Dissertations / Theses on the topic 'Stainless Steel Columns'

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 149-154). Also available in electronic version. Access restricted to campus users.

PhD
Abstract: The objective of this research is to investigate the interaction of local and overall flexural buckling in cold-formed stainless steel columns. Literature study exposes a lack of understanding of this subject and a need for experimental data, particularly on the local-overall interaction buckling of stainless steel open sections. Two separate experimental programs were therefore carried out. The first program included 36 tests on pin-ended lipped channel columns. Three alloys were considered: AISI 304, AISI 430 and 3Cr12. The specimens were designed to fail by local-overall interaction buckling in the inelastic stress range, thus highlighting the non-linear behaviour of stainless steel. Half of the specimens were tested under a concentric load. The other half had the load applied with a nominal eccentricity of Le/1500. The test results demonstrate the imperfection sensitivity of local-overall interaction buckling and illustrate the shift in effective centroid in pin-ended columns with singly symmetric cross-section. The second experimental program studied local-overall interaction buckling in 24 pin-ended stainless steel I-section columns. The specimens consisted of plain channels connected back-to-back using sheet metal screws. Two alloys were considered: AISI 304 and AISI 404. Local and overall imperfections were carefully measured in both experimental programs. Extensive material testing was carried out on the alloys employed in the experimental program, in order to determine tensile and compressive material properties, anisotropic parameters and enhanced corner properties. A detailed finite element model is presented, which includes non-linear material behaviour, anisotropy, increased material properties of the corner areas and local and overall imperfections. The model was verified against the two aforementioned experimental programs and against additional data available in literature on stainless steel SHS columns. The model yielded excellent predictions of the specimen failure mode, ultimate strength and load-deformation behaviour. The finite element model was used to generate additional data for stainless steel columns with lipped channel, plain channel, SHS and I-shaped cross-section, failing by local-overall interaction buckling. The parametric studies covered the practical ranges of overall and cross-sectional slenderness values. The Australian/New Zealand, European and North American standards for stainless steel were evaluated using the available data. The comparison reveals an inability of the design codes to properly account for the interaction effect as the cross-sectional slenderness increases. Predictions are unsafe for I-section columns with intermediate or high cross-sectional slenderness. A direct strength method is proposed for stainless steel columns, accounting for the local-overall interaction effect. The method offers a simple design solution which fits within the framework of the current Australian and North-American standards.

No
In this work, experimental and numerical investigations were performed on the behaviours of circular concrete filled double steel tubular (CFDST) slender columns and beams, in which the external tube employed stainless steel tube. Eighteen specimens, 12 slender columns and 6 beams, were tested to obtain the failure patterns, load versus deflection relationships and strain developments of stainless steel tube. A finite element (FE) model was developed and verified by experimental results. The validated FE model was then employed to investigate the effects of key parameters, including hollow ratio, eccentric ratio and material strength, on the load-carrying capacity. The load distribution among the components and contact stress between steel tube and sandwiched concrete were also analyzed. Finally, the design methods for CFDST, hollow CFST and solid CFST members with carbon steel external tube respectively suggested by Han et al. (2018), Chinese GB 50936-2014 (2014) and AISC 360-16 (2016) were employed to evaluate their applicability for the circular CFDST slender columns and beams with stainless steel outer tube.
The authors gratefully acknowledge the Shanxi Province Outstanding Youth Fund (No. 201701D211006) and the National Natural Science Foundation (No. 51838008).
The full-text of this article will be released for public view at the end of the publisher embargo on 9th Nov 2021.

