yes / The behaviour of seismic-resistant buildings relies heavily upon the inclusion of energy dissipating devices. For concentrically-braced frames, this function is accomplished by diagonal bracing members whose performance depends upon both cross-sectional properties and global slenderness. Traditionally preferred rectangular hollow sections are susceptible to local buckling, particularly in cold-formed tubes, owing to the residual stresses from manufacture. This paper explores the response of hollow and concrete-filled circular tubes under cyclic axial loading. The uniformity of the circular cross-section provides superior structural efficiency over rectangular sections and can be further optimised by the inclusion of concrete infill. A series of experiments was conducted on filled and hollow specimens to assess the merit of the composite section. Comparisons were drawn between hot-finished and cold-formed sections to establish the influence of fabrication on member performance. Two specimen lengths were utilised to assess the influence of non-dimensional slenderness. Parameters such as ductility, energy dissipation, tensile strength and compressive resistance are presented and compared with design codes and empirically derived predictions.

The three-dimensional linear theory of piezo-elasticity is used to analyse steady state vibrations of a simply supported rectangular laminated composite plate with piezoelectric (PZT) actuator and sensor patches either embedded in it or bonded to the its surfaces. It is assumed that different layers are perfectly bonded to each other. The method of Fourier series is used to find an analytical solution of the problem. The analytical solution is then applied to study the shape control of a steadily vibrating composite plate by exciting different regions of a PZT actuator. Numerical results for a thin and a thick plate containing one embedded actuator layer and one embedded sensor layer are presented. For the former case, the optimum location of the centroid of the excited rectangular region that will require minimum voltage to control the out-of-plane displacements is determined. Keeping the location of the centroid and the shape of the excited region fixed, we ascertain the voltage required as a function of the length of its diagonal to nullify the deflections of the plate. The maximum shear stress at the interface between the sensor and the lamina is found to be lower than that between the actuator and the lamina. The point of maximum output voltage from the sensor coincides with that of its peak out-of-plane displacement. The variations of displacement and stress components through the thickness for the thin and thick plates are similar. The transient finite deformations of a neo-Hookean beam or plate with PZT patches bonded to its upper and lower surfaces are simulated by the finite element method. The constitutive relation for the piezoelectric material is taken to be linear in the Green-Lagrange strain tensor but quadratic in the driving voltage. A code using 8-noded brick elements has been developed and validated by comparing computed results with either analytical solutions or experimental observations. The code is then used to study flexural waves generated by PZT actuators and propagating through a cantilever beam both with and without a defect in it. The computed results are compared with test observations and with the published results for the linear elastic beam. The effects of both geometrical and material nonlinearities are discussed. A simple feedback control algorithm is shown to annul the motion of a neo-Hookean plate subjected to an impulsive load. / Ph. D.

Developing machine learning enabled smart manufacturing is promising for composite structures assembly process. It requires accurate predictive analysis on deformation of the composite structures to improve production quality and efficiency of composite structures assembly. The novel composite structures assembly involves two challenges: (i) the highly nonlinear and anisotropic properties of composite materials; and (ii) inevitable uncertainty in the assembly process. To overcome those problems, we propose a neural network Gaussian process model considering input uncertainty for composite structures assembly. Deep architecture of our model allows us to approximate a complex system better, and consideration of input uncertainty enables robust modeling with complete incorporation of the process uncertainty. Our case study shows that the proposed method performs better than benchmark methods for highly nonlinear systems. / Master of Science / Composite materials are becoming more popular in many areas due to its nice properties, yet computational modeling of them is not an easy task due to their complex structures. More-over, the real-world problems are generally subject to uncertainty that cannot be observed,and it makes the problem more difficult to solve. Therefore, a successful predictive modeling of composite material for a product is subject to consideration of various uncertainties in the problem.The neural network Gaussian process (NNGP) is one of statistical techniques that has been developed recently and can be applied to machine learning. The most interesting property of NNGP is that it is derived from the equivalent relation between deep neural networks and Gaussian process that have drawn much attention in machine learning fields. However,related work have ignored uncertainty in the input data so far, which may be an inappropriate assumption in real problems.In this paper, we derive the NNGP considering input uncertainty (NNGPIU) based on the unique characteristics of composite materials. Although our motivation is come from the manipulation of composite material, NNGPIU can be applied to any problem where the input data is corrupted by unknown noise. Our work provides how NNGPIU can be derived theoretically; and shows that the proposed method performs better than benchmark methods for highly nonlinear systems.

