Showing 74 results for Analysis
Afshar M.h.,
Volume 1, Issue 1 (9-2003)
Abstract
In this paper the analysis of the pipe networks is formulated as a nonlinear unconstrained optimization problem and solved by a general purpose optimization tool. The formulation is based on the minimization of the total potential energy of the network with respect to the nodal heads. An analogy with the analysis of the skeletal structures is used to derive tire formulation. The proposed formulation owes its significance for use in pipe network optimization algorithms. The ability and versatility of the method to simulate different pipe networks are numerically tested and the accuracy of the results is compared with direct network algorithms.
Kheyr Aldin A., Mortezaei A.r.,
Volume 2, Issue 1 (3-2004)
Abstract
Structural walls are used extensively in moderate- and high-rise buildings to resist lateral loads induced by earthquakes. The seismic performance of many buildings is, therefore, closely linked to the behavior of the reinforced concrete walls. The analytical models used in this paper are developed to study the push-over response of T-shaped reinforced concrete walls andinvestigate the influence of the flange walls on laterally loaded walls and nonlinear behavior of shear walls, namely strength, ductility and failure mechanisms. A layered nonlinear finite element method is used to study the behavior of T-shaped and rectangular (barbell) shear walls. This paper introduces a computer program to practically study three-dimensional characteristics of reinforced concrete wall response by utilizing layered modeling. The program is first verified bysimulated and reported experimental response of 3-D reinforced concrete shear walls. Subsequently, a study considering eighteen analytical test specimens of T-shaped and barbell shear walls is carried out. Finally, based on analytical results, a new equation for minimum ratio of shear wall area to floor-plan area is proposed.
Ghodrati Amiri G., Sedighi S.,
Volume 2, Issue 4 (12-2004)
Abstract
In the past decade design procedure changed to �performance-based design� from�force-based design�, by this mean many researchers focused on nonlinear static analysis (NSA)and the procedure named �PUSHOVER�. Advantages of this method are defining the inelasticbehavior of structure without nonlinear dynamic analysis (NDA) effort and also defining plastichinges formation in critical elements, and the order of formed plastic hinges. In spite of these goodadvantages NSA is limited to short and planar structures and application of that in tall andtorsionaly asymmetric structures may yield unreliable results.In this study reliability of NSA is investigated by performing both nonlinear static and dynamicanalysis on six 2D moment resisting concrete frames. Non linear dynamic analysis has been doneby the suggested method in FEMA356 guideline called �Target Displacement Method�. A groupof 4 different lateral increasing loads were used in pushover analysis and 3 different groundmotions were applied in NDA. Results indicate that same responses can be obtained by performingNSA, but errors will be increased by frames height increment.
H. Moharrami, S.a. Alavinasab,
Volume 4, Issue 2 (6-2006)
Abstract
In this paper a general procedure for automated minimum weight design of twodimensional
steel frames under seismic loading is proposed. The proposal comprises two parts:
a) Formulation of automated design of frames under seismic loading and b) introduction of an
optimization engine and the improvement made on it for the solution of optimal design. Seismic
loading, that depends on dynamic characteristics of structure, is determined using "Equivalent
static loading" scheme. The design automation is sought via formulation of the design problem in
the form of a standard optimization problem in which the design requirements is treated as
optimization constraints.
The Optimality Criteria (OC) method has been modified/improved and used for solution of the
optimization problem. The improvement in (OC) algorithm relates to simultaneous identification of
active set of constraints and calculation of corresponding Lagrange multipliers. The modification
has resulted in rapid convergence of the algorithm, which is promising for highly nonlinear optimal
design problems. Two examples have been provided to show the procedure of automated design and
optimization of seismic-resistant frames and the performance and capability of the proposed
algorithm.
