element is
capable of cracking in tension and crushing in compression. In concrete applications, for
instance, the solid capability of the element may be used to model the concrete while the rebar
capability is available for modeling of reinforcement behavior. After calibration, optimum
forms and dimensions are recommended. As an illustration, an idea was presented, by which
flanged shear wall could be analyzed more carefully in ultimate strength and ductility. This
analysis showed that the results of squared mesh are closer to the fact. For example, this type
of meshing 6% error in ultimate strength and ductility in accordance to lab Specimen,
presented the closer responses. Furthermore, investigation on the optimum size of the mesh
showed that if the mesh has the same size of the thickness of the connecting element (Shear
Wall Web), the results will have very high accuracy. For instance, squared meshes with same
dimension of meshes equal to web thickness, rather than those with half dimension of that led
to 1% of lateral resistance, which is closer to experimental test. It is possible that web
thickness is 150 mm, thereby, we can use mesh sizes of 150mm, 75mm or 50mm. However,
in order to obtain ultimate loads accurately, the mesh size of 150mm seems reasonable.
Square meshes have four degrees of freedom. If the size of square is chosen to be the same as
the web thickness, nodal forces induced in the web would be proportionate. For thischallenge, a flanged section reinforced concrete shear wall tested was selected to confirm the
web thickness square theory. This shear wall was modeled by finite element program. The
results of analysis showed accuracy in the investigated theory. In this study, the web thikness
square theory has indicated 8% error in ultimate strength.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1819_bf4ed159da0e5924b7611eefe0c8cef2.pdf
Using Depth Average Flow Solver of NASIR Finite Volume
Software for Modeling Air Entrainment from Water Surface
in Chute Flow
S.R.
Sabbagh-Yazdi
author
H.
Rezaei-Manizani
author
text
article
2012
per
In this paper, the results of water flow modeling and computation of air distribution in chute spillways are
described. The depth average flow solver of NASIR finite volume software was utilized for modeling of
water flow in chute spillways. In this module, the shallow water equations modified for steep slopes are
solved using cell-centre and cell-vertex schemes of finite volume method that suits unstructured triangular
meshes. Using the computed velocity components and flow depth at each nodal point, the air entertainment
parameters (air inception point, mean air concentration and vertical distribution of air concentration) are
calculated by utilizing some empirical relations. The empirical relations for the air concentration were
adopted by the pervious researchers using the measurements on large scale flow in chute spillways.
In the present work, three modeling strategies were performed: 1) Solution of flow field and then
calculation of air concentration parameter (as a post-processing operation after convergence of the water
flow solution), 2) Coupled solution of the flow equations and air concentration relations considering the
flow bulking and reduction of global friction parameters due to air entrainment and 3) Adding the air
entrainment on density variation effects to the coupled solution of the flow equations and air concentration
relations considering the flow bulking and reduction of global friction parameters due to air entrainment.
In order to assess the quality of the results of the three modeling strategies, the readily available flow
velocity and air concentration measurements on AVIMORE chute spillway were used for comparison
considering the best experimental relations for simulating the entrainment of air into the flow on chute
spillways. In order to provide better understanding of the velocity and air concentration, the vertical
distribution profiles of these parameters were plotted from the multi-layer treatments of depth averaged
computed results.
Comparison of the computed velocity fields and air concentrations with the reported field measurements at
the stations 503 and 505 of AVIEMORE chute spillway presents promising agreements. However, the
accuracy of the 2nd and 3rd modeling strategies (in which the coupled solutions of water flow equations and
air concentration relations are considered and the effect of air content on the reduction of global friction of
the water flow is taken into consideration) was much better than that of the 1st modeling strategy (in which
the air concentration relations are considered as post processing on water flow equation solution for depth
and velocity fields). Furthermore, no significant differences were observed between the results of the 2nd
and 3rd modeling strategies. Hence, it can be concluded that the effect of air concentration on density
variation of the supercritical water flow does not play an important role on the results of the coupled
solutions of water flow equations and air concentration relations.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1820_30e735d34bb596832235fd0e0df509f3.pdf
Effects of Masonry Infills on Seismic Behavior of Steel Frames
with Khoreeni Connections and Their Elements
S.
Garivani
author
A. A.
Aghakouchek
author
M.
