Dissertations / Theses: 'Non-structural element'

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Wong, Fuk-Lun Alexander. "Investigations into non-destructive methods of structural testing using finite element models." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/11956.

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Ahmed, Khaled I. E. "Finite element modeling of non-linear structural response of transmission towers including bolted joint slippage." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31507.

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Slippage of bolted joints plays an important role in the behavior of transmission tower structures under various loading. Two main types of bolted joints are commonly used in towers; column-to-column and beam-to-column joints. The effect of slippage of the bolted joints on the behavior of transmission towers was previously analyzed using two approximate models; instantaneous and continuous joint slippage models. The previously proposed models of joint slippage implied that joint slippage has little effect on a transmission tower load carrying capacity. These models have also shown that deflections of towers due to slippage are very small compared to the overall deformation. These studies have considered on)y beam-to-column joints, ignoring column-to-column joints. The previous models based on the above assumptions and models based on rigid joint behavior were not able to capture the response of transmission towers under considerable differential settlements caused by frost heave. In this thesis, two common bolted joint types used in transmission tower structure are analyzed and discussed based on a series of full-size tower joint experiments conducted at the University of Manitoba. It is observed that joints stiffness properties such as equivalent modulus of elasticity, yield strength and fracture strength are much lower than that of the connected members. The experimental results also show that previously reported instantaneous and continuous joint slippage models do not accurately simulate the behavior of bolted joints. Two finite element models are proposed in this thesis to simulate the slippage of the two main joint types; column-to-column (type-A joints) and beam-to-column (type-C joints). Stiffness matrices of the new joint finite elements are established with the aid of the experimental data. An elastic geometrically nonlinear finite element code is developed using Fortran 90 to analyze the 3-D response of transmission tower structures taking into account the effect of joint slippage. A graphical user interface based on Visual Basic is attached to the finite element code to allow practicing engineers to input all data, build the tower finite element model and display the tower response in an efficient and convenient manner. The response of a 2-D tower substructure and a 3-D full-scale tower used by Manitoba Hydro is analyzed by using the finite element code. The numerical study shows that slippage of beam-to-column and column-to-column joints have significant effects on the tower load carrying capacity. Column-to-column joint slippage shows the most significant impact on the transmission tower behavior by either reducing the tower load carrying capacity or significantly increasing the tower deflection under working loads. On the other hand, joint slippage has a positive effect on the tower response under frost heave induced displacements as substantial redistribution of tower member forces takes place due to joint slippage and actual member forces are much lower than those predicted by standard structural analysis software based on the rigid joint assumption or simplified slippage models.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

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Chagneau, Anthony. "Méthode de zoom structural étendue aux hétérogénéités non linéaires." Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTS051.

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Une approche multi-échelle introduit une méthode de zoom structural dans une zone d’intérêt, appelé le patch, utilisant uniquement des opérateurs de projection de champs. Les différents comportements dans le patch et dans la structure globale sont pris en compte sans utiliser des paramètres de poids entre énergies locales et globales comme la méthode Arlequin. Notre problème initial est de fiabiliser numériquement la méthode de zoom structural pour le cas linéaire, et plus précisément de choisir un solveur performant sur les espaces de Krylov, ainsi qu’un préconditionnement et une rénumérotation efficaces et adaptés au système à résoudre. Une fois le solveur choisi, cette approche est validée mécanique sur deux essais, un de traction et l’autre de cisaillement. Une étude paramétrique sur le patch est effectué afin d’obtenir une solution acceptable. L’objectif suivant est d’étendre cette approche à des régions comportant des hétérogénéités à comportement non linéaire. On s’est intéressé au comportement élastoplastique. L’hypothèse de départ est de considérer le comportement élastoplastique uniquement à l’intérieur du patch et un comportement élastique sur la structure globale ainsi que sur la zone de raccord. On valide ensuite cette approche avec différents essais comprenant plusieurs défauts et donc plusieurs patchs ainsi que des histoire de chargement différents
A multi-scale approach introduces a structural zoom method into a region of interest, called the patch, using only field projection operators. The different behaviours in the patch and in the overall structure are taken into account without using weight parameters between local and global energies such as the Arlequin method. Our initial problem is to digitally reliable the structural zoom method for the linear case, and more precisely to choose a high-performance solver on Krylov spaces, as well as effective preconditioning and ordering adapted to the system to be solved. Once the solver is chosen, this approach is mechanically validated in the mean of two tests, namely traction and shear. A parametric study of the patch is performed to obtain an acceptable solution. The next objective is to extend this approach to regions with heterogeneities of non-linear behaviour. The method has been reached out for elastoplastic behaviour. Initial hypothesis assumes the elastoplastic behaviour only inside the patch and an elastic behaviour of the overall structure as well as of the gluing area. Finally, this approach is validated with different tests including several faults and therefore several patches as well as different loading history

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Aragao, Almeida Salvio Jr. "Modeling of Concrete Anchors Supporting Non-Structural Components Subjected toStrong Wind and Adverse Environmental Conditions." University of Toledo / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564764404011142.

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Ferrari, Rosalba (ORCID:0000-0002-3989-713X). "An elastoplastic finite element formulation for the structural analysis of Truss frames with application to ha historical iron arch bridge." Doctoral thesis, Università degli studi di Bergamo, 2013. http://hdl.handle.net/10446/28959.

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This doctoral thesis presents a structural analysis of the Paderno d’Adda Bridge, an impressive iron arch viaduct built in 1889 and located in Lombardia region (Italy). The thesis falls in the context of a research activity started at University of Bergamo since 2005, that is still ongoing and aims to perform an evaluation of the present state of conservation of the bridge. In fact, the bridge is currently still in service and its important position in the context of transport network will soon lead to questions about its future destination, with particular attention to the evaluation of the residual performance capacity. To this end, an inelastic structural analysis of the Paderno d’Adda bridge has been performed, up to failure. This analysis has been conducted through an autonomous computer code of a 3D frame structure that runs in the MATLAB environment and has been developed within the classical frame of Limit Analysis and Theory of Plasticity. The algorithm has been developed applying the “exact” and stepwise holonomic step-by-step analysis method. It has shown very much able to track the limit structural behaviour of the bridge, by reaching convergence with smooth runs up to the true limit load and corresponding collapse displacements. The main characteristic ingredients of its elastoplastic FEM formulation are: beam finite elements; perfectly plastic joints (as an extension of classical plastic hinges); piece-wise linear yield domains; “exact” time integration. In the algorithm, the following original features have been implemented: treatment of mutual connections by static condensation and Gaussian elimination; determination of the tangent stiffness formulation through Gaussian elimination. These peculiar contributions are presented in detail in this thesis.

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Guney, Murat Efe. "A Numerical Procedure For The Nonlinear Analysis Of Reinforced Concrete Frames With Infill Walls." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606318/index.pdf.

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Materially non-linear analysis of reinforced concrete frame structures with infill walls requires appropriate mathematical models to be adopted for the beams and the columns as well as the infill walls. This study presents a mathematical model for frame elements based on a 3D Hermitian beam/column finite element and an equivalent strut model for the infill walls. The spread-of-plasticity approach is employed to model the material nonlinearity of the frame elements. The cross-section of the frame element is divided into triangular sub regions to evaluate the stiffness properties and the response of the element cross-section. By the help of the triangles spread over the actual area of the section, the bi-axial bending and the axial deformations are coupled in the inelastic range. A frame super-element is also formed by combining a number of frame finite elements. Two identical compression-only diagonal struts are used for modeling the infill. The equivalent geometric and material properties of the struts are determined from the geometry of the infill and the strength of the masonry units A computer code is developed using the object-oriented design paradigm and the models are implemented into this code. Efficiency and the effectiveness of the models are investigated for various cases by comparing the numerical response predictions produced by the program with those obtained from experimental studies.

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Matthews, Russell Stuart. "The structural behaviour of brick sewer pipes in soft ground : the examination of brick and reinforced plastic pipes, in granular soil, and under plane strain conditions, using fully non-linear finite element models and a large-scale physical testing prog." Thesis, University of Bradford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287758.

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Saadé, Katy. "Finite element modeling of shear in thin walled beams with a single warping function." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211043.

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The considerable progress in the research and development of thin-walled beam structures responds to their growing use in engineering construction and to their increased need for efficiency in strength and cost. The result is a structure that exhibits large shear strains and important non uniform warping under different loadings, such as non uniform torsion, shear bending and distortion.

A unified approach is formulated in this thesis for 3D thin walled beam structures with arbitrary profile geometries, loading cases and boundary conditions. A single warping function, defined by a linear combination of longitudinal displacements at cross sectional nodes (derived from Prokic work), is enhanced and adapted in order to qualitatively and quantitatively reflect and capture the nature of a widest possible range of behaviors. Constraints are prescribed at the kinematics level in order to enable the study of arbitrary cross sections for general loading. This approach, differing from most published theories, has the advantage of enabling the study of arbitrary cross sections (closed/opened or mixed) without any restrictions or distinctions related to the geometry of the profile. It generates automatic data and characteristic computations from a kinematical discretization prescribed by the profile geometry. The amount of shear bending, torsional and distortional warping and the magnitude of the shear correction factor is computed for arbitrary profile geometries with this single formulation.

The proposed formulation is compared to existing theories with respect to the main assumptions and restrictions. The variation of the location of the torsional center, distortional centers and distortional rotational ratio of a profile is discussed in terms of their dependency on the loading cases and on the boundary conditions.

A 3D beam finite element model is developed and validated with several numerical applications. The displacements, rotations, amount of warping, normal and shear stresses are compared with reference solutions for general loading cases involving stretching, bending, torsion and/or distortion. Some examples concern the case of beam assemblies with different shaped profiles where the connection type determines the nature of the warping transmission. Other analyses –for which the straightness assumption of Timoshenko theory is relaxed– investigate shear deformation effects on the deflection of short and thin beams by varying the aspect ratio of the beam. Further applications identify the cross sectional distortion and highlight the importance of the distortion on the stresses when compared to bending and torsion even in simple loading cases.

Finally, a non linear finite element based on the updated lagrangian formulation is developed by including torsional warping degrees of freedom. An incremental iterative method using the arc length and the Newton-Raphson methods is used to solve the non linear problem. Examples are given to study the flexural, torsional, flexural torsional and lateral torsional buckling problems for which a coupling between the variables describing the flexural and the torsional degrees of freedom occurs. The finite element results are compared to analytical solutions based on different warping functions and commonly used in linear stability for elastic structures having insufficient lateral or torsional stiffnesses that cause an out of plane buckling.

Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished

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Yaqoob, Saima. "BRIDGE EDGE BEAM : NON-LINEAR ANALYSIS OF REINFORCEDCONCRETE OVERHANG SLAB BY FINITEELEMENT METHOD." Thesis, KTH, Bro- och stålbyggnad, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-222806.

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Bridge edge beam system is an increasing concern in Sweden. Because it is the mostvisible part of the structure which is subjected to harsh weather. The edge beamcontributes to the stiffness of overhang slab and helps to distribute the concentratedload. The design of edge beam is not only affected by the structural members, but it isalso affected by non-structural members.The aim of the thesis is to investigate the influence of edge beam on the structuralbehavior of reinforced concrete overhang slab. A three-dimensional (3D) non-linearfinite element model is developed by using the commercial software ABAQUS version6.1.14. The load displacement curves and failure modes were observed. The bendingmoment and shear capacity of the cantilever slab is studied.The validated model from non-linear analysis of reinforced concrete slab gives morestiffer result and leads to the high value of load capacity when comparing with theexperimental test. The presence of the edge beam in the overhang slab of length 2.4 mslightly increases the load capacity and shows ductile behavior due to the self-weightof the edge beam. The non-linear FE-analysis of overhang slab of length 10 m leads tomuch higher load capacity and gives stiffer response as compare to the overhang slabof 2.4 m. The presence of the edge beam in the overhang slab of length 10 m giveshigher load capacity and shows stiffer response when comparing with the overhangslab of length 10 m. This might be due to the self-weight of the edge beam and theoverhang slab is restrained at the right side of the slab.

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Nogueira, Caio Gorla. "Um modelo de confiabilidade e otimização aplicado às estruturas de barras de concreto armado." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-21092005-084457/.

