Babak Poursartip; Vahid Lotfi
Morteza Eskandari Ghadi
Amir Ta'ebi; Hamid Ghoddousi
Ali Asghar Mirghasemi; Helia Rahmani
Abstract
In some natural events such as soil failure the deformations are localized in narrow restrictions, which are called shear bands. This event which is a fundamental phenomenon in granular material, has been widely investigated during recent decades within expensive experimental tests and also some numerical ...
Read More
In some natural events such as soil failure the deformations are localized in narrow restrictions, which are called shear bands. This event which is a fundamental phenomenon in granular material, has been widely investigated during recent decades within expensive experimental tests and also some numerical simulations. Most of previously used numerical methods are based on continuum theories describing shear bands as interfaces along which solid masses move like rigid blocks. In this interpretation many physical events such as changes of the soil structure around failure line are neglected. In this paper the discrete element method is used to simulate the shear bands. Since in this method some of the problems of experiments and simulations are solved,
It would be an ideal method to obtain the stresses and strains, and also to investigate the behavior of shear bands in a granular media, while exposing to external forces. In this research by the use of DEM and conducting series of biaxial tests on assemblies of two-dimensional ellipse shaped particles, the effect of different factors such as average grain size, particle shape and confining pressure on the shear bands are studied and the results show that some investigated factors like average grain size and confining pressure have considerable effect on the shear bands characteristics.
The main results can be summarized as follows:
• The amount of rotation is a very sensitive characteristic and it changes considerably by all of the factors measured in this research.
• The most affecting factors on the displacement of the particles across the shear bands are the loading rate and confining pressure. Moreover by increasing the particle size the displacements increase with a great amount but if these values are divided by the particle radius, no significant changes in the particle displacement will be observed. Other factors do not seem to have any effects on this issue.
• 6-13d50 seems to be the best estimation for the shear band thickness, and other controlled factors affect this value within this restriction. The width of the shear bands seems to increase by the loading rate and confining pressure increase.
• The inclination of this localization is mostly affected by confining pressure (which increase leads to angle decrease), porosity (which increase leads to angle decrease), grading (its uniformity causes smaller shear band angles), and size (greater sizes of grains would result in failure with lower angles of sear band). Among these factors grain size has the least effect.
Hamid Zaferani; Asadollah Noorzad; Khosro Bargi
Ghasem Dehghani Eshkezari; Ali Akbar Aghakouchak; Mehrdad Kokabi
Latif Ebrahim Nejad; Reza Attar Nejad
Mehdi Ghassemieh; Vahid Zeynoddini Meymand
Abstract
The use of steel flush end-plate moment connection is practiced in the construction of the light steel frames around the world particularly in parts of Europe and US. In the past most research was concentrated on studying the behavior of the flush end-plate connection subjected to only monotonic type ...
Read More
The use of steel flush end-plate moment connection is practiced in the construction of the light steel frames around the world particularly in parts of Europe and US. In the past most research was concentrated on studying the behavior of the flush end-plate connection subjected to only monotonic type loadings. The majority of that research carried out such investigation through experimental programs. Although experimental results reveal the behavior of such system to some extent, but the cost of using the numerical techniques such as finite element for the analysis appears to be much less and takes not long time and effort in comparison with the test program.
In this study, the numerical behavior of flush end-plate connection using finite element method is investigated. The moment-rotation characteristic of the connection when subjected to cyclic loading is obtained. The numerical results obtained in this study are compared with the experimental results of other researchers. Some of the pertinent parameters effecting on the overall behavior of the connection as well as the design equations obtained from the method of yield line analysis are discussed.
Ourang Farzaneh; Farajollah Askari
Abstract
In this paper, stability of slopes with a shallow foundation located on top including the shape of the failure mechanism is investigated in static and seismic states. This is a three dimensional problem which is analyzed two dimensionally because 3D analyses are complex and appropriate softwares are ...
Read More
In this paper, stability of slopes with a shallow foundation located on top including the shape of the failure mechanism is investigated in static and seismic states. This is a three dimensional problem which is analyzed two dimensionally because 3D analyses are complex and appropriate softwares are not available.
The conventional method of bearing capacity evaluation of foundations on top of slopes is reviewed and results are compared with those obtained from using a specific three dimensional slope stability algorithm based on upper bound limit analysis theorem.
It is concluded that increasing the foundation load to a threshold level, the effect of the load on the stability of the slopes is negligible, a phenomenon which can not be observed in two dimensional analyses. Determination of this threshold by 3D analyses is a useful criterion for selection of the adequate safety factor in static and seismic slope stability analyses.
Morteza Madhkhan; Alireza Arasteh
Mohammad Ali Lotfollah Yaghin; Ali Reza Mojtahedi
Abstract
Using the statistical characteristics is one of the methods to justify the random nature of the ocean waves. Probability function are used to facilitate the studies of the random waves parameters, such as the surface and height and period of the waves. Since, the force of the ocean waves are the prevalent ...
