Thèses : « Lateral instability of beams »

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Lima, Maria Cristina Vidigal de. « Instabilidade lateral das vigas pré-moldadas em regime de serviço e durante a fase transitória ». Universidade de São Paulo, 1995. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-25042018-115223/.

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Este trabalho aborda o estudo da instabilidade lateral das vigas pré-moldadas durante o regime de serviço e durante a fase transitória. Na fase de serviço inclui os casos de apoios indeformáveis e deformáveis à torção. Para a fase transitória, o cálculo da carga crítica é desenvolvido para as diversas disposições dos cabos de içamento. O estudo do equilíbrio no espaço é realizado a partir da resolução das equações diferenciais regentes da instabilidade elástica. A resolução do sistema diferencial composto pelas equações acopladas da flexão lateral e da torção é realizada por vários métodos, incluindo o desenvolvimento e automatização do método numérico de Runge-Kutta, para algumas seções típicas. Apresentam-se ainda os procedimentos empíricos encontrados na literatura técnica, baseados em ensaios experimentais, para o cálculo dos fatores de segurança. Os resultados dos exemplos numéricos mostram que as situações de serviço não são, em geral críticas, ao contrário da fase transitória. Os exemplos mostram ainda que a suspensão com balanços é uma forma de diminuir os problemas de instabilidade lateral desta fase.
This work deals with the lateral stability of precast beams on service and during intermediate phase - handling and transportation. At service phase it is considered rigid and semi-rigid connections with torsion deformation. At handling phase, the critical load is evaluated for several positions of lifting cables. The study of the equilibrium conditions is done with the solution of the differential equation of elastic instability problem. The solution of flexural and torsional coupled equation is gotten by use of some methods, including the one developed and authomatized from the application of Runge-Kutta method, for certain sections. Empirical procedures are presented based on experimental tests, found in technical papers to compute fators of safety. The results of numerical examples show that the service situations are not generally critical, unlike the intermediate situations. The results show also that a possible way to avoid this problem is with the use of lifting points with a distance from the ends.

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Krahl, Pablo Augusto. « Lateral stability of ultra-high performance fiber-reinforced concrete beams with emphasis in transitory phases ». Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-27082018-125631/.

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The development of advanced fiber reinforced cement-based materials to provide higher strength, ductility, and durability, as ultra-high performance fiber-reinforced concrete (UHPFRC), enables the design of precast beams with thin sections and reduced self-weight to meet the required flexural performance. However, such slender elements when subjected to transitory phases, and possibly also in permanent stages, are prone to instability failure. So, the present study aims to provide experimental data and analytical solution for UHPFRC beams during the lifting phase, and studies about the other stages. This type of test is rare and was not reported for UHPFRC beams. For testing, the beams were lifted by inclined cables and subjected to a transversal load applied at midspan to induce lateral instability. The displacements of the beams were monitored with total station equipment. Also, a new analytical solution was proposed to predict the failure load of lifted beams and closed-form analytical solutions to predict the rollover load of beams supported by bearing pads and subjected to different loading conditions. Furthermore, there are limited data that characterizes the constitutive behavior of this material. In this context, the present research also focused on providing such laboratory results for UHPFRC with different fiber contents. Besides, analytical models for damage evolution and stress-strain relationship are proposed and applied in numerical simulations. From the results, the UHPFRC beams failed by instability with a load capacity 3.7 times smaller than the flexural load capacity. Furthermore, the analytical solution for lifting predicted the peak load of the experiment with great accuracy. Also, the proposed equations for beams on bearing pads accurately predicted the experimental results available in the literature. The analytical and experimental rollover loads differed by 4.37% and 13.6% for the two studied cases. From material, the stiffness degradation occurred rapidly in UHPFRC under tensile loading while occurred gradually in compression. Also, fiber content influenced toughness and degradation evolution significantly over the loading cycles. Proposed equations were utilized in the Plastic-Damage model of Abaqus that predicted accurately damage growth and cyclic envelopes during all the phases of the tension, compression, and bending tests. The calibrated numerical model also predicted the experimental results with the UHPFRC beams.
O desenvolvimento de materiais avançados à base de cimento reforçado com fibra para fornecer maior resistência, ductilidade e durabilidade, como o concreto de ultra-alto desempenho reforçado com fibras (UHPFRC), permite o projeto de vigas pré-moldadas com seções esbeltas e peso próprio reduzido que atendem desempenho estrutural requerido. No entanto, esses elementos delgados quando submetidos a fases transitórias e também em serviço são propensos a falhar por instabilidade. Então, o presente estudo tem por objetivo apresentar resultados experimentais e soluções analíticas para vigas de UHPFRC durante a fase de içamento e estudos sobre as outras fases. Este tipo de teste é raro e não foi reportado para vigas de UHPFRC. Para o teste, as vigas foram levantadas por cabos inclinados e submetidas a uma carga concentrada transversal aplicada no meio do vão para induzir a instabilidade lateral. Os deslocamentos das vigas foram monitorados com estação total. Além disso, uma nova solução analítica foi proposta para prever a carga de instabilidade das vigas içadas e soluções analíticas para prever a carga de tombamento de vigas suportadas por aparelho de apoio e submetidas a diferentes condições de carregamento. Além disso, existem poucos resultados experimentais que caracterizam o comportamento constitutivo deste material. Neste contexto, a presente pesquisa também se concentrou em fornecer tais resultados experimentais para UHPFRC com diferentes teores de fibras. Além disso, modelos analíticos para evolução de dano e relação tensão-deformação são propostos e aplicados em simulações numéricas. A partir dos resultados, as vigas em içamento falharam por instabilidade com uma capacidade de carga 3,7 vezes menor que a capacidade à flexão. Além disso, a solução analítica para içamento previu carga máxima do experimento com grande precisão. As equações propostas para vigas sobre aparelhos de apoio previram com precisão os resultados experimentais disponíveis na literatura. As cargas de tombamento analíticas e experimental diferiram em 4,37% e 13,6% para os dois casos estudados. Dos resultados do material, a degradação da rigidez ocorreu de maneira rápida no UHPFRC submetido à tração enquanto ocorreu gradualmente na compressão. O teor de fibras influenciou significativamente a tenacidade e a degradação nos ciclos de carregamento. As equações propostas foram utilizadas em um modelo de Dano acoplado à plasticidade que previu com precisão a evolução do dano e as envoltórias cíclicas durante todas as fases dos testes de tração, compressão e flexão. O modelo numérico calibrado também previu os resultados experimentais das vigas de UHPFRC.

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Ozdemir, Kerem Murat. « Lateral Buckling Of Overhanging Beams ». Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606488/index.pdf.

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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.

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Xiao, Qiuwu. « Lateral Torsional Buckling of Wood Beams ». Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31174.

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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.

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Chen, Shiming. « Instability of composite beams in hogging bending ». Thesis, University of Warwick, 1992. http://wrap.warwick.ac.uk/4009/.

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This work is concerned with local buckling and lateral distortional buckling, two aspects of instability that govern the design of composite beams in hogging regions. Local buckling in hogging regions of a continuous composite beam was modelled by moment curvature characteristics of a cantilever, modified by two curvature ratios, K1 and K2. Test based expressions for K1 and K2, in terms of a combined slenderness λc, were developed, and subsequently used in numerical analyses of 50 two-span composite beams to assess moment redistribution allowed for Class 2 beams by draft Eurocode 4. The analyses include effects of non-linear material properties, residual stresses and local buckling. The parametrical studies include adverse values, in relation to practice, of relative length of adjacent spans, span-to-depth ratio, and ratio of hogging to sagging moment of resistances. It is concluded that the redistribution of elastic bending moments allowed by the draft Eurocode 4 is safe and economical. Distortional lateral buckling of composite beams with both continuous and discrete U-frame actions was studied experimentally. Distortional lateral buckling was found in the tests of two composite beams with inverted U-frame actions. Web distortion was effectively reduced by vertical web stiffeners, which form a part of discrete U-frames together with the slab and the connection of U-frame. The work provides background to assess lateral buckling strength for composite beams with both continuous and discrete U-frame actions. A further theoretical approach on the topic of discrete inverted U-frame action was presented. Strength and stiffness of discrete U-frame connections were also studied. The strength of a discrete U-frame connection was found to be influenced by both the shear failure of concrete, and the yielding of steel top flange in the connection. A simple rule to assure strength of U-frame connections is proposed by checking these two failures separately. The prediction of shear failure of a U-frame connection is based on a truss model, and the prediction of failure in the steel top flange is based on a rigid plastic mechanism. A semi-empirical formula for flexibility of a U-frame connection was derived. They were all checked against test results. Interactive U-frame force and U-frame stiffness were also studied. A tentative design method for discrete U-frame composite beams was proposed.

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Hu, Ye. « Lateral Torsional Buckling of Wooden Beams with Mid-Span Lateral Bracing ». Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35076.

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An analytical and numerical investigation is conducted for the lateral torsional buckling analysis of wooden beam with a mid-span lateral brace subjected to symmetrically distributed loading. Two models are developed; one for the case of a rigid brace and another one for the case of a flexible brace. The analytical solutions are based on the principle of stationary potential energy and a Fourier expansion of the buckling displacement fields and bending moments. The validity of both models are verified against 3D finite element analyses in ABAQUS. Where applicable, verifications were also conducted against available solutions from previous studies. Parametric studies were conducted to investigate the effect of geometric and material parameters on the critical moments. The results indicate the presence of two separate groups of potential buckling modes, symmetric and anti-symmetric, with fundamentally different behavioural characteristics. The governing buckling mode is shown to depend on the bracing height, load height and lateral brace stiffness. The study shows that beyond a certain threshold bracing height, the critical moment is governed by the antisymmetric mode of buckling. Also, above a certain optimum bracing stiffness, no increase is observed in the critical moments. The models developed are used to construct a comprehensive database of parametric investigations which are then employed for developing simplified equations for determining the threshold heights, associated critical moments, and optimum stiffness.