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Neste trabalho, é apresentado um modelo de otimização acoplado à confiabilidade para a análise de estruturas de barras de concreto armado, de modo que a confiabilidade é adicionada ao processo de otimização como uma restrição. O modelo mecânico permite a consideração da não-linearidade física para o concreto e para o aço, além de levar em conta os efeitos não-lineares geométricos. Esse modelo é utilizado para gerar as respostas mecânicas da estrutura, traduzidas em forma de cargas últimas para os estados limites. Os cenários de falha, na análise probabilística, são descritos pelo esmagamento do concreto e deformação excessiva da armadura para o estado limite último. O estado limite de utilização é verificado para o caso de deslocamentos excessivos dos pontos da estrutura. A função de estado limite é construída com o emprego do método das superfícies de respostas para a determinação do índice de confiabilidade e probabilidade de falha considerando somente o modo mais provável ou primeiro modo de falha. Os processos de otimização e confiabilidade são acoplados de maneira independente gerando um sistema de equações aproximadas resolvido analiticamente. A metodologia de otimização empregada é a minimização da função de custo da estrutura. O modelo acoplado de otimização e confiabilidade é empregado para análise de vigas de concreto armado. As técnicas desenvolvidas, no âmbito da modelagem de estruturas e confiabilidade, também permitem a análise mecânico-probabilística de pórticos planos de concreto armado
In this work, a reliability based optimization model is proposed for the analysis of reinforced concrete structures, in which the reliability index is introduced as a constraint. The mechanical model allows to consider the physical non-linearity of the concrete and steel materials, as well as the geometrical non-linear effects. The mechanical model is used to find the structure limit loads. The failure scenarios for the probabilistic analysis are characterized by the concrete ultimate strains in the compressed region of the section and the steel ultimate tensile strains in the reinforcement position. The serviceability limit state is verified for the excessive displacements for the structure bars. The limit state function is build by using the response surface method, computing the reliability index and the failure probability only considering the first failure mode. The optimization and reliability processes are independents built leading two different system of equations that are coupled together to find the final solution. The material cost of the structure was adopted as the objective function to be minimized for the optimization process. The proposed coupled optimization-reliability process is employed to analyse reinforced concrete beams. The developed procedure in the context of reliabilty methods and reinforced concrete structures analysis can also be applied for reliability analysis of reinforced concrete frames

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Neves, Rodrigo de Azevêdo. "Desenvolvimento de modelos mecânico-probabilísticos para estruturas de pavimentos de edifícios." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-13042005-081959/.

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Neste trabalho, são desenvolvidas novas técnicas aproximadas de análise de confiabilidade para grelhas de concreto armado levando-se em consideração as probabilidades de falha de vários modos importantes. Realiza-se um acoplamento entre os métodos de Monte Carlo, elementos finitos e procedimentos de otimização para considerar esses modos de falha importantes e classificá-los. Esse acoplamento também permite a redução do número de chamadas ao modelo de elementos finitos. Os cenários de falha são caracterizados como o encurtamento excessivo do concreto e o alongamento do aço. Estes cenários determinam a capacidade última da estrutura, e podem ser representados por um coeficiente escalar que multiplica todas as ações presentes na estrutura. Para a determinação desses estados estruturais últimos, um procedimento incremental-iterativo é utilizado. A análise de confiabilidade é realizada em diferentes conjuntos de realizações aleatórias das variáveis de projeto. O conjunto de respostas estruturais e de realizações permite a determinação dos coeficientes da superfície de respostas da estrutura. O acoplamento realizado permite também o tratamento com estruturas de concreto com elevado número de modos de falha. Aplicam-se as técnicas em exemplos de grelhas de concreto armado
In this work, new local approaches of reliability analysis applied to reinforced concrete grid structures are developed, taking into account several critical cross-section failure probabilities. Monte Carlo simulations are coupled with finite element analyses and optimization techniques with techniques to take into account the failure in the most important cross-sections, in order to classify the severity of failure modes. The failure scenario is depicted when either a concrete fiber or a steel bar reaches the predefined conventional limit. This scenario gives the structural ultimate capacity, which can be represented by a scalar coefficient multiplying all the loads acting on the structure. To achieve the failure scenario, an incremental and iterative procedure is used. To carry out the reliability analysis, the mechanical analysis has to be performed for different sets of random variable realizations of the mechanical, material and geometrical properties. The set of ultimate coefficients obtained from several mechanical analyses defines the response surface. The coupling between Monte Carlo simulations and response surface techniques applied in this work aims to reduce significantly the number of the finite element model calls, and hence to deal with real, or high-scale, reinforced concrete grids where large number of failure components can be found. The proposed procedure is then applied to reinforced concrete grids in order to show some more complex reinforced concrete examples

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Bennett, Terry. "Finite element-based non-linear dynamic soil-structure interaction." Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/14472/.

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The modelling of unbounded domains is an important consideration in many engineering problems, for example in fluid flow, electro-magnetics, acoustics and solid mechanics. This thesis focuses on the problem of modelling elastic solids to infinity, with the specific purpose of modelling dynamic soil-structure interaction (DSSI). However, the reader should be aware that the techniques presented may also be adapted to address those other physical phenomena. The need for techniques to model the soil domain to infinity and a qualitative introduction into the problems associated with dynamic soil-structure interaction are outlined in chapter 1. This is done to illustrate why such an abstract mathematical concept of modelling infinite domains has an important role to play within the design process of large, safety critical, civil engineering structures. A brief review of a number of alternative ways of addressing this problem is given in chapter 2. Their relative strengths and weaknesses along with the typical applicability of the techniques is discussed. A consequence of this review is the identification of a very promising rigorous approach [59] which is singled-out for further study. A detailed explanation of this (Consistent Infinitesimal Finite Element Cell Method, CIFECM) method is then given in chapter 3. Attention is restricted to the use of the technique for solving the 3-D vector wave equation in the time domain. The features of the non-linear dynamic finite element code, into which the CIFECM has been incorporated, is highlighted in chapter 4. The non-linear (microplane) material model for quasi-brittle materials is described along with the solution strategy employed. It should be mentioned that the soil is treated within this thesis as drained linear elastic medium. The method of coupling the CIFECM into the dynamic equation of force equilibrium for both directly applied and transmitted loading regimes is detailed. Application of the code follows in chapter 5; firstly by introducing the simplest test problem of one finite element coupled with one CIFECM element to model a surface foundation. Comparisons are made between the dynamic displacements resulting from the method and standard FE solutions obtained from the use of extended meshes and fixed boundary conditions, along with a study of the influence input variables. Following these examples a larger (more realistic) engineering problem is tacked involving the simulation of an aircraft impact on a reinforced concrete nuclear containment vessel. This represents the first use of the method in a 3-D nonlinear structural analysis problem. The results illustrate the practical implications of including DSSI in the analysis. III In chapter 6, a series of general observations on the method are made with an assessment of its value together with a discussion on its wider application to other engineering fields. Possible future developments to make the method more computationally efficient are finally suggested.

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Attabi, Mohamed Mohamed Hussein. "La fissuration dans les systemes en beton precontraint." Paris 6, 1987. http://www.theses.fr/1987PA066246.

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Etude experimentale et theorique du comportement d'une membrure tendue de poutre soumise a flexion, pour determiner l'effet global de la combinaison dans un meme element d'armatures classiques et d'armatures precontraintes (precontrainte partielle), ces dernieres etant post-tendues, avec ou sans adherence, ou pretendues. Etude experimentale de l'adherence en fonction de la fissuration, et modelisation par elements finis en conditions planes

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Saab, Hassan A. "Non-linear finite element analysis of steel frames in fire conditions." Thesis, University of Sheffield, 1990. http://etheses.whiterose.ac.uk/1868/.

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The present work is concerned with the development of a finite element approach and its subsequent use for behavioural studies on steel frames in fire conditions. The nonlinear structural analysis is based on a tangent stiffness formulation using large deformation theory. Deterioration in material strength and stiffness at increasing temperature is represented by a set of nonlinear stress-straintemperature relationships using a Ramberg-Osgood equation in which creep effects are implicitly included. The clearly nonlinear form of steel material properties at elevated temperatures is better represented as a set of continuous stressstrain relationship than in a bilinear form although provision is made for any form of relationship to be included. Structures subject to increasing loads or temperatures are analysed using an incremental Newton-Raphson iterative procedure. The analysis permits collapse load or critical temperature to be calculated at a specified temperature or load level respectively, and provides a complete load-deformation and temperature-deformation history for two-dimensional multistorey steel frames. A nonlinear method of frame analysis, based on largedeformation theory, has been used which includes the effect of geometric nonlinearity, temperature-dependent nonlinear material behaviour and variation in temperature distribution both along and across the section. The effects of thermal strains, residual stresses and thermal bowing are also included and different values of the elastic stiffnesses of the support conditions can be considered. A beam element with two nodes and three degrees of freedom at each node is used in the analysis. Gradual penetration of yielding through the cross-section is accounted for using the transformed area approach. The validity of this method is tested by comparing with experimental and analytical data covering as wide a range of problem parameters as possible. The comparisons show good agreement with this data. The method has been used to study a number of aspects of frame behaviour in fire. The influence of slenderness ratio, stress-strain representation and material models, various forms of protection, magnitude of residual stress and thermal gradient along and across the section of a frame are investigated. An approximate curve based on statistical analysis of the derived results is suggested as a simple means of predicting the critical temperature or collapse load of a uniformly heated steel frame. Further examples are presented which illustrate the special form of moment redistribution that occurs at elevated temperatures for frames that contain partially heated elements. Finally, general conclusions and recommendations for future work are presented.

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Ryckelynck, David. "Sur l'analyse des structures viscoplastiques : stratégie adaptative et contrôle de qualité." Cachan, Ecole normale supérieure, 1998. http://www.theses.fr/1998DENS0003.

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Ce mémoire concerne le calcul automatique de problèmes non-linéaires d'évolution et traite en particulier des structures à comportement viscoplastiques. Un contrôle adaptatif des approximations numériques permet d'effectuer une simulation de ces problèmes en respectant une qualité fixée. Ce type de simulation est fait à l'aide de calculs itératifs. Nous proposons une stratégie de calcul adaptatif qui permet d'ajuster l'effort numérique d'une itération à l'autre, lors de l'élaboration de la solution. La résolution est initialisée par un calcul élastique grossier défini sur tout le domaine d'étude (en temps et en espace). Puis, la représentation en temps et en espace est affinée au fur et à mesure que la description des non-linéarités s'améliore. Les gains en temps de calcul sont considérables. La strategie fournit un résultat plus rapidement qu'un calcul classique pour obtenir une solution de qualité comparable. Or d'une part, la strategie proposée construit des approximations adaptées et d'autre part, le calcul classique est assimilable à un calcul d'expert qui connait a priori des approximations adéquates pour le problème étudié. Cette stratégie est bâtie sur un algorithme de résolution issu de la méthode à grand incrément de temps et sur une méthode de contrôle d'erreur en relation de comportement. Un algorithme spécifique a été développé. Facile à programmer, il permet de traiter de façon robuste les zones fortement plastiques. Des indicateurs d'erreurs sont proposes afin de permettre une adaptation efficace des approximations quel que soit le niveau des différentes sources d'erreur.

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Kurniawan, Cyrilus Winatama. "Flexural behaviour and design of the new LiteSteel beams." Thesis, Queensland University of Technology, 2007. https://eprints.qut.edu.au/16674/1/Cyrilus_Kurniawan_Thesis.pdf.

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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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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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Gaiotti, Regina. "Interactive effects of non-structural elements on the behaviour of tall building structures." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39225.

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The lateral stiffening effects of cladding and partition walls, which are usually unaccounted for in a building structure's design, are investigated in this research project. Direct and iterative, linear elastic finite element analyses of representative modules of these components and their supporting primary structure were performed. These were used to study their general lateral load behaviour, and to establish their modes of interaction and induced forces. As a result, new and practical analogous strut models have been devised to allow their incorporation in, and the analysis of, the total building structure. The strut models permitted the effects of the non-structural elements' interaction on the static and dynamic responses of tall building structures to be studied. The ultimate objective of this work has been to contribute towards the development of new procedures of analysis and design of building structures braced by precast concrete cladding panels and non-loadbearing concrete blockwork walls.

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Young, Kuao-John. "A unified approach to the formulation of non-consistent rod and beam mass matrices for improved finite element modal analysis." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-07282008-135633/.

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Vasudevan, S. "Development of new spatially curved non-linear frame finite element using a mixed variational principle and rotations as independent variables." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/13069.

