Showing 7 results for Plasticity
S.a. Sadrnejad,
Volume 4, Issue 2 (6-2006)
Abstract
An important concern in rock mechanics is non-homogeneity as joints or fault. Adopting
the joints as fractures, fractures are well known for their effects on the mechanical and transport
properties of rock.
It has been postulated that through fractured/jointed rock, mainly, the polygons turned to the shear
vector (ti) are involved in the mobilization of shear resistance. Consequently, in order to locate
the contact areas implicated into the shear-test it was firstly necessary to fix the shear direction.
Moreover, since laboratory observations clearly show that only the steepest polygon surfaces
touch the other sample, the identification of the potential sliding areas only requires the
determination of the polygons which are faced to the shear direction and which, among them, are
steep enough to be involved.
The methodology to be discussed here is modeling of slip on the local and global levels due to the
distribution of deformation procedure of the rock joint. Upon the presented methodology, more
attention has been given to slip initiation and propagation through rock joint. In particular,
softening in non-linear behaviour of joint in going from the peak to residual strengths imparts a
behaviour often associated with progressive failure.
A multi-plane based model is developed and used to compute plastic strain distribution and failure
mechanism of rock joints. Validity of the presented model was examined by comparing numerical
and test results showing the behavior of both homogeneous and jointed rock samples under general
stress conditions.
S.a. Naeini, R. Ziaie_moayed,
Volume 7, Issue 2 (6-2009)
Abstract
In recent years, soil reinforcement is considered of great importance in many different civil projects. One of
the most significant applications of soil reinforcement is in road construction. Sub grade soil and its properties are
very important in the design of road pavement structure. Its main function is to give adequate support to the pavement
from beneath. Therefore, it should have a sufficient load carrying capacity. The use of geosynthetics in road and
airfield construction has shown the potential to increase the soil bearing capacity. One category of geosynthetics to
particular, geogrid, has gained increasing acceptance in road construction. A geogrid is a geosynthetic material
consisting of connected parallel sets of tensile ribs with apertures of sufficient size to allow strike-through of
surrounding soil, stone, or other geotechnical material. Geogrid reinforcement of sub grade soil is achieved through
the increase of frictional interaction between the soil and the reinforcement. Geogrid have been successfully used to
provide a construction platform over subgrades. In this application, the geogrid improves the ability to obtain
compaction in overlying aggregates, while reducing the amount of material required be removing and replacing.
Relative agreement exists that substantial benefits can be achieved from the inclusion of geogrids within the pavement
systems however, the quantity of the improvement is in relative disagreement. This paper presents the effects of
plasticity index and also reinforcing of soft clay on CBR values. Three samples of clay with different plasticity index
(PI) values are selected and tested without reinforcement. Then by placing one and two layer of geogrid at certain
depth within sample height, the effects of reinforcement and PI on CBR values are investigated in both soaked and
unsoaked conditions. The results shows that as the PI increase the CBR value decreases and reinforcing clay with
geogrid will increase the CBR value.
S. A. Sadrnejad, S. A. Ghoreishian Amir,
Volume 8, Issue 2 (6-2010)
Abstract
A semi-micromechanical multilaminate model is introduced here to predict the mechanical behavior of soils.
This model is like a bridge between micro and macro scale upon the satisfaction of minimum potential energy level
during any applied stress/strain increments. The concept of this model is based on a certain number of sampling planes
which constitute the elastic-plastic behavior of the soil. The soil behavior presents as the summation of behavior on
these planes. A simple unconventional constitutive equations are used in each of the planes to describe the behavior
of these planes separately. An unconventional plasticity can predict the soil behavior as a smooth curve with
considering plastic deformation due to change of stress state inside the yield surface. The model is capable of
predicting softening behavior of the soil in a reasonable manner due to using unconventional plasticity. The influences
of induced anisotropy are included in a rational way without any additional hypotheses owing to in-nature properties
of the multilaminate framework. Results of this model are compared with test data and reasonable agreement is found.