Previous events have demonstrated the vulnerability of reinforced concrete infrastructure to blast loading. In buildings, ground-story columns are key structural components, and their failure can lead to extensive damages which can cause progressive collapse. To prevent such disasters, the steel reinforcement in such columns must be properly detailed to ensure sufficient strength and ductility. The use of modern concrete materials such ultra-high performance concrete (UHPC) is one potential solution to improve the blast performance of columns. UHPC shows high compressive strength, high tensile resistance and superior toughness, properties which make it ideal for use in the blast-resistant design of columns. The combined use of UHPC and high-performance steels can potentially be used to further enhance the blast resistance of columns. This thesis presents an experimental and analytical study which investigated the use of high-performance materials to increase the blast capacity and ductility of reinforced concrete columns. As part of the experimental study, a total of seventeen columns were tested under simulated blast loading using the University of Ottawa Shock-Tube. Parameters investigated included the effect of concrete type (NSC and UHPC), steel reinforcement type (normal-strength, high-strength or highly ductile), longitudinal reinforcement ratio, seismic detailing and fiber properties. The test program included two control specimens built with normal-strength concrete, five specimens built with UHPC in combination with high-strength steel, and ten columns built with highly ductile stainless steel reinforcement. Each column was subjected to a series of increasing blast pressures until failure. The performance of the columns is investigated by comparing the displacements, impulse capacity and secondary fragmentation resistance of the columns. The results show that using high-performance steels increases the blast performance of UHPC columns. The use of sufficient amounts of high-strength steel in combination with UHPC led to important increases in column blast capacity. The use of ductile stainless steel reinforcement allowed for important enhancements in column ductility, with an ability to prevent rupture of tension steel reinforcement. The study also shows that increasing the longitudinal reinforcement ratio is an effective means of increasing the blast resistance of UHPC columns The thesis also presents an extensive analytical study which aimed at predicting the response of the test columns using dynamic inelastic, single-degree-of-freedom (SDOF) analysis. A sensitivity analysis was also performed to examine the effect of various modelling parameters on the analytical predictions. Overall, it was shown that SDOF analysis could be used to predict the blast response of UHPC columns with reasonable accuracy. To further corroborate the results from the experimental study, the thesis also presents an analytical parametric study examining the blast performance of larger-scale columns. The results further demonstrate the benefits of using UHPC and high-performance steel reinforcement in columns subjected to blast loading.

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

Initially, two experimental programmes studying the structural behaviour of stainless steel beam-to-open column joints and beam-to-tubular column joints under static loads are reported in detail. The joint configurations tested include flush and extended end plate connections, top and seat cleat connections and top, seat and web cleat connections. The full moment-rotation characteristics are reported in detail. It is observed that the connections displayed excellent ductility, superior than that of equivalent carbon steel connections, and attained loads much higher than the ones predicted by design standards for carbon steel joints. Nonlinear FE models have been developed and validated against the experimental results. The FE models are shown to accurately replicate the experimentally determined, initial stiffness, ultimate resistance, overall moment-rotation response and observed failure modes. In addition, a comprehensive parametric study is conducted. The design rules for stainless steel connections, which are based on the specifications of EN 1993-1-8 for carbon steel joints, are reviewed and are found to be overly conservative in terms of strength and inaccurate in terms of stiffness thus necessitating the development of novel design guidance in line with the observed structural response. Hence, simplified mechanical models in line with the observed response are developed.

Ferritic stainless steel is typically used in the automotive industry to fabricate welded tube that is plastically deformed for flanging, bending and necking. The effect of welding parameters during autogenous gastungsten arc welding (GTAW) of thin sheet on the weld metal structure and tensile properties were determined. Two grades of ferritic stainless steels, a titanium-containing Grade 441 and a titanium-free molybdenum-containing Grade 436, were used as base metal. Statistical analysis was used to determine the influence of welding parameters on the microstructure of autogenous GTAW welds. The results of Grade 441 indicated that the welding speed and peak welding current had a statistically significant influence on the amount of equiaxed grains that formed. For Grade 436, the same welding parameters (welding speed and peak welding current) had a statistically significant influence on the grain size of the weld metal grains. The ductility of a tensile test coupon machined parallel to the weld direction, for both base metal grades, was unaffected by the welding parameters or the weld metal microstructure. The elongation was determined by the amount of weld metal in the gauge area of a tensile coupon. The titanium content of the base material seems to have the most significant effect on the formation of equiaxed grains.
Dissertation (MEng)--University of Pretoria, 2019.
Metallurgical Engineering
MEng
Unrestricted

