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Showing 109 results for Dynamic

A. Khodaii, Sh. Fallah,
Volume 7, Issue 2 (6-2009)
Abstract

An experimental program was conducted to determine the effects of geosynthetic reinforcement on mitigating reflection cracking in asphalt overlays. The objectives of this study were to asses the effects of geosynthetics inclusion and its placement location on the accumulation of permanent deformation. To simulate an asphalt pavement overlaid on top of a crack in a concrete or asphalt pavement, an asphalt mixture specimen was placed on top of two discontinuous concrete or asphalt concrete blocks with 100 mm height. Four types of specimens were prepared with respect to the location of geogrid: (I) Unreinforced samples, which served as control specimen, (II) Samples with geogrid embedded on the concrete or asphalt concrete block, (III) Samples with geogrid embeded one-thired depth of asphalt concrete from bottom, (IV) Samples with geogrid embedded in the middle of the asphalt beam. Each specimen was then placed on the rubber foundation in order to be tested. Simulated- repeated loading was applied to the asphalt mixture specimens using a hydraulic dynamic loading frame. Each experiment was recorded in its entirety by a video camera to allow the physical observation of reflection crack formation and propagation. This study revealed that geosynthetic reinforced specimens exhibited resistance to reflection cracking. Placing the geogrid at the one- third depth of overlay thickness had the maximum predicted service life. Results indicate a significant reduction in the rate of crack propagation and rutting in reinforced samples compared to unreinforced samples.
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.
I.a. Hansen,
Volume 8, Issue 1 (3-2010)
Abstract

The paper discusses the current state of research concerning railway network timetabling and traffic

management. Timetable effectiveness is governed by frequency, regularity, accurate running, recovery and layover

times, as well as minimal headway, buffer times and waiting times. Analytic (queuing) models and stochastic microsimulation

are predominantly used for estimation of waiting times and capacity consumption anlong corridors and in

stations, while combinatorial models and stability analysis are suitable for network timetable optimisation. Efficient

traffic management can be achieved by real-time monitoring, fusion, analysis and rescheduling of railway traffic in

case of disturbances. Real-time simulation, optimisation and impact evaluation of dispatching measures can improve

the effectiveness of rescheduling and traffic management. The display of dynamic signal and track occupancy data in

driver cabins, as RouteLint developed by ProRail, can support anticipative actions of the driver in order to reduce

knock-on delays and increase throughput.


F. Jafarzadeh, H. Farahi Jahromi, E. Abazari Torghabeh,
Volume 8, Issue 2 (6-2010)
Abstract

Investigating the parameters influencing the behavior of buried pipelines under dynamic loading is of great

importance. In this study the soil structure interaction of the pipelines with the surrounding soil was addressed using

shaking table tests. Wave propagation along the soil layers was also included in the study. The semi infinite nature of

the field was simulated using a laminar shear box. The soil used in the experiments was Babolsar coastal sand (Iran).

PVC pipes were used due to their analogy with the field. Eight models were constructed with the first four models

having uniform base. In the next models, the non-uniformities of real ground were simulated using a concrete pedestal

installed at the very bottom of the shear box. Pipe deformations under dynamic loading, acceleration distribution in

height, soil settlement and horizontal displacements were measured by strain gauges, acceleratometers and

displacement meters. Analyzing the obtained data, influence of different parameters of dynamic loading such as

acceleration, frequency, soil density, base conditions and shaking direction to pipe axis on the acceleration

amplification ratio and pipe deformation were investigated. Also in order to study the effect of dynamic loading on two

different materials, soil and pipe, the horizontal strains were compared


H. Shahnazari, M. Esmaeili, H. Hosseini Ranjbar,
Volume 8, Issue 2 (6-2010)
Abstract

Considerations on the explosion resistant design of special infrastructures have increased in the recent

years. Amongst the various types of infrastructures, road and railway tunnels have a unique importance due to their

vital role in connection routes in emergency conditions. In this study, the explosion effects of a projectile impacting on

a railway tunnel located in a jointed rock medium has been simulated using 2D DEM code. Primarily, a GP2000

projectile has been considered as a usual projectile and its penetration depth plus its crater diameter were calculated

in rock mass. The blast pressure was, then, calculated via empirical formula and applied on the boundary of crater as

input load. Finally, the wave pressure propagation through the jointed rock medium was investigated. In part of the

study a sensitivity analysis has been carried out on jointed rock parameters such as joint orientation, dynamic modulus

and damping ratio. Their effects on tunnel lining axial force as well as bending moment have also been investigated.


