This study presents a concept that provides a structural dynamicist the ability to analyze the effects of making sophisticated (beam-type) structural changes to a structural system whose modal database is known. The modification technique combines the Dual Modal Space Modification Method (DMSM) and the Transfer-Matrix Method to institute general beam modifications. The DMSM method is employed to implement the beamtype modification, while the transfer-matrix method is used to formulate the modification element. The use of transfer-matrix methods provides the ability to model virtually any beam modification a designer might consider in terms of the two points being connected without the loss of any dynamic information between the points. The result is a modification scheme which is both flexible and universal. Two numerical examples are considered. One example demonstrated the performance of the modification scheme in instituting a severe structural change. The second example demonstrated a change to a complex structure. In both cases, continuum beams were used as modification elements. The results of these two examples show that the modification scheme provides very promising results, providing an adequate modal database was used. Modal truncation was determined to be the primary source of error. / Ph. D.

Optimization is a decision making process to solve problems in a number of fields including engineering mechanics. Bio-inspired optimization algorithms, including genetic algorithm (GA), have been studied for many years. There is a large literature on applying the GA to mechanics problems. However, disadvantages of the GA include the high computational cost and the inability to get the global optimal solution that can be found by using a honeybee-inspired optimization algorithm, called the New Nest-Site Selection (NeSS). We use the NeSS to find optimal parameters for three mechanics problems by following the three processes: screening, identifying relationships, and optimization. The screening process identifies significant parameters from a set of input parameters of interest. Then, relationships between the significant input parameters and responses are established. Finally, the optimization process searches for an optimal solution to achieve objectives of a problem. For the first two problems, we use the NeSS algorithm in conjunction with a third order shear and normal deformable plate theory (TSNDT), the finite element method (FEM), a one-step stress recovery scheme (SRS) and the Tsai-Wu failure criterion to find the stacking sequence of composite laminates and the topology and materials for doubly curved sandwich shells to maximize the first failure load. It is followed by the progressive failure analysis to determine the ultimate failure load. For the sandwich shell, we use the maximum transverse shear stress criterion for delineating failure of the core, and also study simultaneously maximizing the first failure load and minimizing the mass subject to certain constraints. For composite laminates, it is found that the first failure load for an optimally designed stacking sequence exceeds that for the typical [0°/90°]₅ laminate by about 36%. Moreover, the design for the optimal first failure load need not have the maximum ultimate load. For clamped laminates and sandwich shells, the ultimate load is about 50% higher than the first failure load. However, for simply supported edges the ultimate load is generally only about 10% higher than the first failure load. For the atmospheric spray process, we employ the NeSS algorithm to find optimal values of four process input parameters, namely the argon flow rate, the hydrogen flow rate, the powder feed rate and the current, that result in the desired mean particle temperature and the mean particle velocity when they reach the substrate. These optimal values give the desired mean particle temperature and the mean particle velocity within 5% of their target values. / Ph. D. / An optimization process iteratively searches for the best solution from all feasible solutions in the search space that satisfy prespecified criteria. Optimization problems consist of sets of parameters, constraints, and objective functions. Here we use a honeybee-inspired optimization algorithm, called the New Nest-Site Selection (NeSS), to find optimal parameters for three mechanics problems. In the first problem, we optimize the design of an assembly of layers of unidirectional fiber-reinforced materials called composite laminates. Because of their high specific strength and directional-dependent stiffness as compared to those of metals, the composite laminates are being increasingly used in aerospace and automotive industries. After having analyzed deformations of a composite laminate, a failure criterion is used to determine if any point in the structure has failed. The minimum load for which the failure criterion is satisfied at a point is called the first ply failure load. Here we determine the fiber orientation angle in each layer of a rectangular laminate deformed statically by transverse loads applied on the top surface that maximizes the first ply failure load. Subsequently, the load is incrementally increased for the optimally