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McCann, Finian. « Stability of beams with discrete lateral restraints ». Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9619.

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The current work analyses the lateral stability of imperfect discretely-braced steel beams using variational methods. To facilitate the analysis, Rayleigh-Ritz approximations are used to model the lateral deflection and the angle of twist. The applicability of the methods is initially demonstrated for the cases of unrestrained and continuously restrained beams by comparison with both analytical and numerical solutions of the governing differential equations of the respective systems. The method is then applied in full to the case of a discretely-braced beam. Initially, it is assumed that the degrees of freedom (DOFs) can be represented by single harmonics; this is then compared to the more accurate representation of the DOFs as full Fourier series. After carrying out a linear eigenvalue analysis of the system, it is found that the beam can buckle into two separate classes of modes: a finite number of modes, equal to the number of restraints provided, which involve displacement of the restraint nodes and interaction between distinct sets of harmonics, and an infinite number of single harmonic internodal buckling modes where the nodes remain undeflected. Expressions are derived for the elastic critical moment of the beam, the forces induced in the restraints and the threshold stiffness, i.e. the minimum stiffness required to enforce the first internodal buckling mode, whereupon the beam attains its maximum achievable critical moment. The analytical results for the critical moment of the beam are validated by the finite element program LTBeam, while the results for the deflected shape of the beam are validated by the numerical continuation software Auto-07p, with very close agreement between the analytical and numerical results. Design formulae, from which practical design rules can be developed, are given for the critical moment, restraint force and threshold stiffness. The design rules return values close to those predicted from theory. When compared against equivalent design rules developed based on analogies with column behaviour, it is found that the column rules are generally overly conservative for restraints attached close to the compression ange and considerably unsafe for restraints attached close to the shear centre.

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Karimi, Hussain H. (Hussain Habibullah). « Parametric subharmonic instability of internal gravity wave beams ». Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100060.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 113-117).
Internal gravity wave beams are time-harmonic plane waves with general spatial pro- le that arise in continuously stratified fluids owing to the anisotropy of this wave motion. In the last decade, these wave disturbances have been at the forefront of research, both from a fundamental perspective and in connection with various geophysical ow processes. Oceanic internal wave beams, in particular, form the backbone of the internal tide, generated by the interaction of the barotropic tide with sea-floor topography. The internal tide breakdown and its role in deep-ocean mixing have attracted considerable attention. In this context, it is of interest to understand mechanisms by which internal wave beams become unstable and eventually breakdown, thereby contributing to mixing. A possible instability mechanism is via resonant triad interactions that amplify short-scale perturbations with frequency equal to one half of that of the underlying wave. For spatially and temporally monochromatic internal waves, this so-called parametric subharmonic instability (PSI) has been studied extensively and indeed can lead to breakdown. By contrast, the focus here is on understanding how wave beams with locally conned spatial prole, such as those in the field, may differ, in regard to PSI, from monochromatic plane waves. To this end, an asymptotic analysis is made of the interaction of a small-amplitude wave beam with short-scale subharmonic wavepackets in a nearly inviscid stratified Boussinesq uid. A novel system of coupled evolution equations that govern this nonlinear interaction is derived and analyzed. For beams with general localized prole, unlike monochromatic wavetrains, it is found that triad interactions are not strong enough to bring about instability in the limited time that subharmonic perturbations overlap with the beam. On the other hand, for quasi-monochromatic wave beams whose prole comprises a sinusoidal carrier modulated by a locally conned envelope, PSI is possible if the beam is wide enough. In this instance, a stability criterion is proposed which, under given ow conditions, provides the minimum number of carrier wavelengths a beam of small amplitude must comprise for instability to arise. Furthermore, the eect of the Earth's rotation on PSI of internal wave beams is investigated. Even though rotation induces transverse motion, plane waves in the form of beams are still possible. Most importantly, however, in the presence of rotation, short-scale subharmonic wavepackets may experience prolonged interaction with a beam of general localized prole, potentially causing instability. This situation arises when the subharmonic frequency nearly matches the background Coriolis frequency so the group velocity of subharmonic wavepackets is close to zero. In particular, wave beams generated by the M₂ tidal ow over topography encounter this resonance near the critical latitude of 28.8° (N and S). Coupled evolution equations for subharmonic wavepackets riding on a beam of general prole under such resonance conditions are derived. Based on this asymptotic model, it is shown that locally conned beams above a certain threshold amplitude are unstable to near-inertial subharmonic disturbances. The theoretical predictions are supported by recent field observations which show that signicant energy transfer to subharmonic disturbances does indeed occur near the critical latitude and not elsewhere.
by Hussain H. Karimi.
Ph. D.

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Liu, Sheng 1970. « Lateral bracing requirements for cantilever steel I-beams ». Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80126.

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In the design of hot rolled steel structures, stability is one of the most important considerations. In terms of flexural members, e.g., a steel I-section beam, bent about the major principal axis, lateral buckling about the minor principal axis in combination with torsional buckling is the main stability concern. To prevent lateral-torsional buckling from occurring, lateral braces are typically installed perpendicular to the longitudinal axis of the flexural member, either on the top and/or bottom flange or near the shear-centre of the beam. Nethercot developed an equation to predict the critical elastic lateral-torsional moment resistance of cantilever beams, which involves a series of effective length factors, which are dependent on the brace configuration, type and position of loading, as well as cantilever system. This effective length factor approach has become widely used as a simplified method to calculate the elastic lateral-torsional buckling moment resistance of cantilever steel beams. However, no specific guidelines for the design of the lateral braces are available in design standards.
This thesis will include background information on elastic beam buckling theories, an introduction to the development of research on lateral brace requirements, and a discussion on the currently used lateral bracing requirements in North American and British Standards. Details of a study concerning the lateral bracing design requirements for cantilever I-beams, carried out with the use of the finite element software Buckling Analysis of Stiffened Plates (BASP), are provided. Concerning the required brace stiffness, the results from the numerical parametric study are compared with the results from the Canadian Steel Design Standard CSA-S 16 and the SSRC (Structural Stability Research Council) method of the United States.
It is shown that the current code methods are generally conservative for top flange loaded cantilever beam cases in terms of the predicted elastic lateral-torsional buckling capacity. Furthermore, the current bracing design requirements provide adequate results in most cases, except for the prop cantilever scenario without a tip brace.

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Kalkan, Ilker. « Lateral torsional buckling of rectangular reinforced concrete beams ». Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31788.

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Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Zureick Abdul-Hamid; Committee Member: Ellingwood, Bruce R.; Committee Member: Kahn, Lawrence F.; Committee Member: Kardomateas, George A.; Committee Member: Will, Kenneth M. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Pezzi, Luciano Ponzi. « Equatorial Pacific dynamics : lateral mixing and tropical instability waves ». Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274585.

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Nasr, El Sayed Abdel Raouf Abdel Kader. « Linear and nonlinear lateral stability of thin walled beams ». Thesis, Heriot-Watt University, 1989. http://hdl.handle.net/10399/916.

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Chang, Railing. « Instability and chaos of counterpropagating beams in a nonlinear medium ». Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185351.

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The dynamical behavior of counterpropagating light waves interacting with a nonlinear medium is studied numerically. It is found that the wave and the medium form a system that becomes unstable under certain conditions and exhibits self-oscillation. Because the interacting medium is modeled by an ensemble of two-level systems, we recognize the self-oscillation frequency as the Rabi-frequency of the constituent systems. The physical mechanisms responsible for this self-oscillation are the gain and the distributed feedback of the combined lightwave-medium system. When the environment changes, in particular when the intensity is increased, this system becomes more unstable and we find that the oscillation exhibits more complex behavior, including quasi-periodic motion and chaos. We analyze the output fields by using Fourier spectra, phase portraits, and autocorrelation functions. In the chaotic regime, the Lyapunov exponents and dimensions are also calculated. A physical interpretation of the quasiperiodic motion is given by an exact calculation of the absorption spectrum of our two-level medium. The negative absorption (gain) peaks are found at the frequencies of the quasi-periodic motions, thus implying that the gain of the combined light-medium system is responsible at least in part for the observed complex behavior. In addition, we investigate the stability of the propagating plane wave when a transverse wave is added to the system as a perturbation. Instabilities are analyzed by linearizing the nonlinear equations which model the lightwave-medium system. The results show that the instability is highly-correlated with the four-wave mixing phase conjugation.

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Arizou, Ramin. « Distortional Lateral Torsional Buckling of Doubly Symmetric Wide Flange Beams ». Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41574.

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Distortional lateral-torsional buckling theories assume that the flanges remain undistorted, while the web is free to distort as a thin plate. Most theories adopt a cubic polynomial distribution along the web height to relate the lateral displacement of the web to the displacements and angles of twist both flanges. The present study develops a family of finite element solutions for the distortional buckling of wide flange beams in which the flanges are assumed to remain undistorted. In contrast to past theories, the lateral displacement distribution along the web height is characterized by superposing (a) two linear modes intended to capture the classical non-distortional lateral-torsional behavior and (b) any number of user-specified Fourier terms intended to capture additional web distortion. In the longitudinal direction, all displacement fields characterizing the lateral displacements are taken to follow a cubic distribution. The first contribution of the thesis develops a finite element formulation that is able to replicate the classical non-distortional lateral torsional buckling solutions when the distortional modes are suppressed while enabling more accurate predictions for distortional lateral torsional buckling compared to those solutions based on the conventional cubic interpolation of the lateral displacement. The formulation is used to conduct an extensive parametric study to quantify the reduction in critical moments due to web distortion relative to the classical non-distortional predictions in the case of simply-supported beams, cantilevers, and beams with an overhang. The solution is then used to generate interaction curves for beams with an overhang subjected to various proportions of uniformly distributed and point loads. The second contribution of the thesis adds two additional features to the formulation (a) to capture the destabilizing effect due to the load height relative to the shear center and (b) a module that incorporates any number of user-defined multi-point kinematic constraints. The additional features are employed to investigate the effect of load height, bracing height, and combined effects thereof in practical design problems. A distortional indicator is then introduced to characterize the distribution of web distortion along the beam span as the beam undergoes distortional lateral buckling. A systematic design optimization technique is then devised to identify the location(s) along the span at which the addition of transverse stiffeners would maximize the critical moment capacity.

