The design of Long Span Bridges involves complex analysis of the interaction between fluid and bluff body (Fluid Structure Interaction). In the past, the aerodynamic characteristics needed for the design of long span bridge deck sections have been obtained via wind tunnel tests. Recent advances in turbulence modeling, computational fluid dynamics and the increasing affordability of computers have made numerical modeling of these complex studies possible. Much research has been carried out on the applicability of CFD in the study of bluff body aerodynamics, and less relating to long span bridges. Unfortunately, due to computational costs and sometimes lack of complete details from the wind tunnel test results, these studies have been limited in scope; usually the work is 2-dimensional and often limited to the basic section without the parapets and equipment that are part of the super structure. Also, some experimental work has been done on shaped bluff body sections, such as rectangular cylinders, which has provided useful but limited application to a bridge deck section. The work described in this theses consist of modeling and simulation of the sectional wind tunnel test of the Carquinez Strait bridge in California, a real long span bridge deck section. The modeling incorporates the often ignored but important details such as parapets, barriers and most importantly, the effects of the shape of different edge details on aerodynamic characteristics such as lift, drag and moment coefficients, as well as the flow pattern created by the different edge details in the shedding of vortices in their wakes. The simulations were carried out using the kappa-o based Shear Stress Transport RANS (Reynolds Averaged Navier Stokes) turbulence model at an average wind velocity of 3.2 m/s with angles of attack of +/-10°. The basic deck section of the Carquinez Strait Bridge is of trapezoidal box girder with sharp edge detail type, this cross section was modified by modifying the edge detail and replacing it with three different types of details; a round edge detail, an oval and a triangular shaped edge type. Additional studies include the removal of the barrier, parapet and equipment to see their effect and the roles played by them in the aerodynamic static force response and the flow physics. Two grid types were explored to determine the most accurate; tetrahedral and hexahedral dominated meshes. Next, determining the appropriate RANS turbulence model, from the matrix of grid and turbulence model emerges the numerical simulation. Once the wind tunnel test results were corrected for errors, the results from numerical modeling compares very well with the static wind tunnel test, thereby validating the choice of turbulence model and grid type, and demonstrating the viability of CFD in long span bridge design. The results of the fluid flow around the differently modified edge details shows how the mechanics of vortex induced vibration develops off of the recirculating air underside the exterior web at the trailing edge, because of the variation in the velocity of air in this region due to the different edge details, it is reasonable to make deductions on stability. In the simulations where the parapets, barriers and equipments are removed off of the deck sections, the response are markedly different, revealing that they are critical and as important as the edge detail chosen during the preliminary design.

Metal Matrix ceramic-reinforced composites are rapidly becoming strong candidates as structural materials for many high temperatures and aerospace applications. Metal matrix composites combine the ductile properties of the matrix with a brittle phase of the reinforcement, leading to high stiffness and strength with a reduction in structural weight. The main objective of using a metal matrix composite system is to increase service temperature or improve specific mechanical properties of structural components by replacing existing superalloys. The satisfactory performance of metal matrix composites depends critically on their integrity, the heart of which is the quality of the matrix-reinforcement interface. The nature of the interface depends on the processing of the metal matrix composite component. At the micro-level the development of local stress concentration gradients around the ceramic reinforcement, as the metal matrix attempts to deform during processing, can be very different to the nominal conditions and play a crucial role in important microstructural events such as segregation and precipitation at the matrix-reinforcement interface. These events dominate the cohesive strength and subsequent mechanical properties of the interface. At present the relationship between the strength properties of metal matrix composites and the details of the thermo-mechanical forming processes is not well understood. The purpose of the study is to investigate several strengthening mechanisms and the effect of thermo-mechanical processing of SiC_p reinforced A359 aluminium alloy composites on the particle-matrix interface and the overall mechanical properties of the material. From experiments performed on composite materials subjected to various thermo-mechanical conditions and by observation using SEM microanalysis and mechanical testing, data were obtained, summarised and mathematically/statistically analysed upon their significance. The Al/SiC_p composites studied, processed in specific thermo-mechanical conditions in order to attain higher values of interfacial fracture strength, due to precipitation hardening and segregation mechanisms, also exhibited enhanced bulk mechanical and fracture resistant properties. An analytical model to predict the interfacial fracture strength in the presence of material segregation was also developed during this research effort. Its validity was determined based on the data gathered from the experiments. The tailoring of the properties due to the microstructural modification of the composites was examined in relation to the experimental measurements obtained, which define the macroscopical behaviour of the material.

