Within this work a study of the vibrations of laminated composite cantilevers exhibiting structural uncertainties and damage is accomplished. The study is performed within both the Classical Lamination (CLT) and the First-order Transverse Shear Deformation Theories (FSDT). Upon comparing the natural frequencies and mode shapes obtained by both theories, the effects of transverse shear deformation will be emphasized. Other nonclassical effects as e.g. the bending-twist coupling and the warping restraint on the cantilevered structure are also considered. As passive techniques of vibration control, structural tailoring and optimization are implemented. To deal with structural uncertainties, a probabilistic discretization technique for the governing system is developed. Statistical properties of natural frequencies are obtained by means of a second-moment method and a first-order perturbation technique. Structural tailoring is reconsidered to reduce the sensitivity of the dynamic behavior to parameter uncertainties. Next, the damage effect on the structure is considered in the design process. As a result, the problem of the robustness of structures in the presence of damage is addressed. This work also deals with the active feedback control of cantilevered structural systems. An efficient control technique for continuous structures, namely modal control, is adopted and the control gain is obtained by an optimal control law. The comparison of controlled and uncontrolled dynamic responses is made between two models based on CLT and FSDT with emphasis on the influence played by transverse shear deformation and warping restraint. / Ph. D.

Damage states in laminated composites were studied by considering the model problem of a laminated beam subjected to three-point bending. A combination of experimental and theoretical research techniques was used to correlate the experimental results with the analytical stress distributions. The analytical solution procedure was based on the stress formulation approach of the mathematical theory of elasticity. The solution procedure is capable of calculating the ply-level stresses and beam displacements for any laminated beam of finite length using the generalized plane deformation or plane stress state assumption. The beam lamination can be any arbitrary combination of monoclinic, orthotropic, transversely-isotropic, and isotropic layers. Prior to conducting the experimental phase of the study, the results from preliminary analyses were examined. Significant effects in the ply-level stress distributions were seen depending on the fiber orientation, aspect ratio, and whether or not a grouped or interspersed stacking sequence was used. The experimental investigation was conducted to determine the different damage modes in laminated three-point bend specimens. The test matrix consisted of three-point bend specimens of 0° unidirectional, cross-ply, and quasi-isotropic stacking sequences. The dependence of the damage initiation loads and ultimate failure loads were studied, and their relation to damage susceptibility and damage tolerance of the beam configuration was discussed. Damage modes were identified by visual inspection of the damaged specimens using an optical microscope. The four fundamental damage mechanisms identified were delaminations, matrix cracking, fiber breakage, and crushing. The correlation study between the experimental results and the analytical results was performed for the midspan deflection, indentation, damage modes, and damage susceptibility. The correlation was primarily based on the distributions of the in-plane component of shear stress, t_xz. The exceptions were for the case of a very small aspect ratio (less than 1.0) where the crushing mode of damage was predicted based on the maximum contact pressure, and for very large aspect ratios (greater than 12.0) where a maximum tensile bending stress criterion was used for predicting the damage initiation loads. / Ph. D.

Scale model testing can improve the cost-effectiveness of composite structures by reducing the reliance on full size component testing. Use of scale models requires the relationship be known between the responses of the small scale model and full size component. This relationship may be predicted by dimensional analysis or through mechanics formulations. The presence of physical constraints may prevent the complete reproduction of all responses in small scale models. Scaling relationships may not be available at the level necessary to predict all scaled responses. Investigations of the scalability of composite structures are needed in order to evaluate the reliability of small scale model predictions of the responses of full size components. The scaling of the responses of graphite-epoxy laminated composite Z-section stiffeners subjected to uniaxial, compressive loading has been evaluated. The response regimes investigated are prebuckling, initial local buckling, postbuckling and crippling. A mechanistic approach to scaling has been used, in which the scalability of the responses has been judged relative to governing mechanics models. A linked-plate analytical model has been obtained which predicts the buckling loads, and from which two nondimensional load parameters have been obtained. The finite element method has been used for prediction of the buckling and postbuckling responses. The analytical and numerical analyses were used to define an experimental program involving fifty-two specimens of seventeen basic geometrical configurations and three stacking sequences. The buckling, postbuckling and crippling responses were largely determined by the flange-to-web width ratio and both the absolute and relative values of the bending stiffnesses. Buckling loads increased with decreasing flange width and the laminate orthotropy ratio, and increasing flange-to-web corner radii and laminate thickness. The postbuckling load range was the greatest for specimens having wider flanges, but the failure stresses were greatest among the narrower specimens. The crippling mechanisms included flange free edge delamination at both nodal and anti-nodal axial positions, material crushing in the flange-to-web corner at nodal axial positions, and ply splitting in the flange-to-web corner at anti-nodal axial locations. The constraint of the potted end supports of the experimental specimens was not scaled. The effect of displacements within the end supports was manifested by lower prebuckling axial stiffnesses than predicted based on the gage length properties alone. This phenomenon required a post-test adjustment to the data in order to permit comparisons of the experimental and finite element predictions of the response of the gage length on an equivalent basis. Once corrected, the prebuckling stiffnesses were generally observed to have scaled. One of the nondimensional load parameters normalized the buckling loads for specimens of various web widths only. The second parameter normalized the buckling loads for all of the geometric and material variables contained in the model. This parameter also normalized the postbuckling loads, and is, therefore, a general nondimensional parameter for the buckling and postbuckling responses of the Z-section stiffeners. No scale effects were observed in the buckling response. The quality of the postbuckling load predictions degraded with the width of the postbuckling load range. It was not determined whether genuine scale effects were present in the postbuckling response or whether the observed error was a result of inadequate modelling of structural and material nonlinearities or other effects such as damage development in the specimens. Good correlation between experimental and finite element predictions of the out-of-plane displacements and load-axis strains has been demonstrated. Predicted local material strain development has been related to the structural deformation characteristics. Consideration of individual strain values, however, could not predict which of several competing failure modes would determine the actual crippling response. Neither could the strain data provide any quantitative prediction of the crippling loads. Thus, the determination of strength scale effects is hindered by the complex structural-material interaction and the lack of a mechanics-based interactive failure model. / Ph. D.

