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Showing 68 results for Deformation

Mazloom M., Ramezanian Pour A.a.,
Volume 2, Issue 1 (3-2004)
Abstract

This paper presents the long-term deformations of reinforced high-strength concrete columns subjected to constant sustained axial forces. The objective of the study was to investigate the effects of binder systems containing different levels of silica fume on time-dependent behaviour of high-strength concrete columns. The experimental part of the work focused on concrete mixes having a fixed water/binder ratio of 0.35 and a constant total binder content of 500 kg/m3. The percentages of silica fume that replaced cement in this research were: 0%, 6%, 8%, 10% and 15%. The mechanical properties evaluated in the laboratory were: compressive strength secant modulus of elasticity strain due to creep and shrinkage. The theoretical part of the work is about stress redistribution between concrete and steel reinforcement as a result of time-dependent behaviour of concrete. The technique used for including creep in the analysis of reinforced concrete columns was age-adjusted effective modulus method. The results of this research indicate that as the proportion of silica fume increased, the short-term mechanical properties of concrete such as 28-day compressive strength and secant modulus improved. Also the percentages of silica fume replacement did not have a significant influence on total shrinkage however, the autogenous shrinkage of concrete increased as the amount of silica fume increased. Moreover, the basic creep of concrete decreased at higher silica fume replacement levels. Drying creep (total creep - basic creep) was negligible in this investigation. The results of the theoretical part of this researchindicate that as the proportion of silica fume increased, the gradual transfer of load from the concrete to the reinforcement decreased and also the effect of steel bars in lowering the concrete deformation reduced. Moreover, the total strain of concrete columns decreased at higher silicafume replacement levels.
F. Eftekharzadeh,
Volume 2, Issue 3 (9-2004)
Abstract

According to experiences, zones of weaknesses, joint systems and sliding surfaces in rock masses, have a great effect on the deformation behavior of tunnel cross section and the stress development in the shotcrete cover. The loosening and detaching of rock due to roof deformations in turn can take progressive dimensions and lead to roof fall and in extreme case cave to the surface. In this study, the effect of weakness zones on increasing roof deformations is demonstrated and the radius of influence of such weaknesses is determined using a FE- program for 3- dimensional continuum. Furthermore it is shown that the thickness of such disturbances does not significantly affect the development of deformations i.e. if the stiffness conditions remain constant. Also the viscous material causes greater deformations than the elastic one. Finally the study indicates that tangential stresses in the lining are also increased by weakness zones.
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.
M.h. Baziar, Sh. Salemi, T. Heidari,
Volume 4, Issue 3 (9-2006)
Abstract

Seismic behavior of a rockfill dam with asphalt-concrete core has been studied utilizing numerical models with material parameters determined by laboratory tests. The case study selected for these analyses, is the Meyjaran asphalt core dam, recently constructed in Northern Iran, with 60 m height and 180 m crest length. The numerical analyses have been performed using a nonlinear three dimensional finite difference software and various hazard levels of earthquakes. This study shows that due to the elasto-plastic characteristics of the asphalt concrete, rockfill dams with asphalt concrete core behave satisfactorily during earthquake loading. The induced shear strains in the asphalt core, for the case presented in this research, are less than 1% during an earthquake with amax=0.25g and the asphalt core remains watertight. Due to large shear deformations caused by a more severe earthquake with amax=0.60g, some cracking may occur towards the top of the core (down to 5-6 m), and the core permeability may increase in the top part, but the dam is safe.
H. Soltani-Jigheh, A. Soroush,
Volume 4, Issue 3 (9-2006)
Abstract

This paper presents the results of a series of monotonic and post-cyclic triaxial tests carried out on a clay specimen and three types of clay-sand mixed specimens. The focus of the paper is on the post-cyclic mechanical behavior of the mixed specimens, as compared to their monotonic behavior. Analyses of the tests results show that cyclic loading degrade undrained shear strength and deformation modulus of the specimens during the post-cyclic monotonic loading. The degradation depends on the sand content, the cyclic strain level and to some degrees to the consolidation pressure.
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.
S.n. Moghaddas Tafreshi, Gh. Tavakoli Mehrjardi, S.m. Moghaddas Tafreshi,
Volume 5, Issue 2 (6-2007)
Abstract