L'objectif de ce travail de thèse, est de développer un matériau d'apport et un mode opératoire de soudage associé permettant d'assembler des tôles d'acier K44X pour la fabrication de collecteurs d'échappement automobiles. Les propriétés de l'acier K44X ayant été optimisées pour répondre au mieux aux contraintes de l'application, les conditions de soudage recherchées devront, dans la mesure du possible, éviter de dégrader les caractéristiques de l'acier, en particulier en termes de tenue mécanique à haute température et de résistance à l'oxydation et à la fatigue thermique. Ce mémoire est divisé en quatre chapitres. Le premier chapitre est consacré à une présentation synthétique des évolutions dans le domaine de la fabrication des collecteurs d'échappement automobiles, et des connaissances actuelles dans les domaines des aciers inoxydables ferritiques et sa soudabilité, des procédés de soudage à l'arc. Le second chapitre présente les caractéristiques de l'acier K44X et la problématique de l'étude, puis décrit le travail d'élaboration des matériaux d'apport de différentes compositions. Ainsi que les résultats d'une caractérisation préliminaire des soudures obtenues avec les différents matériaux. Le chapitre 3 traite de la caractérisation de la tenue en service de l'assemblage retenu à l'issu du chapitre précédent. Les tests d'oxydation, de traction à chaud sur zone fondue des soudures ou sur assemblages complets, et de fatigue thermique, utilisés pour réaliser cette caractérisation sont décrits, et les résultats sont discutés. La fin de ce chapitre est consacrée à la caractérisation des précipités formés dans les zones fondues. Enfin, le dernier chapitre est consacré à la modélisation thermique du soudage et à la modélisation de la solidification, dans le but de tenter de prédire le type de microstructure de zone fondue formée lors d'une opération de soudage, en fonction des paramètres procédés. Cette modélisation, qui s'appuie sur les résultats d'un essai de soudage instrumenté, doit notamment permettre de prédire si les conditions de soudage, pour une composition d'acier donnée, permettent ou non de former une structure de grains équiaxe en zone fondue des soudures
The objective of this work is to develop a filler metal and an associated welding procedure allowing to join sheets of steels K44X for the manufacturing of exhaust manifolds for automotive. The properties of the steel K44X having been optimized to answer at best the constraints of the application, the welding conditions will have to, as possible, avoid degrading the characteristics of the steel, in particular in terms of mechanical strength with high temperature, oxidation resistance and in thermal fatigue.This report is divided into four chapters.The first chapter is dedicated to a synthetic presentation of the evolutions in the field of the manufacturing of the automotive exhaust manifolds, and current knowledge in the domains of ferritic stainless steels and its weldability, and in arc welding processes.The second chapter presents the characteristics of the steel K44X and the problem of the study, then described the work of elaboration of the filler metals with various compositions. As well as the results of a preliminary characterization of the welds obtained with the various materials.The chapter 3 is about the characterization of the in-service behavior of the assembly stemming from the previous chapter. The tests of oxidation, hot traction on molten zone of the welds or on complete assemblies, and of thermal fatigue, used to realize this characterization are described, and the associated results are discussed. The end of this chapter is dedicated to the characterization of precipitates formed in the molten zones.Finally, the last chapter is dedicated to the thermal modelling of the welding and to the modelling of the solidification, with the aim of trying to predict the type of microstructure of molten zone formed during a welding operation, according to the process parameters. This modelling, based on the results of a instrumented experimental test of welding, has to allow in particular to predict if the welding conditions, for a given composition of steel, allow or not to form a structure of grains equiaxed in molten zone of the welds

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.

No
Concrete filled steel columns have been used widely in structures throughout the world in recent years especially in Australia and the Far East. This increase in use is due to the significant advantages that concrete filled steel columns offer in comparison to more traditional construction methods. Composite columns consist of a combination of concrete and steel and make use of these constituent material's best properties. The use of composite columns can result in significant savings in column size, which ultimately can lead to significant economic savings. This reduction in column size can provide substantial benefits where floor space is at a premium such as in car parks and office blocks. The use of stainless steel column filled with concrete is new and innovative, not only provides the advantage mentioned above, but also durability associated with the stainless steel material. This paper concentrates on the axial capacity of the concrete filled stainless steel columns. A series of tests was performed to consider the behaviour of short composite stainless steel columns under axial compressive loading, covering austenitic stainless steels square hollow sections filled with normal and high strength concrete. Comparisons between Eurocode 4, ACI-318 and the Australian Standards with the findings of this research were made and comment.

