Dissertations / Theses on the topic 'Finite element analysis preprocessing'

A number of methods for adaptation of existing all-hexahedral grids by localized refinement have been developed; however, none ideally fit all refinement needs. This thesis presents the structure to a method of two-refinement developed for conformal, structured, all-hexahedral grids that offers flexibility beyond what has been offered to date. The method is fundamentally based on pillowing pairs of sheets of hexes. This thesis also suggests an implementation of the method, shows the results of examples refined using it and compares these results to results from implementing three-refinement on the same examples.

Finite element analysis is versatile and used widely in a range of engineering andscientific disciplines. As time passes, the problems that engineers and designers areexpected to solve are becoming more computationally demanding. Often theproblems involve the interplay of two or more processes which are physically andtherefore mathematically coupled. Although parallel computers have been availablefor about twenty years to satisfy this demand, finite element analysis is still largelyexecuted on serial machines. Parallelisation appears to be difficult, even for thespecialist. Parallel machines, programming languages, libraries and tools are used toparallelise old serial programs with mixed success. In some cases the serialalgorithm is not naturally suitable for parallel computing. Some argue that rewritingthe programs from scratch, using an entirely different solution strategy is a betterapproach. Taking this point of view, using MPI for portability, a mesh free elementby element method for simple data distribution and the appropriate iterative solvers,a general parallel strategy for finite element analysis is developed and assessed.

This thesis studies interactions between coupled acoustic domain(s) and enclosing rigid or elastic boundary. Boundary element-finite element (BE-FE) sound-structure interaction models are developed by coupling frequency domain BE acoustic and FE structural models using linear inviscid acoustic and elasticity theories. Flexibility in analyses is provided by discontinuous triangular and quadrilateral elements in the BE method (BEM), and a rectangular plate and a triangular shell element in the FE method (FEM). An analytical formulation is developed for an extended fundamental sound-structure interaction problem that involves locally reacting sound absorptive treatment on interior elastic boundary. This new formulation is built upon existing analytical solutions for a configuration known as the cavity-backed-plate problem. Results from developed analytical formulation are compared against those from independent BE-FE analyses. Analytical and BE-FE analysis results for a selection of cavity-plate(s) interaction cases are given. Single- and multi-domain BE analyses of cavity-Helmholtz resonator interaction are provided as an alternative to modal method of acoustoelasticity. A discrete-form of the existing BE acoustic particle velocity formulation is presented and demonstrated on a basic case study. Both the existing and the discretized BE acoustic particle velocity formulations could be utilized in acoustic studies. A selection of case studies involving fundamental configurations are studied both analytically and computationally (by BE or BE-FE methods). These studies could provide a basis for benchmark case development in the field of acoustics.

Background: Marine umbilicals play a vital role in oil and gas production fields. The oil and gas industry is in constant change, as the resources in the reservoirs are ever decreasing. Today oil and gas exploration takes place at increasing depths, and in harsher environments. This means that components like marine umbilicals are getting more advanced. Thus accurate structural analysis is important. The focus in this thesis is an umbilical consisting of 19 copper conductors. The goal is to model it in ABAQUS, and compare the results with laboratory testing. Results: Stress distribution and fatigue calculations were the main focus. Ultimately, it was proven that ABAQUS was able to represent the umbilical's general behavior. However, due to computational limitations and limits in the material model, the result proved inaccurate. In particular, values for axial stress and strain, exceeds the expected values. Conclusion: The model was able to represent the general behavior from the laboratory results. Effort should be made in the future to overcome the computational problems, and the material model should be revised.

In this thesis we will explore the possibilities of making a finite element solver for partial differential equations using the isogeometric framework established by Hughes et al. Whereas general B-splines and NURBS only allow for tensor product refinement, a new technology called T-splines will open for true local refinement. We will give an introduction into T-splines along with B-splines and NURBS on which they are built, presenting as well a refinement algorithm which will preserve the exact geometry of the T-spline and allow for more control points in the mesh. For the solver we will apply a residual-based a posteriori error estimator to identify elements which contribute the most to the error, which in turn allows for a fully automatic adaptive refinement scheme. The performance of the T-splines is shown to be superior on problems which contains singularities when compared with more traditional splines. Moreover the T-splines along with a posteriori error estimators are shown to have a very positive effect on badly parametrized models, as it seem to make the solution grid independent of the original parametrization.