Soltani Mohammadi
author
text
article
2012
per
Steel frames with Khorjeeni connections have been widely used in the traditional construction
of buildings in Iran during the past decades. In the traditional form of Khorjeeni connections,
double section beams are not cut at the intersection with columns, rather they are connected to
the column by means of two angles places over the top and bottom of the beam flanges. This
type of connection offers advantages for frames, wich carry gravity loads, but it has
deficiencies when the frames are subjected to lateral loads.
Like other structural frames, there are masonry infills in many frames with Khorjeeni
connections. The behavior of composite frames subject to lateral loads differs from that of
bare steel frames. In this paper, positive and negative effects of masonry infills were studied
on the behavior of steel frames with Khorjeeni connections. Finite element method was used
to carry out nonlinear static analysis of subassemblages of this type of frames. Initially, the
results of some experiments were utilized to verify the details of the model. Then numerical
models of toe span or four span frames with different configuration of bracings and masonry
infills were studied. The results showed that infill frames increase the stiffness and strength of
frames in the absence of bracing considerably. Even when bracings are present, the increase
in stiffness and strength is significant. Simplified compressive strut models proposed in recent
guidelines for seismic rehabilitation of existing buildings are also utilized to analyze the
models. The results show agreement with the results of more sophisticated FE models.
The masonry infills, however, have some negative effects on the behavior of Khorjeeni
frames. Parts of the column in the vicinity of connections are prone to plastic damage,
particularly when the infills are relatively strong. The Khorjeeni connections are subjected to
vertical forces and tortional moments. Due to limited vertical strength of these connections,
top stories of this type of frames may suffer when compressive action of strut is mobilized for
other bays. This action introduces additional moments, which may damage the connections.
Therefore, considering of these negative effects of infills is very important when seismic
behavior of the existing frames is assessed, because these effects limit the interstorey drift
ratios.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1821_a9f592c70b0cf75c90820c181d1de910.pdf
Effects of strengthening the masonry infills by reinforced shotcrete on seismic behavior of steel frames with Khoureeni connections and their elements
Sadegh
Garivani
دانشجو/دانشگاه تربیت مدرس
author
Ali
Aghakouchek
استاد/دانشگاه تربیت مدرس
author
Masoud
Soltani Mohammadi
دانشیار/دانشگاه تربیت مدرس
author
text
article
2012
per
A large number of buildings in Iran are constructed with masonry infills for functional and architectural reasons. Often, engineers do not consider masonry infill walls in the design process because the final distribution of these elements may be unknown to them, or because masonry walls are regarded as non-structural elements. However, infill walls tend to interact with the frame when the structure is subjected to lateral loads. Masonry infills contribute to the stiffness of the infilled frame under the action of lateral load. This leads to structural response deviating from what is expected in the design. The effects of the infills on the seismic behavior of buildings may be positive or negative, depending on a large number of parameters. Steel frames with Khorjeeni connections have been widely used in the traditional construction of buildings in Iran during the past decades. In the traditional form of Khorjeeni connections, double section beams are not cut at the intersection with columns, rather they are connected to the column by means of two angles places over the top and bottom of the beam flanges. This type of connection offers advantages for frames, wich carry gravity loads, but it has deficiencies when the frames are subjected to lateral loads. Like other structural frames, there are masonry infills in many frames with Khorjeeni connections. The behavior of composite frames subject to lateral loads differs from that of bare steel frames. In this paper, positive and negative effects of masonry infills were studied on the behavior of steel frames with Khorjeeni connections. Finite element method was used to carry out nonlinear static analysis of subassemblages of this type of frames. Initially, the results of some experiments were utilized to verify the details of the model. Then numerical models of toe span or four span frames with different configuration of bracings and masonry infills were studied. The results showed that infill frames increase the stiffness and strength of frames in the absence of bracing considerably. Even when bracings are present, the increase in stiffness and strength is significant. Simplified compressive strut models proposed in recent guidelines for seismic rehabilitation of existing buildings are also utilized to analyze the models. The results show agreement with the results of more sophisticated FE models. The masonry infills, however, have some negative effects on the behavior of Khorjeeni frames. Parts of the column in the vicinity of connections are prone to plastic damage, particularly when the infills are relatively strong. The Khorjeeni connections are subjected to vertical forces and tortional moments. Due to limited vertical strength of these connections, top stories of this type of frames may suffer when compressive action of strut is mobilized for other bays. This action introduces additional moments, which may damage the connections. Therefore, considering of these negative effects of infills is very important when seismic behavior of the existing frames is assessed, because these effects limit the interstorey drift ratios.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
1
10
http://mcej.modares.ac.ir/article_1882_d41d8cd98f00b204e9800998ecf8427e.pdf
Genetic Algorithm Based Approach for Optimal Design of Multiple
Tuned Mass Dampers (MTMDs) under Earthquake Excitation
M.
