published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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This thesis examines the effects of cold forming on the material properties of steel and stainless steel structural members. Extensive research has been carried out over many years on both of these materials as they are used to manufacture structural sections to various design specifications which exist in many different countries. However, to date, no design code exists in the UK for cold formed stainless steel structural members. A significant amount of research has focused on the localised effect of cold forming on material properties such as the yield and ultimate tensile strengths, particularly of steel, and this is discussed at length in Chapter 1- Literature Review. Less attention has been placed on stainless steel, but over the last 20 years with the advent of design specifications particularly in the USA, stainless steel has gained popularity for cold forming. Chapter 1 describes the research that has been carried out on stainless steel, with particular emphasis on localised forming effects. Chapter 2 gives a general introduction to Thin-Walled Structures since cold-formed structural sections are commonly used as thin-walled members. The deformation and properties of metallic materials are described in Chapter 3 showing the particular relevance to the cold forming process. This chapter is extended into Chapter 4 where the strengthening, forming and properties of metallic materials are discussed in detail, with particular attention given to the cold forming processes. Chapter 5 describes existing analytical and design code approaches to determine the increase in strength of cold formed steel structural sections, along with an empirically derived relationship to calculate the increased yield strength of stainless steel sections. Chapter 6 describes the recommendations provided by various design specifications on evaluation of the axial compression capacity of short struts subject to varying degrees of cold forming. This chapter also describes the recommendations provided by various design specifications on evaluation of both the axial compression and the combined bending and axial compression load capacities of cold formed lipped channel section stainless steel columns of short-to-medium length. The results obtained from Chapters 5 and 6 are compared to the results obtained from an extensive experimental approach as described in Chapter 7. A finite element non-linear analysis using the ANSYS finite element software package is presented in Chapter 8 which models the behaviour of cold formed stainless steel lipped channel section columns of short-to-medium length subject to pure axial compression loading and also combined bending and axial compression loading. Chapter 9 presents the experimental findings showing the relationship between material hardness and material yield strength for cold-formed areas. The results are then compared to the theoretical results from Chapter 6 to determine their accuracy in prediction of the structural behaviour of full cold formed structural member cross-sections. The load capacity obtained for axially compressed steel and stainless steel struts from experiments are compared to those obtained from the various design code predictions described in Chapter 6. Also presented are the experimental findings, design code recommendations and finite element predictions for the load capacity of stainless steel columns. Chapter 10 concludes on the work by discussing the various issues arising from the experiments, from the design code recommendations and from finite element analysis 11 M. Macdonald

This study presents the experimental results of nine full-scale lap spliced glass-fiber reinforced polymer (GFRP) reinforced concrete (RC) columns, and one additional reference steel-RC column with lap splices, under axial and cyclic-reversed loads. The test parameters included type of reinforcement, lap splice length of longitudinal reinforcement, transverse reinforcement spacing, and the effect of using steel fiber-reinforced concrete (SFRC). Test results indicated that a splice length of 60 times the diameter of the longitudinal column bar was adequate in transferring the full bond forces along the splice length and were able to maintain the lateral load carrying capacity when subjected to higher levels of axial loads and drift ratios. In addition, lap spliced GFRP-RC columns with closely spaced transverse reinforcement achieved high levels of deformability. Furthermore, the use of SFRC in columns with inadequate splice increased the peak lateral strength and the energy dissipation of the specimens. / February 2017

Master of Science / Department of Civil Engineering / Asad Esmaeily / Performance-based building design is a necessity in geographic locations where buildings are susceptible to large earthquakes and high winds. This design method requires an analysis of the performance of the structural system with loadings and deflections caused by earthquakes and wind. Current design codes include the load intensity in analysis procedures, but do not consider the effect of load pattern in the performance analysis of reinforced concrete columns. Because a thorough analysis must take into consideration load pattern and load intensity, computer software is ideal to analyze these systems. A computer program was originally developed by Esmaeily (USC_RC), and was revised later to be renamed (KSU_RC) in order to make the analysis of concrete column performance accurate, yet simple for design purposes. This analytical tool used analytical methods and material models, verified against experimental data, to accurately predict the performance of reinforced concrete columns under various loading conditions, including any pattern in lateral direction and independently variable axial load. However, the program was limited to circular, rectangular, hollow circular and rectangular sections and uniaxial lateral curvature and displacement. The next generation of the program, KSU RC 2.0, was developed to overcome the aforesaid limitations.