O. Omidi, V. Lotfi,
Volume 8, Issue 3 (9-2010)
Abstract
Neither damage mechanics model nor elastoplastic constitutive law can solely describe the behavior of concrete satisfactorily. In fact, they both fail to represent proper unloading slopes during cyclic loading. To overcome the disadvantages of pure plastic models and pure damage approaches, the combined effects need to be considered. In this regard, various classes of plastic-damage models have been recently proposed. Here, the theoretical basics of the plastic-damage model originally proposed by Lubliner et al. and later on modified by Lee and Fenves is initially presented and its numerical aspects in three-dimensional space are subsequently emphasized. It should be mentioned that a part of the implementation in 3-D space needs to be reformulated due to employing a hyperbolic potential function to treat the singularity of the original linear form of plastic flow proposed by Lee and Fenves. The consistent algorithmic tangent stiffness, which is utilized to accelerate the convergence rate in solving the nonlinear global equations, is also derived. The validation and evaluation of the model to capture the desired behavior under monotonic and cyclic loadings are shown with several simple one-element tests. These basic simulations confirm the robustness, accuracy, and efficiency of the algorithm at the local and global levels. At the end, a four-point bending test is examined to demonstrate the capabilities of the model in real 3-D applications.
M. Jahanandish, M. Veiskarami, A. Ghahramani,
Volume 9, Issue 4 (12-2011)
Abstract
Foundations behavior is affected by soil behavior which can vary from dilative to contractive depending on the stress level,
particularly in dense frictional soils. The Zero Extension Lines (ZEL) method has been generally developed to predict the
foundations behavior. Knowledge of soil behavior enables the ZEL method to predict the general and local shear failure modes.
In this paper, a relatively simple work hardening/softening soil constitutive model is developed to represent dense frictional soils
behavior under different stress levels. This model is based on the accumulation of the plastic work during a simple direct shear
test and its relationship to stress ratio to establish the hardening law. Verifications have been made for the developed soil model.
The model is then implemented into the ZEL method to theoretically investigate the bearing capacity and load-displacement
behavior of foundations over dense frictional soils. Utilization of this model enables the ZEL method to capture different modes
of failure depending on the foundation size. A numerical study on foundations behavior was performed showing the ability of the
presented approach in capturing both failure modes.
A. R. Rahai, S. Fallah Nafari,
Volume 11, Issue 4 (12-2013)
Abstract
The seismic behavior of frame bridges is generally evaluated using nonlinear static analysis with different plasticity
models hence this paper tends to focus on the effectiveness of the two most common nonlinear modeling approaches
comprising of concentrated and distributed plasticity models. A three-span prestressed concrete frame bridge in Tehran, Iran,
including a pair of independent parallel bridge structures was selected as the model of the study. The parallel bridges were
composed of identical decks with the total length of 215 meters supported on different regular and irregular substructures with
non-prismatic piers. To calibrate the analytical modeling, a large-scale experimental and analytical seismic study on a two-span reinforced concrete bridge system carried out at the University of Nevada Reno was used. The comparison of the results
shows the accuracy of analytical studies. In addition, close correlation between results obtained from two nonlinear modeling
methods depicts that the lumped plasticity approach can be decisively considered as the useful tool for the nonlinear modeling
of non-prismatic bridge piers with hollow sections due to its simple modeling assumption and less computational time.
Mr. Mehdi Goorani, Dr. Amir Hamidi,
Volume 13, Issue 2 (6-2015)
Abstract
This paper presents a model for prediction of the mechanical behavior of sand-gravel mixtures using generalized plasticity and critical state concepts. Proposed model is based on the difference between critical state lines of sand and sand-gravel mixture in e-Lnp' plane. A generalized plasticity model is considered as the base model for sandy soil. Its state parameter, dilation rate and hardening function are modified to involve the effects of gravel particles on the behavior of mixture. Gravel content is considered as a physical parameter for determination of four new added parameters of the model. Verification of the proposed model performed considering four sets of experiments conducted by different researchers on poorly graded sand-gravel mixtures. According to the results, proposed model provides satisfactory qualitative and quantitative predictions of the behavior of sand-gravel mixture. Stress- strain behavior besides volumetric strains in drained condition and induced pore pressure during undrained loading are satisfactory predicted which indicates the possibility of its application in boundary value problems of geotechnical engineering.