The safety of buried pipes under repeated load has been a challenging task in geotechnical engineering. In this paper artificial neural network and regression model for predicting the vertical deformation of high-density polyethylene (HDPE), small diameter flexible pipes buried in reinforced trenches, which were subjected to repeated loadings to simulate the heavy vehicle loads, are proposed. The experimental data from tests show that the vertical diametric strain (VDS) of pipe embedded in reinforced sand depends on relative density of sand, number of reinforced layers and height of embedment depth of pipe significantly. Therefore in this investigation, the value of VDS is related to above pointed parameters. A database of 72 experiments from laboratory tests were utilized to train, validate and test the developed neural network and regression model. The results show that the predicted of the vertical diametric strain (VDS) using the trained neural network and regression model are in good agreement with the experimental results but the predictions obtained from the neural network are better than regression model as the maximum percentage of error for training data is less than 1.56% and 27.4%, for neural network and regression model, respectively. Also the additional set of 24 data was used for validation of the model as 90% of predicted results have less than 7% and 21.5% error for neural network and regression model, respectively. A parametric study has been conducted using the trained neural network to study the important parameters on the vertical diametric strain.
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. Heidarzadeh, M. Dolatshahi Pirooz, N. Hadjizadeh Zaker, M. Mokhtari,
Volume 5, Issue 4 (12-2007)
Abstract

Makran Subduction Zone (MSZ) offshore of Iran and Pakistan is one of the most tsunamigenic sources in the Indian Ocean. Historically, the MSZ has generated some tsunamigenic earthquakes like that of 28 November 1945 with the death tool of more than 4000 people along the coasts of Iran, Pakistan, India, and Oman. In this study, the tsunami hazard associated with the MSZ is investigated. At first, a review of historical tsunamis in the Indian Ocean basin was performed which reveals the Makran region has experienced al least 4 tsunamis including events of 326 BC, 1897, 1008, and 1945. Consequently, since the pattern and extent of vertical ground deformation from an earthquake determines whether or not a tsunami is formed, a computer program is developed to predict the seafloor deformation due to the earthquake occurrence in the MSZ. The model was verified through run of it on some actual tsunamis so far occurred. Then, using the data of the 1945 Makran tsunami, the seismic parameters of the MSZ were calibrated. Finally, we used the developed computer program to calculate seafloor deformation at the location of Makran subduction zone for several earthquake scenarios with moment magnitudes ranging between 6.5 and 8.5. The results of this research show that the risk of tsunami generation from MSZ can be classified into three main categories, as follows: (1) very little risk for tsunami generation in the case of the occurrence of an earthquake having magnitude up to 7 (2) little to medium risk for moment magnitudes ranging between 7 and 7.5 and (3) high risk for moment magnitude greater than 7.5. At the end of the paper, modeling of tsunami propagation is performed for an earthquake scenario with magnitude of 8 offshore Chabahar, in order to give preliminary information about tsunami behavior in this region.
M.a. Khan, A. Usmani, S.s. Shah, H. Abbas,
Volume 6, Issue 2 (6-2008)
Abstract

In the present investigation, the cyclic load deformation behaviour of soil-fly ash layered system is

studied using different intensities of failure load (I = 25%, 50% and 75%) with varying number of cycles (N =

10, 50 and 100). An attempt has been made to establish the use of fly ash as a fill material for embankments of

Highways and Railways and to examine the effect of cyclic loading on the layered samples of soil and fly ash.

The number of cycles, confining pressures and the intensity of loads at which loading unloading has been

performed were varied. The resilient modulus, permanent strain and cyclic strength factor are evaluated from

the test results and compared to show their variation with varying stress levels. The nature of stress-strain

relationship is initially linear for low stress levels and then turns non-linear for high stress levels. The test

results reveal two types of failure mechanisms that demonstrate the dependency of consolidated undrained

shear strength tests of soil-fly ash matrix on the interface characteristics of the layered soils under cyclic

loading conditions. Data trends indicate greater stability of layered samples of soil-fly ash matrix in terms of

failure load (i) at higher number of loading-unloading cycles, performed at lower intensity of deviatoric stress,

and (ii) at lower number of cycles but at higher intensity of deviatoric stress.


