Segui questo link per vedere altri tipi di pubblicazioni sul tema: Buckling.
Tesi sul tema "Buckling"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Buckling".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
CUNHA, PATRICIA CARLA DA. "BUCKLING AND POST-BUCKLING BEHAVIOR OF FOLDED PLATES". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=7691@1.
Testo completoAbstract (sommario):
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO presente trabalho tem por objetivo estudar o comportamento crítico e pós-crítico de placas dobradas. Placas dobradas, tanto de aço quanto de concreto, têm sido usadas com grande freqüência em obras de engenharia, particularmente como paredes portantes e coberturas de grandes vãos. Neste último caso, placas dobradas têm uma aplicação semelhante a de cascas esbeltas, sendo, porém, mais simples de construir, dado que são compostas de superfícies planas. Neste trabalho utiliza-se o software ABAQUS para análise de placas dobradas compostas de duas placas formando um dado ângulo entre si. Estuda-se o uso destas placas como paredes portantes sob compressão, sendo conduzido um estudo paramétrico para determinar a influência dos diversos parâmetros geométricos e condições de contorno nas cargas críticas e modos críticos da placa dobrada. A seguir são determinados os caminhos pós-críticos e estuda-se a influência dos diversos parâmetros na rigidez pós-crítica e sensibilidade a imperfeições. Finalmente, estuda-se o comportamento não-linear destas placas sob flexão, sendo investigados os fenômenos de perda de estabilidade associados a este problema.
The aim of the present work is to study the buckling and post-buckling behavior of folded plates. Folded plates, made of steel or concrete, have been widely used in engineering construction as load-bearing walls designed to carry floor and roof loads or roofs for large spaces. In the last case, folded plates work as a thin shell, being however easier to build since they are formed by flat surfaces joined along the fold lines. In this work the software ABAQUS is used to study the behavior of V-shaped folded plates. Initially it is analyzed the behavior of these plates when used as load-bearing walls under axial compression. A detailed parametric analysis is conducted to identify the influence of the geometrical parameters and boundary conditions on critical loads and modes. The influence of these parameters on the post-buckling response, post-critical stiffness and imperfection sensitivity is also investigated. Finally, the non-linear response of V-shaped folded plates under flexure is investigated and the possible instabilities under these loading conditions are analyzed.
2
Khamisi, Ali. "Stability of Tubular Steel Structures : Buckling and Lateral Torsional Buckling". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0172.
Testo completoAbstract (sommario):
Ce sujet est d’actualité suite à une évolution rapide des types de conception de structures élancées utilisées dans les installations provisoires. C’est seulement depuis une vingtaine d’années que ces structures sont préfabriquées en cadres multidirectionnels (de sections tubulaires en acier ou en aluminium). Ces structures sont légères et leur stabilité réside seulement dans les raideurs internes au niveau des files de montants et au niveau horizontal par les planchers ainsi que dans les liaisons avec l’ouvrage. Ce travail concerne l’étude des instabilités (flambement-déversement) en tenant compte de différents types d’imperfections. De nouvelles courbes de flambement ainsi que les facteurs d’imperfection associés sont proposés dans cette thèse. Ces courbes sont obtenues en imposant une déformée initiale représentant les défauts géométriques et mécaniques (contraintes résiduelles). Les résultats expérimentaux confrontés avec les prévisions théoriques de l’Eurocode 3 montrent que les valeurs des imperfections figurant dans la littérature sont extrêmement exagérées. Les valeurs préconisées dans ce travail pourraient présenter un certain intérêt pour une modification éventuelle des courbes européennes de flambement pour ce type de structure. En ce qui concerne l’instabilité latérale, une méthodologie originale d’essais en vraie grandeur de poutres à treillis formés d’éléments tubulaires a été également mise au point. Le système de chargement à « roues libres » développé permet de libérer le point d’application de l’effort dès le début de l’instabilité. Cette technique conduit à des mesures plus précises du moment critique de déversementThis subject becomes topical following a rapid evolution of design procedures for slender structures used widely in the temporary installations. Only through the last twenty years that these structures are prefabricated of multidirectional frames (steel or aluminium tubular sections). These structures are lightweight and their stability lies only in the internal stiffness at rows of posts and horizontally by the planking as well as the links with the building. This work concerns the study of instabilities (buckling - lateral torsional buckling) taking into account different types of imperfections. New buckling curves and the associated imperfection factors are proposed in this thesis. These curves are obtained by imposing an initial deformed representing the geometrical and mechanical defects (residual stress). The experimental results were confronted with theoretical predictions of Eurocode 3 which show that the values of the imperfections in the literature are extremely exaggerated. The values advocated in this work could be of interest for a possible adjustment of the European buckling curves for this type of structure. Regarding the lateral instability, an original methodology in real scale tests of trusses consist of tubular elements was also developed. The developed loading system of "free wheels" allows releasing the point of application of the force from the beginning of instability. This technique leads to more accurate measurements of the critical lateral torsional buckling moment
3
Clarin, Mattias. "Plate buckling resistance : patch loading of longitudinally stiffened webs and local buckling /". Luleå : Division of Structural Engineering - Steel Structures, Department of Civil, Mining and Environmental Engineering, Luleå University of Technology, 2007. http://epubl.ltu.se/1402-1544/2007/31/LTU-DT-0731-SE.pdf.
Testo completo
4
Mahar, Akshay Mangal. "Buckling and post-buckling behaviour of cold-formed steel built-up columns". Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232829/1/Akshay%20Mangal_Mahar_Thesis.pdf.
Testo completoAbstract (sommario):
This research investigated the stability and strength behaviour of cold-formed steel built-up columns. The stability behaviour was investigated by developing a compound spline finite strip based computational tool, while experiments and finite element studies were performed to investigate the strength behaviour. The results highlighted the shortcomings of the current design standards, including North American and Australian/New Zealand Standards, and led to simplified design procedures and strength equations for cold-formed steel built-up columns. Overall, this research has significantly improved the knowledge of cold-formed steel built-up columns, enabling structurally efficient and safer designs.
5
Sadr-Hashemi, Farshid. "Buckling of conical shells". Thesis, University College London (University of London), 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685403.
Testo completo
6
JUNIOR, WALTER MENEZES GUIMARAES. "BUCKLING OF VISCOELASTIC STRUCTURES". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9164@1.