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21

Abate, Marco. "Seismic Behaviour of Post-Installed Anchors: Non-Structural Components and Art Objects Fastening." Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424126.

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The damage observation in recent seismic events (L’Aquila 2009, Chile 2010, Christchurch 2011, Tohoku 2011, Emilia 2012) helps in the identification of the critical aspects related to the response to earthquake of non-structural components (Miranda et al. 2012). Generally these elements are included in buildings and may belong to the architectural system, to the utility system or to the building content. The failure of the non-structural components can represent a significant danger for life safety and leads to relevant economic losses and this also contributes in amounting to a severe impact for the society (Miranda et al. 2012). This thesis contains the results of an experimental campaign which had the aim of evaluating different typologies of post-installed anchors under seismic actions. The mentioned topic is considered of importance for the central role of these devices in anchoring non-structural elements in order to avoid failures and damages which can cause danger for life safety, huge economic loss and lack of functionality in a building after an earthquake occurs. (Taghavi and Miranda 2003; ATC 69 2008). During an earthquake the non-structural components should withstand to relevant inertial forces, transferred through the connection to the structural elements (beams, slabs, columns, walls) or often to other non-structural elements, such as infill walls. In many cases those connections are realized by means of post-installed anchors which should be designed properly in order to ensure a good behaviour to the seismic actions (Makris and Black 2001; Naumoski et al. 2002; Solomos and Berra 2006; Hoehler et al. 2011). Among all the requirements the reliability in terms of failure modes and strength of post-installed anchors results to be fundamental to obtain a valid design in the dynamic field. For instance the design of fire protection systems in schools, medical equipment in hospitals, masterpieces displayed in museums need an in-depth knowledge on the performance of anchors to use. Such knowledge should cover both the resistance for life safety limit state and the admissible displacements that allow the element functionality for serviceability limit state. The purpose of the experimental campaign presented within this research is to study the seismic behaviour of various anchoring systems through shaking table tests. Two cross-shaped structures were built at full scale, one consisted of concrete walls and one of a RC framed structure with masonry infill panels. Two different conditions were investigated in the case of fasteners installed in concrete, namely non-cracked and cracked support. Poroton® hollow bricks were used to build the specimen with masonry infill walls. Tri-axial shaking table tests were designed on the basis of the standard AC156 (2010) which provides a test setup for the seismic certification of non-structural components by shaking table tests. The experiments were realized by subsequent signals scaled at a growing ZPA (Zero Period Acceleration) to study the effects induced on the specimens at increasing seismic intensity. The results allowed the overall seismic behaviour of each fastening element to be investigated, especially in terms of failure mode, maximum sustained acceleration and anchor slippage from support. The influence of cracks on these aspects was also deepened for the concrete structural unit. The test plan also allowed a complete comparison among different anchoring methodologies, such as mechanical, chemical and undercut anchors. Some recent studies (Rieder 2009; Watkins 2011; Mahrenholtz et al. 2012) focused on the seismic assessment of metal anchors in concrete by means of shake-table testing, whereas the use of fasteners in masonry and the behaviour of plastic anchors in general were not exhaustively investigated until now (Algin 2007; Sinica et al. 2010). Nevertheless these are two fields of interest because of their widespread presence in constructions. Therefore during the experimental study a particular attention has been paid to the issues of plastic anchors and installations in masonry.
L’osservazione del danno nei recenti eventi sismici (L’Aquila 2009, Chile 2010, Christchurch 2011, Tohoku 2011, Emilia 2012) aiuta nell’identificazione delle criticità legate alla risposta al terremoto degli elementi non strutturali (Miranda et al. 2012). Generalmente tali elementi sono parte dei fabbricati e possono appartenere al sistema architettonico, al sistema impiantistico o al contenuto. La rottura degli elementi non strutturali può rappresentare un pericolo rilevante per la salvaguardia della vita umana e porta perdite di grande valore, nonché contribuisce all’impatto gravoso del sisma per la società (Miranda et al. 2012). Questa tesi contiene i risultati di una campagna sperimentale di ricerca che si poneva lo scopo di valutare diverse tipologie di ancoranti post installati sotto azione sismica. L’argomento appena menzionato è considerato di grande importanza per il ruolo centrale di questi dispositivi nell’ancoraggio di elementi non strutturali per evitare rotture e danneggiamenti che possano causare pericolo per le persone, grosse perdite economiche e interruzione dell’operatività di un edificio nelle settimane o mesi nel seguito di un terremoto (Taghavi and Miranda 2003; ATC 69 2008). Durante un terremoto gli elementi non strutturali dovrebbero resistere ad elevate forze d’inerzia, trasferite attraverso la connessione agli elementi strutturali (travi, solai, pilastri, pareti) o spesso ad altri elementi non strutturali, come le pareti di tamponamento. In molti casi questi punti di connessione sono realizzati con l’uso di ancoranti post installati i quali dovrebbero essere adeguatamente progettati per assicurare un buon comportamento alle azioni sismiche (Makris and Black 2001; Naumoski et al. 2002; Solomos and Berra 2006; Hoehler et al. 2011). Tra tutti i requisiti, quello della affidabilità in termini di modalità di rottura e valore di resistenza risulta fondamentale per ottenere un progetto degli ancoranti post installati che sia valido in campo dinamico. Ad esempio, progetti di sistemi antincendio nelle scuole, di attrezzature mediche negli ospedali, di oggetti d’arte esposti nei musei necessitano di una buona conoscenza della prestazione dei sistemi di ancoraggio da impiegare. Tale conoscenza deve coprire sia la resistenza, per lo stato limite di salvaguardia della vita (SLV), che gli spostamenti in grado di permettere la funzionalità dell’elemento non strutturale, per lo stato limite di esercizio (SLE). Lo scopo della campagna sperimentale presentata all’interno di questo lavoro di ricerca è lo studio del comportamento sismico di diversi sistemi di ancoraggio attraverso prove su tavola vibrante. Due strutture con pianta a croce sono state costruite a scala reale, una consisteva di pareti in calcestruzzo e una di un telaio in calcestruzzo armato con pareti di tamponamento in muratura. Due condizioni differenti sono state studiate nel caso di ancoranti installati in calcestruzzo, ovvero supporto non fessurato e fessurato. Mattoni forati Poroton® sono stati utilizzati per costruire il campione con pareti di tamponamento in muratura. Le prove triassiali sono state progettate sulla base dello standard AC156 (2010) che fornisce delle impostazioni di prova per la certificazione sismica di elementi non strutturali da prove su tavola vibrante. Gli esperimenti sono stati realizzati con l’applicazione alla tavola di segnali scalati a ZPA (Zero Period Acceleration) crescenti per studiare gli effetti indotti sui campioni all’aumentare dell’intensità dell’azione sismica. I risultati hanno permesso di studiare il comportamento sismico generale di ciacun fissaggio, specialmente in termini di modalità di rottura, massimo carico dinamico sopportato e sfilamento del campione dal supporto. Anche l’influenza delle fessure per questi parametri è stata aprofondita per l’unità strutturale di calcestruzzo. Il programma di prova ha anche permesso un confronto completo tra diverse metodologie di ancoraggio, come gli ancoranti ad espansione, chimici o a sottosquadro. Recenti studi (Rieder 2009; Watkins 2011; Mahrenholtz et al. 2012) si sono concentrati sulla valutazione sismica di ancoranti metallici in calcestruzzo attraverso prove su tavola vibrante, invece il comportamento di sistemi di fissaggio impiegati in muratura e di ancoranti plastici in generale non sono stati investigati in modo esaustivo fino ad ora (Algin 2007; Sinica et al. 2010). Ciononostante queste applicazioni appena citate sono di elevato interesse per la loro presenza diffusa nelle costruzioni. Quindi durante lo studio sperimentale una particolare attenzione è stata data alle questioni riguardanti gli ancoranti plastici e le installazioni in muratura.

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Baird, Andrew. "Seismic performance of precast concrete cladding systems." Thesis, University of Canterbury. Civil and Natural Resources Engineering, 2014. http://hdl.handle.net/10092/9997.

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Structural engineering is facing an extraordinarily challenging era. These challenges are driven by the increasing expectations of modern society to provide low-cost, architecturally appealing structures which can withstand large earthquakes. However, being able to avoid collapse in a large earthquake is no longer enough. A building must now be able to withstand a major seismic event with negligible damage so that it is immediately occupiable following such an event. As recent earthquakes have shown, the economic consequences of not achieving this level of performance are not acceptable. Technological solutions for low-damage structural systems are emerging. However, the goal of developing a low-damage building requires improving the performance of both the structural skeleton and the non-structural components. These non-structural components include items such as the claddings, partitions, ceilings and contents. Previous research has shown that damage to such items contributes a disproportionate amount to the overall economic losses in an earthquake. One such non-structural element that has a history of poor performance is the external cladding system, and this forms the focus of this research. Cladding systems are invariably complicated and provide a number of architectural functions. Therefore, it is important than when seeking to improve their seismic performance that these functions are not neglected. The seismic vulnerability of cladding systems are determined in this research through a desktop background study, literature review, and postearthquake reconnaissance survey of their performance in the 2010 – 2011 Canterbury earthquake sequence. This study identified that precast concrete claddings present a significant life-safety risk to pedestrians, and that the effect they have upon the primary structure is not well understood. The main objective of this research is consequently to better understand the performance of precast concrete cladding systems in earthquakes. This is achieved through an experimental campaign and numerical modelling of a range of precast concrete cladding systems. The experimental campaign consists of uni-directional, quasi static cyclic earthquake simulation on a test frame which represents a single-storey, single-bay portion of a reinforced concrete building. The test frame is clad with various precast concrete cladding panel configurations. A major focus is placed upon the influence the connection between the cladding panel and structural frame has upon seismic performance. A combination of experimental component testing, finite element modelling and analytical derivation is used to develop cladding models of the cladding systems investigated. The cyclic responses of the models are compared with the experimental data to evaluate their accuracy and validity. The comparison shows that the cladding models developed provide an excellent representation of real-world cladding behaviour. The cladding models are subsequently applied to a ten-storey case-study building. The expected seismic performance is examined with and without the cladding taken into consideration. The numerical analyses of the case-study building include modal analyses, nonlinear adaptive pushover analyses, and non-linear dynamic seismic response (time history) analyses to different levels of seismic hazard. The clad frame models are compared to the bare frame model to investigate the effect the cladding has upon the structural behaviour. Both the structural performance and cladding performance are also assessed using qualitative damage states. The results show a poor performance of precast concrete cladding systems is expected when traditional connection typologies are used. This result confirms the misalignment of structural and cladding damage observed in recent earthquake events. Consequently, this research explores the potential of an innovative cladding connection. The outcomes from this research shows that the innovative cladding connection proposed here is able to achieve low-damage performance whilst also being cost comparable to a traditional cladding connection. It is also theoretically possible that the connection can provide a positive value to the seismic performance of the structure by adding addition strength, stiffness and damping. Finally, the losses associated with both the traditional and innovative cladding systems are compared in terms of tangible outcomes, namely: repair costs, repair time and casualties. The results confirm that the use of innovative cladding technology can substantially reduce the overall losses that result from cladding damage.

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Divoux, Patrick. "Modélisation du comportement hydro-mécanique des discontinuités dans les structures et les fondations rocheuses : application aux barrages en béton." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10192.

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Les incidents et les accidents survenus a des barrages en beton, ainsi que les resultats d'auscultation, ont montre que leur stabilite depend tres largement du comportement mecanique des zones les plus faibles de l'ensemble vallee-barrage. Localises au niveau des discontinuites dans la structure et dans le rocher, ces points faibles sont principalement les failles des zones d'appui, les reprises de betonnage dans le barrage, le contact beton-rocher au niveau de la fondation et les joints de plots du barrage. Nous avons travaille a la modelisation du comportement de ces zones avec les elements finis particuliers que sont les elements d'interface. Un grande partie de ce rapport est consacree a la connaissance du comportement de ces elements, aux hypotheses emises lors de leur formulation et aux difficultes numeriques associees a la prise en compte de comportements fortement non-lineaires. Le mode de construction, les techniques de clavage et de drainage des barrages en beton en font des ouvrages particuliers dont la modelisation est rendue difficile avec les codes aux elements finis classiques. Le code de calcul gefdyn a ete le support du developpement d'outils et de methodes d'analyse du comportement des barrages en beton et des fondations rocheuses. Appliquees aux barrages de puyvalador et de puylaurent, ces methodes permettent de prendre en compte les principales non-linearites du comportement des ouvrages et de mieux comprendre leur fonctionnement. Ces calculs fournissent des renseignements exploitables sur le plan pratique et sur le plan theorique.