F. R. Rofooei, N. K. Attari, A. Rasekh, A.h. Shodja,
Volume 4, Issue 3 (9-2006)
Abstract
Pushover analysis is a simplified nonlinear analysis technique that can be used to
estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first
steps taken in this approximate solution is to assess the maximum roof displacement, known as
target displacement, using the base shear versus roof displacement diagram. That could be done by
the so-called dynamic pushover analysis, i.e. a dynamic time history analysis of an equivalent single
degree of freedom model of the original system, as well as other available approximate static
methods. In this paper, a number of load patterns, including a new approach, are considered to
construct the related pushover curves. In a so-called dynamic pushover analysis, the bi-linear and
tri-linear approximations of these pushover curves were used to assess the target displacements by
performing dynamic nonlinear time history analyses. The results obtained for five different special
moment resisting steel frames, using five earthquake records were compared with those resulted
from the time history analysis of the original system. It is shown that the dynamic pushover analysis
approach, specially, with the tri-linear approximation of the pushover curves, proves to have a
better accuracy in assessing the target displacements. On the other hand, when nonlinear static
procedure seems adequate, no specific preference is observed in using more complicated static
procedures (proposed by codes) compared to the simple first mode target displacement assessment.
Ali Kheyroddin, Hosein Naderpour,
Volume 5, Issue 1 (3-2007)
Abstract
A parametric study is performed to assess the influence of the tension reinforcement
index, ( ω = ρ fy /f Bc), and the bending moment distribution (loading type) on the ultimate
deformation characteristics of reinforced concrete (RC) beams. The analytical results for 15 simply
supported beams with different amounts of tension reinforcement ratio under three different loading
conditions are presented and compared with the predictions of the various formulations and the
experimental data, where available. The plastic hinge rotation capacity increases as the loading is
changed from the concentrated load at the middle to the third-point loading, and it is a maximum
for the case of the uniformly distributed load. The effect of the loading type on the plastic rotation
capacity of the heavily reinforced beams is not as significant as that for the lightly reinforced beams.
Based on the analytical results obtained using the nonlinear finite element method, new simple
equations as a function of the tension reinforcement index, ω, and the loading type are proposed.
The analytical results indicate that the proposed equations can be used for analysis of ultimate
capacity and the associated deformations of RC beams with sufficient accuracy.
A. Yeganeh Bakhtiary, A. Ghaheri, R. Valipour,
Volume 5, Issue 1 (3-2007)
Abstract
Determination of allowable free span length plays a crucial role in design of offshore
pipelines. The seabed intervention cost and safety of an offshore pipelines project are largely
influenced by pipelines free spanning during the project life time. Different criteria are proposed by
both the current designing guidelines and researchers there is however lack of comprehensive
assessment of independent parameters affects the design length of free span. In this note, it is
intended to investigate the effects of seabed formation along with axial force on Natural Frequency
of offshore pipelines. Based on this assessment a new simple formula is proposed. Finally, to
evaluate the result of this study, the allowable free span length of Qeshem Island pipelines is
calculated as a case study and compared with those of the DNV (1998) and ABS (2001) guidelines
and the modal analysis.
A. Rahmani Firoozjaee, M.h. Afshar,
Volume 5, Issue 2 (6-2007)
Abstract
A meshless method namely, discrete least square method (DLSM), is presented in the
paper for the solution of free surface seepage problem. In this method computational domain is
discredited by some nodes and then the set of simultaneous equations are built using moving least
square (MLS) shape functions and least square technique. The proposed method does not need any
background mesh therefore it is a truly meshless method. Several numerical two dimensional
examples of Poisson partial differential equations (PDEs) are presented to illustrate the
performance of the present DLSM. And finally a free surface seepage problem in a porous media is
solved and results are presented.
M.h. Sebt, H. Rajaei, M.m. Pakseresht,
Volume 5, Issue 3 (9-2007)
Abstract
Project participants are becoming more aware of the high costs and risks associated with
delay claims and their litigation. Among delays, weather delay has an important role in projects
performed in severe environmental conditions. This research is the extension of delay analysis
techniques by approving analysis of weather delays using fuzzy logic. At the presented technique,
first using a fuzzy logic model calculated the delay that occurred during the activity execution after
weather event then by the selected delay analysis method (Time impact analysis) and using the risk
of the contractor during the contract approval together with the effect of previous delay in changing
the duration of activities, analyzed weather delays in construction project. A local general
contractor and governmental firms involved in a highway construction project practiced by offering
their experienced and knowledge in delay analysis procedures to provide data for development and
testing of the model specified for rain events. The results indicated that the presented model is in
accordance with practical experiences in weather delay duration except in some circumstances that
can be divided into the separated parts. It also advances the use of fuzzy logic in delay analysis
procedures and becomes it more systematic special for weather delays.