Testo completoAbstract (sommario):
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOEste trabalho apresenta um modelo computacional aplicável à análise de sistemas estruturais viscoelásticos submetidos a grandes deslocamentos, com particular atenção ao fenômeno da instabilidade. A discretização dos modelos é obtida através de elementos finitos isoparamétricos bidimensionais que podem ser empregados na análise de colunas, pórticos, arcos e cascas axissimétricas. A estabilidade elástica do sistema é verificada ao longo de trajetórias de equilíbrio definidas no espaço carga-deslocamentos, onde a ocorrência de pontos de bifurcação ou de pontos-limite é indicada através da troca de sinal do pivô da matriz de rigidez tangente. A inclusão de um modelo viscoelástico linear para o material possibilita a avaliação do efeito do tempo de carregamento sobre a carga de flambagem da estrutura. O mecanismo de instabilidade correspondente à flambagem viscoelástica envolve duas variáveis básicas: a magnitude da carga (carga crítica) e a duração da carga (tempo crítico). Os exemplos apresentados ilustram esses conceitos e fornecem resultados interessantes a respeito dos efeitos da viscoelasticidade sobre a flambagem em diferentes sistemas estruturais.
This thesis presents a computational model for the analysis of viscoelastic structures undergoing large displacements, with particular attention to unstable phenomena. The discrete model utilizes two-dimensional isoparametric finite elements in the analysis of columns, frames, arches and axially symmetric shells. The elastic stability of the system is verified along the equilibrium paths in the multidimensional load-displacements space, with bifurcation or limit points indicated by sign changes of the pivot of the tangent stiffness at every incremental step. A linear viscoelastic model for the material is included, allowing for the consideration of the effect of loading time on the buckling load for the structure. Thus, the mechanism leading to loss of stability, corresponding to viscoelastic buckling, involves two basic variables: load magnitude and duration of the load, designated as critical load and critical time. The examples presented herein enlighten such concepts and provide interesting results about viscoelastic effects on buckling of different structural systems.
7
Moroder, Daniel. "Longitudinal bar buckling behavior". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amslaurea.unibo.it/94/.
Testo completoAbstract (sommario):
Reinforced concrete columns might fail because of buckling of the longitudinal reinforcing bar when exposed to earthquake motions. Depending on the hoop stiffness and the length-over-diameter ratio, the instability can be local (in between two subsequent hoops) or global (the buckling length comprises several hoop spacings).
To get insight into the topic, an extensive literary research of 19 existing models has been carried out including different approaches and assumptions which yield different results. Finite element fiberanalysis was carried out to study the local buckling behavior with varying length-over-diameter and initial imperfection-over-diameter ratios. The comparison of the analytical results with some experimental results shows good agreement before the post buckling behavior undergoes large deformation. Furthermore, different global buckling analysis cases were run considering the influence of different parameters; for certain hoop stiffnesses and length-over-diameter ratios local buckling was encountered. A parametric study yields an adimensional critical stress in function of a stiffness ratio characterized by the reinforcement configuration.
Colonne in cemento armato possono collassare per via dell’instabilità dell’armatura longitudinale se sottoposte all’azione di un sisma. In funzione della rigidezza dei ferri trasversali e del rapporto lunghezza d’inflessione-diametro, l’instabilità può essere locale (fra due staffe adiacenti) o globale (la lunghezza d’instabilità comprende alcune staffe).
Per introdurre alla materia, è proposta un’esauriente ricerca bibliografica di 19 modelli esistenti che include approcci e ipotesi differenti che portano a risultati distinti. Tramite un’analisi a fibre e elementi finiti si è studiata l’instabilità locale con vari rapporti lunghezza d’inflessione-diametro e imperfezione iniziale-diametro. Il confronto dei risultati analitici con quelli sperimentali mostra una buona coincidenza fino al raggiungimento di grandi spostamenti. Inoltre, il caso d’instabilità globale è stato simulato valutando l’influenza di vari parametri; per certe configurazioni di rigidezza delle staffe e lunghezza d’inflessione-diametro si hanno ottenuto casi di instabilità locale. Uno studio parametrico ha permesso di ottenere un carico critico adimensionale in funzione del rapporto di rigidezza dato dalle caratteristiche dell’armatura.
8
Purbolaksono, Judha. "Buckling and post-buckling analysis of cracked plates by the boundary element method". Thesis, Queen Mary, University of London, 2003. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1831.
Testo completoAbstract (sommario):
This thesis presents boundary element formulations for buckling and nonlinear buckling analysis of plates. Dual boundary element formulations are also presented for linear and nonlinear buckling, and large deformation analysis of crack behaviour in plates. Reissner plate theory is adopted to represent shear deformable plate bending, and two dimensional plane stress is used to model the membrane behaviour of plate. By taking into account the nonlinear interaction between forces and rotations in the equilibrium equation, the nonlinear formulation is formed by coupling equations of shear deformable plate bending and two dimensional elasticity. The boundary element formulation for plate buckling is developed. Plate buckling equations are written as a standard eigenvalue problem. Buckling coefficients and buckling modes are obtained using this formulation. Initially, the boundary is discretised into quadratic isoparametric elements, and the domain is discretised using constants cells. Next, the dual reciprocity method is utilized to transform the domain integral into equivalent boundary integrals. Examples are presented for plate buckling problems with different geometry, loading and boundary conditions. The results obtained are shown to be in good agreement with analytical and finite element results. The Dual Boundary Element Method (DBEM) for buckling analysis of plate is also developed. The plate buckling equations are also presented as a standard eigenvalue problem, which would allow direct evaluation of critical load factor and buckling modes for cracked plates. Geometrically nonlinear boundary element formulation is developed to analyse large deformation and nonlinear buckling of plates. Different load incremental approaches and solution procedures are presented. Nonlinear terms are evaluated using a radial basis function. Large deformation analysis for Fracture Mechanics problems is also presented. Five stress intensity factors are calculated, i. e. three for plate bending and two for membrane. Crack Opening Displacement (COD) is used to compute the stress intensity factors. The nonlinear buckling of thin plate is also presented. Two models of imperfection are introduced in the formulation, i. e. a small uniform transverse loads and distributed transverse loads based on eigenvectors. A simple numerical algorithm is presented to analyse the problems. Finally, nonlinear buckling analysis of cracked plate is presented. Numerical examples of nonlinear buckling and large deformation problems are presented. The BEM results presented are shown to be in good agreements with analytical and other numerical results.
9
SOLTANI, GHULAM H. "BUCKLING AND POST-BUCKLING RESPOSNE OF SINGLE CURVATUE BEAM-COLUMNS UNDER THERMAL (FIRE) LOADS". OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2147.
Testo completoAbstract (sommario):
The main objective of this research was to study the buckling and post-buckling response of axially restrained beam-columns under thermal loading. Also the effects of slenderness ratios on pre-buckling and post-buckling behavior which is neglected in AISC specification was examined. The results of this study indicate that: a) Both the deflection and end moment amplification factors are significantly smaller for the restrained beam-columns subjected to temperature increase than the corresponding unrestrained beam-columns subjected to (mechanical) axial loads. b) The deflection amplification factors tend to decrease with decreasing ratio of end moments. However, reverse seems to occur for the moment amplification factors and as the moment amplification factors tend to increase with decreasing moment ratio particularly in the pre-buckling and the initial post-buckling range (0.1 < T/Tcr < 1.5). c) The thermal amplification factors tend to be smaller than the AISC values even in the pre-buckling range with those for the slender beam-columns significantly smaller than those for the shorter beam-columns.