Mohebbi
author
K.
Shakeri
author
H.
Majzoub
author
text
article
2012
per
To improve the behavior of building structures subjected to lateral loads, such as wind and
earthquake excitations, tuned mass damper (TMD) has been used extensively theoretically
and experimentally in previous researches. To increase the effectiveness of TMD mechanism,
different methods have been proposed to determine the optimal values of TMD parameters
including its mass, stiffness and damping. In using single TMD on the structures subjected to
external vibrations, the mistuning of TMD, variation of TMD damping and changes in
structural dynamic characteristics cause significant reduction in the effectiveness of TMD.
Multiple tuned mass dampers (MTMDs) have been proposed to overcome the shortcomings
of single TMD where each TMD has different dynamic characteristics. Based on the results of
different researches, it has been concluded that the performance of MTMDs is less sensitive
to uncertainty of structural dynamic parameters than that of a single TMD.
In the previous researches, for designing MTMDs on the linear structures subjected to various
external excitations, several methods have been proposed based on different kinds of design
criteria. In most of the proposed methods, to simplify the design procedure of MTMDs, some
limitations such as identical masses and damping ratios for TMDs or uniform distribution for
the frequency or damping of TMDs have been considered. Also these methods require
extensive numerical analysis. To generalize the design problem of MTMDs, in this paper, an
effective method has been proposed for optimal design of MTMDs on the multi-degree-offreedom
linear structures subjected to any desired excitation. In this method, an optimization
problem is defined for designing the optimal MTMDs. The minimization of the maximum
displacement of structure is considered as objective function and the parameters of TMDs are
considered as variables. Since the design problem includes a large number of variables, hence,
in this paper, it has been decided to use Genetic Algorithm (GA) for solving the optimization
problem.
To illustrate the procedure of the proposed method and also to assess the effectiveness of
MTMDs in improving the seismic behavior of structures, a ten–storey linear shear building
frame was subjected to white noise excitation and for different values of TMDs mass ratio
and TMDs number, optimal MTMDs were designed for minimizing the maximum
displacement of structure. To focus on the main objective of this paper and avoid the
complexity of the problem, TMDs were located on the top floor in parallel configuration. The
results of numerical simulations showed the capability of GA in solving complex MTMDsdesign problem with a large number of variables as well as the simplicity of the method under
any desired external excitation. Also it was concluded that increasing of the mass ratio of
TMDs could improve the effectiveness of MTMDs. To assess the performance of optimal
MTMDs under other earthquakes, which are different in characteristics with design record,
optimal structure-MTMDs was tested under near-fault and far-fault earthquakes and the
results have been reported.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1822_dab7e30f71e5c909b3a75abae54fe0e2.pdf
Post Treatment of Composting Leachate by Means of Ozonation
and Granular Activated Carbon (GAC) Adsorption
A.
Nasiri
author
N.
Mokhtarani
author
H.
Ganjidoust
author
text
article
2012
per
There are different methods for treatment of composting leachate. Parameters dictating which
method to be chosen include quantity and quality of the leachate, required amount of
treatment and economical issues. Integration of ozonation and GAC adsorption into a single
process is one of the attractive methods for post treatment of wastewater. Therefore, post
treatment of composting leachate by means of ozonation and granular activated carbon (GAC)
adsorption was considered as the main objective of this study.
This study was conducted in laboratory scale and in batch mode. The set-up of batch system
consisted of a Plexiglas column with 20 mm inner diameter and 800 mm height. The tall
height of the column provides the required contact time between ozone and pollutants. Ozone
was supplied to the column through a diffuser sited at its bottom. The outlet gas of the reactor
may contain some residual ozone and can cause air pollution. Therefore, it is dangerous for
the people working nearby the reactor. Thus, the ozone in the gas phase leaving the column
was removed by KI solution. All experiments were conducted at room temperature (24 ±2°C).
The leachate used in this study was obtained from the effluent of the Leachate Treatment
Plant of Rasht Composting Facility (Guilan, Iran). All the chemicals employed for analysis
were analytical grade and obtained from the reliable companies.