H. Behbahani, S.a. Sahaf,
Volume 5, Issue 3 (9-2007)
Abstract
The available methods for predicting mechanical characteristics of pavement layers are
categorized into two general groups, Destructive and Non-destructive. In destructive method, using
coring and pavement subgrade and performing necessary experiments on them, the quantities of
layers properties will be identified. In Non-destructive method, the attained deflection is measured
by applying the loading on pavement surface using equipments such as FWD which charges the
impact dynamic load, and the mechanical characteristics of pavement layers are determined using
back calculations. The procedure of conducting these calculations is that by knowing the thickness
of the pavement layers and assuming the initial amounts for mechanical characteristics of the layer,
the attained deflection at the desired points on the pavement surface will be calculated. Then, new
figures are assumed for the characteristics of layers in a reattempt and calculations are repeated
again. This trial and error is continued until the produced basin deformations from the calculations
with true value, differs in an acceptable range. Using this method may have no accurate and single
answer, since the various compositions of layers characteristics can produce similar deformations
in different points of pavement surface. In this article, using an innovative method, a measurement
is taken in constructing and introducing a mathematical model for determining the elastic module
of surface layer using deflections attained from FWD loading equipment. The procedure is such that
by using dynamic analysis software of finite elements like ABAQUS and ANSYS, the deformation of
corresponding points on the surface of the pavement will be attained by FWD loading equipment.
This analysis will be performed on a number of pavements with different thicknesses and different
layers properties. The susceptibility analysis of different points deformations show, which will be
performed as a result of the change of properties and layers thicknesses. Using this artificial data
base as well as deflection basin parameters (DBP), a measurement will be taken toward
constructing a regression model for determination of asphalt layer model, i.e. Eac =f(DBP) function
shall be attained. To achieve the maximum correlation coefficient, an attempt is made to use the
parameters of deformations basin which has the most susceptibility in changing asphalt layer
module.
M.kazem Sharbatdar,
Volume 6, Issue 1 (3-2008)
Abstract
FRPs (fiber reinforced polymer) possess many favorable characteristics suitable and applicable for
construction industry when compared with steel reinforcement. There are new ideas to use FRPs as
longitudinal or transverse reinforcement for new concrete elements particularly for bridge decks or beams.
Although high tensile strength of FRP is main characteristic for applications at both areas, its weakness to
bending and linear stress-strain behavior with virtually no ductility, makes it vulnerable to probably
premature failures under reversal tension-compression loading during earthquake. A pilot research project
has been conducted to explore the characteristics of large-scale cantilever concrete beams reinforced with
FRP re-bars and grids and were tested under either simulated cyclic loading or monotonically increasing
lateral loading. This paper presents the test parameters and results obtained during research. The analytical
relationships are compared with those recorded experimentally, and test results showed the diagonal cracks
and either rupturing of FRP bars in tension or stability failure in compression bars at long or short shear span
beams. The comparison of nominal moment capacities between analytical and experimental values confirms
that plane section analysis is applicable to FRP reinforced concrete members.
Faradjollah Askari, Orang Farzaneh,
Volume 6, Issue 1 (3-2008)
Abstract
Although some 3D slope stability algorithms have been proposed in recent three decades, still role
of pore pressures in three dimensional slope stability analyses and considering the effects of pore water
pressure in 3D slope stability studies needs to be investigated. In this paper, a limit analysis formulation for
investigation of role of the pore water pressure in three dimensional slope stability problems is presented. A
rigid-block translational collapse mechanism is used, with energy dissipation taking place along planar
velocity discontinuities. Results are compared with those obtained by others. It was found that water pressure
causes the three-dimensional effects to be more significant, especially in gentle slopes. This may be related to
the larger volume of the failure mass in gentle slopes resulting in more end effects. Dimensionless stability
factors for three dimensional slope stability analyses are presented - including the 3D effect of the pore water
pressure – for different values of the slope angle in cohesive and noncohesive soils.
