Application of Zero-Inflated Regression Models in
Modeling Accidents on Urban Highways
A
Ayati
author
A
Abbasi
author
text
article
2011
per
We handle in this paper, the research that have been performed to recognize the factors that affect
crash frequency and severity in urban highways and use crash data of Mashhad urban highways as a
case study. Statistical models that have been used in this research include Poisson, Negative binomial,
Zero-inflated poisson and Zero-inflated negative binomial regression models. Traffic flow related
variables and road geometric related variables have been used as independent variables of models. We
are interested in this study, to inspect the efficiency of Zero-inflated models against simple Poisson
and Negative binomial regression models in modeling accidents on urban highways. Special task that
have been done in this research, is separation of total traffic volume into passenger cars, heavy
vehicles and light non-passenger vehicles volume. Through this special, Researcher intend to have an
especial look at the role of traffic volume in accident occurrence to see precisely, which part of traffic
have effective role or more effective role in crash occurrence.
Accident data are two-level data, the first level is road segments i.e. highway is divided into several
segments. The segmentation is based on total traffic volume i.e. each segment has a constant volume.
The second level is daily hours; peak hour traffic considered as the first sublevel, day non-peak hour
traffic the second and night non-peak hour traffic as the third sublevel. SAS 9.1 software has been
used to fulfill statistical computations. It turns up, after statistical analyses, which factors affect crash
occurrence and which do not have much effect. Comparisons between obtained results and other
researchers’ results have been made then. The main object of researcher is to assess the efficiency of
Zero-inflated models against Poisson and Negative binomial regression models in modeling urban
highways crashes. This aim is followed by, with evaluating goodness of fit and making comparison
between models.
The Results of study show that the presence and number of access roads and horizontal curves on
highway segments increase the likelihood of accidents, both no injury and more severe. Also
increment of speed and number of lanes increase the likelihood of no injury accidents, but not more
severity ones. The conclusions also demonstrate that the volume of passenger cars and light nonpassenger
car vehicles increase the likelihood of no injury accidents, but heavy vehicles volume does
not have much effect on occurrence of no injury accidents, also light vehicles increase the likelihood
of more severe accidents, but passenger cars and heavy vehicles volume does not have much effect on
occurrence of severe accidents. Finally, the results of research indicate that Zero-inflated negative
binomial regression model is best fitting the modeling of accidents, whether no injury or more severe
and consequently, the efficiency of zero-inflated models in modeling accidents on urban highways is
approved.
Modares Civil Engineering journal
Tarbiat Modares University
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2011
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http://mcej.modares.ac.ir/article_1807_f9d41a72b3f60aa3db04d1d3939f88ca.pdf
Estimation of the Scale of Fluctuation of Geotechnical
Properties in Natural Deposits Using
Random Field Theory
R
Jamshidi Chenari1
author
R.
Oloomi Dodaran
author
text
article
2011
per
One of the main distinctions between geomaterials and other engineering materials is the
spatial variation of their properties in different directions inside them. This characteristic of
geomaterials (so- called as heterogeneity) is studied herewith. Almost all natural soils are
highly variable in their properties and rarely homogeneous. Soil heterogeneity can be
classified into two main categories. The first is lithological heterogeneity, which can be
manifested in the form of thin soft/stiff layers embedded in a stiffer/softer media or the
inclusion of pockets of different lithology within a more uniform soil mass. The second
source of heterogeneity can be attributed to inherent spatial soil variability, which is the
variation of soil properties from one point to another in space due to different deposition
conditions and different loading histories. Inherent spatial variability of geomaterials is itself
devided into the random component, which is attributed to different depositioaln conditions,
and the deterministic trends, which are attributed to the variation in soil properties, such as
increase in soil strength with depth due to increase in confining pressure.
Different elements of soil inherent spatial variability such as mean, variance, and spatial
correlation characteristics were introduced with the main focus on the importance of spatial
correlation distane and the way to handle it. Several spatial distributions introduced to
describe the probabilistic variation of geotechnical properties of soils. Among all, absolute
normal distribution was adopted as appropriate distribution, which best presents these
properties in horizontal direction.