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Poole, Harrison Walker. « Lateral load distribution for steel beams supporting an FRP panel ». Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/12027.

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Master of Science
Department of Civil Engineering
Hani G. Melhem
Fiber Reinforced Polymer (FRP) is a relatively new material used in the field of civil engineering. FRP is composed of fibers, usually carbon or glass, bonded together using a polymer adhesive and formed into the desired structural shape. Recently, FRP deck panels have been viewed as an attractive alternative to concrete decks when replacing deteriorated bridges. The main advantages of an FRP deck are its weight (roughly 75% lighter than concrete), its high strength-to-weight ratio, and its resistance to deterioration. In bridge design, AASHTO provides load distributions to be used when determining how much load a longitudinal beam supporting a bridge deck should be designed to hold. Depending on the deck material along with other variables, a different design distribution will be used. Since FRP is a relatively new material used for bridge design, there are no provisions in the AASHTO code that provides a load distribution when designing beams supporting an FRP deck. FRP deck panels, measuring 6 ft x 8.5’, were loaded and analyzed at KSU over the past 4 years. The research conducted provides insight towards a conservative load distribution to assist engineers in future bridge designs with FRP decks. Two separate test periods produced data for this thesis. For the first test period, throughout the year of 2007, a continuous FRP panel was set up at the Civil Infrastructure Systems Laboratory at Kansas State University. This continuous panel measured 8.5 ft by 6 ft x 6 in. thick and was supported by 4 Grade A572 HP 10 x 42 steel beams. The beam spacing’s, along the 8.5 ft direction, were 2.5 ft-3.5 ft-2.5 ft. Stain gauges were mounted at mid-span of each beam to monitor the amount of load each beam was taking under a certain load. Linear variable distribution transformers (LVDT) were mounted at mid-span of each beam to measure deflection. Loads were placed at the center of the panel, with reference to the 6 ft direction and at several locations along the 8.5 ft direction. Strain and deflection readings were taken in order to determine the amount of load each beam resisted for each load location. The second period of testing started in the fall of 2010 and extended into January of 2011. This consisted of a simple-span/cantilever test set-up. The test set-up consisted of, in the 8.5 ft direction, a simply supported span of 6 ft with a 2.5 ft cantilever on one side. As done previously both beams had strain gauges along with LVDTs mounted at mid-span. There were also strain gauges were installed spaced at 1.5ft increments along one beam in order to analyze the beam behavior under certain loads. Loads were once again applied in the center of the 6 ft direction and strain and deflection readings were taken at several load locations along the 8.5 ft direction. The data was analyzed after all testing was completed. The readings from the strain gauges mounted in 1.5 ft increments along the steel beam on one side of the simple span test set-up were used to produce moment curves for the steel beam at various load locations. These moment curves were analyzed to determine how much of the panel was effectively acting on the beam when loads were placed at various distances away from the beam. Using these “effective lengths,” along with the strain taken from the mid-span of each beam, the loads each beam was resisting for different load locations were determined for both the continuously supported panel and the simply supported/cantilever panel data. Using these loads, conservative design factors were determined for FRP panels. These factors are S/5.05 for the simply supported panel and S/4.4 for the continuous panel, where “S” is the support beam spacing. Deflections measurements were used to validate the results. Percent errors, based on experimental and theoretical deflections, were found to be in the range of 10 percent to 40 percent depending on the load locations for the results in this thesis.

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Weeks, N. J. « Lateral instability of slender reinforced concrete columns in a fire environment ». Thesis, Aston University, 1985. http://publications.aston.ac.uk/14237/.

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The research concerns the development and application of an analytical computer program, SAFE-ROC, that models material behaviour and structural behaviour of a slender reinforced concrete column that is part of an overall structure and is subjected to elevated temperatures as a result of exposure to fire. The analysis approach used in SAFE-RCC is non-linear. Computer calculations are used that take account of restraint and continuity, and the interaction of the column with the surrounding structure during the fire. Within a given time step an iterative approach is used to find a deformed shape for the column which results in equilibrium between the forces associated with the external loads and internal stresses and degradation. Non-linear geometric effects are taken into account by updating the geometry of the structure during deformation. The structural response program SAFE-ROC includes a total strain model which takes account of the compatibility of strain due to temperature and loading. The total strain model represents a constitutive law that governs the material behaviour for concrete and steel. The material behaviour models employed for concrete and steel take account of the dimensional changes caused by the temperature differentials and changes in the material mechanical properties with changes in temperature. Non-linear stress-strain laws are used that take account of loading to a strain greater than that corresponding to the peak stress of the concrete stress-strain relation, and model the inelastic deformation associated with unloading of the steel stress-strain relation. The cross section temperatures caused by the fire environment are obtained by a preceding non-linear thermal analysis, a computer program FIRES-T.

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Bradley, T. Patrick. « Stability of Castellated Beams During Erection ». Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/31117.

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The increased depth of castellated beams presents stability problems, specifically during erection. During erection the castellated beam must support the weight of an erector and self-weight until the continuous bracing of the floor deck is in place. The stability of the unbraced member is based on its resistance to lateral-torsional buckling.

The cross-sectional properties that are related to lateral-torsional buckling, such as out-of-plane bending, warping constant, and torsional constant were calculated using three different approaches to model the unique geometry of castellated beams. These properties were used in various lateral-torsional buckling solutions to determine which procedure should be used to check for this mode of failure.

Two specimens were tested to evaluate the results of the analytical unbraced length determination process. The tests results were used to better model the contribution of the web-to-column flange double angle connection on the stability of the castellated beam.
Master of Science

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18

Cojocaru, Razvan. « Lifting Analysis of Precast Prestressed Concrete Beams ». Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/32464.

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Motivated by Robert Mastâ s original papers on lifting stability, this research study provides a method for predicting beam behavior during lifting, with application in the construction of bridges. A beam lifting cracking limit state is developed based on analytical equations for calculating the roll angle of the beam, the internal forces and moments, the weak-axis and strong-axis deflections, and the cross-sectional angle of twist. Finite element simulations are performed to investigate the behavior of concrete beams during lifting and to validate the proposed method. Additionally, a statistical characterization of beam imperfections is presented, based on recently conducted field measurements of beam lateral sweep and eccentricity of lift supports. Finally, numerical examples for two typical precast prestressed concrete beam cross-sections are included to demonstrate the proposed method.
Master of Science

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19

Hassan, Rusul. « Distortional Lateral Torsional Buckling Analysis for Beams of Wide Flange Cross-sections ». Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24008.

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Structural steel design standards recognize lateral torsional buckling as a failure mode governing the capacity of long span unsupported beams with wide flange cross-sections. Standard solutions start with the closed form solution of the Vlasov thin-walled beam theory for the case of a simply supported beam under uniform moments, and modify the solution to accommodate various moment distributions through moment gradient expressions. The Vlasov theory solution is based on the assumption that cross-sectional distortional effects have a negligible effect on the predicted elastic critical moment. The present study systematically examines the validity of the Vlasov assumption related to cross-section distortion through a parametric study. A series of elastic shell finite element eigen-value buckling analyses is conducted on simply supported beams subject to uniform moments, linear moments and mid span point loads as well as cantilevers subject to top flange loading acting at the tip. Cross-sectional dimensions are selected to represent structural steel cross-section geometries used in practice. Particular attention is paid to model end connection details commonly used in practice involving moment connections with two pairs of stiffeners, simply supported ends with a pair of transverse stiffeners, simply supported ends with cleat angle details, and built in fixation at cantilever roots. The critical moments obtained from the FEA are compared to those based on conventional critical moment equations in various Standards and published solutions. The effects of web slenderness, flange slenderness, web height to flange width ratio, and span to height ratios on the critical moment ratio are systematically quantified. For some combinations of section geometries and connection details, it is shown that present solutions derived from the Vlasov theory can overestimate the lateral torsional buckling resistance for beams.

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20

Chase, Robert P. « Large 3-D deflection and force analysis of lateral torsional buckled beams / ». Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1644.pdf.

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21

Chase, Robert Parley. « Large 3-D Deflection and Force Analysis of Lateral Torsional Buckled Beams ». BYU ScholarsArchive, 2006. https://scholarsarchive.byu.edu/etd/1040.

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This thesis presents research on the force and deflection behavior of beams with rectangular cross-sections undergoing lateral torsional buckling. The large 3-D deflection path of buckling beam tips was closely approximated by circular arcs in two planes. A new chain algorithm element was created from pseudo-rigid-body segments and used in a chain calculation that accurately predicted the force deflection relationship of beams with large 3-D deflections.

