Addis Ababa Institute of Technology
http://localhost:80/xmlui/handle/123456789/9
2018-11-20T19:22:45ZApplication of a Generalized Subgrade Model in the Analysis of Circular Plates on Elastic Foundations
http://localhost:80/xmlui/handle/123456789/14317
Application of a Generalized Subgrade Model in the Analysis of Circular Plates on Elastic Foundations
Meron, Alebachew
The solution to the problem of beams and plates on an elastic foundation has been attempted in
the past using various subgrade models developed by many researchers, one of the pioneers
being Winkler. Most recently, a new calibrated and more advanced multifaceted continuum
foundation model has been presented by Worku without neglecting any stress, strain, or
deformation component in the continuum unlike previously proposed models.
The study of interaction between a plate and an elastic medium has useful applications in
geotechnical engineering. This research investigates the use of a generalized continuum subgrade
model of Worku for analyzing circular plates resting on an elastic foundation. The approach
employed is both analytical and numerical. In the analytical work, the governing differential
equations of an axisymmetric circular plate on a homogeneous elastic foundation has been
formulated that incorporates Winkler and Pasternak-type subgrade models. Closed form
particular solutions have been presented for different loading conditions of small and large
circular plates after obtaining a general solution of the differential equations. A math solving
software (i.e. Mathematica) is used to compute the deflections and internal actions in a
spreadsheet program due to the complexity of the functions. In the numerical study a FEM based
software (i.e. PLAXIS 2D) is used to calibrate the analyzed circular plate using the presented
models by seeking adequate agreements with the FE outputs. At last, numerical examples are
solved using these models and compared with PLAXIS 2D for small and large radii circular
plates of some loading conditions. From the plots of the outputs, it is observed that the
generalized models of Worku are suitable and more appropriate than classical models to analyze
circular plates on elastic foundations.
2018-06-01T00:00:00ZAnalysis of Strip Plates on Elastic Foundation Using Generalized Subgrade Model
http://localhost:80/xmlui/handle/123456789/14314
Analysis of Strip Plates on Elastic Foundation Using Generalized Subgrade Model
Amlesu, Teklebrhan
A concrete plate supported directly by the soil continuum is a very common construction form.
The response of the plate when it carries external load is influenced by the soil, and the response
of the soil is also influenced by the action of the plate under the load. Thus, developing a
subgrade model for soil-structure interaction problem is essential in order to predict the
response of both components of the system and arrive at an optimum design.
Many subgrade models have been developed in order to improve on the inherent lack of shear
interaction among the individual springs found on the long-enduring model of Winkler.
Moreover, these models still have shortcomings with the nature of simplifying assumptions
they make to ease the mathematical equation. Recently a generalized model is presented for a
subgrade idealized as an elastic layer overlying a rigid base. In contrast to previous works no
stresses, strains or displacements are neglected a priori.
The main objective of this work is implementing, verifying and calibrating this improved
continuum-based generalized subgrade model in the analysis of strip plates on an elastic
foundation. The governing differential equation of a strip plate on elastic foundation is
formulated. Then, closed form particular solutions, when using Winkler type and Kerr
equivalent Pasternak models, are obtained by considering different boundary conditions of long
and short length of a strip plate, under different loading conditions. Microsoft excel programs
are written for the computation of deflection, moment and shear force. The subgrade models
are then calibrated using Finite Element based Plaxis 2D software. Lastly, numerical
illustration is provided using these models in comparison with Plaxis 2D model for long and
short strip plates subjected to selected symmetrical loading conditions. The result of the
comparison shows that the calibrated variants give good outcome in agreement with FE
outputs. Consequently, these findings display that the calibrated models can be used in routine
analysis of strip plate on elastic foundation and also can be incorporated in commercial
software.
2018-06-01T00:00:00ZCorrelation of CBR with Index Properties of Soils in Sululta Town
http://localhost:80/xmlui/handle/123456789/14311
Correlation of CBR with Index Properties of Soils in Sululta Town
Alemayehu, Bekele
Soils are the oldest and most complex engineering materials. The California Bearing Ratio (CBR)
has been acknowledged as an important parameter to characterize the bearing capacity of earth
structures, such as earth dams, road embankments, airport runways, bridge abutments and
pavements.
This research presents and discusses the results from a study on the prediction of CBR. In the
current study, CBR testswere performed on thirty one samples of fine-grained soils in the
laboratory, collected from various locations in Sululta Town. Based on the test results, the soils are
categorized in to red clay and black/gray clay soils and the correlationswere done independently for
the two categories.
Then various linear relationships between index properties and CBR of the samples were
investigated using simple and multiple linear regression analysis, predictive equation estimating
CBR from the experimental index values were developed by multiple linear regression analysis and
alesser empirical correlation was found with a correlation coefficient R
2
= 0.319for Red clay and
satisfactory empirical correlation was obtained with a correlation coefficient R
2
=0.720for
black/gray clay of the experimental soils. The equations are developed by using SPSS 23 for
windows software. The equations are then tested for two control samples for the two categories.
The most important equations are proposed, and applicable with sufficient accuracy for preliminary
identification of material for the local area.
2017-05-01T00:00:00ZStress and Deflection Analysis of Cracked Composite PressureVessel by Finite Element Method
http://localhost:80/xmlui/handle/123456789/14306
Stress and Deflection Analysis of Cracked Composite PressureVessel by Finite Element Method
Tekeliye, Tasachew
The aim of this thesis is to develop crack and investigate techniques and parameters that could be
used to identify crack if it exist in a composite pressure vessel. Many researchers discovered
formation or propagation of a crack in a composite pressure vessel will cause a catastrophic
failure. Thus, health monitoring for a pressure vessel due to crack using crack detection
techniques will minimize or reduce the failure that probably to occur.
This research first focused on mathematical and numerical relation which, represent the
governing equation of composite material winding on in a pressure vessel. For modeling
different crack size in the composite overwrapped pressure vessel fracture stress theories applied.
Different surface Crack size are considering according to the literature standard values. Model
actual size of composite pressure vessel with varied crack size “a” develops on the surface of
composite pressure vessel. This research thoroughly analysis the effect of crack on the surface of
composite pressure vessel. Those parameters are considered to see the variation of result due to
presence of crack. The main parameters are considering stress, principal stress, von mises stress,
deflection and fracture stress. According to the parameters it shows that as crack size increase,
the average stress will be increase with the given pressure in composite pressure vessel. In
contradict; the fracture stress will be decrease as the crack size increase.
In this study, optimal angle-ply orientations of symmetric [55
0
, -55
0
] shells designed for
maximum burst pressure with allowable crack size were investigated. It is shown that all the
strength characteristics of carbon fiber relevant to structural engineering can be explained by the
cracks present in the carbon fiber and can be analyzed using fracture mechanics. The stress and
deformation are affected due to the presence of crack in composite pressure vessel. These
parameter are takes a design crack as the basis for design. Rather than an allowable stress as in
current approaches, with which it is compared cracked composite pressure vessel. A full size
cylindrical shell of composite pressure vessels is conducted. A mathematical method, A finite
element method and compare experimental test are studied to verify a maximum allowable crack
size in composite over wrapped pressure vessel with a given optimum winding angles. The roll of
crack size design within the wider philosophy of limit state design is discussed.
2015-10-01T00:00:00Z