designed laminate and the strength of the failed elements is degraded till the structure cannot support any additional load. The maximum load a structure can support is called the ultimate load. It is found that for a laminate with all edges clamped, the ultimate load can be 40% more than the first ply failure load. We extend the above work to design an optimal geometry and an optimal combination of materials of the facesheets and the core that simultaneously maximizes the first failure load, minimizes the weight of a doubly curved sandwich shell, and satisfies pre-specified constraints. The doubly curved sandwich structure of interest here is comprised of two thin parallel unidirectional fiber-reinforced facesheets bonded to and enclosing a relatively thick mid-layer made of a material softer and lighter than that of the facesheets. The sandwich structures are widely used in aircraft, marine, automobile, and civilian infrastructures. It is found that optimal designs for doubly curved sandwich shells strongly depend upon how the shell edges are supported, and shells designed for the maximum first failure load need not have the maximum ultimate load. An atmospheric plasma spray process (APSP) has been successfully used to coat components for gas turbines, airframe, engines and drive trains, and silicon chips. In the APSP, coating powder is injected into the plasma, which is a mixture of ionized gases such as argon, hydrogen, and helium, through a powder port generally oriented perpendicular to the plasma jet axis. Through interactions with the plasma jet, the particles are accelerated, heated and partially melted before they strike the substrate and are deposited on it to form a coating. It is believed that the coating properties and its quality depend on the particles’ temperature and velocity when they hit the substrate. Here we determine optimum values of four input parameters, namely, the argon flow rate, the hydrogen flow rate, the current, and the powder feed rate to achieve the desirable mean particles’ temperature and the mean particles’ velocity. It is found that the four processes input parameters can be optimized to attain particles’ characteristics within 5% of their prespecified desired values.

Yes / Despite the abundant use of polyethylene oxides (PEOs) and their integration as an excipient in numerous pharmaceutical products, there have been no previous reports of applying this important thermoplastic polymer species alone to fused deposition modelling (FDM) 3D printing. In this work, we have investigated the manufacture of oral doses via FDM 3D printing by employing PEOs as a backbone polymer in combination with polyethylene glycol (PEG). Blends of PEO (molecular weight 100 K, 200 K, 300 K, 600 K or 900 K) with PEG 6 K (plasticiser) and a model drug (theophylline) were hot-melt extruded. The resultant filaments were used as a feed for FDM 3D printer to fabricate oral dosage forms (ODFs) with innovative designs. ODFs were designed in a radiator-like geometry with connected paralleled plates and inter-plate spacing of either 0.5, 1, 1.5 or 2 mm. X-ray diffraction patterns of the filaments revealed the presence of two distinctive peaks at 2θ = 7° and 12°, which can be correlated to the diffraction pattern of theophylline crystals. Blends of PEO and PEG yielded filaments of variable mechanically resistance (maximum load at break of 357, 608, 649, 882, 781 N for filament produced with PEO 100 K, 200 K, 300 K, 600 K or 900 K, respectively). Filaments of PEO at a molecular weight of 200–600 K were compatible with FDM 3D printing process. Further increase in PEO molecular weight resulted in elevated shear viscosity (>104 Pa.S) at the printing temperature and hindered material flow during FDM 3D printing process. A minimal spacing (1 mm) between parallel plates of the radiator-like design deemed essential to boost drug release from the structure. This is the first report of utilising this widely used biodegradable polymer species (PEOs and PEG) in FDM 3D printing.

Yes / This paper presents an integrated model for shear friction strength of monolithic concrete interfaces derived from the upper-bound theorem of concrete plasticity. The model accounts for the effects of applied axial stresses and transverse reinforcement on the shear friction action at interfacial shear cracks. Simple equations were also developed to generalize the effectiveness factor for compression, ratio of effective tensile to compressive strengths and angle of concrete friction. The reliability of the proposed model was then verified through comparisons with previous empirical equations and 103 push-off test specimens compiled from different sources in the literature. The previous equations considerably underestimate the concrete shear transfer capacity and the underestimation is notable for the interfaces subjected to additional axial stresses. The proposed model provides superior accuracy in predicting the shear friction strength, resulting in a mean between experimental and predicted friction strengths of 0.97 and least scatter. Moreover, the proposed model has consistent trends with test results in evaluating the effect of various parameters on the shear friction strength.