[pt] As vigas mistas são um exemplo das cada vez mais difundidas estruturas mistas, e resultam da associação de uma viga de aço com uma laje de concreto ou mista, ligadas por meio dos conectores de cisalhamento. Dentre os diversos tipos existentes pode-se citar os pernos com cabeça (stud bolts), perfis C e o Perfobond. Um conector alternativo foi proposto para estruturas mistas, o TPerfobond, que deriva do conector Perfobond acrescentando a componente da mesa, que trabalha como um bloco. Combina portanto a alta resistência do conector tipo bloco com a ductilidade e resistência ao levantamento dos furos do Perfobond. Para determinação da sua capacidade resistente foi realizado um programa experimental envolvendo cinquenta e dois ensaios do tipo push-out com conectores Perfobond, T-Perfobond e T, um ensaio em escala real e uma modelagem numérica. Os ensaios push-out estabeleceram a carga máxima e a capacidade de deformação dos conectores. Procurou-se com o ensaio em escala real determinar a resistência última da estrutura, o modo de ruína, as deflexões e as deformações, e validar o comportamento do conector TPerfobond em uma estrutura real. Os resultados indicaram que o modelo de plastificação total pode ser adotado para a determinação do momento fletor resistente em vigas mistas bi-apoiadas com conectores T-Perfobond. Os modelos numéricos auxiliaram no estudo da capacidade de deformação da mesa do conector T-Perfobond, e na investigação das vigas com interação total ou parcial ao cisalhamento. Sob o ponto de vista econômico, um estudo comparativo dos custos dos conectores Perfobond, T-Perfobond e Studs foi conduzido e concluiu-se que os conectores Perfobond e T-Perfobond são mais econômicos em até 33% que os conectores Studs. Dentre as vantagens estruturais e construtivas de utilizar os tipos de conectores alternativos destacam-se: a alta resistência, a fácil produção e instalação no perfil de aço através de solda corrente, e bom comportamento à fadiga. / [en] Steel and composite beams have been extensively used in buildings and bridges. The component that assures the shear transfer between the steel profile and the concrete deck, enabling the composite action to develop, is the shear connector. Among the different types of connectors the headed studs, C sections and the Perfobond may be referred. An alternative connector has been proposed for composite structures, the T-Perfobond. The main difference between the studied Perfobond and T-Perfobond connectors is the presence of a flange, providing a further anchorage to the system. This connector combines the high strength of the block connector with ductility and resistance to uplift of the Perfobond holes. To evaluate their shear capacity an experimental programme that consisted of fifty-two push-out test and one full-size test, and some numerical analysis were performed. The push-out tests have established the maximum load capacity and deformation of the connectors. The full-size test has determined the composite beam load carrying capacity, typical failure modes, associated stresses and displacements, and has validated the behaviour of the T- Perfobond connector in an actual structure. The results indicated that the plastic distribution can be adopted for T- Perfobond connectors. The numerical analysis helped in the assessment of the deformation capacity of the T-Perfobond flange connector, and the investigation of the composite beam with total or partial connection. From the economic point of view, a comparative study of the cost of Perfobond, TPerfobond and Studs connectors was conducted and it was concluded that the Perfobond and T-Perfobond connectors lead to an economy of up to 33% when comparing to the Studs connectors. Among the structural and constructive advantages of the use of alternative types of connectors, an high resistance, easy manufacturing and installation of steel beam by current welding and good performance to fatigue may be referred.