Farnad Nasirzadeh, Abbas Afshar, Mostafa Khanzadi,
Volume 6, Issue 2 (6-2008)
Abstract
Presence of risks and uncertainties inherent in project development and implementation plays
significant role in poor project performance. Thus, there is a considerable need to have an effective risk
analysis approach in order to assess the impact of different risks on the project objectives. A powerful risk
analysis approach may consider dynamic nature of risks throughout the life cycle of the project, as well as
accounting for feedback loops affecting the overall risk impacts. This paper presents a new approach to
construction risk analysis in which these major influences are considered and quantified explicitly. The
proposed methodology is a system dynamics based approach in which different risks may efficiently be
modeled, simulated and quantified in terms of time, cost and quality by the use of the implemented object
oriented simulation methodology. To evaluate the performance of the proposed methodology it has been
employed in a bridge construction project. Due to the space limitations, the modeling and quantification
process for one of the identified risks namely “pressure to crash project duration” is explained in detail.
Kourosh Shahverdiani, Ali Reza Rahai, Faramarz Khoshnoudian,
Volume 6, Issue 2 (6-2008)
Abstract
Large capacity cylindrical tanks are used to store a variety of liquids. Their Satisfactory
performance during earthquake is crucial for modern facilities. In present paper, the behavior of cylindrical
concrete tanks under harmonic excitation is studied using the finite element method. Liquid sloshing, liquid
viscosity and wall flexibility are considered and additionally excitation frequency, liquid level and tank
geometry is investigated. The results show a value for wall thickness to tank diameter ratio which may be used
as a guide in the consideration of wall flexibility effects.
Mehdi Poursha, Faramarz Khoshnoudian, Abdoreza S. Moghadam,
Volume 6, Issue 2 (6-2008)
Abstract
The nonlinear static pushover analysis technique is mostly used in the performance-based design of
structures and it is favored over nonlinear response history analysis. However, the pushover analysis with
FEMA load distributions losses its accuracy in estimating seismic responses of long period structures when
higher mode effects are important. Some procedures have been offered to consider this effect. FEMA and
Modal pushover analysis (MPA) are addressed in the current study and compared with inelastic response
history analysis. These procedures are applied to medium high-rise (10 and 15 storey) and high-rise (20 and
30 storey) frames efficiency and limitations of them are elaborated. MPA procedure present significant
advantage over FEMA load distributions in predicting storey drifts, but the both are thoroughly unsuccessful
to predict hinge plastic rotations with acceptable accuracy. It is demonstrated that the seismic demands
determined with MPA procedure will be unsatisfactory in nonlinear systems subjected to individual ground
motions which inelastic SDF systems related to significant modes of the buildings respond beyond the elastic
limit. Therefore, it’s inevitable to avoid evaluating seismic demands of the buildings based on individual
ground motion with MPA procedure.
Shahram Feizee Masouleh, Kazem Fakharian,
Volume 6, Issue 3 (9-2008)
Abstract
A finite-difference based continuum numerical model is developed for the pile-soil dynamic response
during pile driving. The model is capable of simulating the wave propagation analysis along the pile shaft and
through the soil media. The pile-soil media, loading and boundary conditions are such that axisymmetric
assumption seems to be an optimized choice to substantially reduce the analysis time and effort. The
hydrostatic effect of water is also considered on the effective stresses throughout the soil media and at the pilesoil
interface. The developed model is used for signal matching analysis of a well-documented driven pile. The
results showed very good agreement with field measurements. It is found that the effect of radiation damping
significantly changes the pile-soil stiffness due to the hammer blow. The pile tip response shows substantial
increase in soil stiffness below and around the pile tip due to driving efforts.
S. N. Moghaddas Tafreshi,
Volume 6, Issue 4 (12-2008)
Abstract
This paper presents the numerical analysis of seismic soil-pile-superstructure interaction in soft clay using free-field soil analysis and beam on Winkler foundation approach. This model is developed to compute the nonlinear response of single piles under seismic loads, based on one-dimensional finite element formulation. The parameters of the proposed model are calibrated by fitting the experimental data of largescale seismic soil-pile-structure tests which were conducted on shaking table in UC Berkeley. A comparative evaluation of single piles shows that the results obtained from the proposed procedure are in good agreement with the experimental results.