Amir Hamidi, S. Mohsen Haeri,
Volume 6, Issue 3 (9-2008)
Abstract

The deformation and stiffness characteristics of a cemented gravely sand was investigated using triaxial equipment. The triaxial tests were conducted in both dry and saturated undrained conditions. Artificially cemented samples are prepared using gypsum plaster as the cementing agent. The plaster was mixed with the base soil at the weight percentages of 1.5, 3, 4.5 and 6. The applied confining pressure varied between 25 to 500 kPa in triaxial tests. The process of yielding of the soil was investigated for the considered soil and the bond and final yield points were identified for the cemented soil with different cement contents. The variations of deformation and stiffness parameters with cement content and confining stress were studied as well. Some of the parameters were determined for both drained and undrained conditions to investigate the effect of drainage condition on the stiffness and yield characteristics of the tested cemented gravely sand. According to the results, the difference between drained and undrained tangent stiffness decreases with increase in confining stress. Finally the effect of cement type was investigated as an important parameter affecting the stiffness at bond yield. The rate of increase in tangent stiffness at bond yield changes with cement content for different cementing agents.
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.
Arash Nayeri, Kazem Fakharian,
Volume 7, Issue 4 (12-2009)
Abstract

Abstract: This paper presents the results of pullout tests on uniaxial geogrid embedded in silica sand under monotonic and cyclic pullout forces. The new testing device as a recently developed automated pullout test device for soil-geogrid strength and deformation behavior investigation is capable of applying load/displacement controlled monotonic/cyclic forces at different rates/frequencies and wave shapes, through a computer closed-loop system. Two grades of extruded HDPE uniaxial geogrids and uniform silica sand are used throughout the experiments. The effects of vertical surcharge, sand relative density, extensibility of reinforcement and cyclic pullout loads are investigated on the pullout resistance, nodal displacement distributions, post-cyclic pullout resistance and cyclic accumulated displacement of the geogrid. Tell-tale type transducers are implemented along the geogrid at several points to measure the relative displacements along the geogrid embedded length. In monotonic tests, decrease in relative displacement between soil and geogrid by increase of vertical stress and sand relative density are the main conclusions structural stiffness of geogrid has a direct effect on pullout resistance in different surcharges. In cyclic tests it is observed that the variation of post-cyclic strength ranges from minus 10% to plus 20% of monotonic strength values and cyclic accumulated displacements are increased as normal pressure increase, but no practical specific comment can be made at this stage on the post-cyclic strength of geogrids embedded in silica sand. It is also observed that in loose sand condition, the cyclic accumulated displacements are considerably smaller as compared to dense sand condition.
M.r. Abdi, S. A. Sadrnejad, M.a. Arjomand,
Volume 7, Issue 4 (12-2009)
Abstract

Large size direct shear tests (i.e.300 x 300mm) were conducted to investigate the interaction between clay reinforced with geogrids embedded in thin layers of sand. Test results for the clay, sand, clay-sand, clay-geogrid, sandgeogrid and clay-sand-geogrid are discussed. Thin layers of sand including 4, 6, 8, 10, 12 and 14mm were used to increase the interaction between the clay and the geogrids. Effects of sand layer thickness, normal pressure and transverse geogrid members were studied. All tests were conducted on saturated clay under unconsolidated-undrained (UU) conditions. Test results indicate that provision of thin layers of high strength sand on both sides of the geogrid is very effective in improving the strength and deformation behaviour of reinforced clay under UU loading conditions. Using geogrids embedded in thin layers of sand not only can improve performance of clay backfills but also it can provide drainage paths preventing pore water pressure generations. For the soil, geogrid and the normal pressures used, an optimum sand layer thickness of 10mm was determined which proved to be independent of the magnitude of the normal pressure used. Effect of sand layers combined with the geogrid reinforcement increased with increase in normal pressures. The improvement was more pronounced at higher normal pressures. Total shear resistance provided by the geogrids with transverse members removed was approximately 10% lower than shear resistance of geogrids with transverse members.
E. Kermani, Y. Jafarian, M. H. Baziar,
Volume 7, Issue 4 (12-2009)
Abstract