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Smith, Chandler B. "Sparsity Constrained Inverse Problems - Application to Vibration-based Structural Health Monitoring." ScholarWorks @ UVM, 2019. https://scholarworks.uvm.edu/graddis/1143.

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Vibration-based structural health monitoring (SHM) seeks to detect, quantify, locate, and prognosticate damage by processing vibration signals measured while the structure is operational. The basic premise of vibration-based SHM is that damage will affect the stiffness, mass or energy dissipation properties of the structure and in turn alter its measured dynamic characteristics. In order to make SHM a practical technology it is necessary to perform damage assessment using only a minimum number of permanently installed sensors. Deducing damage at unmeasured regions of the structural domain requires solving an inverse problem that is underdetermined and(or) ill-conditioned. In addition, the effects of local damage on global vibration response may be overshadowed by the effects of modelling error, environmental changes, sensor noise, and unmeasured excitation. These theoretical and practical challenges render the damage identification inverse problem ill-posed, and in some cases unsolvable with conventional inverse methods. This dissertation proposes and tests a novel interpretation of the damage identification inverse problem. Since damage is inherently local and strictly reduces stiffness and(or) mass, the underdetermined inverse problem can be made uniquely solvable by either imposing sparsity or non-negativity on the solution space. The goal of this research is to leverage this concept in order to prove that damage identification can be performed in practical applications using significantly less measurements than conventional inverse methods require. This dissertation investigates two sparsity inducing methods, L1-norm optimization and the non-negative least squares, in their application to identifying damage from eigenvalues, a minimal sensor-based feature that results in an underdetermined inverse problem. This work presents necessary conditions for solution uniqueness and a method to quantify the bounds on the non-unique solution space. The proposed methods are investigated using a wide range of numerical simulations and validated using a four-story lab-scale frame and a full-scale 17 m long aluminum truss. The findings of this study suggest that leveraging the attributes of both L1-norm optimization and non-negative constrained least squares can provide significant improvement over their standalone applications and over other existing methods of damage detection.

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Nasu, Daichi [Verfasser], Harald [Akademischer Betreuer] Kolmar, and Gerd [Akademischer Betreuer] Buntkowsky. "Non-Natural Elements for Peptide-Based Molecular Design, Structural Analysis, and Functional Modifications / Daichi Nasu. Betreuer: Harald Kolmar ; Gerd Buntkowsky." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1112044949/34.

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26

Gaignebet, Yvon. "Approche non incrémentale des calculs de chocs pour des structures viscoplastiques." Cachan, Ecole normale supérieure, 1996. http://www.theses.fr/1996DENS0008.

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Le travail présenté dans ce mémoire a pour cadre le calcul en dynamique de structures à comportement viscoplastique par une approche non incrémentale. En rupture avec les méthodes incrémentales classiques, la méthode à grand incrément de temps (latin method) permet de traiter de manière itérative les non-linéarités des équations sur la totalité de l'intervalle de temps d'étude. Elle est développée ici, dans sa dernière version, en association avec l'utilisation d'une base réduite pour la représentation spatiale des processus-champs qui décrivent l'état de la structure. La méthode à grand incrément de temps est itérative, elle permet de connaitre une approximation de plus en plus fine de la solution au cours des itérations. Après le calcul de l'initialisation élastique, les inconnues sont recherchées à chaque itération sous la forme de corrections à apporter aux processus-champs. Une base réduite, constituée des premiers modes propres élastiques de la structure, permet de convenablement représenter ces corrections. Un logiciel (ladyn) est réalisé et permet par le calcul d'exemples simples de fournir des informations sur les performances des différentes variantes de la méthode. Notamment, des stratégies sont élaborées pour diminuer le cout numérique du calcul lors des premières itérations et pour optimiser lors des dernières itérations la représentation espace-temps des processus-champs par rapport à une qualité souhaitée pour la solution

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Bajaj, Srikanth. "EVALUATION OF RESIDUAL STRENGTH OF CORRODED STRUCTURAL STEEL PLATES AND STIFFENED PANELS." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1543570329693244.

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28

Singh, Gurjashan. "Health Monitoring of Round Objects using Multiple Structural Health Monitoring Techniques." FIU Digital Commons, 2010. http://digitalcommons.fiu.edu/etd/330.

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Structural Health Monitoring (SHM) techniques are widely used in a number of Non – destructive Evaluation (NDE) applications. There is a need to develop effective techniques for SHM, so that the safety and integrity of the structures can be improved. Two most widely used SHM methods for plates and rods use either the spectrum of the impedances or monitor the propagation of lamb waves. Piezoelectric wafer – active sensors (PWAS) were used for excitation and sensing. In this study, surface response to excitation (SuRE) and Lamb wave propagation was monitored to estimate the integrity of the round objects including the pipes, tubes and cutting tools. SuRE obtained the frequency response by applying sweep sine wave to surface. The envelope of the received signal was used to detect the arrival of lamb waves to the sensor. Both approaches detect the structural defects of the pipes and tubes and the wear of the cutting tool.

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Bakešová, Martina. "Stavební průzkum a diagnostika zděné konstrukce." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227513.

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The aim of my master’s thesis is to develop a brief overview of the historical development of brick, diagnosis methodologies of masonry structures and their application in the practical part for evaluation of structural survey masonry, carried out at the Faculty of Philosophy, Masaryk University in Brno.

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SPERANZA, ELISA. "The Importance of Calibration and Modelling Non-Structural Elements in the Evaluation of Seismic Vulnerability Index of Strategic Buildings Before and After Retrofitting." Doctoral thesis, Università Politecnica delle Marche, 2020. http://hdl.handle.net/11566/274486.

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Questa tesi si propone di indagare sulla modellazione degli elementi non strutturali relativi alle pareti di tamponamento interne ed esterne, cercando di quantificare la differenza indotta dalle diverse strategie di modellazione sul valore dell'indice di vulnerabilità sismica con riferimento a edifici strategici. A tale scopo vengono analizzati due casi studio: il liceo Benedetto Croce di Avezzano e il liceo Varano di Camerino, entrambi edifici a telaio in c.a. oggetto di adeguamento sismico tramite torri dissipative esterne dotate di dissipatori viscosi alla base. Per entrambi i casi di studio, sono stati implementati tre modelli sia prima che dopo l'adeguamento, caratterizzati da un livello crescente di dettaglio: modello A con solo le componenti strutturali, modello B con tamponature esterne modellate come puntoni equivalenti secondo letteratura e modello C con pareti di tamponamento esterne ed interne calibrate attraverso i risultati dei test dinamici in situ. Per quanto riguarda la fase di pre-retrofitting, il calcolo dell'indice di vulnerabilità sismica è stato effettuato mediante analisi statica non lineare (pushover). Per quanto riguarda la fase post-retrofitting, il calcolo dell'indice di vulnerabilità sismica è stato effettuato mediante analisi dinamica non lineare (I.D.A). I risultati sono mostrati in termini di confronto tra le curve di capacità ottenute con analisi push over (pre-retrofitting) e con analisi dinamiche incrementali, per i diversi modelli implementati. Inoltre, i risultati sono mostrati anche in termini di livello di intensità dell'azione sismica necessaria per raggiungere uno stato limite predeterminato per il modello A, il modello B e il modello C.
This thesis aims to investigate on the modelling of the non-structural elements related to internal and external infill walls, trying to quantify the difference induced by different modelling strategies on the value of the seismic vulnerability index with reference to strategic buildings. On this purpose, two case studies are analysed: the Benedetto Croce high school in Avezzano and the Varano high school in Camerino, r.c. frame buildings retrofitted with external steel towers equipped with viscous dampers at the basis. For both case studies, three models are implemented, before and after the retrofitting, which are characterized by an increasing level of detail: model A with only structural components, model B with external infill panels modelled as equivalent connecting struts according to literature, and model C with external and internal infill walls calibrated through the results of in-situ dynamic tests. As regards the pre-retrofitting phase, the calculation of the seismic vulnerability index was carried out by means of nonlinear static analysis (pushover). As for the post-retrofitting phase, the calculation of the seismic vulnerability index was carried out by means of non-linear dynamic analysis (I.D.A). The results are shown in terms of comparison between the capacity curves obtained with push over analyses (pre-retrofitting) and with incremental dynamic analyses for the different model. In addition, the outcomes are shown also in terms of intensity level of the seismic action necessary to reach a predetermined limit state for model A, model B and model C.

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Jayasooriya, Jayasooriya Hevavitharanage Aruna Ruwan. "Vulnerability and damage analysis of reinforced concrete framed buildings subjected to near field blast events." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/67925/1/Ruwan_Jayasooriya_Thesis.pdf.

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Terrorists usually target high occupancy iconic and public buildings using vehicle borne incendiary devices in order to claim a maximum number of lives and cause extensive damage to public property. While initial casualties are due to direct shock by the explosion, collapse of structural elements may extensively increase the total figure. Most of these buildings have been or are built without consideration of their vulnerability to such events. Therefore, the vulnerability and residual capacity assessment of buildings to deliberately exploded bombs is important to provide mitigation strategies to protect the buildings' occupants and the property. Explosive loads and their effects on a building have therefore attracted significant attention in the recent past. Comprehensive and economical design strategies must be developed for future construction. This research investigates the response and damage of reinforced concrete (RC) framed buildings together with their load bearing key structural components to a near field blast event. Finite element method (FEM) based analysis was used to investigate the structural framing system and components for global stability, followed by a rigorous analysis of key structural components for damage evaluation using the codes SAP2000 and LS DYNA respectively. The research involved four important areas in structural engineering. They are blast load determination, numerical modelling with FEM techniques, material performance under high strain rate and non-linear dynamic structural analysis. The response and damage of a RC framed building for different blast load scenarios were investigated. The blast influence region for a two dimensional RC frame was investigated for different load conditions and identified the critical region for each loading case. Two types of design methods are recommended for RC columns to provide superior residual capacities. They are RC columns detailing with multi-layer steel reinforcement cages and a composite columns including a central structural steel core. These are to provide post blast gravity load resisting capacity compared to typical RC column against a catastrophic collapse. Overall, this research broadens the current knowledge of blast and residual capacity analysis of RC framed structures and recommends methods to evaluate and mitigate blast impact on key elements of multi-storey buildings.

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Darcy, Greg. "Structural behaviour of an innovative cold-formed steel building system." Thesis, Queensland University of Technology, 2005. https://eprints.qut.edu.au/16589/1/Greg_Darcy_Thesis.pdf.

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Cold-formed steel structures have been in service for many years and are used as shelters for both domestic and industrial purposes. To produce an economical product, manufacturers have typically based their designs on the simple portal frame concept. As there is almost a direct relationship between overall cost and the weight of steel in a portal frame structure, it is of great importance to provide a structure with the minimum amount of steel whilst providing structural adequacy. Portal frame sheds have been refined continuously for many years, with only minimal amounts of savings in steel. Therefore, to provide even greater savings in steel, an innovative building system is required. Modern Garages Australia (MGA) is one of the leading cold-formed steel shed manufacturers in Queensland. MGA has recently developed such an innovative building system that has significant economic savings when compared with portal frame structures. The MGA building system has two key differences to that of the conventional portal frame system. These differences are that the MGA system has no conventional frames or framing system, and it has no purlins or girts. This results in the MGA system being completely fabricated from thin cladding, which significantly reduces the quantity of steel. However, the key problem with this building system is that the load paths and structural behaviour are unknown, and therefore the structure cannot be analysed using conventional methods. Therefore, the objectives of this research were to first investigate the structural behaviour of this new building system and its adequacy for an ultimate design wind speed of 41 m/s using full scale testing. The next objectives were to use finite element analysis to optimise the original MGA building system so that it is adequate for an ultimate design wind speed of 41 m/s, and to develop a new improved cold-formed steel building system that has greater structural efficiency than the original MGA building system. This thesis presents the details of the innovative MGA building system, full scale test setup, testing program, finite element analysis of the MGA building system and the results. Details and results from the optimisation of the MGA building system, and the development of a new improved cold-formed steel building system are also presented. The full scale experimental investigation considered the required loadings of cross wind, longitudinal wind and live load test cases and simulated them on the test structure accurately using an innovative load simulation system. The wind loads were calculated for a 41 m/s ultimate design wind speed. Full scale test program included both non-destructive and destructive tests. The finite element analyses contained in this thesis have considered cross wind, longitudinal wind and live load cases, as well as the destructive load case of the MGA building system. A number of different model types were created and their results were compared with the experimental results. In general, two main model types were created. The first type consisted of a 'strip' of the MGA building system (Strip model) and the second modelled the full structure (Full model). Both of these model types were further divided into models which contained no contact surfaces and those which contained contact surfaces to simulate the interfaces between the various components such as the brackets and cladding. The experimental test results showed that the MGA test structure is not suitable for an ultimate design wind speed of 41 m/s. This conclusion is a result of a number of observed failures that occurred during the extensive testing program. These failures included local buckling, crushing failures, and distortional buckling of the cladding panels. Extremely large deflections were also observed. It was calculated that for the MGA building system to be adequate for the design wind speed of 41 m/s, a cladding thickness of 0.8 mm was required. This also agreed well with the finite element analysis results which concluded that a cladding thickness of 0.8 mm was required. In order to avoid the increased use of steel in the building system, a new improved cold-formed steel building system was developed and its details are provided in this thesis. A finite element model of this new improved cold-formed steel building system was created and the results showed that the new building system was able to achieve a load step equivalent to an ultimate design wind speed of 50.4 m/s and was approximately 250% stiffer than the original MGA building system, without any increase in the overall weight of the building system. It is recommended that this new improved cold-formed steel building system be further developed with the aid of finite element modelling and be tested using a similar full scale testing program that was used for the original MGA building system.