Machine learning techniques promise to greatly accelerate structural design and optimization. In this thesis, deep learning and active learning techniques are applied to different non-convex structural optimization problems. Finite Element Analysis (FEA) based standard optimization methods for aircraft panels with bio-inspired curvilinear stiffeners are computationally expensive. The main reason for employing many of these standard optimization methods is the ease of their integration with FEA. However, each optimization requires multiple computationally expensive FEA evaluations, making their use impractical at times. To accelerate optimization, the use of Deep Neural Networks (DNNs) is proposed to approximate the FEA buckling response. The results show that DNNs obtained an accuracy of 95% for evaluating the buckling load. The DNN accelerated the optimization by a factor of nearly 200. The presented work demonstrates the potential of DNN-based machine learning algorithms for accelerating the optimization of bio-inspired curvilinearly stiffened panels. But, the approach could have disadvantages for being only specific to similar structural design problems, and requiring large datasets for DNNs training. An adaptive machine learning technique called active learning is used in this thesis to accelerate the evolutionary optimization of complex structures. The active learner helps the Genetic Algorithms (GA) by predicting if the possible design is going to satisfy the required constraints or not. The approach does not need a trained surrogate model prior to the optimization. The active learner adaptively improve its own accuracy during the optimization for saving the required number of FEA evaluations. The results show that the approach has the potential to reduce the total required FEA evaluations by more than 50%. Lastly, the machine learning is used to make recommendations for modeling choices while analyzing a structure using FEA. The decisions about the selection of appropriate modeling techniques are usually based on an analyst's judgement based upon their knowledge and intuition from past experience. The machine learning-based approach provides recommendations within seconds, thus, saving significant computational resources for making accurate design choices. / Doctor of Philosophy / This thesis presents an innovative application of artificial intelligence (AI) techniques for designing aircraft structures. An important objective for the aerospace industry is to design robust and fuel-efficient aerospace structures. The state of the art research in the literature shows that the structure of aircraft in future could mimic organic cellular structure. However, the design of these new panels with arbitrary structures is computationally expensive. For instance, applying standard optimization methods currently being applied to aerospace structures to design an aircraft, can take anywhere from a few days to months. The presented research demonstrates the potential of AI for accelerating the optimization of an aircraft structures. This will provide an efficient way for aircraft designers to design futuristic fuel-efficient aircraft which will have positive impact on the environment and the world.

A crescente utilização do aço inoxidável como elemento estrutural despertou o interesse de clientes, arquitetos e engenheiros nos últimos anos. Apesar do custo ainda elevado, a sua aplicação na construção civil vem substituindo outros elementos estruturais. Seja por sua alta resistência à corrosão, aumentando a relação custo benefício; sua estética, proporcionando formas cada vez mais ousadas ou; seu apelo ambiental, gerando menos resíduos no meio ambiente. As subestações representam um papel importante no fornecimento de energia. Como possuem grande complexidade para manutenção, foi escolhida a estrutura suporte de seu barramento, para o dimensionamento em aço inoxidável. Desta forma, minimizando as paradas para realização de manutenções das estruturas, possibilitando maior qualidade no fornecimento de energia elétrica. Para fins comparativos foi escolhido o projeto de uma SE existente, cuja estrutura de suporte do barramento, foi construída por treliças formadas por cantoneiras de aço carbono galvanizado. Inicialmente, o dimensionamento foi desenvolvido utilizando perfis H e I funcionando como viga-coluna para os dois tipos de aço. Num segundo momento, a estrutura foi dimensionada como treliças planas. Todos os dimensionamentos foram realizados de acordo com as prescrições normativas do EUROCODE 3. Após realização dos dimensionamentos, foram apresentadas as análises comparativas dos custos envolvidos para os tipos de aço. Abordando o investimento inicial, os gastos com manutenção ao longo da vida e os custos elétricos agregados à redução das paradas para manutenção. / The increasing use of stainless steel as a structural element motivated, in recent years, the continuous interest of customers, architects and engineers. Despite its high cost, its application in construction have been replacing other structural elements. This is mainly due to its high corrosion resistance that increases its cost-effective ratio, its aesthetic that enables the construction of increasingly bold forms and its environmental appeal that generates less environmental waste. The electric power substations represent an important role in the global energy supply. Since its maintenance is a complex and costly process, one of its bus support structure was chosen to be designed in stainless steel. This strategy minimizes the number of stoppages for structural maintenance, enabling a higher quality power supply. For comparative purposes an existing power substation has been chosen where the bus supporting structure was made of galvanized carbon steel angle bar trusses. Initially, the design adopted I and H profiles functioning as beam-column for the two types of steel analyzed. In a second stage, the structure was designed as a plane truss. All designs were performed in accordance to the requirements of EUROCODE 3 standard. This was followed by comparative analyses of the costs involved for the studied steel types. These analyses involved the initial investment assessment properly contextualized with the posterior spending on maintenance and electrical costs of the stoppages and were set against the gains in reducing the downtime for maintenance of the stainless steel solution.