Thesis (M.S.)--West Virginia University, 2007.
Title from document title page. Document formatted into pages; contains xii, 86 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 80-82).

The main objective of this research is to develop techniques for the analysis of the load-deformation behaviour of bodies made of structured and composite media using the finite element method and the homogenisation technique. The conventional finite element method is not economical for the analysis of structured and composite media as a large number of elements are required to model different constituents and their interfaces. In this study, an approximate method called homogenisation technique, in which average mechanical characteristics of the structured media are considered, is developed through appropriate equilibrium as well as kinematic conditions, and the resulting constitutive relations are implemented in a finite element program. This technique has been applied to a number of engineering problems and, through numerical examples, the versatility of the proposed model for the analysis of structured media has been demonstrated. Comparison between the proposed model and the conventional methods are next made to illustrate the simplicity and effectiveness of the proposed homogenisation technique. The following conclusions have been reached: For the problems of media having pre-existing discontinuities such as rock joints and interfaces between two materials, the dimensions of the zone of homogenisation along the discontinuity do not show significant difference on the overall behaviour of the structure. For the problems of media in which a structure or fabric evolves during the process of deformation such as tensile fracturing and shear localisation, the proposed model shows mesh-independent behaviour and results appear to be in good agreement with the experimental results in many cases.

A variety of pathologies exist which increase the likelihood of bone fracture. Present methods for determining the fracture risk of a specific patient are based exclusively on the amount of bone present. While the quantity of bone tissue is correlated with strength, it neglects to account for bone’s intricate microarchitecture. To assess the effect of bone quality on strength, a methodology was developed for the structural analysis of cancellous bone biopsies. Thirty biopsies were selected from a pre-existing biopsy bank, and scanned using a SCANCO µCT-40 at a resolution of 30 microns. Cortical bone was removed from the resulting three-dimensional geometry, and the remaining cancellous bone was meshed with solid tetrahedral elements. A linear static uniaxial compression test was performed using ANSYS v14.0 to determine the apparent-level Young’s modulus. The maximum von Mises stress was also investigated, but showed poor convergence with increased mesh density. Consistent with the methodology of Pistoia et al., the failure load was assumed to occur when 2% of the bone volume exceeded 7000 µstrain. The results of the finite element analysis compared favorably with known values for cancellous bone strength.

In this thesis, the Finite Element (FE) Analysis of aircraft tyres is presented. The modelling and simulations of detailed construction of tyre enable tyre manufacturers to evaluate new designs and development before a prototype is fabricated, and aim to reduce the research costs and efforts to optimise the current tyre design of tyres. The material properties is key in the FE modelling and analysis, a number of sample from the rubber compounds and reinforcement were used to characterise the elastic, hyperelastic and viscoelastic behaviour of material. In this research, two aircraft tyres were employed for correlation study to a number of design checks and standard tests such as profile growth, sidewall deformation, footprint, contact pressure, and load-deformation data. The burst simulation was carried out to investigate when and where the failure in tyre occurs and compares it with what happens in real-world burst test as an important procedure in tyre safety certification by aviation authorities. As a result, the virtual testing would shorten the design procedure by checking the design parameters in advance of tyre prototyping. Moreover, the FE parameters such as mesh size and tyre geometry are investigated for optimisation of the runtime and accuracy and improvements in the FE results. A number of simulations were run to determine generated forces and moments across the contact patch using a steady-state approach in presence of air as the tyre inflator to obtain a higher accuracy in prediction of the vertical stiffness and footprint area. In addition, the tyre was freely rolled on the runway using an explicit approach to investigate the energy dissipation and heat build-up per tyre rotation due to the tyre viscoelasticity. Finally, TAIS (Tyre Analysis Interface System) development is explained in response to the design requirements from Dunlop Aircraft Tyres.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1997, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.
Includes bibliographical references (leaves 158-161).
by Yung-Chin Hsiao.
M.S.