Variation of geotechnical parameters in vertical direction is, however, conceived to follow a
deterministic trend. Using random field theory, local average subdivisions (LAS) formulation
and MATLAB Mathworks, virtual data with different correlations was produced, and by
employing autocorrelation function, a trend for this function was invoked for different
predetermined values of the scale of fluctuations. It was found that autocorrelation function
has a deterministic trend as far as the scale of fluctuation has not been exceeded. It is clearly
concluded that, for distances farther than the specific scale of fluctuation, the behavior is
chaotic and this can be an index to calculate the scale of fluctuation of the experimental data.
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http://mcej.modares.ac.ir/article_1808_24810af4dc6924ce42ab919ffffb9674.pdf
Application of Zero -Inflated Regression Models for Modeling Accidents on Urban Highways
Ehsan
Abbasi
Hashemieh boulevard the 10-th, number 24
author
esmaeel
ayati
هنرستان15 پلاک16
author
text
article
2011
per
we handle in this paper, the research that have been performed to recognize the factors that affect crash frequency and severity in urban highways and use crash data of mashhad urban highways as a case study. Statistical models that have been used in this research include Poisson, Negative binomial, Zero-inflated poisson and Zero-inflated negative binomial regression models. Traffic flow related and road geometric related variables have been used as independent variables of models. Special task that have been done in this research ,is separation of total traffic volume into passenger cars, heavy vehicles and light non-passenger car vehicles volume to have an especial and thorough look at the role of traffic volume in crash occurrence , whether crashes with property loss only or more severe crashes, and see ,precisely which part of traffic have an effective role or more effective role in crash occurrence. In this research, the efficiency of Zero-inflated models is investigated against Poisson and Negative binomial regression models in modeling accidents on urban highways. Results of the research show that the number of access roads and horizontal curves on highway segments and the volume of light non-passenger car vehicles have increasing role in likelihood of accidents. Furthermore, Zero-inflated negative binomial regression model is the best and fittest model for modeling accidents, whether with property loss only or more severe and consequently the efficiency of Zero-inflated models in modeling accidents on urban highways of Mashhad is approved.
Modares Civil Engineering journal
Tarbiat Modares University
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2011
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1
http://mcej.modares.ac.ir/article_1909_d41d8cd98f00b204e9800998ecf8427e.pdf
Advanced Analysis of Ambient and Cement Hydration
Thermal Effects on a RCC Dam Considering Construction
Schedule
N
Heydari
author
M.T
Ahmadi
author
text
article
2011
per
Mass concretes including roller-compact concrete are materials with poor tensile behavior.
When subjected to shrinkage or heat in their very early ages such concretes may easily crack.
Thus for controlling and minimizing the risk of thermal cracks, it is crucial to study the
effects of such parameters as the rate of concrete pouring in construction layers, seasons of
start, pause of construction, and the extent of pre-cooling of concrete materials. Therefore,
thermal stresses and probable cracks should be controlled based on a sound construction
schedule. In practice, most cases are dealt with using a simple one-dimensional analysis
pertaining only internal concrete evolution and thus disregarding the surface concrete story.
At the same time, the induced surface stresses are not accounted for in such analyses.
However, as a minimum requirement, a two dimensional model of the dam body across its
vertical section is needed to account for the main effects mentioned above. Despite that many
analyses have been carried out by others so far, in this research, concrete thermal conductivity
coefficient is considered as a function of concrete temperature throughout a transient heat
conduction analysis. The material is assumed as isotropic in both thermal and mechanical
senses. The topology of model as well its top boundaries are continuously updated according
to the construction schedule. Furthermore, accounting for the dam construction schedule, heat
generation due to both ambient and cement hydration phenomena, as well as inclusion of
convection and radiation boundary conditions due to solar effects are considered. In addition,
when dealing with stress analyses and safety evaluation against cracks, the dependencies of
concrete elasticity modulus on time and temperature, and concrete compressive as well as
tensile strengths on time (i.e., the ages of layers) are all considered. Indeed, the thermal
analyses are carried out after performing each single layer. Also after every 10 layers are
performed, a full stress analysis is conducted under the current thermal and gravity loads.