No
This paper presents the behaviour and design of axially loaded concrete filled stainless steel circular and square hollow sections. The experimental investigation was Conducted using different concrete cube strengths varied from 30 to 100 MPa. The column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with existing design methods for composite carbon steel sections-Eurocode 4 and ACI. It was found that existing design guidance for carbon steel may generally be safely applied to concrete filled stainless steel tubes. though it tends to be over-conservative. A continuous strength method is proposed and it is found to provide the most accurate and consistent prediction of the axial capacity of the composite concrete filled stainless steel hollow sections due largely to the more precise assessment of the contribution of the stainless steel tube to the composite resistance.

This paper presents the behaviour and design of axially loaded concrete filled stainless steel circular and square hollow sections. The experimental investigation was conducted using different concrete cube strengths varied from 30 to 100 MPa. The column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with existing design methods for composite carbon steel sections ¿ Eurocode 4 and ACI. It was found that existing design guidance for carbon steel may generally be safely applied to concrete filled stainless steel tubes, though it tends to be over-conservative. A continuous strength method is proposed and it is found to provide the most accurate and consistent prediction of the axial capacity of the composite concrete filled stainless steel hollow sections due largely to the more precise assessment of the contribution of the stainless steel tube to the composite resistance.

This paper presents the details of an experimental investigation on the behaviour of axially loaded concrete-filled stainless steel elliptical hollow sections. The experimental investigation was conducted using normal and high strength concrete of 30 and 100 MPa. The current study is based on stub column tests and is therefore limited to cross-section capacity. Based on the equations proposed by the authors on concrete-filled stainless steel circular columns, a new set of equations for the stainless steel concrete-filled elliptical hollow sections were proposed. From the limited data currently available, the equation provides an accurate and consistent prediction of the axial capacity of the composite concrete-filled stainless steel elliptical hollow sections.

M.Ing.
Because cold-formed stainless steel is a new type of light steel material and dose not have a long history of utilisation in structures, there are many issues that need to be researched and discussed. Making a more thorough investigation and study of cold-formed stainless steels is essential. As a numerical analysis tool, the finite element method proves to be useful in structural analysis. The buckling modes of cold-formed stainless steel members, such as local, flexural, torsional and torsional-flexural buckling, are well known and well documented in design specifications. Distortional buckling is a special kind of buckling mode, which is less well known. Researchers have recently paid more attention to this problem. For stainless steel structures, it is necessary to investigate their behaviour when distortional buckling occurs. In this project, the distortional buckling of cold-formed stainless steel columns under axial compression is investigated. The finite element method is used to analyse and calculate different buckling modes, especially distortional buckling. This is compared to experimental results and other theoretical predictions. The ABAQUS finite element code is used throughout. Finite element modelling is very important prior to processing and analysis. ABAQUS models are created to study distortional buckling. The initial imperfection of structural members is taken into account with these models, using specific sine wave descriptions with respect to different structural parameters. A dynamic processing approach is chosen in the finite element analysis. The effectiveness and accuracy of these models have been verified by both experimental tests and theoretical calculations. Buckling mode and behaviour are predicted and analysed in terms of the finite element models and processes. Suggestions are made for buckling analysis and design based on the research results.

Yes
In recent years, a new low nickel content stainless steel (EN 1.4162) commonly referred as ‘lean duplex stainless steel’ has been developed, which has over two times the tensile strength of the more familiar austenitic stainless steel but at approximately half the cost. This paper presents the finite element analysis of concrete filled lean duplex stainless steel columns subjected to concentric axial compression. To predict the performance of this form of concrete filled composite columns, a finite element model was developed and finite element analyses were conducted. The finite element model was validated through comparisons of the results obtained from the experimental study. A parametric study was conducted to examine the effect of various parameters such as section size, wall thickness, infill concrete strength, etc. on the overall behaviour and compressive resistance of this form of composite columns. Through both experimental and numerical studies, the merits of using lean duplex stainless steel hollow sections in concrete filled composite columns were highlighted. In addition, a new formula based on the Eurocode 4 was proposed to predict the cross-section capacity of the concrete filled lean duplex stainless steel composite columns subjected to axial compression.