10
Ozdemir, Kerem Murat. "Lateral Buckling Of Overhanging Beams". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606488/index.pdf.
Testo completoAbstract (sommario):
Lateral torsional buckling should be taken into account during the design of overhanging steel beams. One special type of overhanging beams is the crane trolley monorails. Lateral buckling of overhanging monorails under idealized loading and
boundary conditions has been studied in the past using classical mathematical procedures. This thesis aims to present a detailed investigation of overhanging monorails using finite element analysis. Effects of different loading and boundary
conditions were studied in detail. It was found out that the location of loading and supports on the cross section have significant effects on the buckling capacity. Beams having different warping and torsional properties were analyzed. The effects of cross section distortion on buckling capacity were investigated for beams with single and double overhangs. The reduction in capacity due to cross section distortion has been
quantified. Based on the analysis results simple design recommendations were developed for lateral buckling of overhanging monorails and they are presented herein.
11
Miles, David John. "Lateral thermal buckling of pipelines". Thesis, University of Cambridge, 1998. https://www.repository.cam.ac.uk/handle/1810/251654.
Testo completo
12
Elmahdy, Ghada. "Buckling of built-up columns". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30272.pdf.
Testo completo
13
Ahmed, Hesham. "Parametric buckling analyses of plates". Thesis, Oxford Brookes University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616317.
Testo completoAbstract (sommario):
Classical methods for solving plate buckling problems involve using different forms of solution on case by case basis. In place of this approach, This thesis presents a novel single form equation and the parameters required to account for the interaction of geometry, boundary conditions and different forms of edge load distribution. The thesis also presents more results for different combination of plate edge boundary conditions than can be found in most design manuals such as the ESDD. The method presented is titled 'Parametric Buckling Analysis (PBA),. It combines a number of concepts in a heuristic manner to achieve the single form solution proposed. Among the concepts is an extension of the Euler column buckling boundary condition coefficients to represent various possible plate edge boundary conditions. The geometry parameter introduced reflects the combined effect of plate aspect ratio and the number of buckle waves. The load parameter introduces a regularising factor that allows the effect of different load distribution forms to be included in the equation. The method is tested on flat plates of different rectangular, triangular, evolutive trapezoidal shapes and on slightly curved plates with cylindrical geometries. Eighteen (18) different combinations of free, simple and clamped edges boundary conditions were considered. Uniform and linearly varying edge stress loading conditions were also considered. The results obtained arc compared with those obtained using analytical and finite element analysis. Excellent agreement is obtained in most cases. Possible causes of discrepancies are highlighted in the other cases. The PBA method is useful and will save time in the pre-sizing buckling design analysis of structures especially in the aerospace industry. This stage is usually followed by detailed analysis using finite clement or other numerical techniques. When programmed PBA should prove easier to use by desigoel1' than existing manuals such as the ESDU because of its unified formula approach.
14
Straume, Jonas Gullaksen. "Dynamic buckling of marine structures". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-26350.
Testo completoAbstract (sommario):
In this report the buckling resistance of marine structures when dynamic effects is important is investigated. A review of the governing theory is presented for both beam and plates. A sample of the different ways of solving the bucking problem is presented, and what kind of assumptions that are made. The overall conclusion from this study is that a structure may have a significant reserve capacity with respect to buckling when dynamic effects are important.A selected solution to the dynamic buckling problem for unstiffened plates is chosen. A MATLAB program is written using this basis with numerical time integration. This program is compared with the finite element analysis programs USFOS and Abaqus FEA. The results were very similar to the finite element programs, and could predict for example the axial load with high accuracy.An unstiffened plate was investigated with respect to dynamic buckling. Both displacement and load control was used. From this it was found that the dynamic buckling in an elastic analysis was not critical for the capacity of the plate. Buckling of the plate combined with a yield stress found that the capacity increased with dynamic effects.An analysis of a tension leg in an offshore wind turbine was conducted. The top of the tension leg was displaced to simulate vertical motions of the wind turbine. The motions made the tension leg take compression forces. The result from this analysis was that the capacity of the tension leg increased substantially with fast-applied loads. The buckling motion of the leg could give large tension forces during the straightening of the leg. These forces could be critical for the leg, and larger than the corresponding compressive load.The last type of marine structure investigated was a steel riser. The scenario examined was a production riser that was dropped from the platform, and the following impact with a subsea structure at the bottom. It was concluded that the energy of the impact was dependent on the curvedness of the riser. For a curved riser, a smaller amount of energy was dissipated to the deformation of the ground. The energy dissipation was also dependent on the deformation strength of the ground. If the riser yielded, the energy dissipated was much smaller. Risers with a lot of kinetic energy had high buckling modes as response near the impact. These modes were very similar to the eigenmode corresponding to the impact durations. From this it could be said that the eigenmodes may have influence on the buckling mode, and strength.For further work it is recommended that a design strength formulation is found for dynamic buckling, for both columns and plates. It is also recommended that the analyses of the marine structures gets expanded. Doing analyses on more complex structures with other actions included could give more insight on the effect of dynamic buckling.
15
Wright, Jennifer Edith. "Compound bifurcations in delamination buckling". Thesis, University of Bath, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432375.
Testo completo
16
Wadee, Mohammad Ahmer. "Localized buckling in sandwich structures". Thesis, University of Bath, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266473.
Testo completo
17
Yang, Zhicheng. "Dynamic buckling of square tubes". Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243260.
Testo completo
18
Louca, Louca A. "Buckling behaviour of stiffener outstands". Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/782/.
Testo completo
19
Tran, Vinh Cong. "Imperfect upheaval subsea pipeline buckling". Thesis, Sheffield Hallam University, 1994. http://shura.shu.ac.uk/3179/.
Testo completoAbstract (sommario):
The objective of the research programme has been to develop a set of theoretical models suited to the perceived needs of industrial practice with regard to in-service, subsea pipeline buckling. The role of imperfections is shown to be of central importance. These factors are considered in the context of modern offshore engineering practice, including the particular employment of trenching and/or burial for purposes of protection. Novel, small scale, full thermo-mechanical system testing is presented, the design and construction of the actual experimental set-up being a key feature of the research programme. Subsidiary geotechnical experimentation is also undertaken. Theoretical studies employing the empirical data provided by latter are assessed against the resulting full system experimental data. With an introduction to the purpose of the research programme and the physical problem and its mechanical demands given in Chapter 1, Chapter 2 serves to clarify the factors involved. Although novelty involving the testing of burial pipe elements is present in the experimental studies of Chapter 3 the majority of original work lies in the theoretical studies of Chapters 4 to 6 and the full system experimentation reported in Chapter 7. The results of forty-five tests are therein provided and theoretical/experimental correlation considered. Definition of the upheaval state, crucial to offshore engineering requirements, is considered to be effectively provided for with regard to symmetric prototype configurations and a software suite of complementary models has been developed.