J. Sadeghi,
Volume 8, Issue 3 (9-2010)
Abstract

 Investigations on vibration behaviors of railway track systems were attempted in this research. This was made by conducting a comprehensive field investigation into the free vibration of track systems and response of tracks to train moving loads. In-situ modal analysis was used in a railway track field as an efficient method of investigating dynamic properties of railway track systems. Natural frequencies and mode shapes of the track system in different insitu track conditions were obtained for the fist time. The sensitivity of the natural frequencies of the track to the types of sleepers, fastening systems, ballast conditions, and rail joints were studied. Efficiency of rail welded joints in CWR tracks and the effects of replacing timber sleepers with concrete sleepers on dynamic behavior of a track were investigated. Advantages of flexible sleeper fastening system from the aspects of serviceability and passenger riding comfort were discussed. The effects of the track accumulative loading as a main indicator of ballast degradation on track dynamic behavior were studied. Rail deflections were calculated by using auto-spectra obtained from vibrations of the track under trainloads, leading to the development of a new mathematical expression for the calculation of the rail dynamic amplification factor.


H. Shakib, F. Omidinasab, M.t. Ahmadi,
Volume 8, Issue 3 (9-2010)
Abstract

Elevated water tanks as one of the main lifeline elements are the structures of high importance. Since they are extremely vulnerable under lateral forces, their serviceability performance during and after strong earthquakes is a matter of concern. As such, in recent years, the seismic behavior of water tanks has been the focus of a significant amount of studies. In the present work, three reinforced concrete elevated water tanks, with a capacity of 900 cubic meters and height of 25, 32 and 39 m were subjected to an ensemble of earthquake records. The behavior of concrete material was assumed to be nonlinear. Seismic demand of the elevated water tanks for a wide range of structural characteristics was assessed. The obtained results revealed that scattering of responses in the mean minus standard deviation and mean plus standard deviation are approximately 60% to 70 %. Moreover, simultaneous effects of mass increase and stiffness decrease of tank staging led to increase in the base shear, overturning moment, displacement and hydrodynamic pressure equal to 10 - 20 %, 13 - 32 %, 10 - 15 % and 8 - 9 %, respectively.


F. Hajivalie, A. Yeganeh Bakhtiary,
Volume 9, Issue 1 (3-2011)
Abstract

In this paper, a two-dimensional Reynolds Averaged Navier-Stokes (RANS) model is developed to simulate the shoaling, breaking and overtopping of a solitary wave over a vertical breakwater. Turbulence intensity is described by using a k turbulence closure model and the free surface configuration is tracked by Volume Of Fluid (VOF) technique. To validate the numerical model the simulation results is compared with the Xie (1981) experimental data and a very good agreement between them is observed. The results revealed that wave height and wave energy decrease considerably during the reflection from vertical wall, which illustrates a considerable energy lost during the impaction and wave overtopping process. The turbulence production during the broken wave interaction with vertical breakwater is very significant consequently the vertical breakwater undergoes sever turbulent and dynamic drag force.


Mr. Mehdi Mahdavi Adeli, Dr. Mehdi Banazadeh, Dr. Ardeshir Deylami,
Volume 9, Issue 3 (9-2011)
Abstract

The objective of this paper is to determine the drift demand hazard curves of steel moment-resisting frames with different number
of stories in territory of Tehran this is done through the combination of the results obtained from probabilistic seismic hazard
analysis and the demand estimated through the best probabilistic seismic demand models. To select the best demand model, in
this paper, a Bayesian regression has been used for the statistical analysis of the results obtained from incremental dynamic
analysis in order to estimate the unknown parameters of model and to select the best Intensity Measure (IM) parameter also the
probability of overall collapse of structures has been computed. Considering the efficiency and sufficiency of the models, the
results indicate that the accuracy of models with one single IM is a function of the number of stories, consequently the current
widely used model with spectral acceleration in first period as IM is not suitable for all structural heights. Furthermore,
regarding the fact that it is difficult to prepare a seismic hazard curve for a combined IM, it seems that the best model can be
found among models with two single IMs. In other words, the best model to cover all structural heights is the one with linear
combination of spectral acceleration of the first and the second period. Furthermore, using different models to calculate the
curves shows that regardless of the number of IMs, estimated demands strongly depend on the standard deviation of model.