Read More
Using the statistical characteristics is one of the methods to justify the random nature of the ocean waves. Probability function are used to facilitate the studies of the random waves parameters, such as the surface and height and period of the waves. Since, the force of the ocean waves are the prevalent principal forces on the offshore structures, the assignment of the significant structural responses such as applied inline and transverse forces and also total moment on the piles is the main step for design and construction of the structures.
In this paper, the random waves and their effects on the cylindrical pile will be investigated. These waves have been recorded during some tests which will be illustrated separately. The oscillation of some linear or nonlinear responses of the pile have been discussed statistically and then spectral analysis performed and their extremity amplitude statistical analysis interpreted and prevalent probability functions determined.
Ali Kheiroddin; Ali Reza Morteza'ee
Abstract
Flanged shear 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. They must be carefully designed to provide not only adequate ...
Read More
Flanged shear 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. They must be carefully designed to provide not only adequate strength, but also sufficient ductility to avoid brittle failure under strong lateral loads, especially during an earthquake. When concrete in the compression zone of a shear wall is confined by transverse reinforcement, both the strength and ductility of the wall would be increased. However, none of the existing analysis methods in the codes allows for such effect. Herein, a finite element model that takes into account the effect of concrete confinement is developed for nonlinear analysis of reinforced concrete structures. In this model, the confinement effect of the transverse reinforcement is incorporated by adjusting the compressive stress-strain relation of the concrete according to the confinement index proposed by Kappos. Shear wall models tested by others under constant vertical load and monotonically increasing horizontal load are analyzed and the analytical results for the failure modes and load-deflection curves of the walls are found to be in good agreement with the experimental results. Using the finite element model, a parametric study on the effect of concrete confinement on the behavior of shear walls has been carried out. It is revealed that the confinement of the concrete in the compression zone can significantly increase the lateral strength and ductility of the wall. The increases in lateral strength and ductility due to concrete confinement are greater in walls with greater height to width ratio and/or subjected to larger vertical loads. There is an obvious diminishing return of the further gain in lateral strength or ductility as the quantity of confinement reinforcement increases to beyond certain limit. The contribution of the concrete confinement to ductility is generally more significant than the corresponding contribution to lateral strength especially when the amount of confinement reinforcement is relatively large.
Davoud Ali Jamshidi; Bahram Navay'i Nia; Javad Vaseghi Amiri
Abstract
Because of different behavior of reservoir water and dam material, the determination of hydrodynamic pressure during earthquake is very complicated. Thus, different formulations have been presented for modeling of the dam reservoir system under dynamic loading such as earthquake. These formulations can ...
Read More
Because of different behavior of reservoir water and dam material, the determination of hydrodynamic pressure during earthquake is very complicated. Thus, different formulations have been presented for modeling of the dam reservoir system under dynamic loading such as earthquake. These formulations can be categorized into two general groups, which are Lagrangian and Eulerian, each having advantages and disadvantages. In this paper, a proper formulation is presented for modeling of reservoir of concrete dams and determination of the hydrodynamic pressure based on finite element, and the Lagrangian and Eulerian methods. The Lagrangian and Eulerian methods are then compared with together for the determination of hydrodynamic pressure on the dam upstream and the displacement of the crest of dam for a variety of dimensions of dam under different types of earthquake. The results brought up from these two formulations are then compared with each other in different aspects such as accuracy, the required amount of calculations, the frequency effect, the boundary conditions, the dam upstream slope, the sediment in energy absorption, the reservoir height and its bed slope and eventually, the type of elements used in finite element method.
Furthermore, the formulation of reservoir using Lagrangian method for applying boundary conditions as especial element has been used and the results show that this method is an improvement of the existing finite element method in comparison with usual Lagrangian method in other to decrease the degree of freedom.
Mahmoud Golabchi; Mohammad Hassan Sebt; Hossein Naghash Tousi
Abstract
One of the common questions in all projects, is "How much would be the final cost of the project?" or "How much would be the completion duration of the project?". Earned Value Management presents a method for estimation of these results. In general methods and formula of Earned Value Management, future ...
Read More
One of the common questions in all projects, is "How much would be the final cost of the project?" or "How much would be the completion duration of the project?". Earned Value Management presents a method for estimation of these results. In general methods and formula of Earned Value Management, future trend of project, are anticipated completely based on its previous trend, and changes in environmental conditions or other effective elements in future performance of the project are neglected. But risk management looks a future horizon in project's future and explores unknown future to identify potential threats and opportunities and control their occurrence results on project performance. In this paper, using risk management process and challenging effective aspects & elements on project future performance in different visions, a risk coefficient in accordance with current coefficient of "EVMS", is presented for better estimate of final results of projects. The goal of this method is concentration of management's attention on reaching project goals, by using interaction of these two methods in determining exact performance coefficient of project future. Anticipating exact results of project is attainable by this coefficient.