The serious consequence of ship collisions necessitates the development of regulations and requirements for the subdivision and structural design of ships so that damage and environmental pollution is reduced, and safety is improved. A simplified collision model (SIMCOL) is currently being developed at Virginia Tech to conduct probabilistic analysis of damage in ship collisions and ultimately optimize ship structural designs to improve crashworthiness. Collision data for validation of SIMCOL is very difficult to obtain, and model testing is very costly. Finite Element Analysis (FEA) provides an alternative to physical validation that can be used to increase confidence and insight in simplified model results. This thesis develops a complete methodology for ship-to-ship collision simulations using the explicit non-linear FE code LS-DYNA3D. Various modeling alternatives are considered. The ability to model a complete ship-to-ship collision is developed incrementally starting with bow collisions with a rigid wall. A super-element (intersection model) approach is considered to increase the calculation speed of bow models. A conventional fine mesh finite element bow model is also developed. Results from both models are compared with each other, and with a closed-form calculation from Pedersen. A fine mesh model is developed for a struck tanker cargo section and integrated in a total ship framework modeling external dynamics and ship-to-ship contact. A series of collision scenarios is simulated using the conventional bow model and a rigid bow model striking a double hull tanker. Results are compared with SIMCOL, DAMAGE, DTU and ALPS/SCOL models. LS-DYNA provides detailed and reasonable results for ship collision analysis and comparison to increase confidence in simplified models.
Master of Science

This dissertation describes enhancements made to the finite element program, SAGE, and research on the performance of deep excavations. SAGE was developed at Virginia Tech for analysis of soil-structure interaction problems (Morrison, 1995). The purpose of the work described in this text with SAGE was to increase the capabilities of the program for soil-structure analysis. The purpose of the research on deep excavations was to develop a deeper understanding of the behavior of excavation support systems. The significant changes made to SAGE during this study include implementation of Biot Consolidation, implementation of axisymmetric analysis, and creation of a steady state seepage module. These changes as well as several others are described. A new manual for the program is also included. A review of published studies of deep excavation performance and recent case histories is presented. Factors affecting the performance of excavation support systems are examined, and performance data from recent published case histories is compared to data from Goldberg et al.'s 1976 report to the Federal Highway Administration. The design, construction, and performance of the deep excavation for the Dam Number 2 Hydroelectric Project is described. Finite element analyses of the excavation that were performed with SAGE are presented and discussed.
Ph. D.

The Breast Implant Lifetime Study at Virginia Tech, on which this thesis is based, seeks to develop methods and data for predicting the lifetime of saline-filled implants. This research developed Finite Element Analysis (FEA) models to evaluate the stresses that are present in the silicone breast implant material under different loading situations. The FEA work was completed using the commercial codes PATRAN and ABAQUS. PATRAN was used for pre- and post-processing, while ABAQUS was used for the actual analysis and to add fluid and contact elements not supported by PATRAN. Many different loading situations and constraints were applied to these models, as well as variations in the material and model properties. Varying the Poisson's ratio of the implant material from 0.45 to 0.49 did not make a significant difference in the results. Changing the elastic modulus of the implant material from the modulus of a Smooth implant to the modulus of a Siltex implant had a noticeable effect on the stress results, increasing the maximum stresses by almost 8%. Changing the modulus of the surrounding tissue had marked effects as well, with stiffer tissue (E=300 psi) decreasing the implant's stresses by about 60% as compared to softer tissue (E=100 psi). A ten percent decrease in implant thickness yielded a 17% average increase in stress experienced by the implant. For both the 2.5" radius and the 4" radius tissue models, using CAX4 elements produced higher overall stresses in the tissue with the same loading conditions. However, in the 2.5" tissue model, the implant itself experienced less stress with the CAX4 tissue than the CAX3 tissue. In the 4" tissue model, the implant experienced more stress when surrounded by the CAX4 tissue elements. These models will be combined with implant fatigue data to develop a life prediction method for the implant membrane.
Master of Science

The three-dimensional behavior of geotextile tubes is studied using finite element modeling. Two initial shapes are investigated, one with a flat length-to-width ratio of 2:1 and the other with a flat length-to-width ratio of 5:1. The tubes are modeled resting on elastic foundations. For each initial shape, the elastic foundation is modeled using two different stiffnesses; one allows a minimum amount of "sinking" into the foundation and the other allows a considerable amount. The weight of the geotextile is included. Hydrostatic pressure is applied internally to each initially flat tube to model the pumped slurry. The shape of the tube is studied along with the contact region between the tube and its foundation, the stresses which develop in the geotextile along the planes of symmetry, and the relationship between the height of the tube and the amount of applied hydrostatic pressure.
Master of Science

Includes bibliographical references.
The purpose of this study was to develop a computational Finite Element model, validated by experimentation, to assist in the understanding of groundwater contamination problems. It was mainly aimed at studying the extent and manner of travel of contaminants in the saturated soil of unconfined aquifers which may be pumped by of wells.