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22

NINA, JULIO CESAR COAQUIRA. « NONLINEAR OSCILLATIONS AND DYNAMIC INSTABILITY OF THIN-WALLED BEAMS WITH OPEN CROSS-SECTION ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33893@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Estruturas com elementos de seção aberta e paredes delgadas são amplamente utilizados em estruturas metálicas. Estes elementos têm, em geral, baixa rigidez a torção. Para seções monosimétricas e assimétricas, quando o centro de cisalhamento não coincide com o centro de gravidade, pode ocorrer acoplamento entre flexão e torção. Devido à baixa rigidez à torção, podem ocorrer grandes rotações das seções transversais da viga. Assim, uma análise do comportamento de tais elementos estruturais, levando em consideração a não linearidade geométrica, é desejável. Com este objetivo, equações diferenciais parciais de movimento que descrevem o acoplamento flexão-flexão-torção são utilizadas, em conjunto com o método de Galerkin, para se obter um conjunto de equações discretizadas de movimentos, que é resolvido pelo método Runge-Kutta. A partir das equações linearizadas, obtêm-se as frequências naturais, cargas críticas axiais e a relação entre carga axial e frequência para vigas com diferentes condições de contorno. A seguir, estudam-se as oscilações não lineares e bifurcações de uma viga engastada-livre submetida a cargas laterais harmônicas. Uma análise paramétrica detalhada, usando várias ferramentas de dinâmica não linear, investiga o comportamento dinâmico não linear e não planar da viga nas três primeiras regiões de ressonância e a influência da não linearidade, posição do carregamento, restrições à torção e parâmetros de controle do carregamento na estabilidade dinâmica da estrutura.
Structural elements with open and thin-walled section are widely used in metal structures. These elements have, in general, low torsional stiffness. For monosymmetric and asymmetric sections, when the shear center does not coincide with the center of gravity coupling between bending and torsion may occur. Due to the low torsional stiffness, large twist beam cross sections may arise. Thus, an analysis of the behavior of such structural elements, taking into account the geometric nonlinearity, is desirable. For this purpose, partial differential equations describing the flexural-flexural-torsional coupling are used in conjunction with the Galerkin method to obtain a set of discretized equations of motion, which is solved by the Runge-Kutta method. From the linearized equations, we obtain the natural frequencies, axial critical loads, and the axial load and frequency relationship for beams with different boundary conditions. Next, we study the nonlinear oscillations and bifurcations of a clamped-free beam subjected to harmonic lateral loads. A detailed parametric analysis, using various nonlinear dynamics tools, investigates the nonlinear dynamic behavior and nonplanar motions of the beam for the first three regions of resonance and the influence of the non-linearity, loading position, torsional restraints and load control parameters on the dynamic stability of the structure.

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23

Tyagi, P. K. « Linear Instability Of Laterally Strained Constant Pressure Boundary Layer Flows ». Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/265.

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The linear instability of laterally diverging/converging flows is an important aspect towards understanding the laminar-transition process in many viscous flows. In this work the linear instability of constant pressure laterally diverging/converging flow has been investigated. The laminar velocity field for laterally diverging/converging flows, under the source/sink approximation, has been reduced to two-dimensional flows. This reduction is alternative to the Mangier transformation used earlier. For a constant pressure laterally strained flow, the laminar velocity is found to be governed by the Blasius equation for flow over a flat plate. The non-parallel linear instability of constant pressure laterally strained flows has been examined. The instability equation is found to be same as that for the Blasius flow. This implies that the stability is same as that for the Blasius flow. A lateral divergence/convergence is shown to alter the Reynolds number from that in a two-dimensional flow. The instability of a laterally converging/diverging flow thus can be obtained from the available results for the Blasius flow by scaling the Reynolds numbers. This leads to the result that while a diverging flow is more unstable than the Blasius flow, a converging flow is more stable. Some additional relevant results are also presented.

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24

Villasenor, Aguilar Jose Maria. « Lateral-Torsional Buckling Instability Caused by Individuals Walking on Wood Composite I-Joists ». Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19212.

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Recent research has shown that a significant number of the falls from elevation occur when laborers are working on unfinished structures. Workers walking on wood I-joists on roofs and floors are prone to fall hazards. Wood I-joists have been replacing dimension lumber for many floor systems and a substantial number of roof systems in light-frame construction. Wood I-joists are designed to resist axial stresses on the flanges and shear stresses on the web while minimizing material used. However, wood I-joists have poor resistance to applied lateral and torsional loads and are susceptible to lateral-torsional buckling instability. Workers walking on unbraced or partially braced wood I-joists can induce axial and lateral forces as well as twist. Experimental testing demonstrated that workers cause lateral-torsional buckling instability in wood I-joists. However, no research was found related to the lateral-torsional buckling instability induced by individuals walking on the wood I-joists. Furthermore, no research was found considering the effects of the supported end conditions and partial bracing in the lateral-torsional buckling instability of wood I-joists.
The goal of this research was to derive mathematical models to predict the dynamic lateral-torsional buckling instability of wood composite I-joists loaded by individuals walking considering different supported end conditions and bracing system configurations. The dynamic lateral-torsional buckling instability was analyzed by linearly combining the static lateral-torsional buckling instability with the lateral bending motion of the wood I-joists. Mathematical models were derived to calculate the static critical loads for the simply supported end condition and four wood I-joist hanger supported end conditions. Additionally, mathematical models were derived to calculate the dynamic maximum lateral displacements and positions of the individual walking on the wood I-joists for the same five different supported end conditions. Three different lean-on bracing systems were investigated, non-bracing, one-bracing, and two-bracing systems. Mathematical models were derived to calculate the amount of constraint due to the lean-on bracing system. The derived mathematical models were validated by comparison to data from testing for all supported end conditions and bracing systems.
The predicted critical loads using the static buckling theoretical models for the non-bracing system and the static buckling theoretical models combined with the bracing theoretical models for the simply and hanger supported end conditions agreed well with the critical loads obtained from testing for the two wood I-joist sizes investigated. The predicted maximum lateral displacements and individual positions using the bending motion theoretical models for the simply and hanger supported end conditions agreed well with the corresponding maximum lateral displacements and individual positions obtained from testing for both wood I-joist sizes. Results showed that; a) the supported end condition influenced the critical loads, maximum lateral displacements and individual positions, b) the bracing system increased the critical loads and reduced the maximum lateral displacements, c) the critical load increased as the load position displaced away from the wood I-joist mid-span, d) the critical load reduced as the initial lateral displacement of the wood I-joist increased and e) the wood I-joist mid-span was the critical point in the dynamic lateral-torsional buckling instability.

Ph. D.

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25

Zhang, Shu. « Lateral-torsional buckling of simply supported and cantilevered fiber reinforced polymeric I-beams ». Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/20305.

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26

St-Amour, Rémi. « Lateral Torsional Buckling of Wood I-Joist ». Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35161.

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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.

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27

Rosen, Adam B. « Differences in lateral drop-jumps from an unknown height among individuals with ankle instability ». Access to citation, abstract and download form provided by ProQuest Information and Learning Company ; downloadable PDF file, 74 p, 2008. http://proquest.umi.com/pqdweb?did=1605135941&sid=6&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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28

Kanatani, Kentaro. « Interfacial instability induced by lateral vapor pressure fluctuation in bounded thin liquid-vapor layers ». 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124394.

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29

Kurniawan, Cyrilus Winatama. « Flexural behaviour and design of the new LiteSteel beams ». Queensland University of Technology, 2007. http://eprints.qut.edu.au/16674/.

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The flexural capacity of the new hollow flange steel section known as LiteSteel beam (LSB) is limited by lateral distortional buckling for intermediate spans, which is characterised by simultaneous lateral deflection, twist and web distortion. Recent research based on finite element analysis and testing has developed design rules for the member capacity of LiteSteel beams subject to this unique lateral distortional buckling. These design rules are limited to a uniform bending moment distribution. However, uniform bending moment conditions rarely exist in practice despite being considered as the worst case due to uniform yielding across the span. Loading position or load height is also known to have significant effects on the lateral buckling strength of beams. Therefore it is important to include the effects of these loading conditions in the assessment of LSB member capacities. Many steel design codes have adopted equivalent uniform moment distribution and load height factors for this purpose. But they were derived mostly based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. In contrast LSBs are made of high strength steel and have a unique crosssection with specific residual stresses and geometrical imperfections along with a unique lateral distortional buckling mode. The moment distribution and load height effects for LSBs, and the suitability of the current steel design code methods to accommodate these effects for LSBs are not yet known. The research study presented in this thesis was therefore undertaken to investigate the effects of nonuniform moment distribution and load height on the lateral buckling strength of simply supported and cantilever LSBs. Finite element analyses of LSBs subject to lateral buckling formed the main component of this study. As the first step the original finite element model used to develop the current LSB design rules for uniform moment was improved to eliminate some of the modelling inaccuracies. The modified finite element model was validated using the elastic buckling analysis results from well established finite strip analysis programs. It was used to review the current LSB design curve for uniform moment distribution, based on which appropriate recommendations were made. The modified finite element model was further modified to simulate various loading and support configurations and used to investigate the effects of many commonly used moment distributions and load height for both simply supported and cantilever LSBs. The results were compared with the predictions based on the current steel code design rules. Based on these comparisons, appropriate recommendations were made on the suitability of the current steel code design methods. New design recommendations were made for LSBs subjected to non-uniform moment distributions and varying load positions. A number of LSB experiments was also undertaken to confirm the results of finite element analysis study. In summary the research reported in this thesis has developed an improved finite element model that can be used to investigate the buckling behaviour of LSBs for the purpose of developing design rules. It has increased the understanding and knowledge of simply supported and cantilever LSBs subject to non-uniform moment distributions and load height effects. Finally it has proposed suitable design rules for LSBs in the form of equations and factors within the current steel code design provisions. All of these advances have thus further enhanced the economical and safe design of LSBs.

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Frick, Kyle. « Effect of Temperature Increase on Lateral Response of Axially Restrained Beams Subjected to Concentrated Loads ». OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/1968.