 


M. Miraboutalebi, F. Askari, O. Farzaneh,
Volume 9, Issue 4 (12-2011)
Abstract

In this paper, the effect of bedrock inclination on seismic performance of slopes is investigated. The study was conducted based

on dynamic analysis of different slopes, evaluation of the earthquake acceleration in sliding mass, and calculating the

permanent displacement of the slope, using Newmark sliding block. The investigation indicates that variation of the bedrock

inclination may cause the acceleration magnitude and the displacement in the sliding mass to reach to their maximum level.

This may happen in conditions that the mean period of the acceleration time history on failure surface (Tmt) and the

predominant period of the slope (Ts ) are close to each other. Typical results are presented and discussed. A two dimensional

model of a typical slope was considered and conducting dynamic analyses, the slope performance was studied for different

geometries, strength parameters and shear wave velocities. Such a performance has been studied by assessing the record of

acceleration in sliding mass (the mass above the critical sliding surface) and calculating the slope displacement using Newmark

method. It is shown that neglecting the effect of bedrock inclination, would lead to non-real results in assessing the seismic slope

performance.


A. Hassanipour, A. Shafiee, M.k. Jafari,
Volume 9, Issue 4 (12-2011)
Abstract

Shear modulus and damping ratio are important input parameters in dynamic analysis. A series of resonant column tests was

carried out on pure clays and sand-clay mixtures prepared at different densities to investigate the effects of aggregate content,

confining stress, void ratio and clay plasticity on the maximum shear modulus and minimum damping ratio. Test results revealed

an increase in the maximum shear modulus of the mixture with the increase in sand content up to 60%, followed by a decrease

beyond this value. It was also found that the maximum shear modulus increases with confining stress, and decreases with void

ratio. In addition, minimum damping ratio increases with sand content and clay plasticity and decreases with confining stress.

Finally, on the basis of the test results, a mathematical model was developed for the maximum shear modulus.


R. Attarnejad, F. Kalateh,
Volume 10, Issue 1 (3-2012)
Abstract

This paper describes a numerical model and its finite element implementation that used to compute the cavitation effects on

seismic behavior of concrete dam and reservoir systems. The system is composed of two sub-systems, namely, the reservoir and

the dam. The water is considered as bilinear compressible and inviscid and the equation of motion of fluid domain is expressed

in terms of the pressure variable alone. A bilinear state equation is used to model the pressure–density relationship of a cavitated

fluid. A standard displacement finite element formulation is used for the structure. The Structural damping of the dam material

and the radiation damping of the water and damping from foundation soil and banks have been incorporated in the analysis. The

solution of the coupled system is accomplished by solving the two sub-systems separately with the interaction effects at the damreservoir

interface enforced by a developed iterative scheme. The developed method is validated by testing it against problem for

which, there is existing solution and the effects of cavitation on dynamic response of Konya gravity dam and Morrow Point arch

dam subjected to the first 6 s of the May 1940 El-Centro, California earthquake, is considered. Obtained results show that impact

forces caused by cavitation have a small effect on the dynamic response of dam-reservoir system.


E. Alamatian, M. R. Jaefarzadeh,
Volume 10, Issue 1 (3-2012)
Abstract

In this article, the two-dimensional depth-averaged Saint Venant equations, including the turbulence terms, are solved in a

supercritical flow with oblique standing waves. The algorithm applies the finite volume Roe-TVD method with unstructured

triangular cells. Three depth-averaged turbulence models, including the mixing length, k-&epsilon and algebraic stress model (ASM),

are used to close the hydrodynamic equations. The supercritical flow in a channel downstream from a side-baffle in plan is then

simulated, and the numerical results are compared with the data obtained from a laboratory model. The application of different

models demonstrates that the consideration of turbulence models improves the results at the shock wave positions. The qualitative

study of the results and error analysis indicates that the ASM offers the most desirable solutions in comparison with the other

models. However, our numerical experiments show that, amongst the source term components, the negligence of turbulence terms

produces the least error in the depth estimation in comparison with the removal of the bed slope or bed friction terms.