Although there is enough knowledge indicating on the influence of frequency content of input motion on the deformation demand of structures, state-of-the-practice seismic studies use the intensity measures such as peak ground acceleration (PGA) which are not frequency dependent. The v max/a max ratio of strong ground motions can be used in seismic hazard studies as the representative of frequency content of the motions. This ratio can be indirectly estimated by the attenuation models of PGA and PGV which are functions of earthquake magnitude, source to site distance, faulting mechanism, and local site conditions. This paper presents new predictive equations for v max/a max ratio based on genetic programming (GP) approach. The predictive equations are established using a reliable database released by Pacific Earthquake Engineering Research Center (PEER) for three types of faulting mechanisms including strikeslip, normal and reverse. The proposed models provide reasonable accuracy to estimate the frequency content of site ground motions in practical projects. The results of parametric study demonstrate that v max/a max increases through increasing earthquake moment magnitude and source to site distance while it decreases with increasing the average shear-wave velocity over the top 30m of the site.
T. Dahlberg,
Volume 8, Issue 1 (3-2010)
Abstract

The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation may be

very large within a short distance. One example is when an unsupported sleeper is hanging in the rail. Track stiffness

is then, locally at that sleeper, very low. At insulated joints the bending stiffness of the rail has a discontinuity implying

a discontinuity also of the track stiffness. A third example of an abrupt change of track stiffness is the transition from

an embankment to a bridge. At switches both mass and stiffness change rapidly. The variations of track stiffness will

induce variations in the wheel/rail contact force. This will intensify track degradation such as increased wear, fatigue,

track settlement due to permanent deformation of the ballast and the substructure, and so on. As soon as the track

geometry starts to deteriorate, the variations of the wheel/rail interaction forces will increase, and the track

deterioration rate increases. In the work reported here the possibility to smooth out track stiffness variations is

discussed. It is demonstrated that by modifying the stiffness variations along the track, for example by use of grouting

or under-sleeper pads, the variations of the wheel/rail contact force may be considerably reduced.


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


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.


A.r. Khaloo, I. Eshghi, P. Piran Aghl,
Volume 8, Issue 3 (9-2010)
Abstract

In this paper the response of cantilevered reinforced concrete (RC) beams with smart rebars under static lateral loading has been numerically studied, using Finite Element Method. The material used in this study is SuperelasticShape Memory Alloys (SE SMAs) which contains nickel and titanium elements. The SE SMA is a unique alloy that has the ability to undergo large deformations and return to their undeformed shape by removal of stresses. In this study, different quantities of steel and smart rebars have been used for reinforcement andthe behavior of these models under lateral loading, including their load-displacement curves, residual displacements, and stiffness, were discussed. During lateral loading, rebars yield or concrete crushes in compression zone in some parts of the beams and also residual deflections are created in the structure. It is found that by using SMA rebars in RC beams, these materials tend to return to the previous state (zero strain), so they reduce the permanent deformations and also in turn create forces known as recovery forces in the structure which lead into closing of concrete cracks in tensile zone. This ability makes special structures to maintain their serviceability even after a strong earthquake


D. P. Chen, C. X. Qian, C. L. Liu,
Volume 8, Issue 4 (12-2010)
Abstract

 Concrete deformation due to temperature and moisture condition will always develop simultaneously and interactively. The environmentally (hygral and thermally) induced stress and deformation are essential to concrete durability. To simulate the deformation of concrete caused by the coupling effect of temperature and moisture, a numerical simulation approach is proposed comprising analytical process and finite element analysis is proposed based on the mechanism of heat and moisture transfer in porous medium. In analytical method, Laplace transformation and transfer function were used to simplify and solve the coupled partial differential equations of heat and moisture transfer. The hygro-thermal deformation of concrete is numerically simulated by finite element method (FEM) based on the obtained temperature and moisture stress transformed from the solved moisture distribution. This numerical simulation approach avoids the complex eigenvalues, coupling difficulty and low accuracy in other solving method, and also effectively calculates the moisture induced shrinkage which is almost impossible using familiar FEM software. Furthermore, a software named Combined Temperature and Moisture Simulation System for concrete (CTMSoft) was represented and developed by a mix programming of Visual Basic, Matlab and ANSYS. CTMSoft provided a simple and more intuitive interface between user and computer by providing a graphical user interface (GUI). The validity of the numerical simulation approach was verified by two cases analysis.



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