M.Ing. (Civil Engineering) / The results of a study presented on the behaviour of cold-formed stainless steel beams subjected to shear taking into account elastic shear buckling, inelastic shear buckling and shear yielding, as well as an investigation into the interaction relationship between shear and bending are presented. From this investigation the results obtained show good relation to the theory. The local shear buckling stress was experimentally determined and it was found that for unreinforced beam webs the shear buckling coefficient is that of an infinitely long plate, namely k=5,34. A good agreement between the experimental ultimate shear strength and the predicted ultimate shear strength was found. Stainless steel beams comprising of lipped channels were manufactured and tested to failure. The types of stainless steels used in this investigation were Types 304, 316, 430 and Type 3CR12 corrosion resiting steel, a modified Type 409 stainless steel. The stress-strain relationship for stainless steels differs from that of carbon steel in that stainless steel is a gradual yielding material. It was concluded in this investigation that Gerard's plasticity reduction factor, Gs/G o, should be used as a plasticity reduction factor in calculations concerning shear. It was found that present design criteria are adequate.

Cold-formed stainless steel sections have been increasingly used in architectural and structural applications. Yet the high price of stainless steel limits the application to construction projects. The lean duplex stainless steel (EN 1.4162) offers an opportunity for stainless steels to be used more widely due to its competitive in price, good mechanical properties and corrosion resistance. The lean duplex stainless steel is a relatively new material, and research on this material is limited. Currently, the lean duplex stainless steel is not covered in any design specification, and no design rules are available for such material. Therefore, the behaviour and design of cold-formed lean duplex stainless steel members are investigated in this study. The investigation focused on columns, beams and beam-columns of square and rectangular hollow sections. Both experimental and numerical investigations were performed and reported. Design rules for cold-form lean duplex stainless steel members are proposed. The experimental investigation included material tests, column tests, beam tests and beam-column tests at room and elevated temperatures ranged from 24 – 900 °C. The test specimens were cold-rolled from flat strips. The test program consists of two square hollow sections and four rectangular hollow sections. Coupon specimens were extracted from each hollow section, and their material properties were obtained from tensile coupon tests at room temperature and elevated temperatures. In this study, a modified design rule was proposed to predict the cold-formed lean duplex stainless steel material properties at elevated temperatures. The local and overall geometric imperfections were measured. A total of 38 column tests were conducted. The effective column length ranged from 75 to 1660 mm in order to obtain a column curve for each test series. The test program for beams included 10 pure bending tests, and the bending capacities of the specimens were determined. A total of 37 beam-column specimens were compressed between pinned ends at different eccentricities in order to obtain an interactive curve for each series of test. Numerical investigation on columns, beams and beam-columns at room temperature as well as elevated temperatures are also presented. Accurate finite element models were developed and verified against the experimental results for columns, beams and beam-columns at room temperature. The structural members at elevated temperatures were simulated by replacing the material properties with those obtained at elevated temperatures. Extensive parametric studies were carried out, including 150 columns, 126 beams and 150 beam-columns at room temperature, as well as 180 columns, 125 beams and 195 beam-columns at elevated temperatures. Column, beam and beam-column strengths obtained from the experimental and numerical investigations as well as available data were compared with the design strengths calculated using American, Australian/New Zealand, European specifications for stainless steel structures of duplex material, since lean duplex material is not covered by these specifications. In addition, direct strength method for carbon steel and stainless steel as well as continuous strength method for stainless steel were assessed for cold-formed lean duplex stainless steel. Modified design rules were proposed. The reliability of the current and modified design rules was evaluated using reliability analysis. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

In this study, the structural behaviour of cold-formed steel built-up compression members with longitudinal stiffeners was investigated by experiments and numerical simulation. The influence of different screw spacings on the ultimate strengths of built-up compression members was also investigated. In current design specifications, generally there are no direct and explicit design rules for cold-formed steel built-up sections. Therefore, design rules for built-up open sections and closed sections have been proposed. The test program was conducted for cold-formed steel built-up sections, which were compressed axially between fixed ends with various column lengths ranged from 300 to 3200 mm. Two identical open sections were connected by self-tapping screws to form a built-up section. The material properties and initial geometric imperfections of the test specimens were measured. The experimental investigation consisted of built-up open sections with edge and web stiffeners, and built-up closed sections with inward or outward web stiffeners. In total, 47 specimens were tested with a screw spacing of 100 mm, and another 25 specimens were tested with screw spacings of 300 and 600 mm. A further investigation on the structural behaviour of cold-formed steel built-up compression members was performed using finite element analysis (FEA). Firstly, accurate and reliable finite element models (FEMs) were developed and verified against the test results. Secondly, extensive parametric studies of cross-section geometry and the screw spacing were carried out by the verified FEMs. The parametric study contained 442 specimens for built-up open sections, built-up closed sections, and built-up sections with different screw spacings. Therefore, the complex structural behaviour of built-up compression members with edge and web stiffeners, together with different spacings of self-tapping screws were studied thoroughly, as reported in this thesis. The current direct strength method (DSM) is a favored design method for cold-formed steel columns and beams due to its ease of calculation. However, DSM does not cover the design of cold-formed steel built-up sections. The appropriateness of DSM for cold-formed steel built-up compression members was accessed by both experimental and numerical investigation. It was found that the current DSM is not quite suitable for the design of built-up compression members. Therefore, the current DSM was modified for built-up open and closed sections. The results show that the modified design rules are generally conservative and reliable for the design of built-up compression members. In addition, design recommendations are proposed for built-up sections with different screw spacings. The reliability of the current and modified design rules was evaluated using reliability analysis. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