20
Hakmi, M. R. "Local buckling of sandwich panels". Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234622.
Testo completo
21
Fan, Chun Keung Roger. "Buckling in continuous composite beams". Thesis, University of Warwick, 1990. http://wrap.warwick.ac.uk/106724/.
Testo completoAbstract (sommario):
Two aspects of the buckling behaviour of continuous composite beams of steel and concrete are considered. The first part relates to the study of moment redistribution in braced slender beams (Class 3 draft Eurocode 4) due to local buckling in the hogging moment regions. The second part describes the experimental work to investigate the ultimate load behaviour of unbraced compact beams (Classes 1 and 2 draft Eurocode 4) in the hogging moment regions. For a braced continuous slender composite beam, local buckling at an internal support allows a redistribution of bending moment from the hogging regions to the sagging regions, in addition to material nonlinearity. This effect was studied by a computer simulation on two-span beams. The program takes into account not only the effect of local buckling, but also material nonlinearity and residual stresses, on moment redistribution. The ultimate loads designed to the less conservative method for Class 3 beans in the draft Eurocode 4 were used as a datum in the parametric study. The simulation then gave an independent assessment of the appropriateness and safety of these loads at the ultimate limit state. It is shown that the design method is slightly conservative. Residual stresses have very little effect on the ultimate carrying capacity. Furthermore, in design to the draft Eurocode 4, unpropped construction is more restrictive than propped construction, and hence the results are also more conservative. Lateral buckling of continuous unbraced composite beams in the hogging moment regions can only occur in a distortional mode, and is most unlikely to happen in practical building or bridge structures using hot-rolled steel sections of span up to about 30m. Various design methods based on numerical studies now exist to predict the ultimate strength of continuous composite beams affected by distortional lateral buckling, but few experimental results are available to validate their theoretical assumptions and accuracy. Tests at realistic scale on two T-beams and two inverted U-frames at the Class 2-3 Interface, in accordance with the draft Eurocode 4, are reported. Their results are compared with predictions by five design methods, four of which are satisfactory for the beams tested except BS5400:Part 3. Due to premature fracture of reinforcing fabric in one of the U-frame tests, it is recommended not to include their contribution in moment resistance, when the composite cross-section is plastic and a design requires a large amount of rotation capacity in the hogging moment regions. Based on limited test results, a tentative method is proposed to provide a quick check, whether distortional lateral buckling needs to be considered or not, for continuous composite beams with Class 1 or 2 cross-sections.
22
Vollmecke, Christina. "Nonlinear buckling of delaminated panels". Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/5729.
Testo completoAbstract (sommario):
Laminated structures have increasingly gained popularity in engineering applications owing to their advantageous properties. Particularly in aerospace applications, laminated components, typically comprising fibre-reinforced composites, have a soaring demand owing to their high strength to weight ratio. However, owing to the complex nature of the material, several different failure mechanisms may occur; amongst them is delamination, i.e. the separation at the interface between two laminates. This defect is often difficult to detect, yet may significantly reduce a component's load carrying capacity and subsequently may severely affect its safe working conditions. It is therefore of utmost importance to assess the effects of delaminations on the structural elements carefully. Since components in aerospace applications often comprise laminated panels, a geometrically nonlinear plate delamination model is derived analytically by extending a previously developed two-layer strut model. This type of structural component is commonly analysed as an engineering simplification since at plates are often used as an archetype to simplify more complex structural forms. Thus, an isotropic plate is currently considered, which re ects the simplest constitutive behaviour, and it can represent to some extent the behaviour of a laminated composite that has a uniform or symmetric lay-up sequence. A rectangular defect is located in the centre of this uniformly compressed, isotropic rectangular plated panel representing the delamination. Whilst trigonometric out-of-plane displacement functions are used in a Rayleigh{Ritz procedure yielding the governing equations that describe the mechanical behaviour of the plate, in-plane deformations are obtained via von Karman's compatibility equation. An indication of the residual capacity of the panel after critical buckling is obtained by investigating the nonlinear postbuckling range, where delamination propagation is incorporated by introducing a discrete cohesive zone model at the boundaries of the delaminated region. Different configurations are investigated in the neighbourhood of the previously evaluated transitional depth of delamination, which constitutes the boundary between local and global buckling. Initially, a uniformly spreading defect is investigated for various different defect sizes and depths. Subsequently, geometric parameters are linked to the response of the panel to generalize the outcomes with quantitative comparisons being undertaken against previous results and those obtained with the commercial nite element software ABAQUS. It is found that the model compares well and several criteria for the initial design of the damaged panels are proposed such that delamination growth may be accommodated safely and e ciently. Furthermore, uni-directional growth of the delamination is considered in a pilot study with suggestions being made regarding the growth direction tendency.
23
CHAKRABARTI, SEKHAR KUMAR. "INELASTIC BUCKLING OF GUSSET PLATES". Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184188.
Testo completoAbstract (sommario):
The strength and behavior of gusset plates in buckling is evaluated herein based on data from the experimental investigations conducted by other researchers and the analytical work presented herein. A set of design guidelines has been recommended through the review of the current practice. Representative single and double brace gusset plates normally adopted for connections with compressive bracing/diagonal members in braced frames and trusses, were modeled and analyzed using linear and nonlinear finite element methods to determine the buckling loads. The buckling analysis data along with the test data indicated the occurrence of inelastic buckling of the gusset plates. Current design practice and a set of formulas for determination of gusset plate thickness have been reviewed. A set of guidelines has been recommended for the design and evaluating gusset plate buckling loads.
24
Mohamedien, Mohamed Ahmed. "The buckling of grid shells". Thesis, University of Bath, 1990. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254000.
Testo completo
25
Schleyer, Graham Klaus. "Buckling of tank roofs : a buckling analysis and experimental investigation of storage tank domed roofs". Thesis, University of Strathclyde, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362804.
Testo completo
26
Cai, Junle. "Interactive Buckling and Post-Buckling Studies of Thin-Walled Structural Members with Generalized Beam Theory". Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/75055.
Testo completoAbstract (sommario):
Most thin-walled metallic structural members experience some extent of interactive buckling that corrodes the load carrying capacity. Current design methods predict the strength of thin-walled metallic structural members based on individual buckling limit-states and limited case of interactive buckling limit state. In order to develop design methods for most coupled buckling limit states, the interaction of buckling modes needs to be studied.
This dissertation first introduces a generally applicable methodology for Generalized Beam Theory (GBT) elastic buckling analysis on members with holes, where the buckling modes of gross cross-section interact with those of net cross-section. The approach treats member with holes as a structural system consisting of prismatic sub-members. These sub-members are connected by enforcing nodal compatibility conditions for the GBT discretization points at the interfaces. To represent the shear lag effect and nonlinear normal stress distribution in the vicinity of a hole, GBT shear modes with nonlinear warping are included. Modifications are made to the GBT geometric stiffness because of the influence from shear lag effect caused by holes. In the following sections, the GBT formulation for a prismatic bar is reviewed and the GBT formulation for members with holes is introduced. Special aspects of analyzing members with holes are defined, namely the compatibility conditions to connect sub-members and the geometric stiffness for members with holes. Validation and three examples are provided.