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33

Darcy, Greg. "Structural behaviour of an innovative cold-formed steel building system." Queensland University of Technology, 2005. http://eprints.qut.edu.au/16589/.

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Cold-formed steel structures have been in service for many years and are used as shelters for both domestic and industrial purposes. To produce an economical product, manufacturers have typically based their designs on the simple portal frame concept. As there is almost a direct relationship between overall cost and the weight of steel in a portal frame structure, it is of great importance to provide a structure with the minimum amount of steel whilst providing structural adequacy. Portal frame sheds have been refined continuously for many years, with only minimal amounts of savings in steel. Therefore, to provide even greater savings in steel, an innovative building system is required. Modern Garages Australia (MGA) is one of the leading cold-formed steel shed manufacturers in Queensland. MGA has recently developed such an innovative building system that has significant economic savings when compared with portal frame structures. The MGA building system has two key differences to that of the conventional portal frame system. These differences are that the MGA system has no conventional frames or framing system, and it has no purlins or girts. This results in the MGA system being completely fabricated from thin cladding, which significantly reduces the quantity of steel. However, the key problem with this building system is that the load paths and structural behaviour are unknown, and therefore the structure cannot be analysed using conventional methods. Therefore, the objectives of this research were to first investigate the structural behaviour of this new building system and its adequacy for an ultimate design wind speed of 41 m/s using full scale testing. The next objectives were to use finite element analysis to optimise the original MGA building system so that it is adequate for an ultimate design wind speed of 41 m/s, and to develop a new improved cold-formed steel building system that has greater structural efficiency than the original MGA building system. This thesis presents the details of the innovative MGA building system, full scale test setup, testing program, finite element analysis of the MGA building system and the results. Details and results from the optimisation of the MGA building system, and the development of a new improved cold-formed steel building system are also presented. The full scale experimental investigation considered the required loadings of cross wind, longitudinal wind and live load test cases and simulated them on the test structure accurately using an innovative load simulation system. The wind loads were calculated for a 41 m/s ultimate design wind speed. Full scale test program included both non-destructive and destructive tests. The finite element analyses contained in this thesis have considered cross wind, longitudinal wind and live load cases, as well as the destructive load case of the MGA building system. A number of different model types were created and their results were compared with the experimental results. In general, two main model types were created. The first type consisted of a 'strip' of the MGA building system (Strip model) and the second modelled the full structure (Full model). Both of these model types were further divided into models which contained no contact surfaces and those which contained contact surfaces to simulate the interfaces between the various components such as the brackets and cladding. The experimental test results showed that the MGA test structure is not suitable for an ultimate design wind speed of 41 m/s. This conclusion is a result of a number of observed failures that occurred during the extensive testing program. These failures included local buckling, crushing failures, and distortional buckling of the cladding panels. Extremely large deflections were also observed. It was calculated that for the MGA building system to be adequate for the design wind speed of 41 m/s, a cladding thickness of 0.8 mm was required. This also agreed well with the finite element analysis results which concluded that a cladding thickness of 0.8 mm was required. In order to avoid the increased use of steel in the building system, a new improved cold-formed steel building system was developed and its details are provided in this thesis. A finite element model of this new improved cold-formed steel building system was created and the results showed that the new building system was able to achieve a load step equivalent to an ultimate design wind speed of 50.4 m/s and was approximately 250% stiffer than the original MGA building system, without any increase in the overall weight of the building system. It is recommended that this new improved cold-formed steel building system be further developed with the aid of finite element modelling and be tested using a similar full scale testing program that was used for the original MGA building system.

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34

Bertran, Rojo Marc. "Correr entre los escombros - Courir entre les débris. La mobilité individuelle en période de crise sismique : facteur d'exposition humaine dans le cas du séisme de Lorca (Espagne 2011)." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU040/document.

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Le 11 mai 2011, un double séisme a frappé la ville de Lorca, dans le sud-est de l'Espagne. Ce séisme a eu de lourdes conséquences pour la population et provoqué de nombreux dégâts sur les bâtiments de la ville. Les tremblements de terre sont des phénomènes caractérisés par leur relative faible fréquence et par leur violence. Dans le bassin méditerranéen, la grande majorité des séismes ne sont perceptibles qu'à l'aide d'instruments de mesure. Certains événements récents ont néanmoins surpris la communauté scientifique par leur magnitude modérée mais leur intensité élevée. C'est notamment le cas du tremblement de terre de Lorca. Depuis 40 ans, l'administration espagnole essaye de se prémunir davantage contre ce phénomène. Cela se traduit par l'évolution des normes parasismiques appliquées à la construction ou encore par la création de cartes de zonages sismiques intégrant à chaque révision une plus grande portion du territoire exposée au risque. Cependant, ces mesures évoluent au rythme des événements. Or, la localisation des villes en zone sismique et la vulnérabilité des bâtiments préalablement construits sont des variables difficilement ajustables à ces nouvelles normes. Lorsqu'un séisme affecte une ville, l'origine des dommages corporels réside dans la coïncidence temporelle et spatiale entre l'individu et le danger, danger la plupart du temps lié aux bâtiments. Dans ce contexte, nous avons proposé une démarche focalisée sur l'individu. Pendant la période de crise sismique, la mobilité individuelle apparaît comme l'élément qui va permettre la coïncidence spatiale entre le danger et l'individu. A partir d'entretiens qualitatifs, nous avons analysé la mobilité individuelle en période de crise sismique, par la collecte d'informations très fines sur les aspects spatiaux et temporels de celle-là. Parallèlement, nous proposons une étude des principaux dangers observés pour le cas de Lorca et comment ceux-ci peuvent toucher la population. En général, la plupart des décès en cas de séismes se produisent à l'intérieur des bâtiments à cause de leur effondrement. Cependant, dans le cas de séismes d'intensité faible à modérée, c'est la chute d'éléments non structuraux, notamment d'éléments de façade, qui constitue un danger. En croisant spatialement et temporellement la mobilité des individus avec les dangers, nous concluons que la mobilité individuelle est un facteur déterminant de l'exposition humaine. Les facteurs qui vont conditionner la mobilité sont principalement liés à la mise en protection immédiate ainsi qu'à l'organisation en famille préalablement à l'évacuation de la ville. Après avoir permis d'évaluer les dangers, les analyse spatiales ont mis en avant que la grande incertitude de cette évaluation rend difficiles les études très fines. Cependant, elles ouvrent des perspectives intéressantes pour des travaux futurs. Enfin, notre travail de thèse a proposé l'adaptation d'une méthodologie de collecte et d'analyse des dynamiques spatiales et temporelles liées aux individus, à la base créée pour les crues rapides. Cette méthode s'est montrée facilement transposable à de futurs événements, ce qui permettrait de réaliser des études comparatives
May the eleventh, 2011, a double earthquake struck the town of Lorca in southeastern Spain. The earthquake had serious consequences for the population and caused extensive damage to buildings in the town. Earthquakes are phenomena characterized by their relatively low frequency and their violence. In the Mediterranean Basin, most earthquakes are only perceptible using measuring instruments. Recent seismic events have surprised the scientific community by their moderate magnitude associated with a high intensity. This is particularly the case of Lorca's earthquake. In the last 40 years, the Spanish authorities have tried to develop prevention towards seismic phenomenon. Measures have been taken by improving seismic building codes or by updating the seismic zoning, each revision taking into account wider zones at risk. In general, events give rhythm to the evolution of these measures. However, variables like the location of cities in seismic zones and the vulnerability of existing buildings can hardly be adjusted to these new standards. When an earthquake affects a town, danger is mostly caused by building failure. However, injuries and fatalities are due to the spatial and temporal coincidence between the individual and the danger. In this context, we propose an approach focused on the individual. During a seismic crisis, individual mobility appears to be the element that will allow the spatial coincidence between the danger and the individual. We analyzed individual mobility during seismic crisis by collecting very precise information regarding spatial and temporal aspects of mobility through qualitative interviews. Simultaneously, we carried out a study of dangers observed in the case of Lorca. In general, most of the fatalities caused by earthquakes occur inside collapsed buildings. However, in the case of low-to-moderate-intensity earthquakes, danger is related to the fall of non-structural elements, especially frontage elements. By combining spatial and temporal mobility of individuals with dangers, we conclude that individual mobility is a determinant factor of human exposure. The factors that will determine mobility are mainly related to the immediate protection measures as well as the family organization prior to the town evacuation. Finally, spatial analysis allowed assessing dangers. The associated uncertainty of this evaluation makes it difficult a more accurate study, but offers perspectives for future work. This work proposes the adaptation of a methodology to collect and analyze spatial and temporal dynamics related to individuals. Developed initially for flash flood analysis, this methodology is transferable to future events, enabling comparative studies

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Aquino, João José Redondo de. "Structural numerical simulation code development with isogeometric anakysis (IGA)." Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22375.

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Mestrado em Engenharia Mecânica
In the present day most product development industries uses the Finite Element Method (FEM) for structural analysis. Designers model the product geometries using Computer-Aided Design (CAD) software, the geometries are then fitted for analysis, by the analysts, with a mesh approximation that inevitably results in loss of accuracy. Achieving the best geometry description for complex components can be a complex task and it can take a lot of time. Considering this drawback, a new method was developed which takes advantages of curve representation tools and uses them as bases for analysis. Aiming for no loss of geometrical precision, this new method has been called "Isogeometric Analysis" (IGA). The smoothness of Spline representations used in Isogeometric Analysis can be useful for a particular branch of structural analysis which is the analysis of plates and shells. The classic thin plate theory developed by Gustav Kirchhoff requires a geometry description with C1 continuity between elements which is normally defined by high order polynomial functions, which typically represents a problem with the piecewise Lagrangian shape functions used in conventional FEM. The present work explores parametric descriptions used as basis for Isogeometric Analysis, such as Bézier curves, B-splines and NURBS, taking advantage of its smoothness to develop formulations for thin plate elements. The 4-node rectangular derived by Melosh, O. Zienkiewicz and Y. Chung called MCZ thin plate element based on Kirchhoff assumptions, was the starting point to build up to a NURBS-based thin plate element. MCZ thin plate elements, NURBS-based thin plate elements (with different order geometries) and Abaqus commercial software shell elements are evaluated by means of classical plate benchmarks comparing the elements convergences and overall performance. It can be shown that the proposed NURBS-based formulation is reliable for the analysis of thin structures.
Nos dias de hoje a maioria da indústria de desenvolvimento do produto utiliza o Método dos Elementos Finitos (MEF) na análise estrutural. Os desenhistas modelam o produto através de ferramentas de Computer-Aided Design (CAD). As geometrias são depois ajustadas para a análise pelos analistas que constroem uma aproximação através de uma malha de elementos finitos, o que inevitavelmente resulta numa perda de precisão geométrica. Para conseguir a melhor aproximação à geometria original para componentes complexos o processo pode ser complicado e pode consumir muito tempo. Considerando esta desvantagem foi desenvolvido um novo método que tira partido da descrição geométrica das ferramentas de desenho e utiliza as funções base das curvas para analise, com o objectivo de não haver perda de precisão geométrica, este novo método tem o nome de “Análise Isogeométrica” (IGA). A suavidade das geometrias Splines usadas na análise isogeometrica pode ser muito útil num ramo particular da análise estrutural, no estudo das placas e cascas. A teoria clássica de análise de placas finas de Kirchhoff requer uma descrição geométrica que tenha continuidade C1 entre elementos, que é normalmente definida por polinómios de ordem elevada, que são tipicamente um problema para as funções de forma Lagrangeanas usadas em MEF. O presente trabalho explora as descrições geométricas utilizadas como funções de forma para a análise isogeométrica como as curvas de Bézier, as B-splines e as NURBS, tirando vantagem da facilidade de estas conseguirem a requerida continuidade entre elementos para criar elementos de placas finas com as funções de base NURBS como funções de forma. É utilizado o elemento de placa fina MCZ desenvolvido por Melosh, O. Zienkiewicz e Y. Chung com base nas premissas de Kirchhoff como ponto de partida para desenvolver o elemento com base em NURBS. No fim os elementos de placas finas MCZ, os elementos com funções de base NURBS (com geometrias de diferentes ordens) e elementos do tipo casca do software comercial Abaqus são avaliados através de uma série de diferentes problemas clássicos de placas, comparando a convergência e o desempenho global. É possivel ver que a formulação proposta é fidedigna na análise de estruturas de placa fina.

