Until recently, the hot-rolled steel members have been recognized as the most popular and widely used steel group, but in recent times, the use of cold-formed high strength steel members has rapidly increased. However, the structural behavior of light gauge high strength cold-formed steel members characterized by various buckling modes is not yet fully understood. The current cold-formed steel sections such as C- and Z-sections are commonly used because of their simple forming procedures and easy connections, but they suffer from certain buckling modes. It is therefore important that these buckling modes are either delayed or eliminated to increase the ultimate capacity of these members. This research is therefore aimed at developing a new cold-formed steel beam with two torsionally rigid rectangular hollow flanges and a slender web formed using intermittent screw fastening to enhance the flexural capacity while maintaining a minimum fabrication cost. This thesis describes a detailed investigation into the structural behavior of this new Rectangular Hollow Flange Beam (RHFB), subjected to flexural action The first phase of this research included experimental investigations using thirty full scale lateral buckling tests and twenty two section moment capacity tests using specially designed test rigs to simulate the required loading and support conditions. A detailed description of the experimental methods, RHFB failure modes including local, lateral distortional and lateral torsional buckling modes, and moment capacity results is presented. A comparison of experimental results with the predictions from the current design rules and other design methods is also given. The second phase of this research involved a methodical and comprehensive investigation aimed at widening the scope of finite element analysis to investigate the buckling and ultimate failure behaviours of RHFBs subjected to flexural actions. Accurate finite element models simulating the physical conditions of both lateral buckling and section moment capacity tests were developed. Comparison of experimental and finite element analysis results showed that the buckling and ultimate failure behaviour of RHFBs can be simulated well using appropriate finite element models. Finite element models simulating ideal simply supported boundary conditions and a uniform moment loading were also developed in order to use in a detailed parametric study. The parametric study results were used to review the current design rules and to develop new design formulae for RHFBs subjected to local, lateral distortional and lateral torsional buckling effects. Finite element analysis results indicate that the discontinuity due to screw fastening has a noticeable influence only for members in the intermediate slenderness region. Investigations into different combinations of thicknesses in the flange and web indicate that increasing the flange thickness is more effective than web thickness in enhancing the flexural capacity of RHFBs. The current steel design standards, AS 4100 (1998) and AS/NZS 4600 (1996) are found sufficient to predict the section moment capacity of RHFBs. However, the results indicate that the AS/NZS 4600 is more accurate for slender sections whereas AS 4100 is more accurate for compact sections. The finite element analysis results further indicate that the current design rules given in AS/NZS 4600 is adequate in predicting the member moment capacity of RHFBs subject to lateral torsional buckling effects. However, they were inadequate in predicting the capacities of RHFBs subject to lateral distortional buckling effects. This thesis has therefore developed a new design formula to predict the lateral distortional buckling strength of RHFBs. Overall, this thesis has demonstrated that the innovative RHFB sections can perform well as economically and structurally efficient flexural members. Structural engineers and designers should make use of the new design rules and the validated existing design rules to design the most optimum RHFB sections depending on the type of applications. Intermittent screw fastening method has also been shown to be structurally adequate that also minimises the fabrication cost. Product manufacturers and builders should be able to make use of this in their applications.