Safety factors are calculated considering the material properties and strength available at the
same instance in each layer.
To study the effect of these parameters on heat generation, and the subsequent thermal
stresses in the body of RCC dam, "THA-DAN" dam in Thailand was chosen as a benchmark
introduced by ICOLD. This dam has been built of 160 layers of 30 centimeter thickness.
Program ANSYS-6.1 was employed in a special manner to allow such a coupled transient
Abstracts
140
analysis for both thermal and stress parts.
Initially, a basic verification of calculated temperatures versus the measured ones (as provided
by ICOLD) was done for the layered construction at the dam site. The results of this study
showed that maximum hydration temperature occurs at the layers poured in the hottest season.
The efficiency of pre-cooling techniques is rather low, because by each 5˚C pre-cooling, only
1˚C drop in the temperature of internal concrete and 0.3 MPa drop in tensile stresses are
gained. Tensile stresses are concentrated on the free surfaces of the concrete as well as on the
ground interface due to constraints. This happens at a 3-4 meter thick layer there due to the
high thermal gradients. Inclusion of gravity load in the stress analyses helps reducing the
tensile stresses, particularly near the ground. Furthermore, if the frost of concrete materials
could be avoided, winter would be the most efficient season for starting the construction. The
most critical case is to start the construction in summer. Elongated construction pause in hot
seasons is very effective for controlling the thermal cracks, although it has only negligible
effect in cold season on the final distribution of heat and the maximum temperatures induced
in the dam body. It is interesting to notice that the lower is the speed of concrete pouring, the
cooler the core concrete becomes. At lowest speeds the warm core approaches to the ground
surface. Although the above observations were found through a single dam being
investigated, but they could also be mostly true for most of the gravity type RCC dams.
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http://mcej.modares.ac.ir/article_1809_acf564c0a0de4e2fcdff8ddeab0cb8e0.pdf
Confined Masonry Walls Retrofitted with FRP
A
Khaffaf
author
F
Arbabi
author
text
article
2012
per
Masonry buildings with confined walls have performed well during the past earthquakes. The
same cannot be said for unreinforced masonry walls. In the former buildings, even when
damage occurs, falling roofs and losses of life do not usually follow. This is because confined
masonry walls have higher strength ductility and are more stable. The Iranian Seismic Code
(Standard 2800) makes the use of horizontal and vertical ties mandatory for masonry
buildings. In spite of this, such confined walls have not been studied sufficiently.
In this study, the nonlinear behavior of masonry walls is examined using finite element
discretization. From the two types of modeling that are commonly used for the study of
masonry material, namely macro- and micro- modelings, the latter are employed here. This is
because such a model can provide more detailed information. Micro- models are the best tools
available for understanding the behavior of masonry structures. They can depict all the failure
mechanisms of the system. The behavior of mortar joints and masonry unit-mortar interface is
lumped into a set of discontinuous elements. In this way, each joint, consisting of mortar and
two unit-mortar interfaces, is modeled by a zero-thickness interface element. In other words,
the masonry structure is modeled by a set of elastic blocks bonded together with potential
fracture/slip lines at the joints. The composite interface model includes a tension cut-off for
mode I failure, a coulomb friction envelope for mode II failure and a cap mode for
compressive failure. For modeling the behavior of concrete, a model suggested by
Thorenfeldt and Hordijk is used.
For the longitudinal reinforcing bars, the failure criterion is that of Von Mises. The hardening
of steel is also considered. The interface between the reinforced concrete members and the
masonry units panel is modeled by the coulomb friction model including a tension cut-off
mode. A parametric study is conducted for confined masonry walls by changing with different
dimensions, boundary conditions and loading patterns. The results indicate that failure has
one of the two failure modes: diagonal tension or rocking. In cantilever walls with rather large
heights compared to their length, the failure mode is rocking. In the other cases, diagonal
tension failure mode occurs. The use of tie also affects the capacity of the wall. This can be
considered in the design of masonry structures. The results of nonlinear analyses show that
deboning does not occur between the ties and the body of masonry walls. Therefore, in
analytical studies, the adjoining nodes for the two parts can be merged.