碩士
國立臺灣科技大學
營建工程系
98
The cyclic behavior of precast segmental concrete bridge columns with high performance(HP) steel rebar and that with conventional steel rebar as energy dissipation (ED) barswere investigated. The HP steel rebar is characterized by higher strength, greater ductility and superior corrosion resistance in comparison to the conventional steel rebar. Three large-scale columns were tested. One was designed with the HP ED bars and two with the conventional ED bars. The HP ED bars were fully bonded to the concrete. The conventional ED bars were fully bonded to the concrete for one column while unbounded for a length to delay fracture of the bars and to increase energy dissipation for the other column. Test results showed that the column with the HP ED bars had greater drift capacity, higher lateral strength and larger energy dissipation than that with fully-bonded conventional ED bars. The column with unbonded conventional ED bars achieved the same drift capacity and similar energy dissipation as that with the HP ED bars. All three columns showed good self-centering capability with residual drifts not greater than 0.4% drift. Good agreement was found between analytical predictions and the envelope responses of the three columns in terms of drift versus lateral force, amount of joint opening, ED bar strain, and tendon force.

This paper presents the axial compressive behaviour of stub concrete-filled columns with elliptical stainless steel and carbon steel hollow sections. The finite element method developed via ABAQUS/Standard solver was used to carry out the simulations. The accuracy of the FE modelling and the proposed confined concrete stress-strain model were verified against experimental results. A parametric study on stub concrete-filled columns with various elliptical hollow sections made with stainless steel and carbon steel was conducted. The comparisons and analyses presented in this paper outline the effect of hollow sectional configurations to the axial compressive behaviour of elliptical concrete-filled steel tubular columns, especially the merits of using stainless steel hollow sections is highlighted.

M.Ing. (Civil Engineering)
The purpose of this investigation was to develop the basic information necessary for formulating creteria for the design of Type 3CR12 steel hot-rolled sections as columns. The mechanical properties needed for structural design are established. Investigations into the behaviour of axially loaded compression members indicated that the overall column buckling of compression members may be predicted with confidence by the tangent modulus approach. Finally simplified design recommendations are made for the design of Type 3CR12 steel hot-rolled columns. The need for future research are identified.

The first part of this research work regards the assessment of the mathematical modelling of reinforced concrete columns confined with carbon fibre (CFRP) sheets under axial loading. The purpose was to evaluate existing analytical models, contribute to possible improvements and choose the best model(s) to be part of a new model for the prediction of the behaviour of confined columns under bending and compression. For circular columns, a wide group of authors have proposed several models specific for FRP-confined concrete. The analysis of some of the existing models was carried out by comparing these with several tested columns. Although several models predict fairly the peak load only few can properly estimate the load-strain and dilation behaviour of the columns. Square columns confined with CFRP show a more complex interpretation of their behaviour. Accordingly, the analysis of two experimental programs was carried out to propose new modelling equations for the whole behaviour of columns. The modelling results show that the analytical curves are in general agreement with the presented experimental curves for a wide range of dimensions. An analysis similar to the one done for circular columns was this turn carried out for square columns. Few models can fairly estimate the whole behaviour of the columns and with less accuracy at all levels when compared with circular columns. The second part of this study includes seven experimental tests carried out on reinforced concrete rectangular columns with rounded corners, different damage condition and with confinement and longitudinal strengthening systems. It was concluded that the use of CFRP confinement is viable and of effective performance enhancement alone and combined with other techniques, maintaining a good ductile behaviour for established threshold displacements. As regards the use of external longitudinal strengthening combined with CFRP confinement, this system is effective for the performance enhancement and viable in terms of execution. The load capacity was increased significantly, preserving also in this case a good ductile behaviour for threshold displacements. As to the numerical nonlinear modelling of the tested columns, the results show a variation of the peak load of 1% to 10% compared with tests results. The good results are partly due to the inclusion of the concrete constitutive model by Mander et al. modified by Faustino, Chastre & Paula taking into account the confinement effect. Despite the reasonable approximation to tests results, the modelling results showed higher unloading, which leads to an overestimate dissipated energy and residualdisplacement.