Elementos estruturais como as placas finas fazem parte de um grande número de aplicações nas mais diversas áreas da engenharia e são de grande importância para a engenharia naval e aeronáutica, na construção de cascos de embarcações e estruturas offshore, e na construção de fuselagens de aviões. Por constituírem-se em um elemento estrutural esbelto, estão sujeitas a um comportamento mecânico diferenciado denominado de flambagem, proveniente de um carregamento de compressão uniaxial. O fenômeno da flambagem pode ser dividido em flambagem elástica e elasto-plástica, sendo dependente de aspectos dimensionais, construtivos e/ou operacionais. A inclusão de perfurações em placas provoca uma redistribuição de suas tensões internas, afetando não apenas a sua resistência, mas também as suas características de flambagem. Neste trabalho, desenvolveu-se a análise do comportamento mecânico de placas finas perfuradas de aço, simplesmente apoiadas em suas bordas, e submetidas à compressão. Serão analisados dois graus de liberdade: H/L e H0/L0. Para H/L, serão analisadas placas com H/L = 1,00 e H/L = 0,50, sendo que H e L representam, respectivamente, a largura e o comprimento da placa. Para H0/L0, serão analisadas infinitas possibilidades, sendo que H0 e L0 representam, respectivamente, a largura e o comprimento da perfuração. As placas utilizadas possuem espessura (h) de 10,00 mm e perfuração centralizada. Quanto às perfurações, estas serão dos tipos: oblonga longitudinal, oblonga transversal, elíptica, retangular, losangular, hexagonal longitudinal e hexagonal transversal. Ainda em relação às perfurações, serão consideradas as seguintes frações ϕ = 0,08; 0,10; 0,15; 0,20 e 0,25, sendo que (ϕ) corresponde ao volume da perfuração. Para a determinação das cargas crítica e última de flambagem, foi utilizada a simulação numérica com o auxílio do software Ansys®, que é baseado no método dos elementos finitos. A aplicação do método Design Construtal, possibilitou a determinação das geometrias ótimas para todos os tipos de perfurações, todos os valores de (ϕ) e para todas as relações de H/L. Os resultados obtidos mostram que há influência do tipo, da forma e do tamanho da perfuração na definição das curvas limites à flambagem e das curvas à flambagem elasto-plástica. Foi possível definir, para cada tipo de perfuração e para todos os valores de (ϕ), os pontos de transição entre a flambagem elástica e à elasto-plástica, assim como os pontos que definem os valores máximos para o fator TLNMáx (tensão limite normalizadora). / Structural elements such as thin plates are part of a large number of applications in various areas of engineering and are of great importance for marine and aerospace engineering, construction and offshore structures hulls, and the construction of airplane fuselages. Being a slender structural element, they are subject to a different mechanical behavior known as buckling, caused by a compressive loading. The phenomenon of buckling can be divided in elastic and elasto-plastic buckling, being dependent dimensional, construction and / or operational aspects. The inclusion of perforations in plates causes a redistribution of its internal stress, affecting not only their resistance but also their buckling characteristics. In this work it was performed the analysis of the mechanical behavior of thin perforated steel plates, simply supported on its edges, and subjected to compression. In the analysis it was considered two degrees of freedom: H/L and H0/L0. For H/L will be analyzed plates with H/L = 1.00 and H/L = 0.50, wherein H and L represent respectively the width and length of the plate. There are endless possibilities for the relation H0/L0. The studied plates have a thickness (h) of 10.00 mm and centralized perforation. The following types of perforation will be used: longitudinal oblong, transverse oblong, elliptical, rectangular, diamond, longitudinal hexagonal and transverse hexagonal. Also in relation to perforations, it will be considered the following fractions (ϕ = 0.08; 0.10; 0.15; 0.20 and 0.25), wherein (ϕ) corresponds to the volume ratio of the perforation. For determining the critical and ultimate buckling loads it was utilized numerical simulation with the assistance of Ansys® software, which is based on the finite element method. The application of the Constructal Design method of this study made it possible to determine the optimal geometries for all types of perforations, for all values of (ϕ) and all the relations H/L. The results show that there is an influence of the perforation type, shape and size, in defining the limit curves of the buckling and the curves of the elasto-plastic buckling. It was also possible to define, for each type of perforation and for all (ϕ) values, the transition points between elastic and elasto-plastic buckling; as well as the points that define the maximum values for the TLNMáx factor (normalized limit stress).