In this thesis, the failures that occurred during the construction of the Jamuna Bridge Abutment in Bangladesh have been investigated. In particular, the influence of heterogeneity on slope stability has been studied using statistical methods, random field theory and the finite element method. The research is divided into three main parts: the statistical characterization of the Jamuna River Sand, based on an extensive in-situ and laboratory database available for the site; calibration of the laboratory data against a double-hardening elastoplastic soil model; and stochastic finite element slope stability analyses, using a Monte Carlo simulation, to analyse the slope failures accounting for heterogeneity. The sand state has been characterised in terms of state parameter, a meaningful quantity which can fully represent the mechanical behaviour of the soil. It was found that the site consists of predominantly loose to mildly dilative material and is very variable. Also, a Normal distribution was found to best represent the state parameter and a Lognormal distribution was found to best represent the tip resistance.The calibration of the constitutive model parameters was found to be challenging, as alternative approaches had to be adopted due to lack of appropriate test results available for the site. Single-variate random fields of state parameter were then linked to the constitutive model parameters based on the relationships found between them, and a parametric study of the abutment was then carried out by linking finite elements and random field theory within a Monte Carlo framework.It was found that, as the degree of anisotropy of the heterogeneity increases, the range of structural responses increases as well. For the isotropic cases, the range of responses was relatively smaller and tended to result in more localised failures. For the anisotropic cases, it was found that there are two different types of deformation mechanism. It was also found that, as the vertical scale of fluctuation becomes bigger, the range of possible structural responses increases and failure is more likely. Finally, it was found that the failed zones observed during the excavation of the West Guide Bund of the Jamuna Bridge Abutment could be closely predicted if heterogeneity was considered in the finite element analyses. In particular, it was found that, for such a natural deposit, a large degree of anisotropy (in the range of 20) could account for the deformation mechanisms observed on site.

This thesis applies the method of finite element software to calculate pulsed high field magnets. The calculations address the structural and thermal load of pulsed magnets during discharge and at peak field. The most successful currently-used coil designs from different magnet laboratories are assessed with these methods. The results are compared against wellestablished analytic programs; arising differences are discussed. Particular emphasis is on the coil designs developed for the pulsed field facility in the Clarendon Laboratory, Oxford, UK. The facility, named after Nikolas Kurti, is described and classified. The coil designs are based on a novel high strength copper-silver conductor, which is compared to other common conductors. In combination with the novel calculation methods this established a new quality of high magnetic fields: the local record was broken in March 2007 by creating the highest magnetic field to date in the Clarendon Laboratory. Present and future trends in pulsed magnet design are discussed and evaluated. These include a discussion of foil coils, braiding of conductors and the matching of conductors with suitable reinforcement. Particular emphasis is placed on the verification of the simulation results. To this end a finite element method is developed which can be used to predict the irreversible change of the inductance of pulsed magnets due to plastic deformation. Preliminary results of residual strains in a magnet using neutron scattering are also considered. Another focus is on reducing the cool-down time of pulsed magnets by using rapid cooling methods. The concept of the so-called 'cooling disc' is new in this respect. Experimental and theoretical results are contrasted with other methods. Other work has contributed to the design of the magnetic channel of the international Muon Ionization Cooling Experiment; this thesis gives a summary. The work comprises force calculations, quench considerations and magnetic shielding issues.

A research group at University of Skövde has developed an interphase element for implementation in the commercial FE-software Abaqus. The element is using the Tvergaard & Hutchinson cohesive law and is implemented in Abaqus Explicit version 6.7 using the VUEL subroutine. This bachelor degree project is referring to evaluate the interphase element and also highlight problems with the element.

The behavior of the interphase element is evaluated in mode I using Double Cantilever Beam (DCB)-specimens and in mode II using End Notch Flexure (ENF)-specimens. The results from the simulations are compared and validated to an analytical solution.

FE-simulations performed with the interphase element show very good agreement with theory when using DCB- or ENF-specimens. The only exception is when an ENF-specimen has distorted elements.

When using explicit finite element software the critical time step is of great importance for the results of the analyses. If a too long time step is used, the simulation will fail to complete or complete with errors. A feasible equation for predicting the critical time step for the interphase element has been developed by the research group and the reliability of this equation is evaluated.

The result from simulations shows an excellent agreement with the equation when the interphase element governs the critical time step. However when the adherends governs the critical time step the equation gives a time step that is too large. A modification of this equation is suggested.