M.Comm.
In manufacturing companies where raw material is transformed into an endproduct, data pertaining to that transformation process are transported from the physical machine (workstation) to a central database and visa versa. To ensure a successful end-product creation, the company needs to ensure that the data being transported is correct, accurate and trustworthy at all times. As unreliable data seems to be a general problem for large manufacturing companies an investigation was launched to establish what integrity problems are being experienced and possible solutions to these problems in manufacturing companies such as Columbus Stainless Steel. On completion of the investigation it was found that the main causes for late deliveries and data fixes being performed was that the data being transmitted at the source was not always the same data received at the destination, hence a lack of data integrity during data transmission was identified. As it was decided to reduce or eliminate the integrity causes rather than correcting the incorrect results the data transportation process was analyzed. During the analysis the main causes for data integrity problems (errors) were identified. In the environment being investigated, data strings (messages) were created at the workstation and then transported via the use of a transporter (protocol) over an established network to the destination database. The more complex the contents of the message (data string), the more advanced features were needed within the functionality of the protocol to ensure the accurate and correct transmission and processing. Once the main causes for these data integrity errors were identified the investigation was broadened to incorporate the search for various protocols with the ability to reduce or eliminate the causes identified previously.

碩士
明新科技大學
營建工程與管理研究所
99
Cold-Formed stainless steel structural members are commonly used in the architectural and car-body engineering, as well as some typical structures due to their characteristic of high strength, light weight, and maintenance-free. This study presents the comparison of compression strength of cold-formed stainless steel, type 304, columns determined by using the ASCE Specification and the Simplified Design Formula. The material properties of type 304 stainless steel were conducted in accordance with CNS requirements. The software “MATLAB” was used to determine the mechanical properties of modules of elasticity(E0), yield strength(Fy), and curve coefficient(n). In general, the tangent modulus theory is used for the design of cold-formed stainless steel columns. The modified Ramberg-Osgood equation given in the ASCE Standard can be used to determine the tangent modulus at specified level of stresses. However, it is often tedious and time-consuming to determine the column buckling stress because several iterations are usually needed in the calculation. The Simplified Design Formula was developed by using the numerical approximation to calculate the column flexural buckling strength without iteration process. A comparison of computed compression strength determined by ASCE Specification and Simplified Design Formula was made in this study. These cold-formed stainless steel columns varied with different values of KL/r, n, E0 and Fy. It is noted that the column strengths determined by using the Simplified Design Formula have good agreement with those calculated from ASCE Specification. The difference of computed values from the ASCE Specification and Simplified Design Formula is very minimum. The Simplified Design Formula are shown to be valid to determine the flexural buckling stress of cold-formed stainless steel columns.