Elementos estruturais como as placas finas fazem parte de um grande número de aplicações nas mais diversas áreas da engenharia e são de grande importância para a engenharia naval e aeronáutica, na construção de cascos de embarcações e estruturas offshore, e na construção de fuselagens de aviões. Por constituírem-se em um elemento estrutural esbelto, estão sujeitas a um comportamento mecânico diferenciado denominado de flambagem, proveniente de um carregamento de compressão uniaxial. O fenômeno da flambagem pode ser dividido em flambagem elástica e elasto-plástica, sendo dependente de aspectos dimensionais, construtivos e/ou operacionais. A inclusão de perfurações em placas provoca uma redistribuição de suas tensões internas, afetando não apenas a sua resistência, mas também as suas características de flambagem. Neste trabalho, desenvolveu-se a análise do comportamento mecânico de placas finas perfuradas de aço, simplesmente apoiadas em suas bordas, e submetidas à compressão. Serão analisados dois graus de liberdade: H/L e H0/L0. Para H/L, serão analisadas placas com H/L = 1,00 e H/L = 0,50, sendo que H e L representam, respectivamente, a largura e o comprimento da placa. Para H0/L0, serão analisadas infinitas possibilidades, sendo que H0 e L0 representam, respectivamente, a largura e o comprimento da perfuração. As placas utilizadas possuem espessura (h) de 10,00 mm e perfuração centralizada. Quanto às perfurações, estas serão dos tipos: oblonga longitudinal, oblonga transversal, elíptica, retangular, losangular, hexagonal longitudinal e hexagonal transversal. Ainda em relação às perfurações, serão consideradas as seguintes frações ϕ = 0,08; 0,10; 0,15; 0,20 e 0,25, sendo que (ϕ) corresponde ao volume da perfuração. Para a determinação das cargas crítica e última de flambagem, foi utilizada a simulação numérica com o auxílio do software Ansys®, que é baseado no método dos elementos finitos. A aplicação do método Design Construtal, possibilitou a determinação das geometrias ótimas para todos os tipos de perfurações, todos os valores de (ϕ) e para todas as relações de H/L. Os resultados obtidos mostram que há influência do tipo, da forma e do tamanho da perfuração na definição das curvas limites à flambagem e das curvas à flambagem elasto-plástica. Foi possível definir, para cada tipo de perfuração e para todos os valores de (ϕ), os pontos de transição entre a flambagem elástica e à elasto-plástica, assim como os pontos que definem os valores máximos para o fator TLNMáx (tensão limite normalizadora). / Structural elements such as thin plates are part of a large number of applications in various areas of engineering and are of great importance for marine and aerospace engineering, construction and offshore structures hulls, and the construction of airplane fuselages. Being a slender structural element, they are subject to a different mechanical behavior known as buckling, caused by a compressive loading. The phenomenon of buckling can be divided in elastic and elasto-plastic buckling, being dependent dimensional, construction and / or operational aspects. The inclusion of perforations in plates causes a redistribution of its internal stress, affecting not only their resistance but also their buckling characteristics. In this work it was performed the analysis of the mechanical behavior of thin perforated steel plates, simply supported on its edges, and subjected to compression. In the analysis it was considered two degrees of freedom: H/L and H0/L0. For H/L will be analyzed plates with H/L = 1.00 and H/L = 0.50, wherein H and L represent respectively the width and length of the plate. There are endless possibilities for the relation H0/L0. The studied plates have a thickness (h) of 10.00 mm and centralized perforation. The following types of perforation will be used: longitudinal oblong, transverse oblong, elliptical, rectangular, diamond, longitudinal hexagonal and transverse hexagonal. Also in relation to perforations, it will be considered the following fractions (ϕ = 0.08; 0.10; 0.15; 0.20 and 0.25), wherein (ϕ) corresponds to the volume ratio of the perforation. For determining the critical and ultimate buckling loads it was utilized numerical simulation with the assistance of Ansys® software, which is based on the finite element method. The application of the Constructal Design method of this study made it possible to determine the optimal geometries for all types of perforations, for all values of (ϕ) and all the relations H/L. The results show that there is an influence of the perforation type, shape and size, in defining the limit curves of the buckling and the curves of the elasto-plastic buckling. It was also possible to define, for each type of perforation and for all (ϕ) values, the transition points between elastic and elasto-plastic buckling; as well as the points that define the maximum values for the TLNMáx factor (normalized limit stress).