Upon determination of failure modes, different patterns of FRP were investigated for the
dominant mode in order to select the most suitable pattern. The FRP configuration patterns
considered for strengthening the wall were:
1. FRP in vertical direction;
2. FRP at both ends in vertical direction;
3. FRP in diagonal direction;
4. FRP covering the whole surface of the wall.
The last pattern was considered only for reference as it cannot be justified because of the
increased cost. In confined masonry walls with diagonal tension or rocking mode, the best
strengthening configuration is diagonal.
The increase in the capacity of strengthened walls with rocking and diagonal tension failure
modes depends directly on the amount of FRP. In fact, the capacity increases from 1.2 to 2 for
the walls with rocking mode. For the walls with diagonal tension mode, this increase is from
1.5 to 3.
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http://mcej.modares.ac.ir/article_1810_148e23ca1238fbd691bbe7426adc8b84.pdf
An Optimum Model for Hub-and-Spoke Network
Based on the Current Demand
(Case Study: Iran Airport Network)
M
Zabihi Tari
author
M
Saffarzadeh
author
M
Sharifi Yazdi
author
A
Abdi
author
text
article
2012
per
Air transportation has an important position among the other modes of transportation due to its
significant impact in the economy and welfare of a society. Within the several components of
air transportation market, flight network plays a fundamental role and considerably affects the
airlines revenue. Improvement of the network system requires an accurate plan and
programming. Hub-and-spokes are of further interest; as such networks reduce the operational
costs, create proper ground for flight network development and extension, and help in
competition. However, several models have been introduced for hub-and-spokes design
purposes based on the diversity of the effective factors, decision-making variables and different
forms of the network.
Generally speaking, hub-and-spokes are categorized into two principal sectors: single allocation
and dual or multiple allocations. Within a single allocation, traffic is accumulated in a single
hub and then distributed to the destinations, while within a dual-allocation network, the
gathered traffic at the first hub is again distributed to another hub before directing it to the final
destination. This research presents a linear model for hub-and-spokes evaluation and planning,
determining optimum flight routes and fleet assignment. The model considers both direct flights
and hub connections, and outputs an optimum network based on the mixture of these two
options. Sets of airport connections are so designed to well cover all the necessary inter-airport
trips. This particular is done by utilizing hub-and-spoke system as the airport networks. To
fulfill the requirements of the study location (Iran), in this paper, single allocation was selected
to develop the models, meaning that just one hub has been considered in the modeling process.
Inter-airport demands of the passengers were inputted in the network and the model works only
for passenger transportation. The objective was to design the hubs so as to obtain an optimum
network. In other words, the model is to suggest the best option with which the demand is
handled cost-effectively. Trips are planned to be either direct or meeting a one-hub maximum.
As the model is to minimize the cost, such variables as demand for variety of routes and type
and quantity of the available aircrafts were included. The model was developed in two stages to
ease the process. The first stage dealt with the target function and the fleet was assigned to the
Abstracts
136
outputs of the stage one. Iran's internal flight network was chosen as the case of study to
develop the model based on the country's geographical situation and available data. 59 airports
were chosen as the total set of airports and trip origins. The number of hub candidates and
destination airports were eight including Isfahan, Ahwaz, Bandar Abbas, Tabriz, Tehran,
Shiraz, Kerman and Mashhad airports. Based on the availability, the data of five types of
aircrafts were used in the model development. Lingo Version 8 has run the model using branchand-
bound method to obtain accurate and reliable outputs. Up to eight hub networks were
considered by the model and the model confirmed that with increase in the number of hubs,
operational cost decreased. However, cost reduction had lower rate for the systems with six
hubs and over. The results also suggested that the probability of stop in a hub rises for longer
trips. Flights longer than 1.5 hours had to stop at one hub in three-, four-, five-, six- and eighthub
networks.