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Kesawan, Sivakumar. "Fire performance and design of light gauge steel frame wall systems made of hollow flange sections." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/120153/1/Kesawan_Sivakumar_Thesis.pdf.

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Load bearing Light Gauge Steel Frame (LSF) wall system is a cold-formed steel structure made of cold-formed steel studs and lined on both sides by gypsum plasterboards. In recent times its use and demand in the building industry has significantly increased due to their advantages such as light weight, acoustic performance, aesthetic quality of finished wall, ease of fabrication and rapid constructability. Fire Resistant Rating (FRR) of these walls is given more attention due to the increasing number and severity of fire related accidents in residential buildings that have caused significant loss of lives and properties. LSF walls are commonly made of conventional lipped channel section studs lined with fire resistant gypsum plasterboards on both sides. Recently, greater attention has been given to innovative cold-formed steel sections such as hollow flange sections due to their improved structural efficiency. The reliance on expensive and time consuming full scale fire tests, and the complexity involved in predicting the fire performance of LSF wall studs due to their thin-walled nature and their exposure to non-uniform temperature distributions in fire on one side, have been the main barriers in using different cold-formed steel stud sections in LSF wall systems. This research overcomes this and proposes the new hollow flange section studs as vertical load bearing elements in LSF wall systems based on a thorough investigation into their fire (structural and thermal) performance using full scale fire tests and extensive numerical studies. Test wall frames made of hollow flange section studs were lined with fire resistant gypsum plasterboards on both sides, and were subjected to increasing temperatures as given by the standard fire curve in AS 1530.4 (SA, 2005) on one side. Both uninsulated and cavity insulated walls were tested with varying load ratios from 0.2 to 0.6. LiteSteel Beam (LSB), a welded hollow flange section, which was available in the industry was used to fabricate the test wall panels. Axial deformations and lateral displacements along with the time-temperature profiles of the steel stud and plasterboard surfaces were measured. Five full scale tests were performed, and the test results were compared with those of LSF walls made of lipped channel section studs, which proved the superior fire performance of LSF walls made of hollow flange section studs. The reasons for the superior fire performance are presented in this thesis. The effects of load ratio and plasterboard joint on the fire performance of LSF walls and temperature distribution across the stud cross-sections were identified. Improved plasterboard joints were also proposed. The elevated temperature mechanical properties of cold-formed steels appear to vary significantly as shown by past research. LSBs were manufactured using a combined cold-forming and electric resistance welding process. Elevated temperature mechanical properties of LSB plate elements are unknown. Therefore an experimental study was undertaken to determine the elevated temperature mechanical properties of LSB plate elements. Based on the test results and previous researchers' proposed values, suitable predictive equations were proposed for the elastic modulus and yield strength reduction factors and stress-strain models of LSB web and flange elements. Uninsulated and insulated 2D finite element models of LSF walls were developed in SAFIR using GiD as a pre- and post processor to predict the thermal performance under fire conditions. A new set of apparent thermal conductivity values was proposed for gypsum plasterboards for this purpose. These models were then validated by comparing the time-temperature profiles of stud and plasterboard surfaces with corresponding experimental results. The developed models were then used to conduct an extensive parametric study. Uninsulated and insulated LSF walls with superior fire performances were also proposed. Finite element models of tested walls were also developed and analysed under both transient and steady state conditions to predict the structural performance under fire conditions using ABAQUS. In these analyses, the measured elevated temperature properties of LSB plate elements were used to improve their accuracy. Finite element analysis results were compared with fire test results to validate the developed models. Following this, a detailed finite element analysis based study was conducted to investigate the effects of stud dimensions such as web depths and thicknesses, elevated temperature mechanical properties, types of wall configurations, stud section profiles, plasterboards to stud connections and realistic design fire curves on the fire performance of LSF walls. It was also shown that the commonly used critical temperature method is not appropriate in determining the FRR of LSF walls. Gunalan and Mahendran's (2013) design rules based on AS/NZS 4600 (SA, 2005), and Eurocode 3 Part 1.3 (ECS, 2006) were further improved to predict the structural capacity of hollow flange section studs subjected to non-uniform temperature distributions caused by fire on one side. Two improved methods were proposed and they predicted the FRRs with a reasonable accuracy. Direct Strength Method (DSM) based design rules were then established and they also predicted the FRR of LSF walls made of hollow flange section studs accurately. Finally, spread sheet based design tools were developed based on the proposed design rules. Overall, this research has developed comprehensive fire performance data of LSF walls made of hollow flange section studs, accurate design rules to predict their fire rating and associated design tools. Thus it has enabled the use of innovative hollow flange sections as studs in LSF wall systems. Structural and fire engineers can now use these tools to undertake complex calculations of determining the structural capacities and fire rating of hollow flange section studs subjected to non-uniform temperature distributions, and successfully design them for safe and efficient use in LSF walls of residential and office buildings.

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Amancio, Daniel de Traglia. "Avaliação da integridade estrutural de elementos de concreto armado a partir das propriedades modais obtidas por técnicas de excitações aleatórias e transientes." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-25052016-085152/.

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A análise dinâmica experimental tem sido amplamente pesquisada como uma ferramenta de avaliação de integridade de estruturas de concreto armado. Existem técnicas de identificação de danos baseadas em propriedades modais como frequências de ressonâncias, deformadas modais, curvaturas modais e amortecimento. Há também técnicas baseadas na não linearidade da resposta dinâmica, que apesar do grande potencial na detecção de danos, têm sido pouco exploradas nos últimos anos. Este trabalho tem por objetivo avaliar a integridade estrutural de vigas de concreto armado através do comportamento da resposta dinâmica. Foram realizados ensaios dinâmicos em duas vigas de concreto armado com 3,5 m de comprimento, 25 cm de largura, 35 cm de altura e idênticas taxas de armaduras, mas configuradas com barras de aço de diferentes diâmetros, 2 ϕ 16 mm e 8 ϕ 8 mm, respectivamente. Tais vigas, inicialmente íntegras, foram submetidas a ciclos de carregamento e descarregamento com intensidades crescentes até atingir a ruptura do elemento. Após cada ciclo, as propriedades dinâmicas foram avaliadas experimentalmente, com o emprego de técnicas de excitação por sinais do tipo aleatório e tipo transiente, respectivamente, visando determinar parâmetros que indiquem a deterioração gradativa do elemento. Nesses ensaios dinâmicos aplicaram-se diferentes amplitudes da força de excitação. Verificou-se que o aumento da amplitude da força dinâmica de excitação provocou reduções nos valores das frequências de ressonância de 1,1% e 2,4%, associadas, respectivamente, às excitações aleatórias e transientes; e um comportamento não linear dos índices de amortecimento, associados às excitações aleatórias, mantendo um crescimento linear com as excitações transientes. Constatou-se, ainda, que os valores das frequências de ressonância decrescem com a redução de rigidez mecânica, diminuída com o aumento do nível de fissuração induzido nos modelos. Já os valores dos índices de amortecimento, após cada ciclo, se comportaram de forma não linear e assumiram diferentes valores, conforme a técnica de excitação empregada. Acredita-se que esta não linearidade está relacionada aos danos provocados no elemento pela solicitação estrutural e, por consequência, ao processo de como a dissipação de energia é empregada no processo de instauração, configuração e propagação das fissuras nos elementos de concreto armado.
The experimental dynamic analysis has been widely investigated as a tool to assess integrity of reinforced concrete structures. State-of-the-art modal-based techniques for structural damage analysis use resonance frequencies, modal deformed, curvature and modal damping analysis. There are also techniques based on nonlinear dynamic response that despite the large potential for damage detection, have not been considered in recent years. This work aims to evaluate the structural integrity of reinforced concrete beams through the dynamic response behavior. Dynamic tests were performed on two reinforced concrete beams with 3.5 meters of length, 250 mm of width, 350 mm of height and identical reinforcement rates, but different steel bars diameters, 2 ϕ 16 mm e 8 ϕ 8 mm, respectively. Beams were initially intact and were subjected to loading and unloading cycles with increasing intensity until the rupture of the concrete beam. After each cycle, the dynamic properties were evaluated experimentally with random and transient excitation signals to determine parameters that indicate gradual deterioration of the beam. Different amplitudes of the excitation force were applied during dynamic testing of concrete beams. These results indicated that an increase in amplitude of dynamic excitation force caused reductions in frequency resonances by 1.1% and 2.4%, associated with the random and transient excitations, respectively. Furthermore, a non-linear behavior of the damping ratios related to random excitations was observed while a linear relationship with transient excitation was found. Moreover, it was found that the resonance frequency decreased with the cracking-related reduction of beam stiffness, caused by increasing level of loading. Additionally, the values of the damping ratios after each cycle behaved non-linearly assuming different values according to the used excitation technique. It is believed that this non-linearity can be related to the loading-related structural damage of the reinforced concrete beam. Therefore, the energy dissipation related to cracking initiation, configuration and propagation in reinforced concrete elements played an important role in the damping ratios of concrete beams.

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38

Pecorella, Daniele. "Methodology for the design and optimization of a morphing wing droop-nose structure for greener aircraft." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.

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Droop-Nose Leading Edge (DNLE) morphing wings are one of the most promising devices in order to achieve aerodynamic drag and noise reduction during take-off and landing phases. An accurate design of these structures could lead to the decrease of aircraft fuel consumption in the perspective of reaching a greener aviation, following the objectives indicated by Flightpath 2050 issued by the E.U. However, due to the challenges related to the realization of this technology and TRL reached, DNLE are more likely implemented in Unmanned Aerial Systems (UAS) for testing and evaluation purposes. In the present study, an optimization methodology for the DNLE composite laminate skin and morphing mechanism structure is proposed and applied to a study case represented by the UAS-S45 aircraft. The work starts from the morphing leading edge structure developed by the LARCASE laboratory at ETS Montreal. The results showed that by means of the optimization strategy adopted, the force required on the actuator mechanism is 88% lower than the original design. A significant improvement on the profile smoothness along its section and in the spanwise direction in morphing conditions has been obtained too. However, further investigations are still needed in order to achieve a more appropriate morphing shape. Despite this, it appears from the results obtained that the proposed methodology can be useful to tackle the DNLE design problem in an effective and efficient way. What developed in this work has been conceived to support the investigation of DNLE in the small leading edge profiles typical of the UAS. In this way, an easier procedure for the set up of the design flow, and a decrease in the computational effort for the optimization process can be obtained. An experimental validation of the results obtained is currently being performed at ETS, and future development regards the assessment of the errors of the numeric procedure herein presented respect to real data.

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Susila, Gede Adi. "Experimental and numerical studies of masonry wall panels and timber frames of low-rise structures under seismic loadings in Indonesia." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/experimental-and-numerical-studies-of-masonry-wall-panels-and-timber-frames-of-lowrise-structures-under-seismic-loadings-in-indonesia(3ceb094b-4e6e-432a-b3de-3d4c306b0551).html.