In this thesis, the coupling of boundary element and finite element methods and its application to analyze bridges are studied for the first time. The coupling technique is implemented to analyze slab on girders and box girder bridges. The boundary element method is employed to model the bridge deck while the finite element method is used to model the girders. The finite elements and boundary elements are connected at a number of interface nodes in the longitudinal direction. For the finite element region, a static condensation technique is applied to condense the non-interface degrees of freedom. Then the finite element equations are transformed into boundary element equations and the compatibility interface mechanism required to combine the two methods is developed. A computer program which combines boundary element and finite element methods in one solution is developed in this thesis. Different types of bridges with different load cases are considered in the study in order to test the performance of the combined method. It has been shown that the results obtained by the combined method (BEM-FEM) are in good agreement with the finite strip solution. The numerical examples, considered in this thesis, demonstrated the accuracy of the results and the simplicity and reduction of the input data.

Contact is a phenomenon faced in every day life, which is actually a complex problem to tackle for engineers. Most of the times, may be impossible to get analytic or exact results for the interaction of bodies in contact. In this thesis work, solution of the frictionless contact of an elastic body, touching to a rigid planar surface for two-dimensional elasticity
namely plane stress, plane strain and axi-symmetric formulations is aimed. The problem is solved numerically, with Finite Element Method, and an Object Oriented computer program in C++ for this purpose is written, and the results are verified with some basic analytic solutions and ABAQUS package program. It is not aimed in this thesis work to give a new solution in the area of solution of contact problems, but instead, it is aimed to form a strong basis, and computational library, which is extendible for further development of the subject to include friction, plasticity, and different material modeling in this advanced field of mechanics.

This dissertation describes a new version of the Generalized Finite Element Method (GFEM), which is well suited for problems set in domains with a large number of internal features (e.g. voids, inclusions, etc.), which are practically impossible to solve using the standard FEM. The main idea is to employ the mesh-based handbook functions which are solutions of boundary value problems in domains extracted from vertex patches of the employed mesh and are pasted into the global approximation by the Partition of Unity Method (PUM). It is shown that the p-version of the Generalized FEM using mesh-based handbook functions is capable of achieving very high accuracy. It is also analyzed that the effect of the main factors affecting the accuracy of the method namely: (a) The data and the buffer included in the handbook domains, and (b) The accuracy of the numerical construction of the handbook functions. The robustness of the method is illustrated by several model problems defined in domains with a large number of closely spaced voids and/or inclusions with various shapes, including the heat conduction problem defined on domains with porous media and/or a real composite material.

A new methodology is introduced where the natural hierarchical character of model descriptions and simulation results are exploited to expedite analysis of problems. The philosophy and the different concepts involved are illustrated by implementing the strategy to solve some practical problems. The end result was a mix of mechanics, well-designed data structures and software interfaces that forms a rapid analysis environment. This can be very advantageous for cases where a sequence of analyses is required because of safety concerns or cost. When designing a structure, it is common to make frequent modifications to the model during the process. In such cases, the ability to use data from different models within the same analysis environment becomes a major advantage. The proposed system's forte is its hierarchical framework that allows models to communicate with each other and share information with one another. This makes it ideal for global local analyses where solutions from a global model are used to derive the boundary conditions for the local model. The system was also used to conduct a micro mechanical analysis on unidirectional composites that have a non-uniform spatial distribution of the fibers. The hierarchical strategy is not tied to any specific methodology and can be adapted to solve problem using different technologies. This allows the strategy to be used across multiple length scales and governing equations.

The wrist is a very anatomically complex joint and little has been reported about the biomechanics of the wrist joint. Cadaveric measurements have been carried out to investigate the load transfer characteristics. Due to the complexity of the joint, analytical models are difficult to create, but the finite element method is generally employed to create a numerical model of the joint. Current finite element studies of the wrist have only looked at a small subset of the joint or created a simplified model using un-physiological boundary conditions. The presented work reports on the creation of subject specific models of the whole wrist, during gripping, using loading conditions obtained through biomechanical experiments in order to be able to predict in-vivo stresses in the wrist joint, with the wrist in three different positions: neutral position, radial deviation and ulnar deviation.