Alireza Mortezaei, Ali Kheyroddin,
Volume 7, Issue 1 (3-2009)
Abstract
The work presented in this paper investigates the causes of size effects in structural-concrete members. It is
based on the use of a finite-element model found to yield realistic predictions of structural-concrete behavior in all
cases investigated to date. In fact, the previous use of this model in investigations of size effects in reinforced-concrete
beams indicated that such effects reflect the dependence of load-carrying capacity on small unintended eccentricities
of the applied load and/or load-induced anisotropy, rather than, as widely considered, on fracture-mechanics
characteristics. The present work extends the scope of the above investigation so as to include the case of reinforced
concrete flanged shear walls, the behavior of which is already established experimentally. It is found that, unlike the
flanged shear walls with a height-to-length ratio larger than 2, the shear walls investigated in the present work, in
contrast with the interpretation given to recently published experimental findings, are size-effect independent.
M.h. Sebt, A. Gerei, H. Naghash Toosi,
Volume 7, Issue 3 (9-2009)
Abstract
Risks mean cases of uncertainty of project, the impact of which is realized as a threat (negative aspect)
and/or opportunity (positive aspect). The traditional viewpoint on risk is a negative viewpoint that implies damages,
loss and harmful consequences. Judgments such as this on risk merely emphasize on risks management and pay less
attention to opportunities management. It is clear that some uncertainties might be profitable for the project as in
many cases, it could be the source of loss. In a developed attitude, focus is made on a common process that could
address the integrated management of both opportunities and risks to aim at maximizing the positive effectsopportunities-,
and minimizing negative effects- risks-. Therefore, existence of causal-effect relations between risks,
relationship, effects of risks and opportunities on each other and variety of strategies in facing risks gives no
alternative for risk management team than taking integrated management of risks and opportunities. In another word,
reaction to risks, with respect to risks and/or relevant opportunities, separately, will be never effective. In this paper,
for the purpose of integrated management of risks and opportunities, the stages of quality analysis and reactions to
risk are combined. The method which is used for reaction towards risk is a procedure based on dynamic system.
Dynamic system is highly important among uncertainties due to considering the type and intensity of effects. By using
dynamic system and attention to the relationship between uncertainties (risks/ opportunities), reaction to risk and
decision making on employing suitable strategies to face risks will be more precise and accurate.
M.a. Goudarzi, S.r. Sabbagh-Yazdi,
Volume 7, Issue 3 (9-2009)
Abstract
The main objective of this article is evaluation of the simplified models which have been developed for
analysis and design of liquid storage tanks. The empirical formulas of these models for predicting Maximum Sloshing
Wave Height (MSWH) are obtained from Mass Spring Models (MSM). A Finite Element Modeling (FEM) tool is used
for investigating the behavior the some selected liquid storage tanks under available earthquake excitations. First, the
results of FEM tool are verified by analyzing a liquid storage tank for which theoretical solution and experimental
measurements are readily available. Then, numerical investigations are performed on three vertical, cylindrical tanks
with different ratios of Height to Radius (H/R=2.6, 1.0 and 0.3). The behaviors of the tanks are initially evaluated using
modal under some available earthquake excitations with various vibration frequency characteristics. The FEM results
of modal analysis, in terms of natural periods of sloshing and impulsive modes period, are compared with those
obtained from the simplified MSM formulas. Using the time history of utilized earthquake excitations, the results of
response-history FEM analysis (including base shear force, global overturning moment and maximum wave height)
are compared with those calculated using simplified MSM formulations. For most of the cases, the MSWH results
computed from the time history FEM analysis demonstrate good agreements with the simplified MSM. However, the
simplified MSM doesn’t always provide accurate results for conventionally constructed tanks. In some cases, up to
30%, 35% and 70% average differences between the results of FEM and corresponding MSM are calculated for the
base shear force, overturning moment and MSWH, respectively.