Four-hub network was found to be the optimum one due to having the shortest stop slot where
fixed cost has been allocated for selecting an airport as the hub. The hubs of the optimum fourhub
network are Tehran, Shiraz, Kerman and Isfahan airports. The results showed that demand
is not the only effective factor in the selection of the hub; it means that another key factor,
geographical positions, has effect and the airport with higher demand is not necessarily selected
as the hub. Therefore, hub-and-spokes can enhance the efficiency of the airports with lower
demands. As an example out of the results, passengers intended to use Isfahan and Kerman
airport as their hubs in a four-hub network were more than the ones targeting Isfahan and
Kerman airports as destinations. Analysis of the four-hub network cleared that, according to the
current demand and operational costs of different aircrafts, large planes (e.g. Airbus 300) and
small lpanes (e.g. Foker 50) will perform more flights in comparison the with other types. Using
the model developed in this research, airlines will be able to forecast and plan their required
fleet combination based on the demands.
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http://mcej.modares.ac.ir/article_1811_5e5aee678a0d6fb7b52c88e432a320aa.pdf
APPLICATION OF SHEAR-FRICTION HINGE CONNECTION IN MID-STORY STAIR SLABS TO COLUMN JOINT
Hamid
Farshchi
Farmaniyeh, Dibaji Shomali, Arghavan, No:21
author
text
article
2011
per
Providing mid-story stair slab to column hinge connection is practically difficult in concrete moment resisting frame structures. The problem is due to the fact that this connection is modeled as hinge connection in the modeling phase of structural analysis but in practice because of lack of proper detailing this is not fully satisfied and can lead to inappropriate column behavior and may affect the structural behavior as a whole. In this article, a simple hinge connection detailing based on shear-friction behavior has been proposed. This connection is based on the Iranian national building code and can provide the proper hinge connection in the mentioned joint.
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http://mcej.modares.ac.ir/article_1913_d41d8cd98f00b204e9800998ecf8427e.pdf
Experimental and Analytical Study of Connection
Strength Effects in X-Type Braced Frames
H.R
Farshchi
author
A.S
Moghadam
author
R
Jazany
author
text
article
2012
per
SCBF (Special Concentrically Braced Frame) is a common structural system for steel construction in
Iran. This system could be used where increasing of strength and stiffness is the main concern for a
structural system over the ductility. In SCBF, it is assumed that most of stiffness and strength are
provided by the brace element. The contribution of gusset plates in total stiffness and strength values
is even overlooked in the structural analysis and design. Ignoring these effects is conservative for
controlling of seismic responses and is on the safe side. But, in practice, this hypothesis is not valid
since this extra portion of stiffness and strength values is not included in the design of gusset plates
and the connections. The importance of this phenomenon will be more noticeable when the brace
element material behavior significantly enters the nonlinear phase.
Based on previous descriptions, experimental and analytical study of this kind of structural system
under seismic loading seems necessary in order to evaluate the contribution of stiffness and strength of
each mentioned element i.e. gusset plates and double- seat angle connections. Three test specimens
were built in half scale and designed regarding the AISC seismic provisions (2005); the first test
specimen consisted of one-by-one story frame with simple connection, i.e. double seat angle
connections, known as simple frames. The second specimen was simple frame with gusset plate
connections without brace elements. The third specimen was braced frame; the specimens were tested
cyclically and companion Finite Element (FE) analysis was then conducted. Verification of FE models
in ANSYS finite element program using “Solid 45” element with proper mesh dimensions, obtained
by sensitivity analysis, showed good agreement between the analytical and experimental responses.
The experimental results showed that the stiffness value of simple frame and simple frame with gusset
plates reached 60% to 65% and 86% to 98% of stiffness values of the braced frame, respectively. Also
energy absorption values of simple frame and simple frame with gusset plate reached 4 % and 10% of
the energy absorption value of braced frame, respectively. Moreover, ultimate strength value for
simple frame and simple frame with gusset plate reached 11% and 25% of the ultimate strength values
of braced frame. As a result, it could be mentioned that gusset plates and double seat angle
connections have significant contribution in the total stiffness values of a braced frame whereas their
contributions in strength value of a braced frame are insignificant. The results of FE analysis also
confirmed the above-mentioned results with a definite low tolerance.