The objective of the research is to improve the solution capability of a finite element system by the use of parallel processing techniques. Initial research began with the transputer system at a time when the transputer was considered the ultimate parallel machine. The transputer based parallel program LINSUB was developed to solve linear static stress analysis problems using a modified Cholesky algorithm for substruturing. Further developments in this field were halted when it became clear that other parallel systems, namely, those concerned with workstation clusters, were moving rapidly ahead of the transputer in terms of performance and the transputer was rapidly becoming obsolete. Further work concentrated on parallel processing on workstation clusters in a local area network and the effectiveness of the Parallel Virtual Machine (PVM) used as the supportive parallel environment was investigated. This work was then extended onto a shared memory - MIMD system on the Silicon Graphics Power Challenge workstation. The program PARFEI (PARallel Finite Element Implementation) was developed for large linear static stress analyses and nonlinear analyses of elasto-plastic problems in particular, using a multifrontal approach based on domain decomposition techniques. An implementation based on a specially designed share memory (SM) synchronization concept was incorporated into the same program, so that PARFEI can run sequentially or in parallel using either PVM or SM. Performance tests were carried out on the workstation clusters using PVM and on the shared memory machine using PVM and SM. The results revealed that, in general, PVM performed better for the linear system and SM was the more efficient of the two when an incremental/iterative process was involved.

In metal forming processes such as extrusion and forging the deformation is due, primarily, to the plastic flow of the material. Nevertheless the deformation and the resulting stress distribution is influenced by an elastic effect albeit small. Attempts to solve elasto-plastic metal forming problems, using finite elements, have resulted in the emergence of two competing approaches, namely the solid mechanics based elasto-plastic schemes and rigid-plastic solution techniques such as the viscous flow formulation. This thesis is concerned with the viscous flow approach which generally appears to offer a cheaper solution in comparison to the traditional 'solid' approach. Before introducing elastic effects stress recovery techniques are considered in order to get accurate continuous stresses which also satisfy the equilibrium equations. The techniques developed for this purpose are equally applicable to standard displacement based solutions as well as viscous flow solutions. A multi-loop iterative finite element procedure, incorporating stress smoothing, is then established in an attempt to include elasticity effects. Numerical experiments have been carried out to investigate the consequences of including elasticity. Whilst the procedure works convergence difficulties were experienced when the effect of elasticity increases. Nevertheless the theoretical exposition together with the numerical results provides a valuable foundation from which most robust enhanced procedures for including elasticity can be developed. The above procedures all result in Eulerian steady state velocity solutions. In contrast a combined Eulerian-Lagrangian solution scheme is developed as a means of progressing the deformation of the material with respect to time. This technique is applied to axisymmetric superplastic forming in which the constitutive behaviour is a power law relation between stress and strain rate. A variety of analytical solutions are devised which enable the finite element superplastic formulation and a number of standard time marching schemes to be evaluated. Finally, the program is successfully applied to the free forming (bulging) of the aluminium and titanium alloys A1-Mg6-Mn1 and Ti-6A1-4V. In the forming case numerical results are compared to published experiment data.

This thesis presents a nonlinear Finite Element analysis of welded tubular connections, addressing several areas of recent interest in the field. A comprehensive study of multiplanar axially loaded T-DT joints in both CHS and RHS was undertaken to add to the available knowledge and interest/ activity in the field of multiplanar connections. Sections of this study are supported by earlier experimental work undertaken at Nottingham (not by the author) and from a combination of these and FE results, a series of design rules to supplement the current IIW planar design formulae developed. Analysis of the effect of brace angle on the difference between axially loaded T and Y joints was undertaken to resolve differences between current codes of practice. Finally an analysis of a family of partial overlapped RHS K joints was undertaken to ascertain the effects of boundary conditions, brace angle, β ratio, reversal of loading and hidden weld on the ultimate capacity and performance of such joints. All of the FE work was undertaken using ABAQUS, including both geometric and material non-linearity. Recommendations for further work are made.