O controle da superfície química em colunas capilares abertas é de fundamental importância para atingir um alto desempenho na análise cromatográfica, sendo muito estudada ao longo das décadas de 70 e 80, mas tendo pouco destaque nos últimos anos por parte dos pesquisadores. A atividade da superfície de uma coluna capilar é causada por grupos silanol (Si-OH) e impurezas como metais, por exemplo. A presença destes grupos silanol faz com que alguns compostos sofram adsorção, principalmente pela formação de pontes de hidrogênio, originando picos com longas caudas no cromatograma. Por isso, a eliminação dos sítios ativos faz-se necessária quando uma amostra apresenta interação com a superfície da coluna. Esta desativação pode ser feita por meio de agentes silanizantes que reagem com os grupos hidroxila. Visto que a maioria dos artigos publicados sobre este assunto envolve colunas de vidro, o presente trabalho estudou os efeitos de cada fase do pré-tratamento de tubos aplicado para as colunas atuais de sílica fundida, verificando os agentes silanizantes HMDS, DPTMDS e TPDMDS que seriam mais adequados para suportar as fases estacionárias OV-73 e OV-17. Também se avaliou o uso de filmes finos de 0,01 , 0,05 e 0,10 ?m de polietileno glicol (PEG) como alternativa para a desativação da parede interna do capilar, o qual mostrou resultados satisfatórios de estabilidade e inatividade. / The control of the inner surface in open tubular capillary columns has fundamental importance to reach a high performance in gas chromatography analysis. It was very studied during 1970´s and 1980´s, but has not interested the researches along last years, not excluding also, the possibility of commercial secrets regarding column preparation. The activity on the surface of capillary column is mainly caused by silanol groups (Si-OH) and impurities such as metal ions and water. These groups favours reversible and irreversible adsorption of polar compounds, which results in tailed peak shapes and incomplete elution from the column. Therefore, the elimination of the active sites is necessary. The deactivation procedures are based on blocking of silanol groups by means of chemical reaction. This present work studied the effects of the surface pretreatment steps applied to fused silica capillary columns. Some silylating agents such as HMDS, DPTMDS and TPDMDS were valued. The coating behavior using OV-73 and OV-17 stationary phases was studied too. Film thickness of 0,01 , 0,05 and 0,10 ?m of poly(ethylene glycol) (PEG) was applied as alternative procedure, showing good stability and column deactivation.

O uso de concreto de alto desempenho constitui tendência irreversível, devido às vantagens que apresenta em relação aos concretos de resistência usual, principalmente na execução de pilares de edifícios, pois as áreas das seções transversais podem ser reduzidas. Este trabalho trata da obtenção e do estudo teórico e experimental de pilares de concreto de alto desempenho, analisando o comportamento de modelos, solicitados à compressão centrada e flexão normal composta. Foram analisados pilares de seções transversais quadradas de 20cm x 20cm e retangulares de 15cm x 30cm e 12cm x 30cm, dimensões que representam pilares usuais em estruturas de edifícios. Na compressão centrada ficou caracterizado que o estado limite último foi atingido por ruptura da seção mais solicitada e comprovado que a ruptura ocorreu quando o núcleo, definido pelo perímetro considerado pelos eixos dos estribos, se rompeu. Nos ensaios de flexão normal composta os resultados mostraram que as hipóteses de distribuição de tensões, utilizadas para os concretos de resistências usuais, não devem ser consideradas para concreto de alta resistência. As forças normais experimentais e as teóricas, calculadas por um modelo proposto pelo Autor, ficaram iguais enquanto que, para os momentos fletores, os valores experimentais ficaram muito acima dos teóricos. / The use of high performance concrete is an irreversible tendency in structural design due to the advantages it presents, compared to the concrete of usual strength, these advantages can be seen mainly in the execution of buildings columns as the cross sections can be reduced. This thesis is about the theoretical and experimental study to obtain high performance concrete columns. The behaviour of models subjected to axial load and bending plus axial load was analysed. Columns with the square (20cm x 20cm) and rectangular (15cm x 30cm and 12cm x 30cm) cross sections were studied, because they are the usual buildings columns dimensions. As far as axial load is concerned, the ultimate state limit was reached when the mostly demanded section broke. It was proven that the rupture occurred when the core, defined by the perimeter considered by the axial stirrups, broke. The results of bending plus axial load tests have shown that the distribution of stress hypotheses used for concrete of usual strength must not be considered for high strength concrete. The experimental axial forces and the internal ones calculated by a given model were the same, whereas the experimental values for the internal moments were much higher.