Precast concrete hollow core floor units are frequently used in multistorey steel- framed buildings where they bear on to the top flanges of universal beams. The steel beam is normally designed in bending in isolation from the concrete slab and no account is taken of the composite beam action available with the precast units. Although some commercial data are avail- able, there is no general design guidance to cover the wide range of material and geometric variables found in this form of construction. This paper summarizes research carried out at the University of Nottingham on this form of construction and presents the results of three full-scale bending tests of steel beams acting com- positely with proprietary precast hollow core slabs. The 150 mm deep units were attached to the universal beams through 19 mm diameter headed shear studs, and tested in four-point bending over a span of 6 m. For typical geometry and serial sizes the composite beams were found to be twice as strong and nearly three times as sti as the equivalent isolated steel beams. The failure mode was ductile, and may be controlled by the correct use of small quantities of tie steel and in situ infill concrete placed between the precast units. To generalize the findings, isolated push- off tests and eccentric compression tests were used to study the horizontal interface shear resistance of the headed studs and the strength of the slab, respectively.

Yes / This paper presents experimental and numerical investigation on an innovative composite floor system with deconstructability. In this system, a composite slab formed with metal profiled decking is connected to a steel beam using demountable shear connectors. A series of push tests was conducted to investigate the behaviour of this form of shear connectors. In addition to the push tests, a full-scale composite beam was tested to failure in the laboratory under a number of cycles of monotonic loading. For direct comparison, a similar composite beam test was conducted using same section size, concrete strength, but using the conventional welded headed stud connectors. Test results showed that the behaviour of the composite beam with demountable shear connectors is comparable with the specimen with welded shear connectors. After the test was terminated, the demountable shear connectors were unfastened and the composite floor can be easily lifted off from the steel beam. Test result showed that these demountable shear connectors possess high ductility in comparison with the equivalent welded shear connectors. Simple design rules currently use in Eurocode 4 for the welded shear connections and Eurocode 3 for bolts are proposed to predict the shear resistance of this form of demountable shear connectors.

Yes / For composite beams with low degrees of shear connection, additional deflections occur due to slip in the shear connectors, which can be significant for beams with low degrees of shear connection. A design formula is presented for the effective stiffness of composite beams taking account of the stiffness of the shear connectors, which is compared to measured deflections of 6 symmetric beams and an 11m span composite beam of asymmetric profile. It is shown that the comparison is good when using a shear connector stiffness of 70 kN/mm for single shear connectors and 100 kN/mm for pairs of shear connectors per deck rib. Results of push tests on a range of deck profiles confirm these initial elastic stiffnesses. To ensure that the slip at the serviceability limit state does not lead to permanent deformations of the beam, it is proposed that the minimum degree of shear connection should not fall below 30% for un-propped beams and 40% for propped beams of symmetric cross-section. / European Commission