The second topic of this dissertation involves a buckling mode decomposition method of normalized displacement field, bending stresses and strain energy for thin-walled member displacement field (point clouds or finite element results) based on generalized beam theory (GBT). The method provides quantitative modal participation information regarding eigen-buckling displacement fields, stress components and elastic strain energy, that can be used to inform future design approaches. In the method, GBT modal amplitudes are retrieved at discrete cross-sections, and the modal amplitude field is reconstructed assuming it can be piece-wisely approximated by polynomials. The unit displacement field, stress components and strain energy are all retrieved by using reconstructed GBT modal amplitude field and GBT constitutive laws. Theory and examples are provided, and potential applications are discussed including cold-formed steel member design and post-disaster evaluation of thin-walled structural members.
In the third part, post-buckling modal decomposition is made possible by development of a geometrically nonlinear GBT software. This tool can be used to assist understanding couple-buckling limit-states. Lastly, the load-deformation response considering any one GBT mode is derived analytically for fast computation and interpretation of structural post-buckling behavior.Ph. D.
27
Ghosh, Biswarup. "Consequences of Simultaneous Local and Overall Buckling in Stiffened Panels". Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/31803.
Testo completoAbstract (sommario):
In this thesis improved expressions for elastic local plate buckling and overall panel buckling of uniaxially compressed T-stiffened panels are developed and validated with 55 ABAQUS eigenvalue buckling analyses of a wide range of typical panel geometries. These two expressions are equated to derive a new expression for the rigidity ratio (EIx/Db)CO that uniquely identifies ¡°crossover¡± panels ¨C those for which local and overall buckling stresses are the same. The new expression for (EIx/Db)CO is also validated using the 55 FE models. Earlier work by (Chen, 2003) had produced a new step-by-step beam-column method for predicting stiffener-induced compressive collapse of stiffened panels. An alternative approach is to use orthotropic plate theory. As part of the validation of the new beam-column method, ABAQUS elasto-plastic Riks ultimate strength analyses were made for 107 stiffened panels ¨C the 55 crossover panels and 52 others. The beam-column and orthotropic approaches were also used. A surprising result was that the orthotropic approach has a large error for crossover panels whereas the beam-column method does not. Some possible reasons for this are suggested. Collapse patterns for the crossover panels are studied and classified from von Mises stress distribution at collapse. The collapse mechanism and load-deflection diagrams suggest stable inelastic post collapse behavior for most panels and an abrupt drop in load carrying capacity in only nine of the 55.Master of Science
28
Murphy, A. "Accurate and efficient buckling and post buckling analysis of fuselage panels loaded in shear and compression". Thesis, Queen's University Belfast, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273230.
Testo completo
29
Nygård, David. "Tensile armour buckling in flexible pipes". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18652.
Testo completoAbstract (sommario):
The exible pipelines has been widely used by the oil and gas industry the lastdecades and this trend is expected to continue as the operating depths are increasedfurther. For deep water applications the radial and lateral buckling modes can becritical. Many studies has been carried out using nite element models to studythese failure modes.In this thesis a nite element model is created with the aim to recreate resultsobtained in a recently published article by Vaz and Rizzo. The model is built upusing pipe, beam, contact and spring elements to represent the complex behaviourof the cross section. The loading is carried out by rst applying the dry mass, thenthe external pressure and nally end compression.When comparing buckling loads generated in this thesis by the ones in thearticle by Vaz and Rizzo the observation made is that the buckling loads from thisthesis are signicantly higher. When comparing only the inclination of the endshortening versus buckling load curves it was seen that the curves from article hada only slightly larger inclination than the results from the analyses in this thesis.This indicates that there is a small dierence in the stiness used. By modifyingthe stiness it should be possible to get the same inclination of the curve.Analyses were also carried out on how the slip distance aects the bucklingloads. By increasing the slip distance by 50% and 100% it was observed thatthe buckling loads were reduced drastically. In the article by Vaz and Rizzo noinformation is given on the slip distance. By tuning the slip distance and stinessof the springs it should therefore by possible to obtain the exact same results as inthe article. This clearly illustrates the importance of stating all assumptions andinput parameters when describing models used for analysis.
30
Maltby, Timothy Crichton. "The upheaval buckling of buried pipelines". Thesis, University of Cambridge, 1993. https://www.repository.cam.ac.uk/handle/1810/251542.
Testo completo
31
Pinna, Rodney. "Buckling of suction caissons during installation". University of Western Australia. School of Civil Engineering, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0008.
Testo completoAbstract (sommario):
Suction caissons are a foundation system for offshore structures which offer a number of advantages over traditional piled foundations. In particular, due to the method of installation used, they are well suited for deep-water applications. The suction caisson consists of an open ended cylindrical shell, which is installed below the seabed in a sequence which consists of two loading phases. The caisson is first installed part way under self weight, with the installation being completed by lowering the pressure within the cylinder and thus allowing the ambient water pressure to force the caisson into the ground. This thesis examines a number of structural issues which result from the form of the caisson — essentially a thin walled cylinder — and the interaction of the caisson with the surrounding soil during installation. To do this, variational analysis and nonlinear finite element analysis are employed to examine the buckling and collapse behaviour of these cylinders. In particular, two issues are considered; the influence of the open end, and the interaction between the cylinder and soil on the buckling and collapse loads. First, the behaviour of open ended cylinders is considered, where the boundary condition at the open end is allowed to vary continuously from completely free to pinned, by the use of a variable lateral spring. This lateral spring restraint may be considered to represent the intermediate restraint provided by a ring stiffener which is not fully effective. The effect of various combinations of boundary conditions is accounted for by the use of a multiplier on the lower bound to the buckling load of a cylinder with classical supports. The variable spring at the open end may also be considered to be an initial, simple representation of the effect of soil restraint on the buckling load. More complex representations of the soil restraint are also considered. A nondimensional factor is proposed to account for the influence of this spring on the buckling load. One combination of boundary conditions, where the upper end of the caisson is pinned, and the lower end free (referred to as a PF boundary condition), is found to have buckling and collapse behaviour which is unusual for cylindrical shells. Buckling loads for such shells are much lower than would be found for cylinders with more typical boundary conditions, and of similar dimensions. More unusually however, PF cylinders are shown to have positive postbuckling strength. The behaviour is found to be a result of the large flexibility which results from the low restraint provided by the PF boundary conditions. This is shown by continuously decreasing the flexibility of the cylinder, by increasing the axial restraint at the pinned end. It is shown that this results in a large increase in buckling load, and a return to more usual levels of imperfection sensitivity. In particular, with an intermediate level of axial restraint, buckling loads and imperfection sensitivity are intermediate between those of PF shells with no, and with full, axial restraint. Overall however, collapse loads for PF cylinders with no additional restraint are well below those of cylinders with stiffer boundary conditions, for equal geometries. Eigenvalue buckling of cylinders fully and partially embedded in an elastic material are examined, and two analytical solutions are proposed. One of these is an extension of a method previously proposed by Seide (1962), for core filled cylinders, to pin ended cylinders which have support from both a core and a surrounding material. The second method represents the elastic support as a two parameter foundation. While more approximate than the first method, this method allows for the examination of a wider range of boundary conditions, and of partial embedment. It is found that the buckling load of the shell/soil system decreases as the embedment ratio decreases. Collapse of fully and partially embedded cylinders is also examined, using nonlinear finite element analysis. The influence of plasticity in the soil is also considered. For cylinders with small imperfections, it is found that the collapse load shows a large increase over that of the same cylinder with no soil support. However, as the size of initial geometric imperfections increases, it is found that the collapse load rapidly approaches that of the unsupported cylinder. In particular, in weak soils the gain in strength over the unsupported shell may be minimal. The exception to this is again PF cylinders. As these have relatively low collapse loads, even very weak soils are able to offer an increase in collapse load over the unsupported case. Finally, a summary of these results is provided in the form of guidance for design of such structures.