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The lateral response of axially restrained beams with various end conditions is presented herein using nonlinear analysis. The beams were studied for three end conditions, with two lengths per end condition and two magnitudes of point loads per length. The method of analysis was performed using geometrically non-linear analysis. Material nonlinear analysis was not considered. This method of analysis, which is based on Eulerian (corotational) formulation and includes thermal effects, was published by Kassimali and Garcilazo (2010). Graphical results are shown for the response of the beams. The results are also compared to published values given in the AISC manual. The following conclusions were shown from this study: 1) When comparing the amplification factors (both deflection and bending moment) found in this study to the amplification factors given in the AISC manual, the data shows similar values in the pre-buckling region. However, once the temperature is raised high enough and the beam enters the post-buckling region, significant difference in the amplification factors can be seen. The beams in this study showed that the amplification factors do not increase greatly during post-buckling. The values given in the AISC manual on the other hand show an indefinite increase in amplification factor once the buckling stage is reached. It is thought that this decrease in amplification factors in post-buckling is due to the increased strength in the beams from catenary forces that are developed. 2) When comparing similar beams (same end conditions and same lateral loads), the length of the beam will play a role in the lateral response to thermal loading. It was consistently shown in all end support conditions that the shorter beams developed higher amplification factors compared to the longer beams. This difference was not substantial in the pre-buckling stage, but once the beam approached the critical temperature and into the post-buckling range, the difference in amplification factors became significant. 3) Along the same lines, comparing beams with the same end conditions and same length, the magnitude of the lateral load also played a role in the lateral response of the beams. The beams with the lighter lateral loads would develop higher amplification factors than the heavier loaded beams. As with the length, the lateral loads didn’t have much difference until the beams would approach the critical temperature. However, after that point, the difference of the amplification factors would become quite large.

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Venter, Simon Herman. « The effect of the adjacent span on the lateral-torsional buckling capacity of overhang beams ». Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/62800.

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32

Ahmadi, Habiburrahman. « Lateral torsional buckling of anisotropic laminated composite beams subjected to various loading and boundary conditions ». Diss., Kansas State University, 2017. http://hdl.handle.net/2097/35402.

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Doctor of Philosophy
Department of Civil Engineering
Hayder A. Rasheed
Thin-walled structures are major components in many engineering applications. When a thin-walled slender beam is subjected to lateral loads, causing moments, the beam may buckle by a combined lateral bending and twisting of cross-section, which is called lateral-torsional buckling. A generalized analytical approach for lateral-torsional buckling of anisotropic laminated, thin-walled, rectangular cross-section composite beams under various loading conditions (namely, pure bending and concentrated load) and boundary conditions (namely, simply supported and cantilever) was developed using the classical laminated plate theory (CLPT), with all considered assumptions, as a basis for the constitutive equations. Buckling of such type of members has not been addressed in the literature. Closed form buckling expressions were derived in terms of the lateral, torsional and coupling stiffness coefficients of the overall composite. These coefficients were obtained through dimensional reduction by static condensation of the 6x6 constitutive matrix mapped into an effective 2x2 coupled weak axis bending-twisting relationship. The stability of the beam under different geometric and material parameters, like length/height ratio, ply thickness, and ply orientation, was investigated. The analytical formulas were verified against finite element buckling solutions using ABAQUS for different lamination orientations showing excellent accuracy.

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33

Back, Sung-Yong. « A shear-flexible finite element model for lateral torsional buckling analysis of thin-walled open beams ». Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/20999.

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34

Li, Ming. « Effect of the Initial Out-of-Straightness on the Lateral Torsional Buckling Strength of Steel Beams ». Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37070.

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The effect of initial out-of-straightness of steel beams with wide flange cross-sections on their elastic lateral torsional buckling strength is investigated analytically and numerically. A variational principle is first developed and then used to obtain the governing equilibrium conditions and associated boundary conditions for a beam with general patterns of initial out-of-straightness and initial angles of twist. The principle is then used to develop a finite element formulation to characterize the lateral torsional response of beams with initial out-of-straightness under general transverse loading. The validity of the finite element formulation is verified through comparison against results from models based thin-walled beam finite element and shell element models available in ABAQUS. Since the load lateral displacement responses do not exhibit a distinct point of loss of stability, two design criteria are proposed for the characterization of the failure. The first criterion is based on a threshold value for additional lateral displacement and the second criterial is based on a threshold value for the normal stresses. Both criteria are applied in conjunction with the analytical solution and finite element formulation in order to determine a moment resistance based on lateral torsional buckling that incorporates the effect of initial out-of-straightness. The moment capacity based on the displacement-based criterion is shown to solely depend on the ratio between the initial out-of-straightness component associated with the first buckling mode and the additional displacement threshold value specified. To the contrary, moment capacity based on the stress criterion, was found to depend upon the initial out-of-straightness magnitude, the normal stress threshold value and the geometry of the cross-section. The effects of the above parameters on the predicted moment capacity were investigated for beams with common sections in a systematic parametric study. Possible means of modifying the present provisions of CAN-CSA S16 relating to elastic lateral torsional buckling to incorporate the effect of initial out-of-straightness effects are discussed and illustrated through examples. The load-deformation plots for beams with initial out-of-straightens as predicted by the formulations developed in the present study are then used to extend the Southwell plot technique, originally developed for buckling of column with initial out-of-straightness, to the lateral torsional buckling of beams with initial out-of-straightness. The study shows that the plot, either experimentally or analytically obtained, of the applied load versus lateral displacement, at any point or angle of twist at any section, for a beam with initial out-of-straightness case can predict (a) the elastic critical moment of an analogous initially straight beam, and (b) the first buckling mode contribution to the initial out-of-straightness.

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35

Mohammadi, Aragh Mahdi [Verfasser], et Hans [Akademischer Betreuer] Burchard. « The impact of advection schemes on lateral shear and baroclinic instability / Mahdi Mohammadi Aragh. Betreuer : Hans Burchard ». Hamburg : Staats- und Universitätsbibliothek Hamburg, 2015. http://d-nb.info/1066898391/34.

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36

Pezeshky, Payam. « Distortional Static and Buckling Analysis of Wide Flange Steel Beams ». Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36074.

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Existing design provisions in design standards and conventional analysis methods for structural steel members are based on the simplifying kinematic Vlasov assumption that neglects cross-sectional distortional effects. While the non-distortional assumption can lead to reasonable predictions of beam static response and buckling strength in common situations, past work has shown the inadequacy of such assumption in a number of situations where it may lead to over-predicting the strength of the members. The present study thus develops a series of generalized theories/solutions for the static analysis and buckling analysis of steel members with wide flange cross-sections that capture distortional effects of the web. Rather than adopting the classical Vlasov assumption that postulates the cross-section to move and rotate in its own plane as a rigid disk, the present theories assume the web to be flexible in the plane of the cross-section and thus able to bend laterally, while both flanges to move as rigid plates within the plane of the cross-section to be treated as Euler-Bernouilli beams. The theories capture shear deformation effects in the web, as well as local and global warping effects. Based on the principle of minimum potential energy, a distortional theory is developed for the static analysis of wide flange steel beams with mono-symmetric cross-sections. The theory leads to two systems of differential equations of equilibrium. The first system consists of three coupled equilibrium differential equations that characterize the longitudinal-transverse response of the beam and the second system involves four coupled equilibrium differential equations of equilibrium and characterizes the lateral-torsional response of the beam. Closed form solutions are developed for both systems for general loading. Based on the kinematics of the new theory, two distortional finite elements are then developed. In the first element, linear and cubic Hermitian polynomials are employed to interpolate displacement fields while in the second element, the closed-form solutions developed are adopted to formulate special shape functions. For longitudinal-transverse response the elements consist of two nodes with four degree of freedom per node for longitudinal-transverse response and for lateral-torsional response, the elements consist of two nodes with eight degrees of freedom per node. The solution is able to predict the distortional deformation and stresses in a manner similar to shell solutions while keeping the modeling and computational effort to a minimum. Applications of the new beam theory include (1) providing new insights on the response of steel beams under torsion whereby the top and bottom flanges may exhibit different angles of twist, (2) capturing the response of steel beams with a single restrained flange as may be the case when a concrete slab provides lateral and/or torsional restraint to the top flange of a steel beam, and (3) modelling the beneficial effect of transverse stiffeners in reducing distortional effects in the web. The second part of the study develops a unified lateral torsional buckling finite element formulation for the analysis of beams with wide flange doubly symmetric cross-sections. The solution captures several non-conventional features. These include the softening effect due to web distortion, the stiffening effect induced by pre-buckling deformations, the pre-buckling nonlinear interaction between strong axis moments and axial forces, the contribution of pre-buckling shear deformation effects within the plane of the web, the destabilizing effects due to transverse loads being offset from the shear centre, and the presence of transverse stiffeners on web distortion. Within the framework of the present theory, it is possible to evoke or suppress any combination of the features and thus isolate the individual contribution of each effect or quantify the combined contributions of multiple effects on the member lateral torsional capacity. The new solution is then applied to investigate the influence of the ratios of beam span-to-depth, flange width-to-thickness, web height-to-thickness, and flange width-to-web height on the lateral torsional buckling strength of simply supported beams and cantilevers. Comparisons with conventional lateral torsional buckling solutions that omit distortional and pre-buckling effects quantify the influence of distortional and/or pre-buckling deformation effects. The theory is also used to investigate the influence of P-delta effects of beam-columns subjected to transverse and axial forces on their lateral torsional buckling resistance. The theory is used to investigate the load height effect relative to the shear centre. Comparisons are made with load height effects as predicted by non-distortional buckling theories. The solution is adopted to quantify the beneficial effect of transverse stiffeners in controlling/suppressing web distortion in beams and increasing their buckling resistance.

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Löfvenberg, Richard. « Chronic lateral instability of the ankle joint : natural course, pathophysiology and steroradiographic evaluation of conservative and surgical treatment ». Doctoral thesis, Umeå universitet, Ortopedi, 1994. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-101304.