A crescente utilização do aço inoxidável como elemento estrutural despertou o interesse de clientes, arquitetos e engenheiros nos últimos anos. Apesar do custo ainda elevado, a sua aplicação na construção civil vem substituindo outros elementos estruturais. Seja por sua alta resistência à corrosão, aumentando a relação custo benefício; sua estética, proporcionando formas cada vez mais ousadas ou; seu apelo ambiental, gerando menos resíduos no meio ambiente. As subestações representam um papel importante no fornecimento de energia. Como possuem grande complexidade para manutenção, foi escolhida a estrutura suporte de seu barramento, para o dimensionamento em aço inoxidável. Desta forma, minimizando as paradas para realização de manutenções das estruturas, possibilitando maior qualidade no fornecimento de energia elétrica. Para fins comparativos foi escolhido o projeto de uma SE existente, cuja estrutura de suporte do barramento, foi construída por treliças formadas por cantoneiras de aço carbono galvanizado. Inicialmente, o dimensionamento foi desenvolvido utilizando perfis H e I funcionando como viga-coluna para os dois tipos de aço. Num segundo momento, a estrutura foi dimensionada como treliças planas. Todos os dimensionamentos foram realizados de acordo com as prescrições normativas do EUROCODE 3. Após realização dos dimensionamentos, foram apresentadas as análises comparativas dos custos envolvidos para os tipos de aço. Abordando o investimento inicial, os gastos com manutenção ao longo da vida e os custos elétricos agregados à redução das paradas para manutenção. / The increasing use of stainless steel as a structural element motivated, in recent years, the continuous interest of customers, architects and engineers. Despite its high cost, its application in construction have been replacing other structural elements. This is mainly due to its high corrosion resistance that increases its cost-effective ratio, its aesthetic that enables the construction of increasingly bold forms and its environmental appeal that generates less environmental waste. The electric power substations represent an important role in the global energy supply. Since its maintenance is a complex and costly process, one of its bus support structure was chosen to be designed in stainless steel. This strategy minimizes the number of stoppages for structural maintenance, enabling a higher quality power supply. For comparative purposes an existing power substation has been chosen where the bus supporting structure was made of galvanized carbon steel angle bar trusses. Initially, the design adopted I and H profiles functioning as beam-column for the two types of steel analyzed. In a second stage, the structure was designed as a plane truss. All designs were performed in accordance to the requirements of EUROCODE 3 standard. This was followed by comparative analyses of the costs involved for the studied steel types. These analyses involved the initial investment assessment properly contextualized with the posterior spending on maintenance and electrical costs of the stoppages and were set against the gains in reducing the downtime for maintenance of the stainless steel solution.