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http://mcej.modares.ac.ir/article_1812_8ef06eabf49b765cfd7fee6d56d26e9f.pdf
Prediction of stress- strain behavior in gravelly material
based on Artificial Neural Networks
R.
Mahin Roosta
author
H.
Farrokh
author
text
article
2012
per
Prediction of stress-strain behavior of geotechnical material is one of the major efforts of engineers
and researchers in the field of geomechanics. Experimental tests like tri-axial shear strength tests are
the most effective apparatus to prepare the mechanical characteristics of gravelly material; but due to
difficulties in preparing test samples and costs of the tests, only several tests will be done in a new
project. Artificial neural network is a kind of method, in which engineer could judge the results based
on numerous data from other similar projects, which enable the engineer to have a good judgment on
the material properties.
In this research, the behavior of gravelly material was simulated by use of multi-layer perceptron
neural network, which is the most useful kind of artificial neural networks in the field of geotechnical
engineering. For instance, first exact information was provided from laboratory tests of various barrow
areas of embankment dams in the country and effective parameters on shear strength of coarse-grained
material were studied. After omitting incorrect or weak data, 95, 20 and 23 sets of data were used for
learning, testing and evaluating data, respectively. Input parameters for the model were as follows:
particle-size distribution curve, dry density, relative density, Los-angles abrasion percent, confining
pressure, axial strain; and outputs were selected as deviator stress. In order to reach a steady state in
the model and force the model to behave homogenous to the all inputs, data was normalized to the
value between .05 and 0.95. In the simulation, back-propagation algorithm was used for learning or
error reduction. The aim of the simulations was defined to reduce error between real data and
predicted values; for instance root mean square error (RMS) was used to be minimized through
simulation and predicted versus real graphs were used to observe the global error of the model. After
modeling the data based on some criteria, it was shown that curves of stress-strain from simulation
tests were in good agreement with those from laboratory. These close coherencies were observed in all
training, testing and evaluation data, in which the RMS errors were 0.038, 0.037 and 0.026,
respectively. To reach this ultimate step, a 10*19*1 multilayer perceptron was used via trial and error.
In order to determine quality and quantity of the effect of inputs on outputs, and prove that the results
were in good agreement with soil mechanic principles, sensitivity analyses were done on the average
data of the inputs. Results show that confine pressure, uniformity coefficient and relative density of
the material were the most effective parameters on the stress-strain curves; thus the model has enough
capability to predict the stress-strain behavior of gravelly soils.
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http://mcej.modares.ac.ir/article_1813_9b94a0d91ee9bf69178b4ed070b296e3.pdf
Local Buckling of Corroded Tubular under Cyclic
Compression & Tension Loadings
M.
Peykanu
author
M.
Zeinodini
author
M.
Daghigh
author
text
article
2012
per
Abstract:
Plastic axial strain, local buckling, wrinkling and plastic buckling of pipeline are caused by cyclic
compression and tension loadings. This kind of local buckling is amplified by initial defect, heat
affected zone and circular welding. Progressive plastic failure or ratcheting is caused by frequent
periods of cyclic loading. On the other hand, life time of the offshore pipelines is decreased by the
corrosion effect caused by fluids inside the pipeline and the sea Environment. This kind of corrosion
can be found with variable size and depth in the inner or/and the outer surface of the pipeline.
Corrosion can effect on the strength of pipeline.
In the current study, an advanced finite element program has been used to simulate the ratcheting
response of carbon steel tubes. The numerical model has been applied to reproduce a series of
laboratory tests on small-scale tubes. These tests were carried out by the authors on intact and defected
tubes, in which wrinkling and ratcheting behaviour of tubes under axial monotonic and cyclic loads
were studied. A nonlinear isotropic/kinematic hardening model has been employed to represent the
cyclic behaviour of the material. The verified model has then been used for a parametric study on
ratcheting behaviour of the defected tubes under cyclic axial loading. Several stabilized cycles of
specimens that are tested experimentally under symmetric strain cycles are used to obtain stress-strain
data and hardening parameters of the material.