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Indonesia is a developing country that suffers from earthquakes and windstorms and where at least 60% of houses are non-engineered structures, built by unskilled workers using masonry and timber. The non-engineered housing units developed in urban region are also vulnerable to seismic hazard due to the use of low quality of material and constructions method. Those structures are not resistant to extreme lateral loads or ground movement and their failure during an earthquake or storm can lead to significant loss of life. This thesis is concerned with the structural performance of Indonesian low-rise buildings made of masonry and timber under lateral seismic load. The research presented includes a survey of forms of building structure and experimental, analytical and numerical work to predict the behaviour of masonry wall and traditional timber frame buildings. Experimental testing of both masonry and timber have been carried out in Indonesia to establish the quality of materials and to provide material properties for numerical simulations. The experimental study found that the strength of Indonesia-Bali clay brick masonry are below the minimum standard required for masonry structures built in seismic regions, being at least 50% lower than the requirement specified in British Standard and Eurocode-6 (BS EN 1996-1-1:2005). In contrast, Indonesian timber materials meet the strength classes specified in British Standard/Eurocode- 5 (BS EN 338:2009) in the range of strength grade D35-40 and C35).Structural tests under monotonic and cyclic loading have been conducted on building components in Indonesia, to determine the load-displacement capacity of local hand-made masonry wall panels and timber frames in order to: (1) evaluate the performance of masonry and timber frame structure, (2) investigate the dynamic behaviour of both structures, (3) observe the effect of in-plane stiffness and ductility level, and (4) examine the anchoring joint at the base of timber frame that resists the overturning moment. From these tests, the structural ductility was found to be less than two which is below the requirement of the relevant guidelines from the Federal Emergency Management Agency, USA (FEMA-306). It was also observed that the lateral stiffness of masonry wall is much higher than the equivalent timber frame of the same height and length. The experimental value of stiffness of the masonry wall panel was found to be one-twelfth of the recommended values given in FEMA-356 and the Canadian Building code. The masonry wall provides relatively low displacement compared to the large displacement of the timber frame at the full capacity level of lateral load, with structural framing members of the latter remaining intact. The weak point of the timber frame is the mechanical joint and the capacity of slip joint governs the lateral load capacity of the whole frame. Detailed numerical models of the experimental specimens were setup in Abaqus using three-dimensional solid elements. Cohesive elements were used to simulate the mortar behaviour, exhibiting cracking and the associated physical separation of the elements. Appropriate contact definitions were used where relevant, especially for the timber frame joints. A range of available material plasticity models were reviewed: Drucker-Prager, Crystalline Plasticity, and Cohesive Damage model. It was found that the combination of Crystalline Plasticity model for the brick unit and timber, and the Cohesive Damage model for the mortar is capable of simulating the experimental load-displacement behaviour fairly accurately. The validated numerical models have been used to (1) predict the lateral load capacity, (2) determine the cracking load and patterns, (3) carry out a detailed parametric study by changing the geometric and material properties different to the experimental specimens. The numerical models were used to assess different strengthening measures such as using bamboo as reinforcement in the masonry walls for a complete single storey, and a two-storey houses including openings for doors and windows. The traditional footing of the timber structures was analysed using Abaqus and was found to be an excellent base isolation system which partly explains the survival of those structures in the past earthquakes. The experimental and numerical results have finally been used to develop a design guideline for new construction as well as recommendations for retrofitting of existing structures for improved performance under seismic lateral load.

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Viljoen, Awie. "Analysis and Optimum Design of stiffened shear webs in airframes." Diss., 2004. http://hdl.handle.net/2263/23127.

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The analysis and optimum design of stiffened, shear webs in aircraft structures is addressed. The post-buckling behaviour of the webs is assessed using the interactive algorithm developed by Grisham. This method requires only linear finite element analyses, while convergence is typically achieved in as few as five iterations. The Grisham algorithm is extensively compared with empirical analysis methods previously used for aircraft structures and also with a refined, non-linear quasi-static finite element analysis. The Grisham algorithm provides for both compressive buckling in two directions as well as shear buckling, and overcomes some of the conservatism inherent in conventional methods of analysis. In addition, the method is notably less expensive than a complete non-linear finite element analysis, even though global collapse cannot be predicted. While verification of the analysis methodology is the main focus of the stud, an initial investigation into optimization is also made. In optimizing stiffened thin walled structures, the Grisham algorithm is combined with a genetic algorithm. Allowable stress constraints are accommodated using a simple penalty formulation.
Dissertation (MEng (Mechanical and Aeronautical Engineering))--University of Pretoria, 2006.
Mechanical and Aeronautical Engineering
unrestricted

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Le, Tri. "Non-linear finite element dynamic analysis of tapered hollow steel poles for passive base isolation." 2008. http://hdl.handle.net/10106/929.

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Nasu, Daichi. "Non-Natural Elements for Peptide-Based Molecular Design, Structural Analysis, and Functional Modifications." Phd thesis, 2016. https://tuprints.ulb.tu-darmstadt.de/5252/1/DISSERTATION_Daichi%20Nasu%20Final%20ver.pdf.

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The present thesis summarizes three research projects addressing fundamental studies aimed on application of non-natural elements to design and synthesis of bioactive peptide mimetics, bioconjugates, and hybrid macromolecules. The study comprised computational and knowledge-based design, total synthesis, and evaluation of biologic activity as well as application to NMR-based structural analysis. Results summarized in the present work were reported in two scientific publications and should be considered as milestones for further investigations aimed on application of the discussed concepts to biomedical studies.

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Ghanbari, Ghazijahani T. "Structural behaviour of thin-walled steel elements with geometric and sectional non-uniformities." Thesis, 2017. https://eprints.utas.edu.au/23788/2/Ghanbari_Ghazijahani_whole_thesis_ex_pub_mat.pdf.

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This PhD program proposes innovative ideas within a comprehensive and yet umbrella definition as indicated through the title. Above all, this thesis provides a comprehensive compendium of experimental results on a variety of aspects of buckling of thin walled steel elements and an invaluable resource of experimental data for the later studies of such structural elements. This thesis experimentally investigates the structural stability of thin-walled steel members with different geometrical and material specifications. For tubular circular members made exclusively from steel, large imperfections in the form of dents were examined under axial loading, bending and external pressure. As another form of geometrical irregularity, different shapes and geometries of cutouts were considered in order to investigate the effect of these imperfections on the structural behaviour of the steel members. Circular shell elements with normal fabrication-related imperfections were investigated under external pressure. Reinforcement of the shell members with additional elements (stiffeners/thickeners) and without additional material (corrugation) was also undertaken. Large imperfections such as dents and cutouts with different sizes were then examined for circular tubes under cyclic loading. Rehabilitation of members with cutouts (using Carbon Fibre Reinforced Polymer, CFRP), fully recovered the reduced capacity resulted from the existence of the cutouts; yet, employed reinforcements manifested capacities well above the intact models. Sectional irregularity was also of a great interest in this PhD thesis, which was adopted for composite members. Composite elements such as CFRP and timber were combined with thin-walled steel members to produce light-weight elements with great structural efficiency. Timber cores with different cross sections were utilised for timber filled CHS steel tubular sections. CFRP reinforced the timber-filled CHS members from outside the steel so that both inward and outward buckling was restricted. The same scenario was used for the CHS members with timber and concrete cores, in which the timber blocks were employed to act as compressive members, alongside their key role to form (cast) the concrete inside the tubes. Bending members including timber, reinforced by U-shape steel members were designed in order to make a light-weight flexural element. The effect of such strengthening on the capacity as well as the ductility of the beams in question was evaluated.

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Chang, Wei-Chung, and 陳威中. "A Research on Evaluating Floor Vibration in Earthquakes for Non-structural Elements Damage Estimate." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/39314646049352560857.

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碩士
國立成功大學
建築學系碩博士班
96
This study surveyed strong motion data of buildings in the 921 Chi-Chi 、1022、331 and the 0401 earthquakes to conclude on two simplified equations for floor velocity and displacement prediction. Damage state of various non-structural elements by different investigators were also collected and summarized in this research. Combining these data, the non-structural element performance in a building can be estimated so long as the fundamental period of the building and the PGA is known. Keywords：non-structural elements、damage evaluation、floor displacement 、floor velocity

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Narasimhan, S. "Three Dimensional Viscoplastic And Geomertrically Non-Linear Finite Element Analysis Of Adhesively Bonded Joints." Thesis, 1998. http://etd.iisc.ernet.in/handle/2005/2166.

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BIANCHI, SIMONA. "Multi-performance evaluation of traditional and low-damage non-structural components." Doctoral thesis, 2020. http://hdl.handle.net/11573/1541562.

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Non-structural components include all the building elements not part of the main loadbearing system of a structure or an industrial facility. These components are designed to provide specific performance, such as controlling the passage of heat or resisting to fire, while the seismic behaviour is typically neglected in the design process. Nevertheless, the response of these elements can significantly affect the building functionality after earthquakes, even for low-intensity events, and their poor performance can result in substantial economic losses and business interruption. Consequently, the non-structural damage has a severe impact on the post-earthquake building recovery in addition to the potential risk to life safety. As either the earthquake engineering community or the public demand a higher level of earthquake protection, improving the seismic performance of structural systems is not enough and the expectation of advanced seismic behaviour for non-structural components is demanded. The need for reduction of non-structural seismic risk is thus being recognized fundamental in the decision-making process and in the performance-based seismic design the attention is nowadays focusing on both the harmonization of structural/non-structural performance and the development of damage-control or low-damage non-structural systems. Considering the previous background, this Thesis mainly aims to: 1) provide evidence on the convenience of implementing innovative low-damage technologies for non-structural components, 2) highlight the importance of including the study of the seismic performance of new or retrofitted elements within an integrated multi-performance design approach. The Thesis initially provides an overview of the damage states/mechanisms evolving during earthquake shakings in different typologies of non-structural elements, i.e. architectural elements, building services and contents. Fragility curves developed from past experimental research are also collected; in fact, determining which parameters mainly influence the failure modes and when a damage condition is achieved can help in the proposal of new solutions. Then, a literature review can be found on the innovative damage-mitigation technologies developed during the last decades for both structural and non-structural components. These solutions can be combined to define an integrated high-performance earthquake-proof building system. The Thesis also describes the experimental investigations (1D shake-table testing) carried out on a new earthquake-resistant solution proposed with the aim of reducing the seismic demand on non-structural systems anchored to concrete structures, i.e. supplemental damping is added to post-installed fasteners. The test results confirm the beneficial effects of this solution to seismically protect the non-structural elements for expansion or chemical fasteners in both un-cracked and cracked concrete. The convenience of implementing low-damage systems is thus investigated through numerical and experimental studies. Cost/performance-based evaluations of multi-storey buildings comprising different traditional vs. low-damage structural systems (frames, walls) and non-structural elements (facades, partitions, ceilings) are performed to highlight that these solutions are able to withstand earthquake shakings with negligible damage, consequently reducing the expected losses in terms of repair costs and downtime. The high performance of such types of technologies, and particularly of the integrated system, is also proved through 3D shake-table tests of a 1:2 scale two storey-two bay building, consisting of a low-damage timber-concrete structural skeleton and high performance or damage-control non-structural components/envelopes. The experimental campaign is fully described from the design of the specimen and of its structural/non-structural detailing, to the construction and assembly phases, to the test setup. Preliminary experimental results are provided, focusing on the seismic demand/performance of all the tested non-structural components. Finally, the importance of implementing a multi-performance design approach for nonstructural components is presented in the last part of the Thesis. An integrated seismic & energy cost/performance investigation of traditional vs. low-energy and/or low-damage façade systems is initially carried out, to highlight that the dynamic behaviour of these systems must be studied to better design the non-structural detailing. Furthermore, a multi-criteria decision analysis, including all the non-structural performance (structural, architectural, long-term) and the initial cost as criteria/sub-criteria, is proposed and developed in order to drive decisions on non-structural systems, i.e. defining the best solution/detailing among alternatives.

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Araújo, Vital Nai Quei Pereira. "Análise comparativa de modelos de cálculo de estruturas de betão armado." Master's thesis, 2013. http://hdl.handle.net/10316/38510.