I. Yitmen,
Volume 10, Issue 4 (12-2012)
Abstract

Learning rapidly and competently has become a pre-eminent strategy for improving organizational performance in the

new knowledge era. Improving dynamic learning capability is an exclusive strategy for corporate success in construction

industry. Thus engineering design firms should implement OL to accomplish a state of readiness for change and develop a

competence to respond and identify future business potentials. This study aims to analyze the relationship between

organizational learning (OL) and performance improvement (PI) in civil engineering design firms of Turkish construction

industry. OL structure in engineering design firms incorporates five constructs: organizational environment, strategy

development and implementation, supportive leadership, leveraging knowledge, and learning capability. The empirical data

was collected through a questionnaire survey conducted to engineering design firms registered to the Turkish Chamber of Civil

Engineers. The hypothesized model relationships were tested using Structural Equation Modeling (SEM). The results show that

each of the variables has a different role and significant positive impact on the OL process and organizational PI. The variables

“Supportive leadership” and “Learning capability” proved to be strongly significant and positively related to organizational

performance in engineering design firms. In engineering design firms, supportive leadership is needed in order to establish a

participative cultural environment that helps design a new form of organization which emphasizes learning, flexibility, and

rapid response. Learning capability is the potential to explore and exploit knowledge through learning flows that make possible

the development, evolution and use of knowledge stocks enacting engineering design firms and their members to add value to

the design business.


F.r. Rofooei, M. R. Mirjalili, N. K. A. Attari,
Volume 10, Issue 4 (12-2012)
Abstract

The nonlinear static procedures (NSPs) proposed by design codes do not lead to reliable results especially for tall buildings.

They generally provide inconsistent estimates of inelastic seismic demands, especially for the top floors due to their inabilities in

considering the higher modes effects. In this paper, a new enhanced pushover procedure is proposed which is based on the

envelope of the structural responses resulting from two separate pushover analyses as a combination rule. Also, the suggested

pushover analyses are performed using a newly proposed modal load pattern, i.e., the Modal Spectra Combination (MSC), and

the ASCE41-06 required first mode load pattern. The MSC load pattern is consisted of a number of mode shapes combined with

appropriate weighting factors that depend on their modal participation factors, modal frequencies and design spectral values. A

number of 2-D steel moment resisting frame models with different number of stories are used to investigate the efficiency of the

proposed method. The inter-story drifts and the maximum plastic beam moment and curvature responses are used as a measure

to compare the results obtained from the nonlinear time-history analyses (NL-THA) and some other NSPs. The results obtained

through rigorous nonlinear dynamic analyses show that the application of the proposed method leads to acceptable results for

steel MRF systems in comparison to other available enhanced NSPs. The OpenSees program is used for numerical analysis.


Y. L. Luo,
Volume 11, Issue 1 (5-2013)
Abstract

The occurrence of piping failures in earth structures demonstrates the urgency and importance of studying piping. With this

intention, a new piping model was developed in the framework of continuum mixture theory. Assuming that porous media are

comprised of solid skeleton phase, fluid phase and fluidized fine particles phase, the fluidized fine particles phase is considered

to be a special solute migrating with the fluid phase. The three phases interact while being constrained by the mass conservation

equations of the three phases, and a sink term was introduced into the mass conservation equation of the solid skeleton phase to

describe the erosion of fluidized fine particles, then a new continuum fluid-particle coupled piping model was established and

validated. The validation indicates that the proposed model can predict the piping development of complicated structures under

complex boundary and flow conditions, and reflect the dynamic changes of porosity, permeability and pore pressure in the

evolution of piping.


