per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Studying the Propagation of Top-Down Cracking
(TDC) in Asphalt Concrete pavements by Means of
Fracture Mechanics Theory
M. Fakhri
1
m Farokhi
2
Abstract
Fatigue can be expressed as the failure of asphalt concrete under repeated loading in such a way that
stress induced in the asphalt layer could be less than ultimate strength of the material. Fatigue cracking
in asphalt concrete layer can be classified into two types regarding the place of crack initiation and the
type of crack propagation. The first type the cracks initiated in the bottom of asphalt layer and
propagates upward. This type of cracking is produced in the thin asphalt layer. The second type of
cracking which is produced in thick asphalt layer is initiated in surface area then propagates downward
which is called Top-Down cracking. The second type of cracking is studied less compared to the first
one. One type of fatigue cracking, is fracture mechanics approach in which the failure in asphalt
mixture is related to number of repeated loading. In this study the fracture mechanics approach was
implemented to understand the effective parameters in propagation of top-down cracking. as well as
developing a model to interpret the crack propagation in pavement also some graphs were produced
for different types of material and loading which gives the length of cracks versus the number of
repeated loading. the results showed that with increasing the load distance from the initial place which
is initiated the stress intensity factor is increased in mode Ι and mode ΙΙ. Also increasing the stiffness
gradient in asphalt concrete due to temperature differential in top and bottom of asphalt layer or
differential increasing between stiffness of asphalt surface and asphalt base course will be increased
the stress intensity factor.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-1114&slc_lang=en&sid=16
Pavement
Asphalt
Top down cracking
Crack propagation
Fracture mechanics
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Modeling and Analysis of Masonry Elements by
Fixed Smeared Crack Approach
Amier barimany
1
M Soltani Mohammadi2
2
A. Tasnimi
3
The objective of this research is to develop nonlinear constitutive models for performance evaluation of masonry
members on the basis of continuum model and fixed smeared crack approach. The finite element program called
"WCOMD", which has basically been developed for modeling and analyzing the reinforced concrete, is used as
the basis for modeling and analyzing in this paper. Constitutive laws and yield criteria according to the available
experimental results on masonry panels are improved, so that it would have the capability of modeling nonlinear
anisotropic behavior of masonry. The post-cracking behavior of masonry in direction normal to the crack
(tension softening) is calculated according to crack band theory and in terms of fracture energy and element size
in finite element. Also, the effect of cracking on compression behavior of masonry is considered on the basis of
compression field theory. The validity of behavior models and analysis methods is measured via analyzing
available experimental results in field of masonry panels and masonry walls.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-8381&slc_lang=en&sid=16
Nonlinear analysis
Smeared crack
Constitutive law
Masonry
FEM
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Research Note»
Examination of Functions of Continuous Wavelet
Transform in Identification of Crack Specification
M.A Lotfollahi Yaghin1
1
M. Koohdarag2
2
Abstract
Most structural failures are because of break in consisting materials. These breaks are initiated with
crack extension, which is a serious threat to the behavior of structure, so different methods have been
developed for distinguishing and showing such cracks. Meanwhile, the new methods based on
original wavelet transform are efficient and very important in the subject of signals. The main aim of
this paper is to fin the methods capable of distinguishing the specifications of cracks practically.
first a modal analysis of the structure was For this purpose, performed using ANSYS software, Then
the structure was analyzed as original wavelet using the wavelet toolbox of MATLAB software the
results are shown in two dimensional charts of coefficient-position.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-5126&slc_lang=en&sid=16
Wavelets transform
Modal Analysis
signal
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Health Monitoring of Cracked Cantilever Beams
Using Artificial Neural Networks Considering
Nonlinear Crack Behavior
ئ. Joharzadeh
1
N. Khaji
2
A Bahreininejad 3
3
Abstract
In this paper, using Artificial Neural Networks (ANNs) and Finite Element Method (FEM),
health monitoring of damaged cantilever beams having longitudinal cracks is discussed. The
main focus is devoted to the nonlinear behavior (breathing) of crack, which, to our knowledge,
is taken into account in the crack detection of structures using ANNs, for the first time. Thus
nonlinear behavior of crack is modeled using FEM.The changes in the natural frequencies
(due to crack) of various vibration modes were implemented as input for training and testing
of ANNs. By producing various scenarios for sound and damaged beams (with different
damage location and severity), two specific classes of ANNs were trained to predict the
location and length of longitudinal cracks. The Results showed a promising prediction for the
length of cracks by the proposed methodology. Also a considerable approximation observed in
the prediction of cracks location.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-6459&slc_lang=en&sid=16
Structural health monitoring
Cantilever beam
ANNs
Nonlinear FEM
Crack
breathing
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Effects of Plastic Hinge Properties in Nonlinear
Analysis of Reinforced Concrete Buildings
A.R Mortezaei1
1
S.M Zahrai
2
Abstract
Due to its simplicity, the structural engineering profession uses the nonlinear static analysis or
pushover analysis. Modeling of such analysis requires the determination of the nonlinear properties of
each component in the structure, quantified by strength and deformation capacities depending on the
modeling assumptions. Pushover analysis is carried out for either user-defined nonlinear hinge
properties or default-hinge properties, available in some programs based on the FEMA guidelines.