The numerical model has then been used to investigate the effect of mean stress, stress amplitude and
geometrical defects on the ratcheting response of steel tubes. It has been noticed that:
a) The ratcheting strain rate was governed by (a) the initial non-linear strain in the tube, (b) by the
stress amplitude and (3) by the mean stress, respectively.
b) The ratcheting strains in the defected tubes had significantly higher rates in comparison to those in
the intact tubes and very rapidly turned exponential.
c) In defected tubes the local wrinkling first initiated from the damaged part. This local buckling then
gradually proceeded to the entire circumference. The ratcheting strains in the defected area very
rapidly turned exponential, while the ratcheting strains in the perfect zone still remained linear
trajectory.
d) It showed that surface corrosion imperfections had a very pronounced effect on the ratcheting
response of the defected tubes, as compared to their monotonic response.
e) The wrinkles in the defected tubes were non-axisymmetric and initiated from the damaged part of
the tube
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http://mcej.modares.ac.ir/article_1814_ebc979bc568a164000f27cc29c75fdbc.pdf
Evaluation of Eulerian and Lagrangian Methods in the
Analysis of Concrete Gravity Dam Including Dam Water
Foundation Interaction under Earthquake
L.
Khan Mohammadi
author
J.
Vaseghi Amiri
author
B.
Navayi-nia
author
text
article
2012
per
Hydrodynamic pressure on the upstream face of the concrete dams under the effect of
earthquake is one of the most important parameters, in planning dams' structure in earthquake
zone. Because of the reservoir effect, dynamic analysis of concrete dams is more involved
than other common structures. This problem is mostly sourced by the differences between
reservoir water, dam body and foundation material behaviors. As a result, researches in this
case must be able to evaluate the response of dam with consideration of dam’s interaction
with reservoir and its foundation. This problem has been studied vastly by different
researchers.
The first research on the analysis of concrete gravity dam has been done by Westergaard in
1930 and hydrodynamic pressure on the dam face was obtained by some simplifications.
There were a lot of other researches which studied the seismic behavior of the dam-reservoir
system, including nonlinear behavior of the dam under pressure and also cavitation. In each
research, different modeling methods are presented which are divided into two main groups.
In first method which is called Eulerian method, pressure is the main unknown variable in
reservoir nodes. In the second method that its main unknown variable is displacement of
nodes is called lagrangian method. Each of the methods contain some advantageous and
disadvantageous.
The purpose of this paper is to evaluate possible advantages and disadvantages of both
methods. Specifically, application of the above methods in the analysis of dam-foundationreservoir
systems is leveraged to calculate the hydrodynamic pressure on dam faces. Within
the frame work of dam- foundation-reservoir systems, dam displacement under earthquake for
various dimensions and characteristics are also studied. To achieve this purpose, visual
C#.NET 2003 computer programming language is used in this investigation that produces
possibility of dynamic analysis of concrete dams under earthquake with system modeling by
both methods. Nine node elements for reservoir and eight node elements for dam and
foundation are used for both methods. Also newmark average acceleration method is used for
solving dynamic’s equilibrium equation.
Modares Civil Engineering Journal (M.C.E.L) Vol.11, No.4, Winter 2011
131
In this paper the response of the tallest, non-overflow monolith of Pine Flat dam in California,
which is 122 m high, to horizontal and vertical component of earthquake is computed. A
water depth of 116 m is considered in full reservoir condition, and the water has the following
properties: unit mass, 1000 kg /m3 , bulk modulus, K 2.07*109 kg/m2 , and pressure wave velocity,
w c 1440m/ s . The finite element model of reservoir consists of 12 isoparametric elements and it
extends upstream a distance of 366 m, three times the dam height. The dam consists of 20
isoparametric elements. The concrete of dam has the unit mass of 2500kg /m3 , young’s
modulus ofE 2.275*1010kg /m3, and poisson`s ratio of 0.25. The concrete of foundation has the
unit mass of , young’s modulus ofE 4.45*1010 kg / m3 f , and poisson`s ratio of
0.25 f . The peak acceleration of S69E and vertical components are 0.18g and 0.1g,
respectively.