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Chronic lateral instability of the ankle (CLI), defined as frequent sprains and recurrent giving way, difficulty in walking and running on uneven surface, is often connected with pain and swollen ankles. It occurs in 10 to 20 percent after acute ankle injuries. Mechanical instability of the talocrural and subtalar joint, peroneal weakness and impaired proprioception has been suggested as etiological factors. Aim. To investigate the natural course in conservatively treated patients with CLI. To assess the mechanical stability in patients with CLI by measuring the three dimensional motions in the talus, the fibula and the calcaneus in relation to the tibia during different testing procedures pre- and postoperatively. To determine if CLI is associated with proprioceptive deficiency. Patients and Methods. This Thesis includes 127 ankles in 78 patients (30 women, 48 men) with CLI. Thirty-seven patients were followed up 20 years after their first contact with the orthopaedic department because of CLI. Forty-six ankles were evaluated radiographically and the result was compared with a gender- and age - matched control-material. The neuromuscular response to a sudden angular displacement of the ankles was studied in 15 ankles in 13 patients using EMG. Thirty-six patients entered a prospective study using roentgen stereophotogrammetric analysis (RSA) in which the ankles were tested at manual adduction, adduction with predetermined torque, with and without external support and at drawer tests (40 N and 160N). Twenty-seven patients were followed five years postoperatively. Result. After 20 years 22 patients, conservatively treated still suffered from instability of the ankle and ten had recurrent giving way symptoms even on plane surface. Six ankles in the patient group and four in the control group displayed osteoarthritic changes Prolonged ipsilateral reaction time (m. per. long, and m. tib. ant.) was found in patients with CLI indicating proprioceptive insufficiency. Increased talar adduction and a tendency toward increased total translation of the talar center was found in ankles with CLI. Concomitant fibular rotations and translations were found but with no conclusive deviation in the ankles with symptoms. The talo-calcaneal adduction reached the same level in the patient and control groups regardless of symptoms. External support (ankle brace) increased the talar stability. The use of predetermined torque and constrained testing procedure did not add information compared with the manual test Twenty-five patients graded the result as excellent or good five years after lateral ligament reconstruction. Talar stability (decreased adduction and translation) was increased two years postoperatively and was improved or remained the same at five years without comprising the range of motion. Conclusion. In more than half the cases symptoms of CLI did not resolve spontaneously. Minor degenerative changes was found after twenty years, but not to a greater extent than in a control group. CLI was associated with proprioceptive insufficiency and talocrural but not subtalar instability. Increased ankle stability can be obtained by the use of an ankle brace and by an anatomical ligament reconstruction.

Diss. (sammanfattning) Umeå : Umeå universitet, 1994

digitalisering@umu

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Perez, Jose Javier. « Finite Element Evaluation of the Effects of Lateral Anchorage Strips on the Behavior of CFRP-Strengthened RC Beams ». Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3116.

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In this thesis, a fully nonlinear finite element study of the flexural behavior of doubly reinforced concrete beams strengthened using different Carbon Fiber Reinforced Polymer (CFRP) composite strengthening configurations has been carried out. Prior to the study, a total of six beams were constructed, pre-cracked, strengthened and tested to failure under a four-point loading condition (Zhao and O'Riordan-Adjah, 2004). Then, for the purpose of this thesis work, detailed three dimensional finite element models were created not only to correlate the results obtained from the experiments, but also to predict the load capacity, failure modes and crack pattern of reinforced concrete (RC) beams strengthened using Fiber Reinforced Polymer (FRP) composites. Knowing the behavior for each of the materials that compose the beam (concrete, steel, bonding material or interface, and FRP laminates) and how to get their properties, an accurate and representative finite element model can be created. Tests and analytical (FE) results showed that the strengthened configuration plays an important role in the overall strength, failure mechanisms, and, more significantly, the ductile behavior of the beams. Considerable increases in the load-carrying capacity of the RC beams were observed. Increases that range from 12% (using FRP only on the bottom of the beam) to 35% (FRP on the bottom + 45 degrees sides' configuration as explained later) compared to the control beam before ultimate failure were obtained. Failure modes were also affected since the beam with only FRP on the bottom failed completely by debonding of the laminate while the beams with side FRP anchorage strips failed by a combination of composite debonding on the sides and concrete crushing. Finally, ductile behavior of the beams was greatly improved due to the application of the strengthening material on the side of the concrete beams, serving as an anchorage to the bottom fabric. The accuracy of the model has been validated comparing the results obtained from the six beam tests to the ones determined using the FE approach. Good agreement between the two has been found.
M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering

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Lima, Maria Cristina Vidigal de. « Contribuição ao estudo da instabilidade lateral de vigas pré-moldadas ». Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-29052006-171714/.

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A verificação da estabilidade lateral de vigas pré-moldadas merece maior atenção em vigas longas e delgadas, especialmente durante as fases transitórias, como o içamento e o transporte, e também quando se leva em conta a deformabilidade das ligações temporárias. Apresenta-se nesta tese, um estado da arte sobre o problema da instabilidade lateral em vigas pré-moldadas, a fim de situar este trabalho no contexto técnico atual, bem como estudos anteriores relacionados à torção pura e quando associada a outras solicitações. Alguns modelos numéricos foram implementados computacionalmente a fim de simular o comportamento não-linear físico de vigas de concreto armado e protendido sob ação conjunta de torção, flexão bi-lateral e força axial. O modelo adequado a situações onde a torção é predominante sobre a flexão baseia-se na analogia ao comportamento de treliça espacial e na extensão da teoria dos campos diagonais comprimidos. Os resultados numéricos obtidos foram satisfatoriamente comparados aos experimentais disponíveis na literatura técnica. Nos casos onde a flexão é predominate, utilizou-se um modelo numérico que permite calcular a rigidez à torção após a fissuração por flexão da viga, sendo este o recomendado para as análises das fases transitórias de içamento por cabos. Duas vigas longas e esbeltas de concreto armado, sob tombamento lateral gradual e ação única do peso-próprio, foram moldadas e ensaiadas no laboratório. Os resultados experimentais obtidos serviram para validar o modelo numérico. No ensaio, a utilização de estações totais para medidas de deslocamentos mostrou ser uma boa alternativa, comparando-se bem aos resultados numéricos calculados. As medidas experimentais das deformações no concreto e nas armaduras concordaram satisfatoriamente com as respostas numéricas. Na aplicação à elementos estruturais com protensão, o comportamento numérico obtido para uma viga protendida de ponte de seção I, sob tombamento lateral gradual, comparou-se satisfatoriamente com a resposta experimental. Enfim, a medida da segurança do içamento de uma viga protendida de ponte e de uma tesoura protendida de cobertura foi calculada numericamente, considerando apoios deformáveis à torção. Os resultados numéricos mostram a importância de se escolher adequadamente o comprimento dos balanços, bem como a inclinação dos cabos de suspensão, garantindo a estabilidade da viga
The lateral stability of long and slender precast concrete beams requires great attention. In particular, it is important to ensure the stability of these members during transitory phases like tilting and transport, and also when the deformability of temporary supports is taken into account. The state of the art of the problem of lateral stability in precast concrete beams is presented in order to place this work in the current technical context. Previous studies of the problem of pure torsion and combined loading are reviewed. Numerical models considering the physical non-linear behavior of reinforced and prestressed concrete beams subjected to combined torsion, bi-axial bending and axial loads were implemented. The appropriate model when torsion dominates over bending is based on the space truss model and an extension of the diagonal compression field theory. The numerical results obtained compared satisfactorily with the experimental ones available in the technical literature. In bending dominated cases, a numerical model that evaluates the torsional stiffness in a cracked state due to bending is recommended for the analyses of temporary phases such as tilting. Two slender reinforced concrete beam models were built and tested under controlled gradual tilting conditions and self-weight action. These experimental results were used to validate the numerical model. Experimental results obtained using total stations for measuring displacements showed to be a good alternative, comparing well with those provided by the numerical model. The experimental measures of deformations in concrete and steel agreed well with the numerical calculations. Good agreement between numerical and experimental results was obtained for a prestressed concrete I-beam gradually tilted. Finally, a numerical analysis considering the flexibility of the supports of a prestressed concrete I-beam and a prestressed concrete truss with variable cross-section was carried out. The numerical results showed the importance of choosing the appropriate overhang length as well as the inclination of the suspension cables, in order to ensure the stability of the beam

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Morrison, Katherine Elizabeth. « The examination of dynamic foot pressure distributions, running mechanics, and a lateral hop in subjects with chronic ankle instability ». Access to citation, abstract and download form provided by ProQuest Information and Learning Company ; downloadable PDF file, 131 p, 2009. http://proquest.umi.com/pqdweb?did=1674095891&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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Gama, Felipe Ozório Monteiro da. « Avaliação numérica de estabilidade lateral de vigas casteladas ». Universidade do Estado do Rio de Janeiro, 2011. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=4090.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Restrições de espaço e altura são frequentemente impostas às edificações residenciais, comerciais, industriais, depósitos e galpões com um ou diversos pavimentos em função de aspectos de regulamentos regionais, técnicos, econômicos ou ainda de natureza estética. A fim de proporcionar a passagem de tubulações e dutos de grande diâmetro sob vigas de aço, grandes alturas são normalmente requeridas, demandando por vezes, magnitudes de altura inviáveis entre pavimentos de edificações. Diversas soluções estruturais podem ser utilizadas para equacionar tais obstáculos, onde dentre outras, pode-se citar as vigas com inércia variável, stub-girders, treliças mistas, vigas misuladas e vigas com uma ou múltiplas aberturas na alma com geometrias variadas. No que tange às vigas casteladas, solução estrutural pautada neste estudo, a estabilidade é sempre um motivo de preocupação tipicamente durante a construção quando os contraventamentos laterais ainda não estão instalados. De qualquer forma, o comprimento destravado em geral alcançado pelos vãos destas vigas, são longos o suficiente para que a instabilidade ocorra. Todavia, o acréscimo substancial da resistência à flexão de tais membros devido ao aumento da altura oriundo de seu processo fabril em relação ao perfil matriz, aliada a economia de material e utilidade fim de serviço, garante a atratividade no aproveitamento destas, para grandes vãos junto aos projetistas. Não obstante, este aumento proporcional no comprimento dos vãos faz com que a instabilidade lateral ganhe importância especial. Neste contexto, o presente trabalho tem por objetivo desenvolver um modelo numérico que permita a realização de uma avaliação paramétrica a partir da calibração do modelo com resultados experimentais, efetuar a análise do comportamento de vigas casteladas e verificar seus mecanismos de falha, considerando comportamento elasto-plástico, além das não-linearidades geométricas. Também é objetivo deste trabalho, avaliar, quantificar e determinar a influência das diferenças geométricas características das vigas casteladas em relação às vigas maciças com as mesmas dimensões, analisando e descrevendo o comportamento estrutural destas vigas de aço para diversos comprimentos de vãos. A metodologia empregada para tal estudo baseou-se em uma análise paramétrica com o auxílio do método numérico dos elementos finitos.
Restrictions of space and height are often imposed to residential, commercial, industrial, warehouses and sheds with one, or several floors, due to aspects like regional regulations, technical, economic or aesthetic nature. In order to provide the passage of pipes and ducts with large diameter under steel girders, that normally requires great heights, sometimes leads to floors building highs with an unviable magnitudes. Several structural solutions can be used to overcome these obstacles, where the most popular are the beams with variable inertia (tapered and haunched beams), stub-girders, trusses, and beams with one or more web openings with various geometries. When castellated beams, structural solution studied and discussed in this dissertation, are considered stability issues at the construction stage becomes to attract the structural engineer attention since the lateral bracing are not yet installed. The unbraced span lengths generally reached by these beams are often long enough to cause instability effects. However, the substantial enhancement in the flexural strength of such members, due to the extra height coming from the manufacturing process in relation with the original profile, combined with the economy of material and utility services, ensures to the designers the attractiveness of this solution, especially when applied to large spans. On the other hand, this proportional increase in span lengths enhances the significance of improving the beam lateral instability resistance. The present investigation aims to develop a numerical model, that calibrated with experimental results, enables the development of a parametric analysis. This analysis aimed to determine the structural behavior of the castellated beams and their associated failure mechanisms, considering an elastic-plastic behavior as well the geometric non-linearities. The investigation was also able to evaluate, quantify and determine the influence of geometry variables like span lengths and cross sections dimensions. The methodology used for this study was developed based on a parametric analysis centred on the finite element method.