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Eccentric discharge of granular solids is widely considered one of the most serious design conditions for thin-walled metal silos, and one which has been the cause of very many silo disasters in the past. Yet the reasons for these consequences have not been very well understood, given the serious difficulties inherent in measuring or modelling flow patterns of granular solids, wall pressures and the associated structural response. To this end, this thesis presents a programme of theoretical and computational analyses which investigate the effects of a very wide range of different discharge flow patterns from silos, including both concentric and eccentric flows. The critical effects of changes of flow channel geometry, silo aspect ratio, changes of plate thickness and geometric and material nonlinearity are explored in detail. The codified procedures and pressure distributions for concentric and eccentric discharge of the EN 1991-4 (2007) European Standard are analysed first on a number of example silos custom-designed according to EN 1993-1-6 (2007) and EN 1993-4-1 (2007), followed by the development and investigation of a more complete mixed flow pressure theory. The computational analyses presented in this thesis are thought to be the first of their kind.

This thesis investigates the application of ultra-high modulus carbon fiber reinforced polymer (CFRP) plates to strengthen damaged reinforced concrete beams and slender columns. In the first phase, two different pre-repair loading histories were simulated in seven 3000x300x150 mm reinforced concrete beams, namely cracking within the elastic range, and overloading in the plastic range. After unloading, the beams were repaired with either high- or ultra-high modulus (210 or 400 GPa) CFRP plates, or a hybrid system, and then reloaded to failure. It was shown that the level of pre-existing damage has an insignificant effect on the strengthening effectiveness and the failure mode at ultimate. The 210 and 400 GPa CFRP of reinforcement ratio ρf = 0.17% increased the ultimate strength by up to 29 and 51%, respectively, despite the 40% lower tensile strength of the 400 GPa CFRP, due to the change in failure mode from debonding to rupture. Doubling ρf of the 400 GPa CFRP to 0.34% resulted in a 63% overall gain in flexural strength, only 8% increase in ultimate strength over ρf = 0.17%, due to change in failure mode from rupture to concrete cover delamination. The beam retrofitted by hybrid CFRP showed remarkable pseudo ductility and warning signs before failure. However, a parametric study revealed a critical balance in proportioning the areas of hybrid CFRP to achieve reliable pseudo ductility. In the beam with ρf =0.34%, this was achieved using a maximum of 30% ρf of the 400 GPa CFRP. The second phase of this thesis presents an analytical model developed by modifying the provisions of the ACI 318-08 code and employing the computer software Response 2000, to predict the performance of CFRP strengthened slender reinforced concrete columns. Response 2000 is used to establish the interaction curve while the modified ACI 318-08 code is used to acquire the slender column loading path to failure including the second order effects. The model predicts that the effectiveness of the FRP strengthening system increases as the slenderness ratio and FRP reinforcement ratio increase. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-24 12:36:48.352

Steel silos are widely used as long-term or short-term containers for the storage of granular solids, of which a huge range are stored, from flour to iron ore pellets, coals, cement, crushed rocks, plastic pellets, chemical materials, sand, and concrete aggregates. The radius to thickness ratio for silos is in the range of 200 to 3000, so they fall into the category of thin shells, for which failure by buckling is the main concern and requires special attention in design. The primary aim of this thesis is to investigate the possible application of Fibre Reinforced Polymer (FRP) as a new repair and strengthening technique to increase the buckling capacity of thin metallic cylindrical shells. Extensive research has been conducted on the use of fibre reinforced polymer (FRP) composites to strengthen concrete, masonry and timber structures as well as metallic beams. However, all these studies were concerned with failure of the structure by material breakdown, rather than stability. As a result, this thesis marks a major departure in the potential exploitation of FRP in civil engineering structures. Many analyses of cylindrical shells are presented in the thesis. These are all focussed on strengthening the shell against different failure modes. Two loading conditions were explored: uniform internal pressure accompanied by axial load near a base boundary, and axial loads with geometric imperfections. For the latter, local imperfections are usually critical, and two categories of imperfection were studied in detail: an inward axisymmetric imperfection and a local dent imperfection. For the first loading condition, which leads to elephant’s foot buckling, an analytical method was used to derive general equations governing the linear elastic behaviour of a cylindrical shell that has been strengthened with FRP subject to internal pressure and axial compression. It was used to identify optimal application of the FRP. All the later studies were conducted using nonlinear finite element analysis (using the ABAQUS program) to obtain extensive predictions of many conditions causing shell buckling and the strengthening effect of well-placed FRP. In all the cases studied in this thesis, it was shown that a small quantity of FRP composite, applied within a small zone, can provide a significant enhancement of the resistance to buckling failure of a thin metal cylinder. These calculations demonstrate that this new technique is of considerable practical value. However, it is clear that not all the relevant questions have been fully answered, so the author poses appropriate questions and makes suggestions for future work.