In order to conduct the experiments, after complete determination of the specifications of
GAC as an adsorbent, different dosages of GAC were added to 800 mL of leachate with the
given initial concentration and pH in the column. The pH value of the solution was adjusted
by Sulfuric Acid or Sodium Hydroxide as needed. Then the ozone gas was introduced into the
column and the samples were taken in different intervals of time. After that required
parameters of the samples were measured. Ozone generator (ARDA-COG 5S) with 5 gr/hr
nominal capacity was used to produce ozone gas from pure and dry oxygen. Before starting
each step of the experiment, the ozone generator was calibrated for ozone concentration.
Pressure and flow rate of ozone gas produced was equal to 2 bara and 1 liter per minute,
respectively.
The results showed that integrated treatment of the leachate with ozonation and activated
carbon adsorption, namely catalytic ozonation, was more effective than each process solely.
In this study, COD removal rate of 44% in adsorption process, 57% in ozonation process and
80% in integrated process was achieved after 60 minutes. According to the results, in the
integrated process, addition of the adsorbent (as long as it floats in the leachate) has positiveeffect on the removal of organic load. The pH value is another important parameter that
affects the removal rate in the integrated process. It was found that removal of organic load is
more evident at basic condition than at acidic condition. In this study, the maximum COD
removal was achieved in the pH values between 8 and 9. Furthermore, in this process,
ozonation along with adsorption process resulted in reactivation of activated carbon and
avoided frequent GAC regeneration. After 5 times of the reuse of virgin GAC through a
consecutive experiment, only 7% loss in COD removal was observed in the integrated
process, while it reached to 95% for single adsorption process at the same condition. This can
be explained either by the predominance of catalytic reactions rather than adsorptionoxidation
reaction in the process or to the in situ regeneration of GAC.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1823_99232ff3b3f243391b19cb45c5fdb78b.pdf
Response of Soil-Structure Systems Subjected to Forward
Rupture Directivity Pulses
Z.
Azarhoosh
author
G. R.
Ghodrati Amiri
author
H.R.
Razeghi
author
text
article
2012
per
The combined effects of two major contributing factors, i.e. inertial soil-structure interaction
(SSI) and near-fault ground motions, on structural responses were studied. Considering nearfault
characteristics, soil-structure systems are subjected to both actual near-fault ground
motion records and their dominant kinematic characteristics, i.e. forward rupture-directivity
pulses, coherently travelling waves seen as a large amplitude and short duration pulse-type
motion at the beginning of each fault-normal component of the record. As a result of the
suitability of forward rupture-directivity pulses for quantifying the salient response features of
structures, a mathematical model, proposed by Makris, was used to represent the forward
rupture-directivity pulse-type motions. Using a comprehensive parametric study, the structure,
a bilinear single degree of freedom (SDOF) system, the soil beneath the structure and a
homogeneous elastic half-space were combined based on a discrete model to constitute the
overall soil-structure model. The results have been presented in the form of elastic strength
demand graphs for a wide range of non-dimensional key parameters, which describe the SSI
effects. Both the soil-structure systems and the corresponding fixed-base structures were
considered and compared. Using numerical time-stepping analyses, it was found that the
response of soil-structure systems subjected to actual near-fault records is similar to those
subjected to forward rupture-directivity pulses. Consequently, the forward rupture-directivity
pulses can be used to predict the salient response features of soil-structure systems in
seismically active regions. They can also be a realistic representation of near-fault ground
motions for predicting the response of long-period structures. It was further observed that
quite interestingly, the response of soil-structure systems subjected to actual near-fault
records, has two maximum regions. However, it was recognized that further study would be
required to clarify these regions. The results also indicated that considering SSI is critical for
a variety of structures. Accordingly, underestimated near-fault responses could be obtained
when the SSI effects are ignored.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1824_112ac38356c569952c82d636d35483f1.pdf
Flow Condition at Sudden Slope Change of Chutes
A.
Attarzadeh
author
A.R.
Zarrati
author
A.
Shanehsazzadeh
author
text
article
2012
per
One of the important parts of many large dams is flood release chute spillway. Aerators are installed
on chute spillways to prevent cavitation phenomenon under very high speed water flow. An aerator
consists of a ramp providing a sudden slope change that separates water from the bed and permits air
to mix with water. For the study of flow condition in aeration zone and for having an insight
knowledge about the aeration, the study of flow condition on the ramp is a prerequisite. The change in
the slope of the bed is common in spillways due to the change in the topographical slope and at the
connection of the spillway and the stilling basin.