32
Dorey, Alfred Boyd. "Critical buckling strains in energy pipelines". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ60288.pdf.
Testo completo
33
Burrell, Geoffrey Scott. "Distortional buckling in steel I-girders". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 143 p, 2007. http://proquest.umi.com/pqdweb?did=1338867451&sid=1&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Testo completo
34
Li, Hong. "Experimental micromechanics of composite buckling strength". Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/11719.
Testo completo
35
Blackmore, Avril. "Dynamical systems analogy in upheaval buckling". Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307455.
Testo completo
36
Xiao, Qiuwu. "Lateral Torsional Buckling of Wood Beams". Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31174.
Testo completoAbstract (sommario):
Structural wood design standards recognize lateral torsional buckling as an important failure mode, which tends to govern the capacity of long span laterally unsupported beams. A survey of the literature indicates that only a few experimental programs have been conducted on the lateral torsional buckling of wooden beams. Within this context, the present study reports an experimental and computational study on the elastic lateral torsional buckling resistance of wooden beams.
The experimental program consists of conducting material tests to determine the longitudinal modulus of elasticity and rigidity modulus followed by a series of 18 full-scale tests. The buckling loads and mode shapes are documented. The numerical component of the study captures the orthotropic constitutive properties of wood and involves a sensitivity analysis on various orthotropic material constants, models for simulating the full-scale tests conducted, a comparison with experimental results, and a parametric study to expand the experimental database.
Based on the comparison between the experimental program, classical solution and FEA models, it can be concluded that the classical solution is able to predict the critical moment of wood beams. By performing the parametric analysis using the FEA models, it was observed that loads applied on the top and bottom face of a beam decrease and increase its critical moment,respectively. The critical moment is not greatly influenced by moving the supports from mid-span to the bottom of the end cross-section.
37
MacLaurin, James Normand. "The buckling of capillaries in tumours". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:ba252220-3c06-4d49-8696-655f6fefcd31.
Testo completoAbstract (sommario):
Capillaries in tumours are often severely buckled (in a plane perpendicular to the axis) and / or chaotic in their direction. We develop a model of these phenomena using nonlinear solid mechanics. Our model focusses on the immediate surrounding of a capillary. The vessel and surrounding tissue are modelled as concentric annulii. The growth is dependent on the concentration of a nutrient (oxygen) diffusing from the vessel into the tumour interstitium. The stress is modelled using a multiplicative decomposition of the deformation gradient F=F_e F_g. The stress is determined by substituting the elastic deformation gradient F_e (which gives the deformation gradient from the hypothetical configuration to the current configuration) into a hyperelastic constitutive model as per classical solid mechanics. We use a Blatz-Ko model, parameterised using uniaxial compression experiments. The entire system is in quasi-static equilibrium, with the divergence of the stress tensor equal to zero. We determine the onset of buckling using a linear stability analysis. We then investigate the postbuckling behaviour by introducing higher order perturbations in the deformation and growth before using the Fredholm Alternative to obtain the magnitude of the buckle. Our results demonstrate that the growth-induced stresses are sufficient for the capillary to buckle in the absence of external loading and / or constraints. Planar buckling usually occurs after 2-5 times the cellular proliferation timescale. Buckles with axial variation almost always go unstable after planar buckles. Buckles of fine wavelength are initially preferred by the system, but over time buckles of large wavelength become energetically more favourable. The tumoural hoop stress T_{ThetaTheta} is the most invariant (Eulerian) variable at the time of buckling: it is typically of the order of the tumoural Young's Modulus when this occurs.
38
Simelane, Philemon Sphiwe. "Thermal buckling of laminated composite plates". Thesis, Peninsula Technikon, 1998. http://hdl.handle.net/20.500.11838/1240.
Testo completoAbstract (sommario):
Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, 1998However, studies were also conducted for the buckling of composite laminates involving temperature distribution. Chen and Chen (1991) studied thermal buckling of laminated plates under uniform and nonuniform temperature distribution using the eight-node Serendipity finite element. Mathew, Singh and Rao (1992) investigated thermal buckling of antisymmetric cross-ply composite laminates with a onedimensional furite element having two nodes and six degrees of freedom. Chandrashekhara (1992) accounted for transverse shear flexibility by using the thermo-elastic version of the first-order shear deformation theory. This will also be the case in this report. Literature on buckling and laminated composites abounds. Brush and Aimroth (1975) published a book on Buckling of Bars, Plates, and Shells, while Bushnell (1985) surveyed the Methods and Modes of Behaviour in Static Collapse. The foundation for the study of composite materials was based on the references [8], [10], [15] and [18]. The use of the Finite Element Method to analyse the buckling behaviour of laminated structures comes from references [I], [4]. [I2]. [16], [24] and [32]. Reference [14] provided the basis for the formulation of the variation of the governing equations. Most of the ideas in this report are based on these publications and references. Chapter I of this report introduces the concept of a composite. the formation of a composite and a brief overview of the elements of a composite material. This chapter also presents the concept of buckling that will form the basis of the development of this project. At the end of this chapter the choice of the element that is used in this study is justified. Chapter 2 provides the fundamentals of elasticity that relate to the deformation of a loaded body. In this Chapter the stresses and strains are defined and the temperature terms are introduced. In Chapter 3 the Mindlin plate theory is presented with a view to laying the foundation for the analysis of laminated plates, and as a starting point in the formulation of thermal buckling behaviour of laminated plates. In Chapter 4 the elements of a composite material are discussed and the constitutive equations of a laminated composite plate are built. Also the idea of lamination is introduced and the various simplifications that can be introduced as a result of lamination are discussed. The non-linear equilibrium equations and the stability analysis of a composite plate are formulated in Chapter 5 using the conventional anal}1ical method. The resulting equations justify the use of the Finite Element Method as introduced in Chapter 6 and it is the method by which the governing equations will be solved in ABAQUS computer analysis. The results for various computer runs are presented for a normal plate, a plate with a square hole, and the plate ""ith a circular cut-out in Chapter 7. Also in chapter 7 a comparison is made between the laminate "ith a central hole and a normal plate to study the effect of a cut-out on a critical buckling temperature. Appendices A deals the transverse shear in plates, and Appendix B deals with the transformation of the laminate elastic constants form the principal material direction to the general Cartesian co-ordinates. Also in Appendix B the laminate stiffness matrices and these matrices are briefly evaluated analytically. Appendix C is about the governing equations of laminated composites, while Appendix D gives a full representation of the abbreviated finite element equations of Chapter 6. Appendix E presents the list of ABAQUS input files that were used in the computer simulation of Chapter 7.