Thesis (MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: The Tubular Track (TT) railway system is a twin beam modular railway system consisting of two reinforced concrete (RC) beams on which steel rails are continuously supported. The beams are linked with galvanised steel gauge tie bars and continuously supported by soil foundations, and can be used to replace conventional sleeper and ballast railway support. The TT railway system has in the past been analysed with various analysis methods, but were found to obtain con icting results. The con icting results means that one of the analysis methods used for the analysis and design of TT railway sections is either an underestimation or overestimation of section displacements, forces, and stresses; or both methods could even be incorrect. The main emphasis of this investigation is therefore to develop and verify static and dynamic analysis methods and modeling techniques which can be used to simulate the TT railway system accurately. The results and models of the previous analyses are not explicitly investigated in this dissertation, but serve as a motivation for this investigation. The TT system is supported by several soil strata providing vertical support, but geometrically modeling the subgrade strata in the analysis models adds a high level of complexity, and is not feasible for general analysis where soil conditions are mostly unknown. The elastic foundation theory is therefore used to accurately simulate the interaction between beam and foundation and therefore su ciently simpli es the analysis models. Simpli cation of a subgrade foundation by simulating a soil sti ness supporting the TT beam is investigated and analysed by comparing nite element analysis (FEA) results of various soil models using parameters of four known soil formations currently in use at TT railway sections. The FEA of the subgrade formations indicates that there is a linear relationship between the modulus of subgrade reaction for a square plate bearing test and a rectangular, in nitely long plate representing the subgrade support for the TT beams. A square plate bearing test can therefore be performed on site and modi ed to represent the actual subgrade support sti ness of the TT railway structure, whereafter it can be used for the analysis and design of the TT system using one of the proposed analysis methods. The analysis models used range from simple theoretical models based on elastic foundation principles, to two-dimensional (2D) beam elements, and ultimately to complex three-dimensional (3D) solid nite element models. The models used for the analyses are the Single and Double Beam elastic foundation, PROKON 2D beams, ABAQUS 2D beams and ABAQUS 3D solid element models. The alternative analysis methods considered should provide a clear indication of which analysis methods are accurate and feasible for design of the TT system. An in-situ reference model with known de ections and design parameters speci c to a TT railway section is used to analyse the di erent analysis methods' accuracy and validity. The Double Beam, ABAQUS 2D and ABAQUS 3D models were found to provide very similar displacements, bending moments and shear forces for a static analysis, whereas the PROKON and Single Beam models provide unsatisfactory results. The PROKON beam model underestimates the bending moments and shear forces in the rail, and overestimates bending moments and shear forces in the RC beam by a considerably margin. This result can lead to the underdesigning of the rail which could possibly force the RC beam to be subjected to larger maximum bending moments and shear forces than for what it was originally designed for, thereby nullifying or possibly even exceeding the amount for which it was overdesigned. This e ectively accelerates material fatigue, which might be the possible cause of the small cracks in the RC beams which have been found on some TT railway sections, which is currently being investigated. A graphical user interface of the Double Beam method is provided for quick and e cient analysis. Empirical methods used to simulate the dynamic nature of a railway system are often used in the industry to simplify the dynamic loading by determining a dynamic amplitude factor (DAF) to be applied to a static load. An implicit dynamic FEA is therefore performed to obtain the DAF for the reference section, which is subsequently used for the comparison with in-situ de ection results. The results of dynamic analysis validates the proposed empirical analysis method, as the displacements obtained were very similar to actual eld test results, thereby also verifying the accuracy of the proposed analysis methods. The sensitivity of the TT system to design parameters is also investigated to indicate to which parameters the design is sensitive to and where small variations of these parameters require due consideration for future and analysis of the TT railway system.