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Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Nesta tese realizou-se uma abordagem não linear de uma viga contínua de betão armado, de dois tramos de um trabalho experimental anteriormente feito por Ana Maria S. Teixeira Bastos (1997, FEUP), e compara-se os resultados com programas comerciais de cálculo de elementos finitos. Na análise não linear utilizaram-se modelos elasto-plásticos e fendilhação para betão, aplicados através do Método de Elementos Finitos (MEF). Efectuou-se o dimensionamento de uma estrutura com modelos de análise-linear elástica com ou sem redistribuição. Comparou-se os resultados experimentais das vigas com os obtidos com os programas comerciais de software midas® FEA e Abaqus® CAE 6.10-1, usando elementos finitos bidimensionais, modelo elasto-plástico e modelo de fendilhação distribuída (“Smeared Crack”). E obteve-se conclusões relativas aos modelos utilizados, documentando de forma conveniente os casos de aplicação das ferramentas e modelos.
This thesis made an approach to linear and non-linear analysis of a reinforced concrete beam, the two spans of structure an experimental work previously done by Ana Maria S. Teixeira Bastos (1997, FEUP). The results were compared with commercial software’s of finite elements calculations. The elasto-plastic and smeared crack models are applied to twodimensional formulations of Finite Element Methods (FEM). The design of the structure considering the linear elastic behaviour with or without redistribution was made. The comparison of experimental results of beams with midas® FEA and Abaqus® CAE 6.10-1 commercial software´s was made, using two-dimensional finite elements with elasto-plasticity and the Smeared Crack models. The conclusions were made about the results obtained with the models used in the cases of application of the tools were documented in an appropriate way.

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Han, Je Heon. "Investigation on Wave Propagation Characteristics in Plates and Pipes for Identification of Structural Defect Locations." Thesis, 2013. http://hdl.handle.net/1969.1/151345.

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For successful identification of structural defects in plates and pipes, it is essential to understand structural wave propagation characteristics such as dispersion relations. Analytical approaches to identify the dispersion relations of homogeneous, simple plates and circular pipes have been investigated by many researchers. However, for plates or pipes with irregular cross-sectional configurations or multi-layered composite structures, it is almost impossible to obtain the analytical dispersion relations and associated mode shapes. In addition, full numerical modeling approaches such as finite element (FE) methods are not economically feasible for high (e.g., ultrasonic) frequency analyses where an extremely large number of discretized meshes are required, resulting in significantly expensive computation. In order to address these limitations, Hybrid Analytical/Finite Element Methods (HAFEMs) are developed to model composite plates and pipes in a computationally-efficient manner. When a pipe system is used to transport a fluid, the dispersion curves obtained from a “hollow” pipe model can mislead non-destructive evaluation (NDE) results of the pipe system. In this study, the HAFEM procedure with solid elements is extended by developing fluid elements and solid-fluid boundary conditions, resulting in the dispersion curves of fluid-filled pipes. In addition, a HAFEM-based acoustic transfer function approach is suggested to consider a long pipe system assembled with multiple pipe sections with different cross-sections. For the validation of the proposed methods, experimental and full FE modeling results are compared to the results obtained from the HAFEM models. In order to detect structural defect locations in shell structures from defect-induced, subtle wave reflection signals and eliminate direct-excitation-induced and boundary-reflected, relatively-strong wave signals, a time-frequency MUSIC algorithm is applied to ultrasonic wave data measured by using an array of piezoelectric transducers. A normalized, structurally-damped, cylindrical 2-D steering vector is proposed to increase the spatial resolution of time-frequency MUSIC power results. A cross-shaped array is selected over a circular or linear array to further improve the spatial resolution and to avoid the mirrored virtual image effects of a linear array. Here, it is experimentally demonstrated that the proposed time-frequency MUSIC beamforming procedure can be used to identify structural defect locations on an aluminum plate by distinguishing the defect-induced waves from both the excitation-generated and boundary-reflected waves.

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DI, RE PAOLO. "3D beam-column finite elements under tri-axial stess-strain states: non-uniform shear stress distribution and warping." Doctoral thesis, 2017. http://hdl.handle.net/11573/937922.

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In many engineering structures, the effects of shear and torsional loads are an important aspect of both the analysis and the design process. These effects are usually neglected in typical framed structures. However, in some relevant cases, such as bridges, shear walls or thin-walled frames, it is essential to account for the shear and torsional loads and their interaction with the other loading conditions to correctly reproduce the structural response. In this framework, the main task is to accurately describe the nonlinear structural response in terms of global behavior and local stress-strain distributions, reproducing the coupling of the stress components and its influence on the global response. This results even more important in large scale structures made of cementitious and/or innovative composite materials, widely adopted in nowadays professional practice. Indeed, these structures usually show degrading mechanisms and softening behavior. Hence, they require sophisticated computational models and ad hoc analysis strategies to predict the structure capacity under severe loading conditions. A standard approach to analyze these structures is the adoption of beam-column finite element (FE) models, which are often preferred with respect to two-dimensional (2D) plate/shell or three-dimensional (3D) FEs, because of their efficiency and low computational cost. However, most beam-column FE formulations are based on theclassical Euler-Bernoulli or Timoshenko theory, assuming the cross-sections to remain plane during the loading process. This assumption requires specific corrective measures, when the shear and torsion and the related warping effects are pronounced. This work discusses the simulation of RC members with a 3D 2-node beam FE that includes warping effects. The FE formulation in [1] is extended to allow the description of structural members with softening material behavior. The governing equations are derived from a four-field Hu-Washizu variational principle, with independent interpolation of the warping displacement field from the rigid section displacements, the generalized section deformations and the material stress fields. In particular, the warping of the cross-section is described by interpolating the out-of-plane displacement with the addition of a variable number of local degrees of freedom to those commonly used for the beam FE. The global nonlinear response and the local distributions of strains and stresses are described introducing a fiber cross-section discretization. Hence, the coupling of axial, flexural, shear and torsional effects in terms of material response is automatically taken into account. Focusing on RC structures, the damaging mechanisms of the concrete material is described by adopting a new 3D nonlinear constitutive relationship with plasticity and damage. This is an enhanced version of that proposed in [2] and introduces the description of the unilateral effects typically appearing in concrete-like materials, due to the crack opening and closure. A Drucker-Prager type plastic model is coupled with a two-parameter isotropic damage model, where two scalar variables are used to describe the damage in tension and compression, respectively. The localization problems and the related mesh-dependency, due to the softening material behavior, are controlled through a regularization technique based on a properly modified nonlocal integral procedure. For beam-column FEs, the nonlocal strain measures are evaluated performing the integration of the local generalized section deformations along the element axis, whereas for 2D FEs the nonlocal integration is performed considering the generalized membrane/plate deformations. The proposed model is implemented and validated through some correlation studies. These consider the numerical analysis of a series of plain concrete and RC beams subjected to torsional loads and of two RC shear walls. The results are compared with experimental measurements and with those of standard FE beam models.

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Ajith, V. "Wave Propagation in Healthy and Defective Composite Structures under Deterministic and Non-Deterministic Framework." Thesis, 2012. http://hdl.handle.net/2005/3253.

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Composite structures provide opportunities for weight reduction, material tailoring and integrating control surfaces with embedded transducers, which are not possible in conventional metallic structures. As a result there is a substantial increase in the use of composite materials in aerospace and other major industries, which has necessitated the need for structural health monitoring(SHM) of aerospace structures. In the context of SHM of aircraft structures, there are many areas, which are still not explored and need deep investigation. Among these, one of the major areas is the development of efficient damage models for complex composite structures, like stiffened structures, box-type structures, which are the building blocks of an aircraft wing structure. Quantification of the defect due to porosity and especially the methods for identifying the porous regions in a composite structure is another such area, which demands extensive research. In aircraft structures, it is not advisable for the structures, to have high porosity content, since it can initiate common defects in composites such as, delamination, matrix cracks etc.. In fact, there is need for a high frequency analysis to detect defects in such complex structures and also to detect damages, where the change in the stiffness due to the damage is very small. Lamb wave propagation based method is one of the efficient high frequency wave based method for damage detection and are extensively used for detecting small damages, which is essentially needed in aircraft industry. However, in order, to develop an efficient Lamb wave based SHM system, we also need an efficient computational wave propagation model. Developing an efficient computational wave propagation model for complex structures is still a challenging area. One of the major difficulty is its computational expense, when the analysis is performed using conventional FEM. However, for 1D And 2D composite structures, frequency domain spectral finite element method (SFEM), which are very effective in sensing small stiffness changes due to a defect in a structure, is one of the efficient tool for developing computationally efficient and accurate wave based damage models. In this work, we extend the efficiency of SFEM in developing damage models, for detecting damages in built-up composite structures and porous composite structure. Finally, in reality, the nature of variability of the material properties in a composite structure, created a variety of structural problems, in which the uncertainties in different parameters play a major part. Uncertainties can be due to the lack of good knowledge of material properties or due to the change in the load and support condition with the change in environmental variables such as temperature, humidity and pressure. The modeling technique is also one of the major sources of uncertainty, in the analysis of composites. In fact, when the variations are large, we can find in the literatures available that the probabilistic models are advantageous than the deterministic ones. Further, without performing a proper uncertain wave propagation analysis, to characterize the effect of uncertainty in different parameters, it is difficult to maintain the reliability of the results predicted by SFEM based damage models. Hence, in this work, we also study the effect of uncertainty in different structural parameters on the performance of the damage models, based on the models developed in the present work. First, two SFEM based models, one based on the method of assembling 2D spectral elements and the other based on the concept of coupling 2D and 1D spectral elements, are developed to perform high frequency wave propagation analysis of some of the commonly used built-up composite structures. The SFEM model developed using the plate-beam coupling approach is then used to model wave propagation in a multiple stiffened structure and also to model the stiffened structures with different cross sections such as T-section, I-section and hat section. Next, the wave propagation in a porous laminated composite beam is modeled using SFEM, based on the modified rule of mixture approach. Here, the material properties of the composite is obtained from the modified rule of mixture model, which are then used in SFEM to develop a new model for solving wave propagation problems in porous laminated composite beam. The influence of the porosity content on the parameters such as wave number, group speed and also the effect of variation in theses parameters on the time responses are studied first. Next, the effect of the length of the porous region (in the propagation direction) and the frequency of loading, on the time responses, is studied. The change in the time responses with the change in the porosity of the structure is used as a parameter to find the porosity content in a composite beam. The SFEM models developed in this study is then used in the context of wave based damage detection, in the next study. First ,the actual measured response from a structure and the numerically obtained response from a SFEM model for porous laminated composite beam are used for the estimation of porosity, by solving a nonlinear optimization problem. The damage force indicator (DFI) technique is used to locate the porous region in a beam and also to find its length, using the measured wave propagation responses. DFI is derived from the dynamic stiffness matrix of the healthy structure along with the nodal displacements of the damaged structure. Next, a wave propagation based method is developed for modeling damage in stiffened composite structures, using SFEM, to locate and quantify the damage due to a crack and skin-stiffener debonding. The method of wave scattering and DFI technique are used to quantify the damage in the stiffened structure. In the uncertain wave propagation analysis, a study on the uncertainty in material parameters on the wave propagation responses in a healthy metallic beam structure is performed first. Both modulus of elasticity and density are considered uncertain and the analysis is performed using Monte-Carlo simulation (MCS) under the environment of SFEM. The randomness in the material properties are characterized by three different distributions namely normal, Weibul and extreme value distribution and their effect on wave propagation, in beam is investigated. Even a study is performed on the usage of different beam theories and their uncertain responses due to dynamic impulse load. A study is also conducted to analyze the wave propagation response In a composite structure in an uncertain environment using Neumann expansion blended with Monte-Carlo simulation (NE-MCS) under the environment of SFEM. Neumann expansion method accelerates the MCS, which is required for composites as there are many number of uncertain variables. The effect of the parameters like, fiber orientation, lay-up sequence, number of layers and the layer thickness on the uncertain responses due to dynamic impulse load, is thoroughly analyzed. Finally, a probabilistic sensitivity analysis is performed to estimate the sensitivity of uncertain material and fabrication parameters, on the SFEM based damage models for a porous laminated composite beam. MCS is coupled with SFEM, for the uncertain wave propagation analysis and the Kullback-Leibler relative entropy is used as the measure of sensitivity. The sensitivity of different input variables on the wave number, group speed and the values of DFI, are mainly considered in this study. The thesis, written in nine chapters, presents a unified document on wave propagation in healthy and defective composite structure subjected to both deterministic and highly uncertain environment.

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Dissertations / Theses on the topic 'Non-structural element'

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