While such documents provide the hinge properties for several ranges of detailing, the programs may
implement averaged values. The user needs to be careful; becduse the misuse of default-hinge
properties may lead to unreasonable displacement capacities for existing structures. This paper studies
the possible differences in the results of push-over analysis due to default and user-defined nonlinear
component properties. Four- and eight-story buildings were considered to represent low- and mediumrise
buildings for this study.
Plastic hinge length and transverse reinforcement spacing were assumed as effective parameters in the
user-defined hinge properties. The observations showed that plastic hinge length and transverse
reinforcement spacing have no influence on the base shear capacity, while these parameters have
considerable effects on the displacement capacity of the frames. The comparisons pointed out that an
increase in the amount of transverse reinforcement improves the Frames displacement capacity. Also
Our findings clearly showed that the user-defined hinge model is better than the default-hinge model
in reflecting the nonlinear behavior compatible with the element properties. However, although the
default-hinge model is preferred due to its simplicity, the user should be aware of the circumstances
provided in the program and thus should avoid the misuse of default-hinge properties.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-2919&slc_lang=en&sid=16
Nonlinear static analysis
Nonlinear hinge properties
Plastic hinge length
Pushover
analysis
Transverse steel reinforcement
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Modification of non-linear model of Fahey for coarsegrained
soils of Tehran, using pressuremeter tests
y. .Hamdollahi
1
Ali fakhr
2
B. .Pahlavan
3
Abstract
The stiffness of soils is not constant and it is highly strain dependent. Some nonlinear models such as
Fahey's model for sands have been proposed for sands but these models can not be the representative of the
behavior of most coarse-grained soils such as alluvial sediments of Tehran.
In this paper, firstly some data of deformation modulus of several coarse-grained soils such as Tehran's soil
are presented as a function of strain. Then the weakness of nonlinear models such as Fahey's model in
predicting the behavior of these kind of geo-materials is presented. In next step, a new proposed model,
which is in fact a type of corrected Fahey model, is explained and then a comparison is done for Tehran
soil. The foundation of Milad tower is modeled using FLAC software incorporating new model and then
calculated settlement is compared with measured one using micro-geodetic method.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-395&slc_lang=en&sid=16
Nonlinear stiffness
Fahey's model
Shear modulus
Nonlinear behavior
Pressuremeter
Coarse-grained soils
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Research Note»
Evaluation of the Methods of Maximum Lateral
Displacement Estimation of R/C Moment Structures
due to Earthquake
Mussa Mahmoudi
1
Abstract
For seismic design, it is important to estimate the, maximum lateral displacement (inelastic
displacement) of the structures due to earthquakes for several reasons. Seismic design
provisions estimate the maximum roof and storey drifts occurring in major earthquakes by
amplifying the roof displacement and drifts of the structures obtained by elastic analysis
subjected to seismic design load, with a coefficient named “displacement amplification
factor” which is greater than one. Here, this coefficient depends on various parameters such
as ductility factor and overstrength factor. The present research aims to evaluate the value of
the displacement amplification factor in seismic design codes and then tries to propose a new
value as displacement amplification factor to estimate the maximum lateral structural
displacement due to severe earthquakes. In seismic codes, since the displacement
amplification factor is related to “force reduction factor”, hence; this aspect has been
accepted in the current study. Meanwhile, two methodologies were applied to evaluate the
value of displacement amplification factor and its relation with the force reduction factor. In
the first methodology, which is applied for all structures, the ratio of displacement
amplification and force reduction factors was determined directly. Whereas, in the second
methodology that is applicable just for the R/C moment resisting frames, the ratio was
obtained by calculating both factors, separately. The results were alike and both of them
could estimate the ratio of the two factors from 1 to 1.2. The results also indicated that the
ratio of the displacement amplification factor and the force reduction factor differs to those
proposed by seismic provisions such as NEHRP, IBC and Iranian seismic code (Standard no.