39
Tiwari, Nachiketa. "Secondary Buckling of Laminated Composite Plates". Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/37789.
Testo completoAbstract (sommario):
The postbuckling load carrying capacity of composite plates offers immense potential to their applications for loads exceeding their primary buckling load. However, such an efficient and economical usage of these plates can be reliable only if the nonlinear postbuckling behavior of these plates, which includes a good understanding of secondary buckling, is understood thoroughly. The present investigation is an attempt to understand secondary buckling of almost square composite clamped-simply supported plates, both unstiffened as well as stiffened, in some detail. With the help of the finite element method, a large number of numerical studies have been conducted to understand the secondary buckling characteristics. The sensitivity of these characteristics to variations in boundary conditions, lamination sequence, imperfections, and stiffener geometry has been considered. It has been found that the occurrence of secondary buckling in clamped-simply supported plates under uniform end shortening critically depends on the intensity of restrictions imposed on the inplane normal displacements along the unloaded simply supported edges of the plate. These restrictions could be due to the actual boundary conditions at these edges, or due to the presence of stiffeners along these edges. It has also been found that the presence of imperfections significantly delays the event of secondary buckling. Finally, it has been found that changes in lamination sequence of the plate alter its secondary buckling characteristics in ways that are, in general, quantitative in nature. The numerical investigations were followed by a limited number of experiments involving the testing of unstiffened as well as stiffened composite plates with the intent of augmenting the confidence in the numerical predictions made. Three different lamination sequences were considered during the testing phase of this investigation. It was found that the agreement between experimental data and numerical predictions was quite good. The occurrence of secondary buckling followed the predictions closely.Ph. D.
40
Maschner, Emil Alexis. "Vertical buckling of heated submarine pipelines". Thesis, London South Bank University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336365.
Testo completo
41
Jowhari, Moghadam Shirin. "Plastic buckling of columns and plates". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/29865.
Testo completoAbstract (sommario):
The theory of buckling strength of compression members in the plastic range has been extensively studied, and numerical methods already exist which deal with such behaviour. However, there is a significant research interest in developing analytical models for the plastic buckling, largely driven by the need for simplified mechanics based design tools, but also by the desire for enhanced understanding of this complex phenomenon. A thorough investigation into the inelastic buckling of columns and plates reveals the existence of two well-known inconsistencies recognised as the 'Column Paradox' and the 'Plate Plastic Buckling Paradox'. In the current research, addressing the conceptual issues related to the plastic buckling of columns and plates, including the two associated paradoxes, has been achieved by means of development and application of analytical models that are verified against nonlinear finite element analysis. These models are based on sound principles of structural mechanics and are intended to illustrate the mechanics of the plastic buckling response of stocky columns/plates by means of a simplified analytical approach, from the point of buckling initiation and considering the post-buckling response. In these models, the Rotational Spring Analogy is used for formulating the geometric stiffness matrix, whereas the material stiffness matrix is obtained with due consideration for the spread of material plasticity. It is shown that the buckling of stocky perfect columns starts at the Engesser load while the von Karman upper limit is typically not realised due to tensile yielding at the outer fibre of the column cross-section. Furthermore, it is established that beyond a threshold level of imperfection, as evaluated directly from the developed model, the plastic post-buckling response of columns is barely affected by a further increase in the out-of-straightness. Besides identifying previous misconceptions in the research literature, the proposed analytical models for the plastic buckling of plates have proven to offer valuable insight into factors that influence the plastic buckling of stocky plates, and hence succeeded in resolving the long-standing paradox. It is the major contention of this thesis, verified through extensive studies, that the 'Plate Plastic Buckling Paradox' is resolved with the correct application of plasticity theory, considering not only the influence of initial imperfections but also the interaction between flexural and planar actions.
42
Coburn, Broderick Howard. "Buckling of stiffened variable stiffness panels". Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687427.
Testo completoAbstract (sommario):
Over the past five decades the aerospace industry has seen the increased use and development of composite materials and structures, largely due to their superior specific strength and stiffness in comparison with metals. These two major attributes, coupled with their increased tailorability, enable the design of lighter, more efficient structures. Traditional tailoring is limited to modifying the orientation of laminate plies to achieve the desired performance. However, recent advancements in tape laying and fibre placement technologies, have led to the possibility of laminates with varying fibre orientations in the plane of a ply, thereby creating variable stiffness (VS) structures. These VS laminates greatly expand the design space and provide designers with additional degrees of freedom and tailorability. In recent years, analytical methods and finite element analysis (FEA) have shown that VS laminates can deliver a significant improvement in buckling and post-buckling performance for plates and shells. A potential application, which exploits this enhanced buckling performance, is the use of VS laminates as the skin of a stiffened panel. Here, the VS skin is designed to redistribute in-plane loads towards the stiffeners, which act as panel breakers, providing an expected increase in buckling performance, thereby facilitating the design of lighter and more efficient structures. The present work was conducted with the main aim of developing fast, robust and accurate tools for the linear buckling analysis of novel stiffened VS panels. The Ritz energy method was used to develop semi-analytical models for various plate configurations subject to uniaxial and biaxial compression; firstly, plates exhibiting discontinuously varying stiffness terms with bend-stretch coupling, a feature commonly present in the skin-flange region of stiffened panels; secondly, thick plates and sandwich panels with continuously varying stiffness terms, through fibre-steering, by including a first-order shear deformation theory; and thirdly, blade stiffened VS panels by utilising the previously developed methods to capture the important features of discontinuous and continuous stiffness variations and transverse shear flexibility. Benchmarked against a commercial FEA package, the semi-analytical models are shown to be both an accurate and computationally efficient alternative, and thus well suited for design and optimisation. To conclude, design and heuristic optimisation case studies for civil airliner blade stiffened panels, with both straight fibre and VS skins, were performed applying practical design and failure constraints. Optimal VS designs showed improvements in structural efficiency compared to standard configurations, with weight savings over 5% and 20% for VS skins satisfying and neglecting the 10 % rule, applied only for 00 and 900 plies, respectively. Furthermore, the mass reductions were shown to be achievable utilising relatively few VS plies in some cases, thus providing an avenue for application without the need for significant changes in stiffener or skin design, rates of deposition, or design rules and guidelines.
