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Volume 15, Issue 3, 2008
Civil and Mechanical Engineering
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Performance Evaluation of Masonry
Buildings Using a Probabilistic Approach
A. Bakhshi (PhD.)
K. Karimi [PhD.]
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In many countries, there are traditional houses made of stone, adobe and brick, which perform
relatively weakly in earthquakes. To mitigate casualties in future earthquakes, it is necessary to
evaluate the current status of these buildings and propose eective methods to retrot them. One
method of evaluating the performance of buildings in earthquakes is through the use of fragility
curves. These diagrams show the probability of exceeding a specic state of damage versus
seismic intensity parameters, such as PGA, MMI, Ia, CAV etc. Fragility curves will provide
an important basis for analytical methods, based on probabilistic approaches. Much work has
been done on bridges, concrete and steel structures, while limited studies have been conducted
on masonry buildings. Considering the prevalence of these buildings and the high seismic activity
in some regions where they are built, fragility curves for dierent types of masonry buildings are
developed in this research. The results obtained show the probable damage to those types of
masonry building chosen in this research for dierent earthquake intensities and restates that, by
providing horizontal and vertical ties and retrotting these buildings, by the methods proposed
in some seismic code provisions (such as FEMA 356 and 357), their behavior in earthquakes are
apparently eected and structural damage reduced. Furthermore, results indicate that soil type
does not signicantly in
uence the seismic behavior of masonry buildings. |
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Comprehensive Simulation of Surface
Texture for an End-Milling Process
B.M. Imani (PhD.)
E. Layegh [PhD.]
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The analysis and simulation of the manufacturing process require extensive and complicated
computations. Nowadays, computer resources and computational algorithms have reached the
stage where they can model and simulate the problem eciently. One of the important processes
in manufacturing is machining. In this research, the end-milling process, which is one of the most
complex and widespread processes in machining, is chosen. The most important parameters in
end-milling are surface roughness and surface location errors. Comprehensive simulation software
is developed to model the end-milling process, in order to anticipate the nishing parameters, such
as surface roughness and errors. The proposed algorithm takes into account cutting conditions,
such as feed, doc, woc and tool run out etc. In addition, the dynamic simulation module
of the software can accurately model the
exible end-mill tool, the milling cutting forces and
regeneration of the waviness eects, in order to construct a realistic surface texture model.
The software can accurately determine the most commonly used index of surface roughness
parameters, such as Ra, P.T.V. and surface errors. |
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Use of Articial Neural Networks
in Predicting Highway Runo
Constituent Event Mean Concentration
M. Kayhanian (Professor)
A. Massoudieh [PhD.]
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In this paper, the large amount of highway runo characterization data that were collected in
California, during a 3-year monitoring season (2000-2003), were assessed in order to develop an
Articial Neural Network (ANN) model for predicting the Event Mean Concentration (EMC)
of the constituent. The initial data analysis performed by a Multiple Linear Regression (MLR)
model revealed that the Total Event Rainfall (TER), the Cumulative Seasonal Rainfall (CSR), the
Antecedent Dry Period (ADP), the contributing Drainage Area (DA) and the Annual Average
Daily Trac (AADT) were among the variables having a signicant impact on the highway
runo constituent EMC. These parameters were used as the basis for developing an Articial
Neural Network (ANN) model. The ANN model was also used to evaluate the impact of various
site and storm event variables on highway runo constituents' EMCs. The ANN model has
proven to be superior to the previously developed MLR model, with an improved R2 for most
constituents. Through the ANN model, one was able to see some non-linear eects of multi
variables on pollutant concentration that, otherwise, would not have been possible with a typical
MLR model. For example, the results showed that copper EMC is more sensitive at higher
Annual Average Daily Trac (AADT), with respect to ADP, compared with lower range AADT. |
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Unaxisymmetric Heat Transfer in the
Axisymmetric Stagnation-Point Flow of a Viscous
Fluid on a Cylinder with Simultaneous Axial and
Rotational Movement Along with Transpiration
A.B. Rahimi (PhD.)
R. Saleh [PhD.]
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The unaxisymmetric heat transfer of an unsteady viscous
ow, in the vicinity of an axisymmetric
stagnation-point of an innite circular cylinder, with simultaneous axial and rotational movement,
along with transpiration, Uo, is investigated, when the angular velocity, axial velocity and wall
temperature or wall heat
ux vary arbitrarily with time. The impinging free stream is steady and
with a strain rate of k. An exact solution of the Navier-Stokes equations and energy equation
is derived in this problem. A reduction of these equations is obtained by the use of appropriate
transformations for the most general case, when the transpiration rate is also time-dependent.
However, results are presented only for uniform values of this quantity. The general self-similar
solution of unsteady unaxisymmetric heat transfer is obtained, in which unaxisymmetry is due to
the sinusoidal variation of the temperature, with respect to the surface position of the rotating
cylinder, and unsteadiness is because of the sinusoidal variation of the temperature of each
point of the cylinder surface, with respect to time and, also the rotation of the cylinder. All
the solutions are presented for Reynolds numbers, Re = ka2=2, ranging from 0.1 to 10.0 for
dierent values of Prandtl number and selected values of the dimensionless transpiration rate,
S = U0=ka, where a is the cylinder radius and is the kinematic viscosity of the
uid. The
local coecient of heat transfer (Nusselt number) is found to be independent of time and place,
though the cylinder wall temperature or wall heat
ux are both functions of time and place. |
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Strong Ground Motion Eects on
Seismic Response Reduction by TLCDs
S.M. Zahrai (PhD.)
A. Kavand [PhD.]
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Nowadays, various types of passive control systems are being used as an eective solution
to reduce the seismic responses of structures. One type of these systems, the Tuned Liquid
Column Damper (TLCD), suppresses the input seismic energy by a combined action, including
the movement of liquid mass in the container, a restoring force on the liquid, due to gravity
loads, and the damping, due to liquid movement through the orices. In this paper, the possible
eects of seismic excitation characteristics, such as frequency content and soil condition, on
the seismic performance of TLCDs, are investigated, using nonlinear time-history analyses.
For this purpose, a ten-story building was modeled as an elastic MDOF structure and used
for numerical analyses. For the time-history analyses, among the past strong ground motion
records of Iran, 16 records with dierent characteristics were selected. The results of this study
show that these characteristics play a substantial role in the performance of TLCDs and they
should be, accordingly, considered in the designing of TLCDs. In some cases, TLCD is able
to reduce structural displacement up to 50%, while, in most cases, the eectiveness of TLCD
in reducing structural acceleration is not signicant. However, it should be mentioned that, in
real applications, de-tuning may occur, due to the inelastic behavior of structures, which can
reduce eectiveness. This study also shows that the displacement reduction capacity of TLCDs
is highly dependent on excitation characteristics, while the acceleration reduction capacity is not
that sensitive. |
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