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Collins, Cristiana Kahl. « Study on the Effectiveness of Strain Counterstrain in the Treatment of Chronic Ankle Instability Resulting from a Lateral Ankle Sprain ». Thesis, NSUWorks, 2010. https://nsuworks.nova.edu/hpd_pt_stuetd/46.

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Purpose: To determine the effect of Strain Counterstrain (SCS) on strength, dynamic balance and subjective sense of instability in individuals with chronic ankle instability (CAI). Subjects: Twenty seven volunteers (17 females and 10 males) between the ages of 18 and 55 (mean ± SD age: 33.6 ± 8.8) with a history of CAI who met the inclusion/exclusion criteria were randomly assigned to the control group (n= 13) and the experimental group (n=14). Methods: All subjects signed an informed consent, completed a demographic questionnaire and the foot and ankle ability measure (FAAM), and underwent a standard evaluation, ankle isokinetic testing and the star excursion balance test (SEBT) at the onset of the study. All subjects participated in a home exercise program and received a SCS treatment or a sham treatment once a week. At four weeks all subjects repeated the initial testing and completed a global rating of change (GROC) form. The primary aim was examined with a 2-way analysis of variance (ANOVA) with the treatment group (SCS versus sham) as the between subjects independent variable and time (baseline and four weeks) as the within subjects independent variable. Results: A significant group-by-time interaction was found for seven directions in the SEBT (p< 0.031) while no significant interaction was found for ankle strength (p>0.76). For subjective measures, no significant group-by-time interaction was found for the FAAM (p>0.548), but the GROC revealed a significant difference (p=0.014) in the mean score for the experimental group (3.92 ± 1.66) when compared to the control group (2.43 ± 1.66). Conclusions: Although SCS does not appear to have an effect on strength and subjective ankle function in subjects with CAI, it appears that SCS can lead to an improvement in dynamic ankle stability and the subjective sense of ankle instability. Recommendations: Continued research on the effectiveness of SCS in CAI and other sprain injuries is needed to confirm the results of this study. Given the significant rate of ankle sprain recurrence in this population, long-term studies are necessary. Lastly, very little evidence exists on the effects of SCS and the theoretical framework of this technique.

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Rodrigues, Karina Aparecida [UNESP]. « A influência da fadiga nos músculos eversores durante a entorse lateral do tornozelo ». Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/134248.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A entorse do tornozelo em inversão e flexão plantar é uma das lesões mais comuns que ocorrem nas atividades de vida diária e no esporte. Embora os sintomas agudos possam se resolver rapidamente, muitos indivíduos relatam persistência de dor e instabilidade. Este tipo de lesão frequentemente acontece na fase final de um treino ou competição, e mesmo sabendo que a entorse é multifatorial, tal particularidade propicia estabelecer uma relação entre o evento da entorse e a fadiga. Diante disto, o presente estudo propõe analisar a latência e a intensidade de ativação dos músculos fibulares curto e longo em condições de fadiga, e ainda comparar indivíduos com estabilidade e instabilidade do tornozelo. Para esse fim, inicialmente foi desenvolvida uma plataforma simuladora da entorse em inversão e flexão plantar, na qual ambos os pés das voluntárias foram fixados e abaixo de onde se apoiava os pés foram acoplados transdutores de força, um de cada lado. Participaram do estudo 23 voluntárias do sexo feminino, fisicamente ativas, separadas em dois grupos: 11 fizeram parte do grupo estabilidade, não apresentavam histórico de lesão no complexo articular do tornozelo nos últimos 12 meses e outras 12 no grupo instabilidade funcional, classificadas pelo Questionário Cumberland Ankle Instability Tool. Para indução da fadiga, inicialmente foi registrada a Contração Isométrica Voluntária Máxima (CIVM) em eversão e flexão plantar. Durante a indução as voluntárias foram orientadas a manter 70% da CIVM. No momento em que a força aplicada fosse menor que 60% da CIVM o protocolo era interrompido e as voluntárias posicionadas em ortostatismo sobre a plataforma simuladora. Antes e após a fadiga foram realizadas dez simulações da entorse bilateralmente de forma randomizada e simultaneamente com o registro do sinal eletromiográfico. Assim, foi possível observar que após a fadiga não houve alteração da latência, no entanto ocorreu uma redução do nível de contração muscular, constatada pela diminuição da amplitude do sinal eletromiográfico. Ainda, não foram notadas diferenças entre os grupos estabilidade e instabilidade e verificouse maior atividade do músculo fibular curto quando comparado ao longo. Portanto, pôde-se concluir que o controle neuromuscular local ficou comprometido em situações de fadiga, devido à redução do nível de atividade dos músculos fibular longo e curto. Além disso, não foi possível observar diferença no comportamento muscular entre tornozelos estáveis e funcionalmente instáveis.
The inversion and plantar flexion ankle sprain is one of the most common injuries that occur in daily life activities and sports. Although acute symptoms can be resolved quickly, many people report persistent pain and instability. This type of injury often occurs in the final phase of a training or competition, and even though the sprain is multifactorial, such particularity provides the establishment of a relationship between the event sprain and fatigue. In this view, the present study aims to analyze the latency and activation intensity of the brevis and longus peroneus muscles in conditions of fatigue and also compare individuals with stability and instability of the ankle. For this purpose it was initially developed a simulated platform sprains in inversion and plantar flexion, in which both feet of the volunteers were fixed and below where rested his feet were coupled force transducers, one on each side. The study included 23 female volunteers, physically active, separated into two groups: 11 were part of the group stability, had no injury history in the joint complex of the ankle in the last 12 months and another 12 in functional instability group, classified by Cumberland Questionnaire Ankle Instability Tool. To induce fatigue, it was initially recorded a Contraction Isometric Maximal Voluntary (MVIC) in eversion and plantar flexion. During the induction, the participants were instructed to maintain 70% of the MVIC. At the time the force applied was below 60% of the MVIC the protocol was interrupted and the volunteers placed in standing position on the simulator platform. Before and after fatigue were held ten simulations sprain bilaterally randomly and simultaneously to record the electromyographic signal. Thus, it was observed that after the fatigue did not change the latency, but there was a reduction of muscle contraction level, evidenced by the reduction in amplitude of the electromyographic signal. Still, there were no noticeable differences between the groups stability and instability and there was a higher activity of the peroneus brevis compared to longus. Therefore, it was concluded that the local neuromuscular control was compromised in fatigue situations, due to reduced activity level of the peroneus longus and brevis muscles. Moreover, it was not possible to observe difference in muscle behavior between stable and unstable functionally ankles.

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Félix, Bautista Renato [Verfasser], et Joao [Akademischer Betreuer] Seco. « Monitoring of lateral positions of therapeuthic carbon-ion pencil beams using secondary ion tracking / Renato Félix Bautista ; Betreuer : Joao Seco ». Heidelberg : Universitätsbibliothek Heidelberg, 2021. http://d-nb.info/1236574311/34.

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Junior, José Wilson Serbino. « Comparação biomecânica do canto póstero-lateral do joelho com e sem reconstrução : estudo em cadáveres ». Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/5/5140/tde-06102007-110815/.