In the present study, the flow condition at the place of sudden slope change was numerically simulated
by FLUENT software. FLUENT is powerful software in simulation of water flow, in which the effects
of turbulent are well considered. In this software, the Navier-Stokes equations are numerically solved.
Volume of fluid method is applied to simulate the free surface water accurately. The results of the
model in terms of pressure distribution at bed, pressure distribution in depth, velocity profile and water
surface profile were compared with the results of an analytical model of streamline method as well as
with the available experimental data. The analytical model is a streamline method based on conformal
mapping with the basic assumption of ideal flow. The results of the model were compared in various
slopes and water velocities. The study showed that numerical model can predict water surface profile
and dynamic pressure properly and the results of numerical model are more accurate as compared to
analytical model for the two important parameters of pressure distribution at the bed and the velocity
profile. The pressure distribution was reasonably predicted by the numerical model at the bed of
channel before the ramp for all the studied degrees and at the bed on the ramp for smaller degrees. The
maximum error was nearly 5-10 percent. The velocity profile calculated by the numerical model was
very close to the experimental data and the maximum error was nearly 5 percent. The analytical
method was found quite capable in prediction of dynamic pressure and water surface profile, and less
accurate in predicting the velocity profile. The study also showed that before and after the slope
change, the influence length, where the dynamic pressures are significant, is dependent on the degree
of sudden slope change and also on the amount of normal depth. Furthermore, the water surface
profiles calculated by the numerical model and the analytical model were quite coincident, showing
that the effects of gravity, viscosity and turbulence parameters on the water surface profile are
insignificant.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1825_0890c63ca48796cc6885ac861b5ed9b0.pdf
Computing the Compressive Strength of Cement Composite
Reinforced with Carbon Nanotube Assuming Isotropic
Behavior for CNT
H
Ghasemzadeh
author
E.
Akbari Jalalabad
author
text
article
2012
per
For extraordinary properties of carbon nanotube (CNT), a lot of research has been done about its
application to reinforce different materials such as electronic and building materials, and good effects
of CNT have been observed. Experimental approach for determining the properties of composites
containing fibers, especially carbon nanotubes, needs using of complex experimental methods and
expensive laboratorial equipments. Theoretical approach can lower the cost of predicting properties of
these composites. So, in this paper, an analytical relation is presented by continuum mechanics method
to predict the compressive strength of cement composite reinforced with carbon nanotube. For
simplicity of computations, carbon nanotubes were assumed to be isotropicand firstly oriented
unidirectionally and uniformly in the cement composite. Representative Elementary Volume(REV), as
anindicatorelement of this nanocompositeis, was chosen and analyzed by continuum mechanics
method. A fiber embedded in a cylinder of cement with certain radius is named REV. The strains
under loads were calculated and the stresses were obtained by Hook’s law. Then, for prediction failure
of composite, von Mises’ yield criterion was applied and by that, the compressive strength of cement
composite reinforced with unidirectionally oriented carbon nanotubes was obtained. For real cases, the
results of this analysis should be generalized to cement composites reinforced with random orientation
of nanotubes, since there is no control on the distribution of fibers in the laboratory and they are
oriented randomly in composites, although researchers are studying on production of CNT/cement
composites with arbitrary orientation of fibers.To apply the random orientation effect, Cox’s method
was used. For this purpose, the fibers' distribution function f ( ) was assumed and it was observed
that the random orientation of fibers reduces the effect of fiber reinforcing with respect to
unidirectional orientation. Therefore, an orientation factor 1 was used considering random
orientation in comparison with unidirectional orientation. As a suggestion, this factor can be
experimentally obtained too. Experimental method was used to determine the orientation factor of
fibers incomposites and good results were obtained. Then the presented analytical relationship was
compared with experimental data. Matches and differences between the analytical method and the
experimental data were studied and the suggestions were presented to lower the differences between
the analytical and experimental methods. The effect of some parameters such as compressive strength
of cement and the amount of carbon nanotubes added on the compressive strength of CNT/cement
composite were obtained too. Accordingly that an ideal nanocomposite with regard to economical
considerations can be obtained.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
12
v.
1
no.
2012
http://mcej.modares.ac.ir/article_1826_5429ab7f92bf7d065159db11abbff921.pdf