Στην παρούσα διδακτορική διατριβή αναπτύσσεται μια νέα τεχνική ενίσχυσης υποστυλωμάτων οπλισμένου σκυροδέματος με βάση τη χρήση συνθέτων υλικών, τα οποία αποτελούνται από πλέγματα ινών σε ανόργανη μήτρα (π.χ. κονίαµα µε βάση το τσιμέντο), αποσκοπώντας στην επίλυση προβλημάτων που χαρακτηρίζουν τα Ινοπλισμένα Πολυμερή (ΙΟΠ) σχετικά µε τη χρήση εποξειδικών ρητινών. Τα Ινοπλέγματα σε Ανόργανη Μήτρα (ΙΑΜ) δοκιμάζονται στη μορφή μανδύα µε στόχο την περίσφιγξη και την αύξηση της πλαστιμότητας υποστυλωμάτων παλαιού τύπου, σχεδιασμένων δηλαδή χωρίς τις νέες αντισεισμικές λεπτομέρειες όπλισης. Εξετάζονται διάφορες παράμετροι, που περιλαμβάνουν τη χρήση ράβδων λείων ή με νευρώσεις, την πιθανή ένωση των ράβδων με υπερκάλυψη στον πόδα των υποστυλωμάτων και το μήκος υπερκάλυψης. Έτσι προσδιορίζεται η αποτελεσματικότητα των μανδυών ΙΑΜ και συγκρίνεται με αυτή τον ΙΟΠ ως μέσου περίσφιγξης στις κρίσιμες περιοχές υφισταμένων υποστυλωμάτων για όλες τις περιπτώσεις καμπτικών αστοχιών στην περιοχή της πλαστικής άρθρωσης. Το πειραματικό πρόγραμμα που ακολουθείται για την απόκτηση δεδομένων γύρω από τη συμπεριφορά υποστυλωμάτων οπλισμένου σκυροδέματος, ενισχυμένων με μανδύες ανόργανης (ΙΑΜ) ή οργανικής (ΙΟΠ) μήτρας, περιλαμβάνει συνολικά 28 δοκιμές επί δοκιμίων υποστυλωμάτων δύο τύπων: (α) 15 πρισματικά δοκίμια οπλισμένου σκυροδέματος που δοκιμάζονται σε κεντρική θλίψη και (β) 13 δοκίμια υποστυλωμάτων πλήρους κλίμακας, τα οποία δοκιμάζονται σε ανακυκλιζόμενη κάμψη με σταθερό αξονικό φορτίο. Καταδεικνύεται ότι η αποτελεσµατικότητα των µανδυών ΙΑΜ είναι υψηλή και γενικώς παρόµοια µε αυτή των µανδυών ΙΟΠ για όλες τις περιπτώσεις που εξετάστηκαν. Επιπροσθέτως, τα πειραματικά αποτελέσματα των 13 υποστυλωμάτων πλήρους κλίμακας που υποβλήθηκαν σε ανακυκλιζόμενη κάμψη (με σταθερό αξονικό φορτίο), συμβάλλουν στη διερεύνηση δύο ακόμα “θολών” μέχρι σήμερα πεδίων, όπως: (α) Ο λυγισμός των διαμήκων ράβδων σε περισφιγμένο με μανδύες ΙΑΜ ή ΙΟΠ σκυρόδεμα. Ιδιαίτερη έμφαση δίνεται στη μελέτη της αλληλεπίδρασης μεταξύ του μανδύα ΙΑΜ ή ΙΟΠ και των διαμήκων ράβδων, κατά την έναρξη και εξέλιξη του λυγισμού των τελευταίων. (β) Η αντοχή σε συνάφεια μεταξύ των ενωμένων με παράθεση ράβδων και του περισφιγμένου με μανδύες ΙΑΜ ή ΙΟΠ σκυροδέματος. Ιδιαίτερη έμφαση δίνεται στην πειραματική και αναλυτική μελέτη του μηχανισμού με τον οποίο η περίσφιγξη με μανδύες ΙΟΠ και ΙΑΜ συνεισφέρει στη βελτίωση των συνθηκών συνάφειας μεταξύ ράβδων οπλισμού και σκυροδέματος. Ακόμα στην παρούσα διδακτορική διατριβή διεξάγεται η πρώτη συστηματική μελέτη καμπτικής ενίσχυσης υποστυλωμάτων υπό ανακυκλιζόμενη κάμψη (και σταθερό αξονικό φορτίο) με Πρόσθετους Οπλισμούς νέου τύπου σε Εγκοπές (ΠΟΕ). Εξετάζονται υποστυλώματα που έχουν ενισχυθεί με πρόσθετο οπλισμό ινοπλισμένων πολυμερών (ελάσματα άνθρακα ή ράβδους γυαλιού) καθώς και με ράβδους ανοξείδωτου χάλυβα τοποθετημένων σε εγκοπές. Άλλη μια καινοτομία που εισαγάγει η παρούσα διατριβή είναι ο συνδυασμός του ΠΟΕ με τοπικούς μανδύες ινοπλεγμάτων σε ανόργανη μήτρα (IAM), οι οποίοι αποτελούν ένα εξαιρετικά αποτελεσματικό και πολλά υποσχόμενο σύστημα περίσφιγξης, όπως αναπτύσσεται και περιγράφεται λεπτομερώς στην παρούσα διδακτορική διατριβή. Η έρευνα που υλοποιείται για την απόκτηση δεδομένων γύρω από τη συμπεριφορά υποστυλωμάτων οπλισμένου σκυροδέματος ενισχυμένων σε κάμψη με ΠΟΕ, περιλαμβάνει τη διεξαγωγή 11 δοκιμών επί υποστυλωμάτων πλήρους κλίμακας, τα οποία υποβάλλονται σε ανακυκλιζόμενη κάμψη υπό σταθερό αξονικό φορτίο. . Καταδεικνύεται ότι μέσω ενός κατάλληλου σχεδιασμού, στα πλαίσια του οποίου ο ΠΟΕ συνδυάζεται με τοπικό μανδύα στα άκρα του υποστυλώματος (κορυφή και πόδα), είναι εφικτό η αύξηση της καμπτικής αντίστασης των υποστυλωμάτων να μην συνοδεύεται από μείωση της διαθέσιμης ικανότητας παραμόρφωσης. Τα χρήσιμα πειραματικά ευρήματα από τα ενισχυμένα