[pt] Nos trabalhos já concluídos nesta linha de pesquisa foram desenvolvidos protótipos de deck-metálico (steel-deck), empregando-se diversas formas de ligação entre a chapa de aço e o concreto armado, tais como: corrugações de alma (Andrade, 1986), parafusos auto-brocantes (Takey, 2001), septos em perfís tipo bandeja (Vieira, 2003) e corrugações circulares profundas (Beltrão,2003). Com a intenção de se desenvolver um novo perfil metálico que apresentasse uma boa aderência mecânica entre o concreto e o aço e com características de comportamento dúctil, estudou-se várias formas da seção transversal ideal. Variáveis como peso, altura, espessura, tensão de escoamento, vão máximo, e capacidade de suporte de carga foram consideradas. Após definição e otimização da seção do perfil metálico, foi efetuado um estudo experimental composto de uma série de ensaios. Foram executados dois ensaios de arrancamento (pull-out), nove ensaios de flexão do perfil metálico e um ensaio em escala real da laje mista. Os ensaios tipo pull-out foram executados para estabelecer a carga última de deslizamento na interface aço/concreto. Os ensaios dos perfis metálicos serviram para verificar a rigidez dos mesmos durante a fase de concretagem. Procurou-se com o ensaio em escala real determinar a resistência última da estrutura, o modo de ruína, as deflexões e as deformações. A fase final compreendeu a comparação dos resultados experimentais com os dos trabalhos desenvolvidos por Takey e Beltrão, bem como com resultados teóricos para validação de resultados do sistema proposto de laje mista. / [en] The research work in composite slabs so far conducted has investigated various alternatives for the development of an economic and efficient composite slab system. These alternatives evaluated the effectiveness of the concrete to steel plate bonding by means of: web corrugations (Andrade, 1986), self-drilling bolts (Takey, 2001), cold formed channel sections with diaphragms (Vieira, 2003), and the used of deep circular corrugations, (Beltrão, 2003). The present investigation main objective was to develop a cold formed profile presenting an efficient connection between the concrete and the steel profile that yields a ductile behaviour for such system. The first step of the investigation was devoted to the assessment of an optimum cold-formed profile geometry. This task was made taking into account parameters like: profile weight, plate thickness, yield stress, maximum span and load carrying capacity among others. Following the definition of the optimum cold formed steel profile an experimental program was conceived and executed. The first part of the experiments consisted on pull-outs tests made to access the concrete to steel bond resistance. This was followed by simple supported tests on the cold formed steel profile to evaluate their stiffness during concrete casting operation. Finally a full-scale composite slab system was performed. The main aim of this test was to determine the composite system load carrying capacity, typical failure modes, associated stresses and displacements. The final phase of this dissertation depicts comparisons of the already mentioned experiments to other tests made by Takey (Takey, 2001), and Beltrão (Beltrão, 2003), as well as comparison of theoretical results, to validate the proposed composite slab system results.

Thesis (MEng (Civil Engineering))--University of Stellenbosch, 2007. / In the past use was made of prescriptive design rules to provide for the fire limit state. Modern Design Codes provide the scope and the means to design for fire in a performance based manner. The Eurocode provides guidance on the actions on structures exposed to fire as well as methods to predict the structural behaviour of elements in fire. Structural designers can now incorporate the use of parametric fire curves to describe compartment fires. These fire models are not an extension of the old nominal standard temperature time curves. Parametric curves are analytical models that are based on natural fire behaviour. The temperature in the fire compartment can be predicted in a scientific manner taking account of fire loads, ventilation conditions and compartment characteristics. The combination of rational fire models and temperature dependant structural behaviour enables designers to predict whether elements will fail during a fire. This is an improvement on the empirical prescriptive fire resistance ratings, used to date. Multi-storey steel framed structures, with composite floors, were identified as structures with high inherent fire resistance and robust behaviour. The composite beams in the floor structure were identified as critical elements when subjected to fire. The deterministic design and the reliability level of these elements were studied. Deterministic fire design procedures are presented that can be used to design unprotected composite beams for the fire limit state. The reliability of the deterministic design procedures was evaluated through a First Order Reliability Method. Parametric fire curves are suitable for reliability analysis due to the fact that they can be described by stochastic variables. The fire load was determined to be the dominant variable influencing the reliability level of the composite beams. The ventilation conditions of the fire compartment also has important implications for the temperature development of the composite beams. The reliability analyses results show that reasonably sized composite beams can be used as unprotected elements in smaller fire compartments with moderate fire loads. It was found that a structural element’s total probability of failure can be improved by the use of active fire fighting measures. The benefit of active fire fighting measures can be quantified by considering their probability of failure. By use of conservative assumptions and basic knowledge of fire engineering principles, rational design methods can provide safe and economical solutions for fire design of composite beams.