43
Liu, Jia. "Buckling Induced Functionality in Soft Structures". Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493413.
Testo completoAbstract (sommario):
A variety of instabilities can be triggered when elastic structures are subjected to mechanical loadings.
While such instabilities have traditionally been considered as a failure, a new trend is emerging in which the dramatic geometric changes induced by them are harnessed to enable new functionalities.
In this thesis, I report a systematic study on the morphology and functionality changes induced by buckling in soft structures. Using a combination of theoretical, numerical and experimental analyses, I investigate the non-linear response of a variety of one dimensional, two dimensional and three dimensional systems, with particular emphasis on their stability. The results show that the deformation induced by buckling can be rather complex even if the undeformed geometry is simple.
Moreover, I demonstrate that a wide range of morphologies can be obtained by carefully controlling the geometric, material and loading parameters. Such tunability may open venues for the design of structures with adaptive and switchable properties.Engineering and Applied Sciences - Engineering Sciences
44
Smith, Frank Harrison. "Elastic buckling solutions for thin-walled metal columns with perforation patterns". Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23680.
Testo completoAbstract (sommario):
Presented are approximate finite strip methods for use in predicting elastic buckling strength of cold-formed steel columns. These methods were developed by examining elemental behavior of cross-sections in eigen-buckling analyses and validated using a large database of finite element rack-type columns with perforation patterns. The influence of perforations is accounted by reduced thicknesses related to the plate buckling coefficient and transverse web rotational stiffness in the prediction of local and distortional buckling respectively. Global buckling prediction including the influence of perforations uses critical elastic loads of an unperforated section multiplied by the ratio of weighted to gross cross-sectional moment of inertia for flexural buckling and the ratios of weighted to gross cross-sectional warping torsion constant and weighted to gross St. Venant torsional constant for flexural-torsional buckling. Concern for end-user was given and methods are presented in a way for incorporation into governing design standards. Data to support these findings are available at http://hdl.handle.net/10919/23797Master of Science
45
Arpaci, Erdogan. "Analysis Of Sinusoidal And Helical Buckling Of Drill String In Horizontal Wells Using Finite Element Method". Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611003/index.pdf.
Testo completoAbstract (sommario):
The number of horizontal wells is increasing rapidly in all over the world with the growth of new technological developments. During horizontal well drilling, much more complex problems occur when compared with vertical well drilling, such as decrease in load transfer to the bit, tubular failure, tubular fatigue and tubular lock-up. This makes selection of appropriate tubular and making the right drill string design more important. As the total compression load on the horizontal section increases, the behavior of the tubular changes from straight to sinusoidal buckling, and if the total compression load continues to increase the behavior of the tubular changes to helical buckling. Determination of critical buckling loads with finite element method (FEM) in horizontal wells is the main objective of this study. Initially, a computer program (ANSYS) that uses FEM is employed to simulate different tubular and well conditions. Four different pipe sizes, four different wellbore sizes and three different torque values are used to model the cases. Critical buckling load values corresponding to significant variables are collected from these simulated cases. The results are classified into different buckling modes according to the applied weight on bit values and the main properties of the simulated model, such as modulus of elasticity, moment of inertia of tubular cross section, weight per unit length of tubular and radial clearance between the wellbore and the tubular. Then, the boundary equations between the buckling modes are obtained. The equations developed in this thesis by simulating the cases for the specific tubular sizes are used to make a comparison between the critical buckling load values from the models in the literature and this work. It is observed that the results of this work fit with literature models as the tubular size increases. The influence of torque on critical buckling load values is investigated. It is observed that torque has a slight effect on critical buckling load values. Also the applicability of ANSYS for buckling problems was revealed by comparing the ANSYS results with the literature models’
results and the experimental study in the literature.
46
Paspuleti, Suma. "Mechanical and thermal buckling of thin films". Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/4302.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of Missouri-Columbia, 2005.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 14, 2006) Includes bibliographical references.
47
St-Amour, Rémi. "Lateral Torsional Buckling of Wood I-Joist". Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35161.
Testo completoAbstract (sommario):
Engineered wood I-joists have grown in popularity as flooring and roofing structural systems in the past 30 years, replacing solid sawn lumber joists. Typical wood I-joists are manufactured with a very slender section, which is desirable to achieve higher flexural capacities and longer spans; however, this makes them susceptible to lateral torsional buckling failure. Continuous beam spans and uplift forces on roof uplift are potential scenarios where lateral instability can occur and reflects the need to investigate the lateral torsional buckling behavior of wood I-joists. Within this context, the present study conducts an experimental investigation on the material properties and the critical buckling load of 42 wood I-joist specimens. A 3D finite element model is built using the experimentally determined material parameters to effectively predict the observed buckling behavior of the specimens while also accounting for initial imperfections in the joists. The adequacy of other analytical models to predict the critical buckling load of wood I-joists are also investigated. It is demonstrated that the American design standard underestimates the critical buckling load of wood I-joists while the classical theory provides an adequate estimate of the buckling capacity. Furthermore, the effects of initial imperfections on the lateral torsional buckling behavior are discussed. The developed and verified FE model is used to reproduce the nonlinear buckling behavior of the wood I-joist and also to provide an accurate estimate of the lateral torsional buckling capacity using the linear buckling analysis.
48
Berlin, Andrew A. "Towards Intelligent Structures: Active Control of Buckling". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/6768.
Testo completoAbstract (sommario):
The buckling of compressively-loaded members is one of the most important factors limiting the overall strength and stability of a structure. I have developed novel techniques for using active control to wiggle a structural element in such a way that buckling is prevented. I present the results of analysis, simulation, and experimentation to show that buckling can be prevented through computer-controlled adjustment of dynamical behavior.sI have constructed a small-scale railroad-style truss bridge that contains compressive members that actively resist buckling through the use of piezo-electric actuators. I have also constructed a prototype actively controlled column in which the control forces are applied by tendons, as well as a composite steel column that incorporates piezo-ceramic actuators that are used to counteract buckling. Active control of buckling allows this composite column to support 5.6 times more load than would otherwise be possible.sThese techniques promise to lead to intelligent physical structures that are both stronger and lighter than would otherwise be possible.
49
El-Adas, Kadmous Moufid. "Linear and nonlinear buckling analysis via ABAQUS". Master's thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-01262010-020017/.
Testo completo
50
Lee, Seungsik. "Flexural-torsional buckling of pultruded T-sections". Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/19496.
Testo completo