AFRIKAANSE OPSOMMING: Die Tubular Track (TT) spoorweg stelsel is 'n dubbel balk modulêre treinspoor sisteem bestaande uit twee gewapende beton balke waarop staal spore voortdurend ondersteun word. Die balke word gekoppel deur gegalvaniseerde staal stawe vir laterale styfheid en word deurlopend ondersteun deur grond fondamente, en kan gebruik word om konvensionele dwarslêer en ballast spoorweg ondersteuning te vervang. Die TT spoorweg stelsel was in die verlede met verskeie analiseringsmetodes ontleed, maar het teenstrydige resultate gewerf. Die teenstrydige resultate beteken dat een van die analise metodes wat gebruik word vir die analisering en ontwerp van TT spoorweg seksies 'n onderskatting of oorskatting van verplasings, kragte, en spannings is; of beide metodes kan selfs verkeerd wees. Die hoofklem van hierdie ondersoek is dus die ontwikkeling en veri kasie van statiese en dinamiese analitiese metodes en modellering tegnieke wat gebruik kan word om die TT spoorweg stelsel akkuraat te simuleer. Die resultate en modelle van die vorige ontledings word nie uitdruklik in hierdie proefskrif ondersoek nie, maar dien as 'n motivering van hierdie ondersoek. Die TT stelsel word ondersteun deur verskeie grond strata wat vertikale ondersteuning verskaf, maar meetkundige modellering van die grond strata in die ontledingsmodelle veroorsaak 'n hoë vlak van kompleksiteit wat nie bruikbaar is vir algemene analises waar grondeienskappe meestal onbekend is. Die elastiese fondament teorie word daarom gebruik om die interaksie tussen die balk en die fondament akkuraat te simuleer, en vereenvoudig dus die analitiese modelle voldoende. Vereenvoudiging van 'n grond fondament deur 'n grond styfheid ondersteuning van die TT balk te simuleer is ondersoek en ontleed deur die resultate van eindige element analises van verskillende grond modelle te vergelyk. Bekende ontwerp parameters van vier bekend grondformasies wat tans gebruik word by TT spoorweg seksies word vir hierdie analises gebruik. Die eindige element analises van die grondformasies dui daarop aan dat daar 'n lineêre verwantskap tussen die modulus van grond reaksie vir 'n vierkantige plaat dratoets en 'n reghoekige, oneindige lang plaat dratoets bestaan. 'n Vierkantige plaat dratoets kan dus op terrein uitgevoer en aangepas word om die werklike styfheid van die grond ondersteuning van die TT spoorweg sisteem voor te stel. Die analitiese modelle wat gebruik word wissel van eenvoudige teoretiese modelle wat gebaseer is op elastiese fondament beginsels, twee-dimensionele (2D) balk elemente, asook komplekse driedimensionele (3D) soliede eindige element modelle. Die modelle wat gebruik is vir die ondersoek is die Enkel en Dubbel Balk elastiese fondament, PROKON 2D balke, ABAQUS 2D balke en ABAQUS 3D soliede element modelle. Hierdie reeks bied 'n duidelike aanduiding watter analiseringsmetodes akkuraat en haalbaar is vir die ontwerp van die TT stelsel. 'n In-situ verwysingsmodel met bekende de eksies en ontwerp parameters wat spesi ek is vir 'n TT spoorweg seksie word gebruik om die akkuraatheid en geldigheid van die verskillende analitiese metodes te analiseer. Die Dubbel Balk, ABAQUS 2D en ABAQUS 3D modelle verkry baie soortgelyke verplasings, buigmomente en skuifkragte vir 'n statiese analise, terwyl die PROKON en Enkel Balk modelle onbevredigende resultate verkry. Die PROKON model onderskat die maksimum buigmomente en skuifkragte in die staal spoor, en oorskat buigmomente en skuifkragte in die gewapende beton balk. Hierdie resultaat kan moontlik lei tot die onderontwerp van die staal spoor en dwing moontlik vir die gewapende beton balk om blootgestel te word aan groter buigmomente en skuifkragte as vir wat dit oorspronklik ontwerp is, en verontagsaam sodoende moontlik die kragte waarvoor dit oorontwerp is. Dit versnel e ektief materiaal vermoeiing, wat die moontlike oorsaak is van die klein krake wat gevind is in die gewapende beton balke op sommige TT spoorweg seksies wat tans ondersoek word. 'n Gra ese gebruikerskoppelvlak van die Dubbel Balk model is verskaf vir vinnige en doeltre ende ontleding. Empiriese metodes om die dinamiese aard van 'n spoorweg-stelsel te simuleer word dikwels gebruik in die bedryf om dinamiese belasting te vereenvoudig deur middel van die gebruik van 'n dinamiese amplitude faktor (DAF) wat op 'n statiese belasting aangewend word. 'n Implisiete dinamiese eindige element analise word dus uitgevoer om die DAF te ondersoek, wat daarna gebruik word vir die vergelyking met die in-situ de eksie resultate van die in-situ verwysingsmodel. Die resultate van die dinamiese analise bevestig dat die voorgestelde empiriese analise metode gebruik kan word, omdat die verplasings wat verkry baie soortgelyk was aan werklike veld toets resultate, en daardeur ook die veri ëring van die akkuraatheid van die voorgestelde analise metodes bewerkstellig. Die sensitiwiteit van die TT stelsel vir ontwerp parameters word ook ondersoek om aan te dui watter parameters die ontwerp voor sensitief is, en waar klein variasie in hierdie ontwerp parameters behoorlike oorweging vereis vir die toekomstige analisering en ontwerp van die TT spoorweg stelsel.