Composite construction is widely used worldwide and is undergoing significant technological development. New Zealand is part of this development, with new beam options incorporating multiple unstiffened web openings and new deck profiles supported by extensive testing. However, one area where relatively little research has been undertaken is in the interaction of the composite slab with the seismic resisting system under lateral loading. In order to provide important new information in this area, a series of full scale beam-column-joint-slab subassemblies were tested at the University of Canterbury. Specimens tested had moment end plate connections and different combinations of deck tray direction, and isolation of the slab from the column. An additional test uses a sliding-hinge type connection to assess the effect of the floor slab in this type of low damage connection. In these tests the lateral capacity of the seismic resisting system was increased by up to 25% due to the presence of the slab in contact with the column. The increase in capacity is 10% greater for decking running in longitudinal direction than in the transverse direction as a result of a more substantial full depth slab bearing on the column. The floor slabs of the subassemblies with the slab cast against the column all showed a higher level of damage than for those with the isolated column and the post ultimate strength degradation of the subassemblies without special detailing was significant. The subassembly with a section of full depth slab surrounding the column also exhibited a higher capacity but with an improved post ultimate strength degradation. All moment end plate subassemblies sustained drifts of up to 5% without significant strength loss. The sliding hinge joint showed little signs of damage under testing to 5% drift. Some inelastic deformation of the connection and beams was noted above 5% drift. Results from both testing and numerical modelling have shown that the current methods used to design these systems are conservative but within 15% of the values observed. Further testing and modelling will be necessary before any meaningful changes can be made to the way in which these systems are designed. Recommendations have been made regarding the placements of shear studs in plastic hinge zones and the provision of slab isolation around beam-column connections.

This thesis investigates the behaviour of hollow and concrete filled steel columns fabricated from thin steel plates. The columns are investigated under axial, uniaxial and biaxial loading. The currently available international standards for composite structures are limited to the design of concrete filled steel columns with compact sections and yield stress of steel up to 460 N/mm2. This thesis consists of both experimental and analytical studies and design recommendations for future use. Three comprehensive series of experimental tests are conducted on hollow and concrete filled steel columns. The principal parameters that have been considered in the test programmes are the slenderness of the component plates, the yield stress of the steel and the loading conditions. In the first test series, three slender hollow steel columns and three slender composite columns are tested under uniaxial loading. The steel utilised is mild steel. High strength steel is utilised in the second test programme. In this test series four stub columns, eight short columns and eight slender columns are tested, each set consists of four hollow and four composite columns. Short columns are tested under axial loading to investigate the confinement effect provided by the steel casing. Slender columns are tested under uniaxial loading to investigate the coupled instability of local and global buckling. The third test programme is quite novel and considers the behaviour of hollow and concrete filled steel columns fabricated with high strength structural steel plate and subjected to biaxial bending. In this test eight short columns and ten slender columns each of them consisting of hollow and composite columns are investigated under biaxial loading. Analytical models are developed herein to elucidate the behaviour of the hollow and composite columns considering cross section slenderness, yield stress and loading conditions. An iterative model considering the coupled global and local buckling in the elastic and plastic range incorporating material nonlinearities is developed to investigate the behaviour of slender columns fabricated from mild steel. An improved deformation control model is developed to investigate the behaviour of slender high strength steel columns considering the confinement effect and local and post-local buckling in the elastic and plastic range. Then a numerical model for biaxial bending is developed to study the behaviour of short and slender concrete filled high strength steel columns under biaxial loading incorporating interaction buckling considering material and geometric nonlinearities. The scope of the thesis presents a wide range of experimental and theoretical studies of an extremely novel nature. It demonstrates the benefit of confinement and the consideration of local and post-local buckling in the elastic and plastic range. It is hoped that this research will contribute to the area of composite steel-concrete structural applications.

Use of composite steel construction with precast hollow core slabs is now popular in the UK,but the present knowledge in shear capacity of the headed shear studs for this type of composite construction is very limited. Currently, all the information is based on the results obtained from experimental push-off tests. A finite element model to simulate the behaviour of headed stud shear connection in composite beam with precast hollow core slabs is described. The model is based on finite element method and takes into account the linear and non-linear behaviour of all the materials. The model has been validated against the test results, for which the accuracy of the model used is demonstrated. Parametric studies showing the effect of the change in transverse gap size, transverse reinforcement diameter and in-situ concrete strength on the shear connection capacity are presented.

Thesis (M.S.) in Civil Engineering--University of Maine, 2001. / Includes vita. Includes bibliographical references (leaves 226-228 (v. 1)).