Advanced aerospace materials, including fibre reinforced polymer and ceramic matrix composites, are increasingly being used in critical and demanding applications, challenging not only the current damage prediction, detection, and quantification methodologies, but also the residual life of the structure. The main objective of this work consists of developing theoretical and experimental studies about residual strength for composite structures, which are damaged by impact loading, aided by a SHM system, which combines different methods. For this, it is necessary: to identify, and to localize damage, as well as to calculate the severity of the damage and to predict the residual strength of the composite structure. To achieve these goals, the research methodology should consider three methods: (1) Vibration Based Method (VBM); (2) Shearography Speckle (SS) and (3) Flexural After Impact (FAI). Composite plates, made of epoxy resin reinforced by carbon or glass fibre, are evaluated. Firstly, VBM provide Frequency Response Functions to be analysed by suitable metrics (including a new metric), which are compared in terms of their capability for damage identification and global location. Afterwards, the extension of impact damage is determined by using shearography speckle. This technique has demonstrated great potential for damage detection in composite laminated structures. The identification of the damage from the measurements performed with the SS technique is based on the analysis of disturbances in the speed field caused because of the different properties of the material. These abnormal deformations can be verified as typical strains in damaged structures. SS is a laser interferometry method sensitive to displacement gradient in a surface direction out of the plane. Under the action of a smaller load, the structure is deformed and the presence of damage is shown through local peculiarities of surface deformation observed field. Finally, a flexure after impact (FAI) test is used to evaluate its limitations and potentialities as a damage tolerance technique. The residual flexural strength of damaged specimens is evaluated by quasi-static four-point bending test. A new criterion based on a relationship between damage metric from VBM and FAI analysis is presented and discussed. Thus, these results are normalized by using the maximum load and the metrics for damage analyses, i.e. if there is no damage in the structure, then the metric returns zero value. If the structure is partially damaged then the metric returns a number between one and zero. In addition, if the structure is totally damaged (i.e. residual strength is lower than specified in design), then the metric returns a value equal one. Finally, it is discussed the advantages and limitations of this combination into the context of SHM system (Structural Health Monitoring System). / Materiais compósitos estão cada vez mais sendo usados em aplicações críticas e exigentes, desafiando não apenas as metodologias atuais de previsão de dano, detecção, quantificação, mas também da vida residual da estrutura. O principal objetivo deste trabalho consiste no desenvolvimento de estudos teóricos e experimentais sobre a resistência residual de estruturas de compósito, que são danificadas pelo carregamento de impacto, auxiliado por um sistema SHM, que combina diferentes métodos. Para isso, é necessário: identificar, localizar danos, bem como determinar a severidade dos danos e estimar a resistência residual da estrutura. Para atingir esses objetivos, a metodologia de pesquisa considerou três métodos: (1) Método baseado em vibração; (2) Shearography Speckle (SS) e (3) Flexão após Impacto (FAI). Placas de compósito, fabricadas em resina epóxi reforçada por fibra de carbono ou de vidro, são avaliadas. Em primeiro lugar, o método baseado em vibração produz Funções de Resposta em Frequência, que são analisadas através de métricas adequadas (incluindo uma nova métrica), que são comparadas em termos de sua capacidade de identificação de danos e de localização global. Depois disso, a extensão de danos causados pelo impacto é determinada empregando SS. Esta técnica tem demonstrado grande potencial na detecção de dano em estruturas laminadas compósito. A identificação do dano a partir das medidas realizadas com a técnica SS tem por base a análise das perturbações no campo de curvaturas causada devido à heterogeneidade das propriedades do material. Estas deformações anormais podem ser verificadas como deformações típicas de estruturas danificadas. A SS é um método de interferometria laser sensível ao gradiente de deslocamento de uma superfície na direção fora do plano. Sob a ação de um pequeno carregamento, a estrutura é deformada e a presença de danos é revelada através de singularidades locais do campo de deformação observado na superfície. Finalmente, teste de flexão após o impacto (FAI) é usado para avaliar suas limitações e potencialidades como uma técnica de tolerância ao dano. A resistência à flexão das amostras intactas e danificadas é avaliada por ensaio de flexão em quatro-pontos quase-estático. Um novo critério baseado em uma relação entre a métrica de dano prevista pelos métodos de vibração e a análise via FAI é apresentado e discutido. Assim, estes resultados são normalizados utilizando a carga máxima e as métricas de dano, ou seja, se não houver nenhum dano na estrutura, a métrica retorna valor igual a zero. Se a estrutura é parcialmente danificada, a métrica retorna um valor entre um e zero. Além disso, se a estrutura está totalmente danificada (ou seja, a resistência residual está abaixo do especificado em projeto), a métrica retorna um valor igual a um. Por fim, discutem-se as vantagens e limitações desta combinação para o contexto de sistema SHM (Sistema de Monitoramento da Integridade Estrutural).