The results of both Lagrangian and Eulerian methods for Pine Flat dam are quantitatively
evaluated and compared in different condition and following results are achieved:
1- In Lagrangian Method, there is only one variable in equilibrium equation and mass and
stiffness matrixes are symmetric. But there is not such a condition in Eulerian method. Also,
the numbers of unknown parameters are different in two methods. By considering these
differentiations, needed time for analysis of Pine Flat Dam under Taft earthquake ,with
mentioned characteristics, by Lagrangian method is 1.17 times more than needed time for
Eulerian method.
2- The effect of material on reservoir's bottom in absorbing energy and `reducing system's
response was considerable especially under vertical component of the earthquake. Results
indicate that this case is not affected by reservoir modeling method. By applying this effect,
the response will decrease about 15% under horizontal component and 60% under vertical
component of the earthquake.
3- By evaluating the effect of reservoir bottom's slope, it is concluded that in the case of rigid
foundation, the response by Lagarngian modeling is about 10% more than Eulerian one. With
the increase of slope, the response will decrease under horizontal component of earthquake
but it will decrease or increase about 13% under vertical component of the earthquake. In
other words, reservoir bottom slope has little effect on response of the system under both
vertical and horizontal component of earthquake. But this effect is not negligible.
4- It is included from the analyses that by decreasing the depth of reservoir the response will
decease up to 50 percent under horizontal component of earthquake. This amount is 80
percent under vertical component. Also in the case of decreased depth, response of
Lagarngian method is about 10% more than Eulerian method.
5-In all analysis, the assumption of rigid foundation results in greater answers than the cases
of flexible foundation.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
11
v.
4
no.
2012
107
116
http://mcej.modares.ac.ir/article_1815_64dc56b55e4f7f0c5aabaf1c9068505e.pdf
Compared to Non-Linear Behavior of Flat and Corrugated
Sheet Steel Shear Walls
S.
YousefiKhatoni
author
H.
Shokati
author
M.
ShaikhBagloo
author
text
article
2012
per
Steel shear walls has been noticed against wind and earthquake lateral loads about high
buildings in the last three decades. This modern phenomenon is growing rapidly worldwide so
that system have been employed highly in construction of new buildings and seismic
upgrading of existing buildings in some countries such as USA and JAPAN. That is a very
simple system from viewpoint of implementing and there isn’t particular complexity. High
strength and ductility are main advantages of these systems. Current paper has investigated
comparatively behavior of steel shear walls made of smooth and corrugated sheets. Also the
paper has assessed push-over curves and cyclic binding. According to this result of the
research, corrugated steel shear walls have lower ductility than smooth shear walls. The
research also founded that despite the high strength of corrugated sheets in low displacement,
behavior of flat shear walls is more stable than corrugated shear walls. On the other hand flat
steel shear walls attract energy more than corrugated shear walls. Therefore using of flat shear
walls is recommended in high seismic regions.
In this research, 18 samples of flat steel shear walls and corrugated shear walls were
modulated. In all models, panels height were 3 m and panels span were 3, 4 and 5 m. the
thickness of sheets in the samples were 3, 4 and 5mm.
According to results of the research:
1- Corrugated sheets are unstable and unpredictable in high thinness. In the low displacements
occurs a mutation state, so it distinguishes the corrugated and flat shear walls behavior.
2- At low displacement, a corrugated sheet bears greater load than a flat sheet.
3- In a constant thickness for thinner corrugated sheets is increased the mutation rate and its
behavior becomes more non-uniform.
4- Despite of the fact, pynchyng phenomenon appears in all samples, but all samples behavior
is stable and significant energy attraction is observed.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
11
v.
4
no.
2012
117
126
http://mcej.modares.ac.ir/article_1816_32fa261fd1c9e3e592c45e6fe2bf13ea.pdf