με ΠΟΕ υποστυλώματα, συμπληρώνονται με την ανάπτυξη ενός αναλυτικού και υπολογιστικού προσομοιώματος, το οποίο έχει διττή συμβολή, καθώς επιτρέπει: (α) την εκτέλεση παραμετρικών αναλύσεων ώστε να μελετηθεί σε βάθος και χωρίς κόπο (πειραματικές δοκιμές) η επίδραση όλων σχεδόν των παραμέτρων, στην καμπτική αντίσταση των ενισχυμένων με ΠΟΕ υποστυλωμάτων. (β) Τη χρήση του ως πολύτιμου υπολογιστικού εργαλείου από το Μηχανικό για το σχεδιασμό καμπτικών ενισχύσεων υποστυλωμάτων με ΠΟΕ και / ή μανδύες συνθέτων υλικών. Η αξία της συμβολής του εν λόγω προσομοιώματος μεγιστοποιείται αν ληφθούν υπόψη ορισμένα χαρακτηριστικά του όπως: (1) Η μείωση των ροπών αντοχής ως προς τους δύο κύριους άξονες (ισχυρός και ασθενής), η οποία οφείλεται στην έντονη σύζευξή τους, για τα ενισχυμένα σε κάμψη υποστυλώματα που υποβάλλονται σε διαξονική κάμψη. (2) Η εφαρμογή ενός τραπεζοειδούς στερεού τάσεων για το σκυρόδεμα σε θλίψη, το οποίο σε σύγκριση με το κλασικό ορθογωνικό στερεό, προσομοιώνει με αρκετά μεγαλύτερη ακρίβεια τον όγκο του σκυροδέματος της θλιβόμενης ζώνης, ιδιαίτερα για τις ενισχυμένες διατομές. (3) Η ταυτόχρονη δράση της εξωτερικής περίσφιγξης με μανδύες συνθέτων υλικών στις ενισχυμένες σε κάμψη διατομές.
The effectiveness of a new structural material, namely Textile-Reinforced Mortar (TRM), was investigated experimentally in this PhD Thesis as a means of confining old-type reinforced concrete (RC) columns with limited capacity due to bar buckling or due to bond failure at lap splice regions. Comparisons with equal stiffness and strength fiber-reinforced polymer (FRP) jackets allow for the evaluation of the effectiveness of TRM versus FRP. Tests were carried out on nearly full scale non-seismically detailed RC columns subjected to cyclic uniaxial flexure under constant axial load. Thirteen cantilever-type specimens with either continuous or lap-spliced deformed longitudinal reinforcement at the floor level were constructed and tested. Experimental results indicated that TRM jacketing is quite effective as a means of increasing the cyclic deformation capacity of old-type RC columns with poor detailing, by delaying bar buckling and by preventing splitting bond failures in columns with lap-spliced bars. Compared with their FRP counterparts, the TRM jackets used in this study were found to be equally effective in terms of increasing both the strength and deformation capacity of the retrofitted columns. From the response of specimens tested in this study, it can be concluded that TRM jacketing is an extremely promising solution for the confinement of RC columns, including poorly detailed ones with or without lap splices in seismic regions. Moreover this PhD Thesis presents the results of a large-scale experimental program aiming to study the behavior of RC columns under simulated seismic loading, strengthened in flexure (of crucial importance in capacity design) with different types and configurations of near-surface mounted (NSM) reinforcing materials. The role of different parameters is examined, by comparison of the lateral load versus displacement response characteristics (peak force, drift ratios, energy dissipation, stiffness). Those parameters were as follows: carbon or glass fiber-reinforced polymers (FRP) versus stainless steel; configuration and amount of NSM reinforcement; confinement via local jacketing; and type of bonding agent (epoxy resin or mortar). The results demonstrate that NSM FRP or stainless steel reinforcement is a viable solution towards enhancing the flexural resistance of reinforced concrete columns subjected to seismic loads. With proper design, which should combine compulsory NSM reinforcement with local jacketing at column ends, it seems that column strength enhancement does not develop at the expense of low deformation capacity.