2800).
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-6253&slc_lang=en&sid=16
Displacement amplification factor
Force reduction factor
Maximum lateral
displacement
Ductility factor
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
The Values of Damage Indices in
Unreinforced and Flange-Plate Connections of
Steel Moment Frames under Earthquake
Loads
S. Dardaei Joghan1
1
F DANASHJO
2
Abstract
Studying the response details of steel moment connections is very important due to the role of
connections in moment resisting frames. The aims of this research were: i) to study the damage indices
of steel material including: Pressure Index, Mises Index, Equivalent Plastic Strain Index, Triaxiality
Index, and Rupture Index and ii) to compare these indices at connections of steel moment frames
under earthquake loads. To achieve this, time history nonlinear dynamic analysis is performed using
selected earthquake records on 2D model of special steel frame with ten storey and one bay to
determine maximum rotations of connections. Then, damages indices of the selected connections
under maximum rotation of records are investigated with selecting two types of moment connections.
The results indicate that damage indices are dependent on type of connection, location of surveying,
and rotations caused by earthquake movements. This dependency is very considerable for Equivalent
Plastic Strain Index and Ruptureindices
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-9440&slc_lang=en&sid=16
Nonlinear Dynamic Analysis
Moment frames
connection
Damage indices
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Effect of Time Dependent Deformations of Concrete
on Prestressing Force in Cylindrical Tank\'s shells
K. Shahverdiani
1
Ali.R Rahai
2
Abstract
Prestressing techniques are generally used for the construction of large
containment shells to overcome tension and to ensure tightness. Thus, the
evaluation of the prestressing force variations considering the geometry and
mechanical characteristics of tendons becomes an important matter. This paper
considers the effects of time dependent deformations of materials on the
circumferential prestress force in prestressed concrete cylindrical containments.
Numerical studies are performed using creep and relaxation models presented in
different codes of practice after checking the numerical model by experimental
data reported elsewhere about a prestressed concrete beam. The effects of vertical
prestressing and wall thickness are also studied. Obtained results show an amount
of 15% to 22% of prestress loss in tendons, specially in those located around wall’s
mid-height , on which relaxation of steel has a dominant effect. Furthermore, the
minor effect of vertical prestresssing might be mentioned. Besides, the creep model
of Iranian concrete code is studied and some suggestions are made for the
modification of the coefficient used for the prestress losses due to relaxation
effects.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-4995&slc_lang=en&sid=16
Keywords :Prestress loss
Cylindrical tank
Concrete creep
Steel relaxation
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2010-12
10
3
0
0
article
Numerical Analysis of Dynamic Pore Water
Pressure in Earth Dams under the Earthquake
Loading
M. Yazdani
1
H.R Paseh2
2
M. Masjoodi
3
Abstract
In this study, the dynamic behaviour and pore water pressure generation in a typical earth dam
were investigated using the non-linear dynamic analyses results. Based on the Byrne version of
the Finn’s Model, variations of pore water pressure ratio against the strength parameters of
materials and also the dilatancy angle of shell material were considered. In addition, using the
scaling method of applying maximum acceleration, the variations of pore water pressure ratio
and liquefaction phenomenon were investigated in different maximum accelerations. The results
demonstrated that excess pore pressure depends strongly on the strength parameters, dilatancy
angle of materials and applied maximum acceleration. Inappropriate compaction of shell
material results in severe increase in liquefaction-induced failure potential. In earth dams with
appropriate compaction of materials, liquefaction probability in the dam body, is negligible
even in large earthquake accelerations.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-657&slc_lang=en&sid=16
Angle of dilatancy
Dynamic Analysis
earth dam
Excess pore water pressure
Liquefaction