Advanced aerospace materials, including fibre reinforced polymer and ceramic matrix composites, are increasingly being used in critical and demanding applications, challenging not only the current damage prediction, detection, and quantification methodologies, but also the residual life of the structure. The main objective of this work consists of developing theoretical and experimental studies about residual strength for composite structures, which are damaged by impact loading, aided by a SHM system, which combines different methods. For this, it is necessary: to identify, and to localize damage, as well as to calculate the severity of the damage and to predict the residual strength of the composite structure. To achieve these goals, the research methodology should consider three methods: (1) Vibration Based Method (VBM); (2) Shearography Speckle (SS) and (3) Flexural After Impact (FAI). Composite plates, made of epoxy resin reinforced by carbon or glass fibre, are evaluated. Firstly, VBM provide Frequency Response Functions to be analysed by suitable metrics (including a new metric), which are compared in terms of their capability for damage identification and global location. Afterwards, the extension of impact damage is determined by using shearography speckle. This technique has demonstrated great potential for damage detection in composite laminated structures. The identification of the damage from the measurements performed with the SS technique is based on the analysis of disturbances in the speed field caused because of the different properties of the material. These abnormal deformations can be verified as typical strains in damaged structures. SS is a laser interferometry method sensitive to displacement gradient in a surface direction out of the plane. Under the action of a smaller load, the structure is deformed and the presence of damage is shown through local peculiarities of surface deformation observed field. Finally, a flexure after impact (FAI) test is used to evaluate its limitations and potentialities as a damage tolerance technique. The residual flexural strength of damaged specimens is evaluated by quasi-static four-point bending test. A new criterion based on a relationship between damage metric from VBM and FAI analysis is presented and discussed. Thus, these results are normalized by using the maximum load and the metrics for damage analyses, i.e. if there is no damage in the structure, then the metric returns zero value. If the structure is partially damaged then the metric returns a number between one and zero. In addition, if the structure is totally damaged (i.e. residual strength is lower than specified in design), then the metric returns a value equal one. Finally, it is discussed the advantages and limitations of this combination into the context of SHM system (Structural Health Monitoring System). / Materiais compósitos estão cada vez mais sendo usados em aplicações críticas e exigentes, desafiando não apenas as metodologias atuais de previsão de dano, detecção, quantificação, mas também da vida residual da estrutura. O principal objetivo deste trabalho consiste no desenvolvimento de estudos teóricos e experimentais sobre a resistência residual de estruturas de compósito, que são danificadas pelo carregamento de impacto, auxiliado por um sistema SHM, que combina diferentes métodos. Para isso, é necessário: identificar, localizar danos, bem como determinar a severidade dos danos e estimar a resistência residual da estrutura. Para atingir esses objetivos, a metodologia de pesquisa considerou três métodos: (1) Método baseado em vibração; (2) Shearography Speckle (SS) e (3) Flexão após Impacto (FAI). Placas de compósito, fabricadas em resina epóxi reforçada por fibra de carbono ou de vidro, são avaliadas. Em primeiro lugar, o método baseado em vibração produz Funções de Resposta em Frequência, que são analisadas através de métricas adequadas (incluindo uma nova métrica), que são comparadas em termos de sua capacidade de identificação de danos e de localização global. Depois disso, a extensão de danos causados pelo impacto é determinada empregando SS. Esta técnica tem demonstrado grande potencial na detecção de dano em estruturas laminadas compósito. A identificação do dano a partir das medidas realizadas com a técnica SS tem por base a análise das perturbações no campo de curvaturas causada devido à heterogeneidade das propriedades do material. Estas deformações anormais podem ser verificadas como deformações típicas de estruturas danificadas. A SS é um método de interferometria laser sensível ao gradiente de deslocamento de uma superfície na direção fora do plano. Sob a ação de um pequeno carregamento, a estrutura é deformada e a presença de danos é revelada através de singularidades locais do campo de deformação observado na superfície. Finalmente, teste de flexão após o impacto (FAI) é usado para avaliar suas limitações e potencialidades como uma técnica de tolerância ao dano. A resistência à flexão das amostras intactas e danificadas é avaliada por ensaio de flexão em quatro-pontos quase-estático. Um novo critério baseado em uma relação entre a métrica de dano prevista pelos métodos de vibração e a análise via FAI é apresentado e discutido. Assim, estes resultados são normalizados utilizando a carga máxima e as métricas de dano, ou seja, se não houver nenhum dano na estrutura, a métrica retorna valor igual a zero. Se a estrutura é parcialmente danificada, a métrica retorna um valor entre um e zero. Além disso, se a estrutura está totalmente danificada (ou seja, a resistência residual está abaixo do especificado em projeto), a métrica retorna um valor igual a um. Por fim, discutem-se as vantagens e limitações desta combinação para o contexto de sistema SHM (Sistema de Monitoramento da Integridade Estrutural).