The structural behaviour of single shear bolted connections and double shear bolted connections of cold-formed stainless steel at elevated temperatures and post-fire condition has been investigated in this study. The current design rules on bolted connections of cold-formed stainless steel are mainly based on those of carbon steel, and are applicable for room (ambient) temperature condition only. These design rules may not be applicable for elevated temperatures. Therefore, design guidelines should be prepared for bolted connections of cold-formed stainless steel structures at elevated temperatures. The key findings of the investigation are described in the following paragraphs. A total of 25 tensile coupon tests were conducted to investigate the material deterioration of three different grades of stainless steel at elevated temperatures. The stainless steels are austenitic stainless steel EN 1.4301 (AISI 304) and EN 1.4571 (AISI 316Ti having small amount of titanium) as well as lean duplex stainless steel EN 1.4162 (AISI S32101). Totally 434 tests on bolted connections of stainless steel were performed in the temperature ranged from 22 to 950 ºC using both steady state and transient state test methods. The test results were compared with the nominal strengths calculated from the American Specification, Australian/New Zealand Standard and European codes for stainless steel structures. In calculating the nominal strengths of the connections, the material properties at elevated temperatures were used in the design equations for room temperature. It is shown that the nominal strengths predicted by these specifications are generally conservative at elevated temperatures. A total of 78 cold-formed stainless steel single shear and double shear bolted connections were tested in post-fire condition. The test results were compared with those tested at room temperature. Generally, it is found that the bolted connection strengths in post-fire condition cooling down from 350 and 650 ºC are higher than those tested at room temperature for all three grades of stainless steel. Finite element models for single shear and double shear bolted connections were developed and verified against the experimental results. Static analysis technique was used in the numerical analyses. Extensive parametric studies that included 450 specimens were performed using the verified finite element models to evaluate the bearing resistances of bolted connections of stainless steel at elevated temperatures. Design equations for bearing resistances of cold-formed stainless steel single shear and double shear bolted connections were proposed based on both the experimental and numerical results in the temperature ranged from 22 to 950 ºC. The bearing resistances of bolted connections obtained from the tests and the finite element analyses were compared with the nominal strengths calculated using the current design rules and also compared with the predicted strengths calculated using the proposed design equations. It is shown that the proposed design equations are generally more accurate and reliable in predicting the bearing resistances of bolted connections at elevated temperatures than the current design rules. The reliability of the current and proposed design rules was evaluated using reliability analysis. The proposed design equations are recommended for bolted connections assembled using cold-formed stainless steels. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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.

The stress corrosion cracking (SCC) of components which are fabricated from austenitic stainless steel has been observed in the primary circuit of pressurised water reactors (PWR). In recent years it has become an increasing concern that cold work can induce susceptibility to SCC in these materials, even when exposed to good-quality flowing coolant. Laboratory studies which were launched in response to this observation have confirmed that SCC susceptibility is enhanced by cold work. The intention of this study is therefore to investigate the link between the effects of cold work on the material and the susceptibility to SCC. The investigation has been conducted on a grade 304 austenitic stainless steel. Characterisation of the microstructure and mechanical properties has been carried out in the annealed condition, and following cold rolling to a reduction in thickness of 20 %. The cold rolled material has then been subjected to SCC tests in simulated PWR primary circuit coolant. Two types of test were utilised: slow strain rate tests (SSRTs) were carried out in order to investigate the initiation of cracks from a smooth surface and constant load tests using pre-cracked specimens were used to investigate the crack propagation behaviour. In both types of test the SCC produced was predominantly intergranular. The SSRTs revealed that the most susceptible grain boundaries separated grains which had dissimilar deformation microstructures (one grain deformed heavily by planar bands, the other more homogenously). It was also observed that initiation could occur on a grain boundary which is adjacent to an annealing twin. In both microstructural configurations the susceptibility is likely to be due to the deformation incompatibility across the failed boundary, possible indicating that shear at the boundary is important for the initiation of cracking. The crack propagation behaviour of the rolled material was particularly anisotropic; regardless of the loading direction (specimens were manufactured to allow loading along the rolling, transverse and normal plate directions) cracking was observed to occur parallel to the rolling-transverse plane. The origin of this behaviour was explored in terms of preferential alignment of the deformation microstructure and the anisotropic mechanical properties of the rolled plate. Limited transgranular cracking was also observed, which occurred along oxidised deformation bands. The results overall indicate that heterogeneous deformation between different regions of the material, and preferential alignment of the deformation microstructure are important with respect to the SCC susceptibility of the rolled material.