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O objetivo desta dissertação foi avaliar biomecanicamente o papel da aplicação de uma técnica cirúrgica utilizando os tendões dos músculos semitendíneo e grácil na reconstrução anatômica de lesão criada no canto póstero-lateral do joelho. Foram estudados 10 joelhos de cadáveres nas situações intacto, lesado, parcialmente reconstruído e reconstruído. As principais estruturas do canto póstero-lateral do joelho foram seccionadas para criar o padrão de lesão. Os momentos de força aplicados foram 2 N.m e 5 N.m, com o joelho a 0º, 30º, 60º ou 90º de flexão. Foi também calculada a rigidez do joelho em cada uma das situações nas diferentes posições testadas. Os ensaios foram realizados em dispositivo criado no Laboratório de Biomecânica LIM-41 da Faculdade de Medicina da USP, e os dados de deformação angular foram obtidos através de programa de fotogoniometria. Os resultados obtidos foram submetidos a análise estatística pela Análise de Variância para Experimento em Blocos Aleatorizados e os tratamentos foram comparados entre si pelo método de Scheffé. Foi possível concluir que: 1) A técnica empregada não corrigiu completamente o aumento da rotação externa. 2)A técnica empregada restaurou a estabilidade em varo.
The purpose of this study was to evaluate the application of a surgical technique for anatomical reconstruction of the structures from the posterolateral corner of the knee. We tested 10 cadaver knees with intact, ruptured, partially reconstructed and reconstructed ligaments. The main posterolatreal structures were cut to produce a lesion pattern. The applied force moments were of 2 N.m and 5 N.m with the knee flexed to 0, 30, 60 and 90 degrees. The stiffness of the knee in each of these situations at the studied angles was also determined. The assays were carried through in a device created at the Laboratory of Biomechanics LIM-41 from of the University of São Paulo School of Medicine. Data from the angular deformation were obtained through a photographic measurement aided by computer software. The results were submitted to ANOVA and the treatments had been compared using statistical method of Scheffé. It was possible to conclude that: 1) The technique employed wasn?t able to restore normal external rotation. 2) The technique employed restored varus stability.

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Payne, Brigid. « Lateral instability and its effect on Atlantic salmon (Salmo salar) habitat in the wandering gravel-bed Rivière Nouvelle, Baie des Chaleurs, Québec ». Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23930.

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Lateral instability exerts considerable influence on the sedimentology, planform, and hydraulic characteristics of gravel-bed rivers. Because Atlantic salmon (Salmo salar) tolerate a narrow range of depths, velocities and substrate sizes, the quality and quantity of habitat available to salmon should vary with level of river instability. In the Riviere Nouvelle, a Gaspe river destabilized by deforestation and past channelization projects, the effect of lateral instability on habitat was variable. Fines content in riffle substrates did not show a significant relationship to local bank erosion rates, even where the rate was as high as 10 myr$ sp{-1}$ and the proportion of fines entering the channel was much higher than that found in riffles substrates (an excess of fines in potential spawning riffles reduces spawning success among salmonids). For juveniles, availability of hydraulically suitable habitat was largest where lateral instability resulted in aggradation of the river bed and development of a braided pattern. Hydraulic habitat availability was lowest where erosion patterns led to high planform curvature levels and to scouring of bed materials. In general, because of the relatively high power of the Riviere Nouvelle, structures or processes leading to diminishment of depths or velocities (e.g. aggradation) resulted in an increase in the amount of juvenile habitat available.

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Fruchtengarten, Jairo. « Sobre o estudo da flambagem lateral de vigas de aço por meio da utilização de uma teoria não-linear geometricamente exata ». Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/3/3144/tde-10102005-222432/.

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O valor do momento crítico à flambagem lateral de vigas em regime elástico-linear é geralmente obtido na literatura técnica por meio de teorias aproximadas e definido apenas para alguns casos usuais. Entretanto, a utilização de modernas técnicas computacionais permite que o estudo da flambagem lateral não fique restrito apenas a esses casos. O objetivo deste trabalho é determinar o valor do momento crítico de vigas de aço em regime elástico-linear para diversos casos de carregamento e de vinculação, por meio de uma Teoria Não-Linear Geometricamente Exata. Estes resultados são comparados aos obtidos com o emprego de expressões baseadas em teorias aproximadas, em particular as normas de projeto NBR8800:1986, prAISC-LRFD:2003, prEN1993-1-1:2002 Stage 54 e prEN1999-1-1:2004 Stage 54. Com o emprego do programa de elementos finitos PEFSYS, realiza-se, para vigas tipo I bissimétricas, uma análise paramétrica que incorpora a faixa usual de utilização destas vigas em projetos usuais de edifícios. Estuda-se a influência da restrição ao empenamento e à rotação no plano ortogonal ao da flexão para quatro condições de vinculo nas extremidades da viga. Consideram-se ainda alguns casos adicionais, como carga aplicada fora do centro de torção e vínculos ao longo do vão, para mostrar o potencial do método de análise utilizado.
The elastic lateral buckling moment is generally obtained in technical literature by means of approximated theories, and defined just for some common cases. However, the use of recent computational techniques allows that lateral-torsional bucklings study doesnt remain restricted to this few cases. The intend of this work is to establish accurate values for the elastic critical moment of steel beams in several cases of loading and end-restraint, using a Geometrically Exact Nonlinear Theory. This results are compared with the ones derived from approximate theories, in particular, Brazilian code NBR8800:1986, American Specification prAISC-LRFD:2003, and European Prestandards prEN1993-1-1:2002 Stage 54 and prEN1999-1-1:2004 Stage 54. A parametrical analysis is performed for doubly-symmetric I-beams using the finite element program PEFSYS for usual range in conventional structures. The influence of warping and lateral rotation restraints is studied for four idealized support conditions. Some other cases, like transverse load applied above and below shear center and presence of bracings along the span, are accounted of to corroborate the validity and the powerful of this procedure.

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Wanniarachchi, Somadasa. « Flexural behaviour and design of cold-formed steel beams with rectangular hollow flanges ». Queensland University of Technology, 2005. http://eprints.qut.edu.au/29810/.

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Until recently, the hot-rolled steel members have been recognized as the most popular and widely used steel group, but in recent times, the use of cold-formed high strength steel members has rapidly increased. However, the structural behavior of light gauge high strength cold-formed steel members characterized by various buckling modes is not yet fully understood. The current cold-formed steel sections such as C- and Z-sections are commonly used because of their simple forming procedures and easy connections, but they suffer from certain buckling modes. It is therefore important that these buckling modes are either delayed or eliminated to increase the ultimate capacity of these members. This research is therefore aimed at developing a new cold-formed steel beam with two torsionally rigid rectangular hollow flanges and a slender web formed using intermittent screw fastening to enhance the flexural capacity while maintaining a minimum fabrication cost. This thesis describes a detailed investigation into the structural behavior of this new Rectangular Hollow Flange Beam (RHFB), subjected to flexural action The first phase of this research included experimental investigations using thirty full scale lateral buckling tests and twenty two section moment capacity tests using specially designed test rigs to simulate the required loading and support conditions. A detailed description of the experimental methods, RHFB failure modes including local, lateral distortional and lateral torsional buckling modes, and moment capacity results is presented. A comparison of experimental results with the predictions from the current design rules and other design methods is also given. The second phase of this research involved a methodical and comprehensive investigation aimed at widening the scope of finite element analysis to investigate the buckling and ultimate failure behaviours of RHFBs subjected to flexural actions. Accurate finite element models simulating the physical conditions of both lateral buckling and section moment capacity tests were developed. Comparison of experimental and finite element analysis results showed that the buckling and ultimate failure behaviour of RHFBs can be simulated well using appropriate finite element models. Finite element models simulating ideal simply supported boundary conditions and a uniform moment loading were also developed in order to use in a detailed parametric study. The parametric study results were used to review the current design rules and to develop new design formulae for RHFBs subjected to local, lateral distortional and lateral torsional buckling effects. Finite element analysis results indicate that the discontinuity due to screw fastening has a noticeable influence only for members in the intermediate slenderness region. Investigations into different combinations of thicknesses in the flange and web indicate that increasing the flange thickness is more effective than web thickness in enhancing the flexural capacity of RHFBs. The current steel design standards, AS 4100 (1998) and AS/NZS 4600 (1996) are found sufficient to predict the section moment capacity of RHFBs. However, the results indicate that the AS/NZS 4600 is more accurate for slender sections whereas AS 4100 is more accurate for compact sections. The finite element analysis results further indicate that the current design rules given in AS/NZS 4600 is adequate in predicting the member moment capacity of RHFBs subject to lateral torsional buckling effects. However, they were inadequate in predicting the capacities of RHFBs subject to lateral distortional buckling effects. This thesis has therefore developed a new design formula to predict the lateral distortional buckling strength of RHFBs. Overall, this thesis has demonstrated that the innovative RHFB sections can perform well as economically and structurally efficient flexural members. Structural engineers and designers should make use of the new design rules and the validated existing design rules to design the most optimum RHFB sections depending on the type of applications. Intermittent screw fastening method has also been shown to be structurally adequate that also minimises the fabrication cost. Product manufacturers and builders should be able to make use of this in their applications.

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Porfiri, Maurizio. « Analysis by Meshless Local Petrov-Galerkin Method of Material Discontinuities, Pull-in Instability in MEMS, Vibrations of Cracked Beams, and Finite Deformations of Rubberlike Materials ». Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27420.

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The Meshless Local Petrov-Galerkin (MLPG) method has been employed to analyze the following linear and nonlinear solid mechanics problems: free and forced vibrations of a segmented bar and a cracked beam, pull-in instability of an electrostatically actuated microbeam, and plane strain deformations of incompressible hyperelastic materials. The Moving Least Squares (MLS) approximation is used to generate basis functions for the trial solution, and for the test functions. Local symmetric weak formulations are derived, and the displacement boundary conditions are enforced by the method of Lagrange multipliers. Three different techniques are employed to enforce continuity conditions at the material interfaces: Lagrange multipliers, jump functions, and MLS basis functions with discontinuous derivatives. For the electromechanical problem, the pull-in voltage and the corresponding deflection are extracted by combining the MLPG method with the displacement iteration pull-in extraction algorithm. The analysis of large deformations of incompressible hyperelastic materials is performed by using a mixed pressure-displacement formulation. For every problem studied, computed results are found to compare well with those obtained either analytically or by the Finite Element Method (FEM). For the same accuracy, the MLPG method requires fewer nodes but more CPU time than the FEM.
Ph. D.

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Bower, Owen J. « Analytical Investigation into the Effect of Axial Restraint on the Stiffness and Ductility of Diagonally Reinforced Concrete Coupling Beams ». University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1211065883.

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Thèses sur le sujet « Lateral instability of beams »

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