Doctor of Philosophy / Department of Civil Engineering / Hayder A. Rasheed / Spherical shells are widely used in aerospace, mechanical, marine, and other industrial applications. Accordingly, the accurate determination of their behavior becomes more and more important. One of the most important problems in spherical shell behavior is the determination of buckling loads either experimentally or theoretically. Therefore, in this study some elastic and plastic buckling problems associated with spherical shells are investigated. The first part of this research study presents the analytical, numerical, and experimental results of moderately thick and thin hemispherical metal shells into the plastic buckling range illustrating the importance of geometry changes on the buckling load. The hemispherical shell is rigidly supported around the base circumference against horizontal translation and the load is vertically applied by a rigid cylindrical boss (Loading actuator) at the apex. Kinematics stages of initial buckling and subsequent propagation of plastic deformation for a rigid-perfectly plastic shell models are formulated on the basis of Drucker- Shield's limited interaction yield condition. The effect of the radius of the boss used to apply the loading, on the initial and subsequent collapse load is studied. In the numerical model, the material is assumed to be isotropic and linear elastic perfectly plastic without strain hardening obeying the Tresca or Von Mises yield criterion. Finally, the results of the analytical solution are compared and verified with the numerical results using ABAQUS software and experimental findings. Good agreement is observed between the load-deflection curves obtained using three different fundamental approaches. In the second part, the Southwell’s nondestructive method for columns is analytically extended to spherical shells subjected to uniform external pressure acting radially. Subsequently finite element simulation and experimental work shown that the theory is applicable to spherical shells with an arbitrary axi-symmetrical loading too. The results showed that the technique provides a useful estimate of the elastic buckling load provided care is taken in interpreting the results. The usefulness of the method lies in its generality, simplicity and in the fact that, it is non-destructive. Moreover, it does not make any assumption regarding the number of buckling waves or the exact localization of buckling

This research study is conducted on one bay-one story non-sway frames where the effects of the rotational restraint and slenderness ratio on the post-buckling strength of the axially restraint column under thermal load are studied. Geometric non-linear analysis of the structures is performed using a research program based on the beam-column theory. A total 32 models are created considering two different bottom end conditions: fixed and hinged, slenderness ratios: 50 and 125, and the beam to column length ratios: 0.5,1,1.5 and 2, to account for the variation in the rotational restraint. All models are subjected to thermal loads and numerical results are obtained to study the post-buckling behavior of the columns of the frames under thermal loads.

The objective of this study is to examine the effect of rotational restraints on thermal post-buckling response of sway columns using geometrically nonlinear analysis. The present design approach considers columns to have failed once they buckle. However, the columns under fire load are found to exhibit significant post-buckling strength which could be utilized for more economical design. The past researchers on the nonlinear thermal analysis used isolated columns with idealized support conditions which mean the columns are assumed to be free or fully restrained in the rotation, lateral and, axial directions. However, that is seldom the case in real structures and the restraint at an end of the column depends upon the members connected at that joint. The restraint provided to the column by the members connected at the joint will be in between the free case and fully restrained case. This study incorporates the variation in rotational restraint due to changes in the properties of members connected at the ends of the column. The columns are assumed to be fully restrained in the axial direction. Since the study is being carried out on sway columns, the restraint in the lateral direction is zero.