Advanced composite materials have high strength-to-weight ratios, corrosion resistance and durability and are extensively used in aerospace, energy and defence industries. This research concentrates on minimising the process-induced residual stresses, and improving the fibre alignment of composites by employing a fibre prestress methodology. A novel flat-bed fibre prestress methodology for autoclave processing of composites was developed. This research investigates the effect of fibre prestress on 1) residual stresses, 2) fibre alignment, 3) static tensile and compression properties and 4) fatigue behaviour of composites. Experimental results show that this prestress methodology, on a 16-ply unidirectional E-glass/ 913 epoxy composite, reduces the residual strain of the composite from –600 µε to approximately zero for a prestress of 108 MPa. The strains measured from optical fibre sensors were in close agreement with those obtained using strain gauge. The results from fibre alignment studies showed that fibre prestressing improved the fibre alignment from 20% of fibres aligned to 0 ° degree in non-prestressed composites to 75% of fibres aligned to 0 ° degree in 108 MPa prestressed composites. Findings have shown that prestressing is beneficial to the static compressive and tensile performance of composites. The results show that fibre prestressing improves the fatigue life and resistance to stiffness degradation in the low stress level fatigue region. Also a change in static and fatigue damage mechanism was observed. The improvement in the static and fatigue properties is due to the reduction in residual stresses and fibre waviness. Overall the fibre prestressing methodology enhances the performance of composites by increasing the resistance to static and fatigue loading. The thesis also suggests that there is an existence of prestress limits to retain optimal material performance.

The main objective of this research is to contribute to the knowledge and understanding of the behaviour of the headed stud shear connector in composite beams with trapezoidal profiled metal decking laid perpendicular to the axis of the beam through experimental and numerical studies. Push tests are used to study the behaviour of composite beams. A three-dimensional finite element model of the push test is developed using the general purpose finite element program ABAQUS and the push test is analysed using different concrete material models, and analysis procedures. The Concrete Damaged Plasticity model with dynamic explicit analysis procedure is found to have matched with experimental results very well in terms of the shear connector resistance, load-slip behaviour and failure mechanisms. The post-failure behaviour of the push test, which has not been modelled in the past, is accurately predicted in this study with the help of this modelling technique. The experimental investigation is conducted with a single-sided horizontal push test arrangement to study the influence of various parameters such as normal load, number of shear studs, reinforcement bar at the bottom trough, number of layers of mesh, position of mesh, position of normalload and various push test arrangements. To assess the accuracy and reliability of the developed finite element model, it is validated against push test experiments conducted in this study and variety of push tests carried out by other authors with different steel decks and shear stud dimensions, positions of the shear stud within a rib and push test arrangements. The results obtained from the finite element analysis showed excellent agreement with the experimental studies. The validated finite element model is used in a parametric study to investigate the effect of shear stud position, thickness of the profiled sheeting, shear connector spacing and staggering of shear studs on the performance of the shear stud. The results of the parametric study are evaluated and findings are used to propose the design equations for shear connector resistance taking into account the position of the shear stud and thickness of the profiled sheeting. The coefficient of correlation between experimental and predicted results is nearly equal to one, which indicates that the predicted results are accurate, and the proposed equations are suitable for future predictions.

No description available.

The thesis seeks to quantify the effect of the following major variables on the stiffening effect of light cladding on steel structures: 1) suction loading 2) flange behaviour 3) sheet length 4) the absence of shear connectors. After an introductory chapter, theoretical analysis is presented to assess each of the above variables (chapters 2-6). Experimental work verifying the theory is presented in chapters 7~12. This comprises three series of tests on full scale roof panels and a comprehensive series of tests on a full scale sheeted building. Other secondary variables investigated include: 1) position and number of rooflights 2) sustained loading 3) cyclic loading 4) shear buckling 5) purlin crippling.

Tbe study consists of an experimental and analytical investigation into the lateral buckling behaviour of steel I-section girders braced by continuous or discrete U-frames. Scaled down laboratory tests on twin I-section girders have been carried out under full instrumentation and are reported. Lateral deflection of the compression flanges and final buckling modes were recorded and the coupling effect of U-frame action is clearly demonstrated. The failure loads obtained were generally higher than the corresponding design values according to BS5400. Using a large displacement elasto-plastic finite element package, ABAQUS, finite element idealisations of the tests were established and analysed. Good correlation between the experiments and the numerical analyses was reached. Validity of the ABAQUS package was confirmed and first order elements were sufficiently effective for the analysis. This was followed by further investigation of a wider range of I-section girders using ABAQUS. The ultimate bending resistance of the girders obtained from finite element analysis was in general greater than the corresponding design values to BS5400, particularly so with girders of high slendemess. Thus the present design method is considered to be unduly conservative. The cause of this conservatism in BS5400 is discussed. The expression for the calculation of effective length of U-frame braced girders was found to be reasonable. Based on the results from ABAQUS and reviews of the limited research directly related to this study, two main parameters in the BS5400 expression for beam slenderness seem inappropriate for lateral buckling of an I-section girder under U-frame restraint. These are the radius of gyration of the whole girder section and the ratio of overall depth of a girder to mean flange thickness. Instead, radius of gyration of the compression flange together with a contribution from the adjoining web section was found to be more appropriate as also was the web slenderness. In addition, a modification is proposed to the present limiting stress curve for lateral buckling of bare steel I-section girders. Empirically derived factors have been introduced. The general procedures in the existing design method to BS5400 remain similar, however.