Designing structures for lightness is an intelligent and responsible way for engineers and architects to conceive structural systems. Lightweight structures are able to bridge wide spans with a least amount of material. However, the quest for lightness remains an utopia without the driving constraints that give sense to contemporary structural design.<p><p>Previously proposed computational methods for designing lightweight structures focused either on finding an equilibrium shape, or are restricted to fairly small design applications. In this work, we aim to develop a general, robust, and easy-to-use method that can handle many design parameters efficiently. These considerations have led to truss layout optimization, whose goal is to find the best material distribution within a given design domain discretized by a grid of nodal points and connected by tentative bars. <p><p>This general approach is well established for topology optimization where structural component sizes and system connectivity are simultaneously optimized. The range of applications covers limit analysis and identification of failure mechanisms in soils and masonries. However, to fully realize the potential of truss layout optimization for the design of lightweight structures, the consideration of geometrical variables is necessary. <p><p>The resulting truss geometry and topology optimization problem raises several fundamental and computational challenges. Our strategy to address the problem combines mathematical programming and structural mechanics: the structural properties of the optimal solution are used for devising the novel formulation. To avoid singularities arising in optimal configurations, the present approach disaggregates the equilibrium equations and fully integrates their basic elements within the optimization formulation. The resulting tool incorporates elastic and plastic design, stress and displacements constraints, as well as self-weight and multiple loading.<p><p>Besides, the inherent slenderness of lightweight structures requires the study of stability issues. As a remedy, we develop a conceptually simple but efficient method to include local and nodal stability constraints in the formulation. Several numerical examples illustrate the impact of stability considerations on the optimal design.<p><p>Finally, the investigation on realistic design problems confirms the practical applicability of the proposed method. It is shown how we can generate a range of optimal designs by varying design settings. In that regard, the computational design method mostly requires the designer a good knowledge of structural design to provide the initial guess. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008. / The South African code for the design loading of building structures, namely SABS 0160 (1989), was revised with the requirements for seismic design prescribed in SANS 10160: Part 4: Seismic actions and general requirements for buildings. SANS 10160: Part 4 incorporates the seismic design provisions of several seismic codes of practice, however, the influence of the value prescribed for the behaviour factor has not been established with regard to South African conditions. The behaviour factor is used by most seismic design codes to account for the energy dissipating effects of plastification in structural systems when subjected to earthquake ground motion, to reduce the elastically determined forces to be designed for. However, a considerable difference is observed in the values of the behaviour factor prescribed for the design of reinforced concrete walls between the leading international seismic codes. The aim of this study is to assess the value of the behaviour factor prescribed in SANS 10160: Part 4 for reinforced concrete structural walls under the influence of South African seismic conditions and code requirements. A method of quantifying the value of the behaviour factor was developed and implemented in the study by Ceccotti (2008). This method entails estimation of the maximum analytical behaviour factor as the ratio of seismic intensity at failure of the structure to the seismic intensity prescribed by the design code. Such a method is adopted for this study where the lateral force resisting systems of six-, eight- and tenstorey buildings are investigated with nonlinear static analysis to quantify the maximum computationally-determined value of the behaviour factor. Firstly, it is observed that it is possible to quantify the value of the behaviour factor through the use of a computational study. The nonlinear static method of analysis is shown to provide reliable results in the estimation of the behaviour factor for a sixstorey building, however, does not perform well for taller buildings. Further investigation with the use of dynamic time-history analysis is proposed to evaluate the influence of the factors identified in this study. The behaviour of structural walls, designed for reduced forces with the prescribed behaviour factor of 5.0, exhibits high yield strengths and resists the design seismic action entirely elastically. This high strength is found to be due to the reliability/redundancy factor prescribed by SANS 10160: Part 4 and because of the high values of structural overstrength. Similar studies observed high values of structural overstrength for buildings designed for low seismic intensity, which were shown to result from the fact that the resistance required to gravity loading became more critical than the seismic loads in the design of the structural system. This study identifies several factors that influence the value of the behaviour factor, such as the number of walls in the lateral force resisting system; the number of storeys of the buildings; available displacement ductility of the structural system; and the ground type designed for.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg 2017 / The present study investigates the possibility of designing a catenary barrel vault, which can be implemented in regions where extreme tropical storms are frequently experienced. It moreover investigated the effect of non-uniform wind loads on catenary barrel vaults, and how to solve for these load conditions efficiently. The effects of high, non-uniform wind loads were assessed, and possible solutions were explored to determine a structurally efficient solution in resisting the loads applied. Different analysis and design techniques were explored in this research. These techniques included the optimization of the geometry, in resisting the applied loads most efficiently, as well as the structural design of the section in ensuring a durable and safe structure. The study revealed that the geometry of the structure cannot be optimised to resist the applied loads in a catenary fashion without external aid. By draping the vault in a post-tensioned basalt geogrid mesh, axial compression can be increased in the section and geometry optimisation can be achieved in resisting the applied loads in a catenary fashion. Three post-tensioning techniques were investigated and discussed. / MT 2018