O objetivo da pesquisa foi obter subsídios para o projeto de pilares de concreto de alta resistência, submetidos à compressão simples, com concreto de resistência média de 60 MPa. Este projeto faz parte de um plano mais amplo onde já se têm resultados experimentais que traduzem o comportamento de pilares moldados com concreto de resistência média à compressão de 80 MPa. Nestes constatou-se a participação isolada do núcleo de concreto definido pelo eixo da armadura transversal como seção resistente dos pilares. Na etapa experimental foram ensaiados pilares com seções transversais quadradas de 200 mm x 200 mm e retangulares de 150 mm x 300 mm. As alturas dos pilares correspondem a seis vezes a menor dimensão da seção transversal, portanto, 1200 mm e 900 mm, respectivamente. Nos modelos de seção quadrada, o valor médio das relações entre as forças últimas experimentais e as forças últimas teóricas, considerando a seção total de concreto, resultou igual a 0,82, indicando que a seção resistente não é a seção total. Por outro lado, a média das relações entre as forças últimas experimentais e as forças últimas teóricas, considerando apenas a área do núcleo limitada pelo eixo dos estribos, resultou igual a 1,21, o que mostra que a seção resistente pode ser considerada, no Estado Limite Último, como a seção do núcleo. / This research\'s aim is to obtain information for design of high strength concrete columns under concentrically loads with medium cylinder compressive strength of 60 MPa. This project belongs to a more extensive plan which already has experimental results that represent the behavior of columns performed with concrete with medium cylinder compressive strength of 80 MPa. In these models has been verified the independent participation of concrete core defined by the transversal reinforcement axis as resistant section near the ultimate load. In the experimental stage it was tested twelve columns with square (200 mm x 200 mm) and rectangular (150 mm x 300 mm) cross sections. The height of the columns corresponds to six times the smallest dimension of the cross section, 1,200 mm and 900 mm, respectively. The medium value of the ratios between the ultimate experimental force and the ultimate theoretical force, regarding the full concrete section, was 0.82, indicating that the resistant section is not the full section. On the other hand, the medium of ratios between the ultimate experimental force and the ultimate theoretical force, considering only the core area limited by the axis of the lateral reinforcement bars, was 1.21, what shows that the resistant section can be considered as the core section in the Ultimate Limit State.