Orientador: Peterson Luiz Ferrandini / Banca: Carlos Triveño Rios / Banca: Manoel Cleber de S. Alves / Resumo: A atual exigência de qualidade de grandes peças forjadas requeridas pelo mercado nos traz a necessidade de dominar completamente cada etapa do processo de produção das mesmas. O tratamento térmico de homogeneização, processo aplicado a lingotes utilizados na fabricação de cilindros de laminação de tiras a frio, tem como objetivo homogeneizar a microestrutura bruta de solidificação que irá sofrer um processo de conformação mecânica posterior, reduzindo o nível de microssegregações nas regiões interdentriticas da estrutura do lingote. Pode-se quantificar o impacto da temperatura e do tempo deste processo pela análise da microestrutura formada a partir de um resfriamento brusco em amostras retiradas de diferentes regiões do lingote. Este trabalho foi realizado a partir de um lingote de aço do tipo A2, fundido, de comprimento ~2 m e diâmetro ~1 m, a ser forjado e utilizado na fabricação de um cilindro de laminação. Foram retiradas e analisadas amostras da estrutura bruta de solidificação e também de amostras homogeneizadas e temperadas. As amostras foram retiradas na superfície do lingote, no meio raio e na região central; foram aplicados tratamentos térmicos a 1150°C e 1200°C, por 8 h, 16 h e 24 h. Foram utilizadas microscopia ótica e eletrônica de varredura. Como esperado, a estrutura bruta de solidificação apresentou altos níveis de segregação, principalmente na região central do lingote. O tempo de homogeneização de 8 h se mostrou insuficiente a despeito da temperatura utilizada. A temperatura de 1150°C é aceitável para tratamentos de 24 h e a completa homogeneização da estrutura só foi alcançada utilizando-se tratamento a 1200°C. A estrutura bruta de solidificação apresenta uma microestrutura heterogênea, caracterizada pelo aspecto dendritico. A estrutura homogeneizada e temperada apresenta microestrutura ... (Resumo completo, clicar acesso eletronico abaixo) / Abstract: The current requirement for large forgings quality required by the market brings the demand to manage completely each stage of the manufacturing process. The homogenizing heat treatment process applied in ingots used in the manufacture of cold rolling mill rolls aims to homogenize the microstructure of raw solidification that will suffer a subsequent mechanical forming process, reducing the level of microsegregations in interdentrite regions structure of the ingot. We quantified the effect of temperature and time of the process through the analysis of the microstructure formed after a sudden cooling, in samples taken from different regions of the ingot. This task was realized applying an A2 kind of steel, cast, length ~ 2 m, diameter ~ 1 m, to be forged and used in the manufacture of a rolling Mill rolls. Samples of the raw structure solidification and the homogenizations and tempered samples were taken and analyzed .The samples were taken at the ingot surface at the middle radius and the central region; Heat treatments were applied with temperatures between 1150°C and 1200°C through 8 h, 16 h and 24 h. Optical microscopy and scanning electron microscopy were used. As expected, the raw solidification structure showed high levels of segregation, especially in the central region of the ingot. The 8 h proved to be insufficient despite the temperature used. The temperature of 1150 ° C is acceptable for treatment of 24 h and complete homogenization of the structure was only achieved by using treatment at 1200 ° C. The raw structure of solidification has a heterogeneous microstructure, characterized by dendritic appearance. The homogenized and quenched structure resulted in a microstructure composed by austenite, grades of martensite, the solidification carbides and precipitates carbides during heat treatment / Mestre

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

As China's stainless steel production capacity has increased since 2005, the world supply of steel products accelerates rapidly. With stainless steel products being included in the early harvest list of the Economic Cooperation Framework Agreement (ECFA), manufacturers in Taiwan can expect the tariff in China to be reduced to zero gradually. Since China itself is expanding its stainless steel production capacity, this shall impact Taiwan¡¦s stainless steel exports a great deal. A large amount of stainless steel is needed for many of China's Eleven Five-Year Constructions which consist of items such as the petrochemical, energy and shipbuilding projects, and policies such as home appliances and automobiles to the countryside. Consequently, enormous business opportunities will be seen for stainless steel in China. However, due to the increase rate of supply is much larger than the increase rate of demand, in the foreseeable future, the oversupply of stainless steel shall become a very serious problem. In this study, we successfully construct the Architecture-Oriented Stainless Steel Cold Roll Producing and Marketing Model (AOSSCRPMM) based on six fundamental diagrams of the structure-behavior coalescence (SBC) architecture. AOSSCRPMM provides an integrated description of structure and behavior of producing and marketing activities in the stainless steel cold roll industry. Organizations, information systems and processes are all integrated in AOSSCRPMM so employees can effectively achieve consensus in corporate communication and ramp up quickly to have a holistic view of the whole enterprise. AOSSCRPMM also helps the stainless steel cold roll industry get better operational qualities for operational management.