Recent developments show the applications of smart structure in different engineering fields. Smart structures can be used for shape and vibration control, structural health monitoring etc. Smart materials can be integrated to composite structure to enhance its abilities. Fiber reinforced composites are the advanced materials of choice in aerospace applications due to its high strength and stiffness, light weight and ability to tailor according to the design requirements. Due to complex manufacturing process and varying operating conditions, composites are susceptible to variation in material properties and damages. The present study focuses on the effect of uncertainties in material properties and damages on a smart composite structure. A cantilevered composite plate with surface mounted piezoelectric sensor/ actuator is considered in this study. The sensors and the actuators are connected through a conventional feedback controller and the controller is configured for vibration control application. Matrix cracks are considered as damage in the composite plate. To study the effect of material uncertainty, probabilistic analysis is performed considering composite material properties and piezoelectric coefficients as independent Gaussian random variables. Numerical results show that there is substantial change in dynamic response of the smart composite plate due to material uncertainties and damage. Deviation due to material uncertainty and damage can be compensated by actively tuning the feedback control system. Feedback control parameters can be properly adjusted to match the baseline response. Here baseline case represents the response of the undamaged smart composite plate with deterministic material properties. The change in feedback control parameters are identified as damage indicator. Feedback control based damage detection method is proposed for structural health monitoring in smart composite structure and robustness of the method is studied considering material uncertainties. Fractal dimension based damage detection method is proposed to detect localized matrix cracks in a composite plate with spatially varying material properties. Variation in material properties follows a two dimensional homogeneous Gaussian random field. Fractal dimension is used to extract the damage information from the static response of composite plate with localized matrix cracks. It is found that fractal dimension based approach is capable of detecting the location of the single and multiple damages from the static deflection curve. Robustness of the fractal dimension based damage detection method is studied considering spatial uncertainties in material properties.

Os pisos mistos aço-concreto de pequena altura caracterizam-se pelo embutimento da laje de concreto na altura da viga de aço, sendo a laje apoiada na mesa inferior do perfil. A principal vantagem deste sistema em relação à viga mista convencional é a redução da altura total do composto. Este trabalho tem como objetivo a criação de um modelo numérico construído no software de elementos finitos TNO DIANA®. O modelo proposto nesta pesquisa buscou subsídios para sua validação em resultados experimentais e numéricos realizados em outras pesquisas. Na fase de validação foram alterados diversos fatores a fim de avaliar a influência de cada um deles, calibrando o modelo até que os resultados se aproximassem dos experimentais. Depois que o modelo foi validado, foi analisada a influência de alguns parâmetros no comportamento global da estrutura, entre eles: a resistência do concreto (fck), a consideração de uma tela de armadura passiva colocada na capa de concreto com diferentes taxas de armadura e a variação da espessura da capa de concreto. Os resultados mostraram que o modelo consegue representar de maneira adequada o comportamento da estrutura apesar das simplificações consideradas para a modelagem. / Composite steel-concrete slim floors are characterized by the inlay of the concrete slab on the same plane of the steel beam, with the slab supported by the bottom flange of the profile. The main advantage of this system compared to the conventional mixed beam is the reduction of the overall height of the compound. This study aims to establish a numerical model built in finite element software TNO DIANA®. The model proposed in this research sought subsidies for its validation in experimental and numerical results achieved in others researches. In the validation phase were changed several factors to evaluate the influence of each of them, calibrating the model until the results come closer to the experimental. After the model has been calibrated, were analyzed the influence of some parameters on the overall behavior of the structure, among them: the strength of concrete (fck), the consideration of reinforcement bars placed on the slab with different rates and the variation of the thickness of the concrete slab. The results showed that the model can adequately represent the structural behavior despite the simplifications considered for modeling.