Este trabalho analisou o comportamento teórico e experimental de pilares de concreto armado submetidos à força de compressão centrada e executados com concreto de resistência à compressão em torno de 25 MPa. Durante a fase experimental, foram ensaiados 16 modelos com dimensões das seções transversais de 200 mm x 200 mm e 150 mm x 300 mm, sendo as alturas iguais a seis vezes a menor dimensão da seção, ou seja, 1200 mm e 900 mm, respectivamente. Além das dimensões dos pilares, outros parâmetros foram considerados, tais como a taxa de armadura longitudinal e o espaçamento e a configuração da armadura transversal. Os ensaios foram realizados em uma máquina hidráulica servo-controlada que permitiu aplicar a força de compressão com controle de deslocamento. Assim, foi possível obter o trecho pós-pico da curva força-deformação dos pilares. Os resultados experimentais mostraram que não há formação de núcleo resistente. Foi notado que as fissuras surgiram em etapa de carga muito próxima do colapso dos modelos. Para as taxas de armadura transversal adotadas, foi verificado um ligeiro cintamento e um expressivo aumento na ductilidade dos pilares. Por fim, verificou-se que o estribo suplementar, em forma de barra reta com ganchos nas extremidades contribuiu para cintar e ductilizar os modelos de pilares. / This work analysed the theoretical and experimental behaviour of reinforced concrete columns under axial compression force with concrete compressive strenght around of 25 MPa. In the experimental stage it was tested 16 specimens with cross sections of 200 mm x 200 mm and 150 mm x 300 mm. The height of the columns were six times the smallest dimension of the cross section, i.e., 1200 mm and 900 mm, respectively. Besides the dimensions of the columns, other parameters, like longitudinal reinforcement ratio and the spacing and arrangement of the transverse reinforcement were varied. The columns were loaded concentrically in an servohidraulically controlled testing machine that permitted applying the compression force with displacement control. Therefore, it was possible to obtain the force-strain curve post-peak. The results showed that were not formed resistent cores. Cracks appeared in a load stage near the failure of the specimens. For the transversal reinforcement ratio adopted, it was verified a small gain in strength and an significant increase in ductility. At last, the supplementary cross ties provided gain of strength and ductility in the columns.

Highly nonlinear structures exhibit complex responses to external loads, and often become unstable. In this thesis, I consider structures with either a nonlinear geometric response or material response. Geometrically nonlinear bistable shells have two stable configurations and can reversibly change between them via snap-through instabilities. This snap-through behavior can cause large geometric deformations in response to small changes in loading, and thus is ideal for designing various devices. For materially nonlinear structures, one recent focus is the potential to utilize granular jamming to construct structures. However, it is not yet fully understood how the stability of such nonlinear structures is governed by geometric and materials properties. This thesis aims to answer this question and propose design guidelines for engineering applications. This research will focus on the statics and dynamics of spherical shells, prestressed bistable shells and elastogranular columns. For spherical shells, we aim to find out under what geometric criteria can a shell be turned inside out, and as the shell goes through the snap-through instability, what dictates the shape and speed of it. Geometric criteria to predict whether a spherical shell is bistable or monostable is proposed based on precisely fabricated soft spherical shells. Point load indentation tests were performed to determine how stable a spherical shell is in its everted configuration. The results show a distinct difference between shallow shells and deep shells, which led to further studies on the snapping dynamics of spherical shells. High speed videos are recorded to track the motion of the apex of an everted spherical shell during its snap-through process, and we find that as the spherical shell goes from shallow to deep, the axisymmetric snapping will transform into asymmetric snapping. This change in snapping modes greatly affects the snapping dynamics of the everted spherical shells, and the shapes they adopt through the instability. Besides spherical shells, we also analyzed prestressed, bistable, cylindrical shells. Prestressed bistable shells fabricated by stretching and bonding multiple layers of elastomers can have various geometric shapes and can snap under external stimuli, but the governing parameters for the fabrication and snapping are not known yet. An analytical model was proposed based on non-Euclidean Plate Theory to predict the mean curvature of the prestressed shell, and the amount of stimulus that is needed to trigger the snapping. Numerical simulations are performed to compare with the analytical results. Based on the proposed theory, for given fabrication parameters and material properties, the final mean curvature of the bistable prestressed shell can be predicted accurately, as well as the amount of stretch that is needed to trigger snapping. This study can be used to design smart actuators or other soft, smart devices. To study material nonlinear structures, we use a mixture of grains and rods to enable the formation of stable structures via granular jamming. Understanding how these constituents govern the mechanical properties of the jammed structures is crucial for devising relevant engineering designs. We examine freestanding columns composed of rocks and string, and propose a simple physical model to explain the resulting structure’s mechanical behavior. The results indicate that exterior fiber mainly contributes to stiffness, while interior fiber increases the stored elastic energy and absorbed total energy of the structures under certain external load. By assembling the grains and strings in an engineer way, structures with robust mechanical properties can be formed. The results provide guidelines that allow the design of jammed elastogranular structures with desired mechanical properties. The research results of this thesis will open and guide a variety of possibilities in designing functional responsive devices or jamming structures.