H. Alielahi, M. Kamalian, J. Asgari Marnani, M. K. Jafari, M. Panji,
Volume 11, Issue 1 (5-2013)
Abstract

In this paper, an advanced formulation of a time-domain two-dimensional boundary element method (BEM) is presented and

applied to calculate the response of a buried, unlined, and infinitely long cylindrical cavity with a circular cross-section subjected

to SV and P waves. The applicability and efficiency of the algorithm are verified with frequency-domain BEM examples of the

effect of cylindrical cavities on the site response analysis. The analysis results show that acceptable agreements exist between

results of this research and presented examples. For a shallow cavity, the numerical results demonstrate that vertically incident

SV wave reduces the horizontal components of the motion on the ground surface above the cavity, while it significantly increases

the vertical component for a dimensionless frequency (&eta) of 0.5 and h/a=1.5. The maximum values of normalized displacements

in vertical component of P waves are larger than horizontal component of SV waves for &eta=1.0. For a deeply embedded cavity,

the effect of the cavity on the surface ground motion is negligible for incident SV wave, but it increases the vertical component of

the displacement for incident P wave. Additionally, far and near distances from the center of the cavity show different amplitude

patterns of response due to the cavity effect. Increasing the distance from the center of the cavity, the amplitude of displacement

and the effect of the cavity attenuates significantly.


R. Prasanna Kumar, G. Dhinakaran,
Volume 11, Issue 1 (3-2013)
Abstract

Delay is one of the principal measures of performance used to determine the Level of Service (LOS) at signalized intersections and several methods have been widely used to estimate vehicular delay. Very few studies only have been carried out to estimate delay at signalized intersections under mixed traffic conditions prevailing in developing countries like India. In the present study, various problems associated with delay estimation under mixed traffic conditions in a developing country (India) and the methods to over come them were discussed and an attempt was made to improve the accuracy estimating the same. Five isolated signalized intersections from a fast developing industrial city located in TamilNadu, India were chosen for the study. Site specific PCU values were developed considering the static and dynamic characteristics of vehicles. Saturation flow was also directly measured in the field for the prevailing roadway, traffic and signalized conditions and expressed in PCU/h. Control delay was also measured following HCM 2000 guidelines. Later, this was compared with that estimated from the theoretical delay model. Even after taking several measures, good correlation between observed and predicted delay could not be obtained. Therefore, in the present scenario field measured control delay was taken into account to define LOS. A new criteria for Indian cities recently published in the literature was used to assign LOS grades of study intersections and found to be better reflecting the field conditions.
F. Nasirzadeh, M. Khanzadi, A. Afshar, S. Howick,
Volume 11, Issue 1 (3-2013)
Abstract

This research presents a dynamic mathematical system for modeling and simulating the quality management process in construction projects. Through sets of cause and effect feedback loops, all factors that internally and externally affect the quality management process are addressed. The proposed system integrates fuzzy logic with system dynamics simulation scheme to consider the uncertainties associated with the model parameters and estimation of the extra cost and time due to quality defects. Quantification of the consequences of the quality failures is performed based on the α-cut representation of fuzzy numbers and interval analysis. The proposed approach is efficient in modeling and analyzing a quality management process which is complex and dynamic in nature and involves various uncertainties. The proposed approach is implemented in a real submarine water supply pipe line project in order to evaluate its applicability and performance. The negative impacts resulting from quality failures are simulated. These negative impacts are mitigated by the implementation of alternative solutions.
F. Khoshnoudian, O. Nozadi,
Volume 11, Issue 2 (6-2013)
Abstract

It has been pointed out the static lateral response procedure for a base-isolated structure proposed in International Building Code (IBC) somewhat overestimates the seismic story force. That is why in the current paper, vertical distribution of base shear over the height of isolated structures considering higher mode effects under near field earthquakes is investigated. Nonlinear behavior of isolation systems cause variation of frequencies transmitted to the superstructure and consequently higher modes effects should be considered. In this study base shear distribution obtained from nonlinear dynamic analysis is compared with that achieved from IBC for assessment of the international building code. This investigation has been conducted in two parts, in order to have an appropriate base shear distribution formula for isolated structures under near field earthquakes. In the first part using three first mode shapes of isolated structure and introducing coefficient corresponding to each mode, extracted from nonlinear dynamic analysis under near field earthquakes, a new formula has been derived. In the second part, the mode shape coefficients have been obtained theoretically and consequently a new base shear distribution over the height of isolated structures including the isolation system properties under near field ground motions was proposed.

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