Currently, in the military and civilian fields, there is an increasing demand for using hybrid systems, which are manmade structural systems combining two or more distinct materials. By carefully studying and designing such kind of structural systems, one can take advantage of heterogeneity of the structure, thus significantly improving the overall structural performance. Hence, the demand for robust analytical and numerical models to predict blast performance of such system has become more important. The primary aim of the present research is to investigate and understand the structural behaviour of several hybrid systems under extreme dynamic loads and to propose concepts for optimisation. Three types of hybrid systems have been studied, improved and their performance has been validated. They are the metal-to-composite hybrid joints, sandwich panels, and the metamaterial. Analytical, numerical and experimental studies have been conducted to analyse the structural behaviour of hybrid joints and sandwich panels under transient high intensity dynamic loading, in order to ensure these systems possess the desired capacity, designed strength, and robustness. Therefore, they are able to resist not only static loadings but also shocks induced by various explosions. For frequency analysis purposes, the perforated hybrid joints and metamaterials have been considered as a 2D lattice. The primitive cell (unit cell) of the lattice is formulated in the Fourier space (k-space) and studied using the Floquet-Bloch’s principle to investigate the attenuation-free shock response characteristics. Plane wave propagation in the hybrid system is thus investigated by constructing the first Brillouin zone and extracting the band structure diagram. As another case for a hybrid system, the structural performance of a circular sandwich panel with symmetric through-thickness architecture subjected to a pulse loading of arbitrary temporal and spatially uniform distribution (UDL) has been investigated by using the third order shear deformation theory. Based on the Hamilton’s principle, the governing partial differential equations (PDE’s) are derived. By applying the weak form Galerkin’s method of weighted residuals, the PDE’s are transformed into ODE’s. By solving the ODE’s with their boundary and initial conditions, results show that there is a strong correlation with finite element results obtained from ABAQUS 6.9. The third-order shear deformation theory allows for accurate assessment of out-of -plane shear in the core where the failure usually occurs. Due to the fact that core of a sandwich panel is more often to be the weakest link, a remedy must sought, e.g. employing additional core layers, to improve its performance. Dynamic response of four circular sandwich panel constructions with different proposed core designs under global and local blast loading conditions has been investigated. Numerical finite element (FE) models have been set up to study the effect of additional core inter-layers on blast resistance enhancement of these sandwich panels. A ductile elastomeric layer of polyurea, and a fairly compressible Divinycell-H200 foam layer have been selected as the additional core inter-layers and have been placed in different arrangements to protect the core of the standard sandwich panels, and maximise overall blast resistance. Comparison of specific kinetic and strain energies shows the effect of additional core layers on blast energy absorption of a sandwich system. The study shows the improvement in shear failure prevention in the core as a result of the use of additional core layers. One qualitative 2DoF system with a viscoelastic spring element representing the integral effects of sacrificial additional core inter-layers and a nonlinear spring representing the stiffness of the conventional sandwich system; and a similar qualitative SDoF model of a conventional sandwich panel have been developed for dynamic analysis. The conclusions drawn from the numerical tests are confirmed by the output of this analysis. The results of this research work give a better understanding of the performance of some generic hybrid systems under blast, which allows the optimised hybrid system to be more confidently designed and should be able to fill the gap in the currently growing demand for high strength, light weight, reliable hybrid systems in various civilian and military industries.

The aim of this project is to develop a new type of composite beam that is light and has high constructability: This is achieved herein with the development of the PCFC beam which consists of a closed cold-formed steel section embedded in concrete. The motivation of the project comes from the availability of cold-formed steel to take any general form, a vital feature as it allows for optimum satisfaction of the composite supply and demand principle. The development of the beam requires several fundamental aspects to be investigated or/and formulated. The first of these is the study of the effect of the normal stresses and the frictional stresses induced as part of the longitudinal force transfer in the composite beam. This requires the derivation and solution of the differential equations describing the partial interaction of the composite beam. It has been found that the normal stresses do not have a significant effect on the elastic performance of the beam. However, the inclusion of the frictional stresses has been found to beneficially contribute to the longitudinal shear resistance of the beam. The complexity of the beam cross-section in terms of shape and materials means that the thesis has had to address calculation procedure developments. Initially, a general procedure is developed for which the key feature is the use of functions to describe the geometrical shape of the cross-section. This allows the procedure to cater for complex shapes as well as to divide the cross-section into its matrix representations, leading to an efficient computer programming coding. However, the discrete nature of the procedure limits it use to the calculation of the plastic moment capacity based on the rectangular stress block method. This limitation is removed in the enhanced version of the procedure where Fourier Series have been used to represent the flexural stress distribution as a single-rule function. This allows the use of more realistic material models and covers various stress stages without requiring iteration. The procedure and its extended version allows for the assessment of the PCFC beam, where it has been found that, although it is slightly less sufficient when considering some serviceability aspects, the beam performs better than the equivalent composite beams in the ultimate condition.

The use of stainless steel in construction is steadily growing, with applications designed to exploit its structural properties, durability, appearance and fire resistance. The mechanical behaviour of stainless steel is fundamentally different from that of carbon steel. The stress-strain curve of stainless steel is rounded without a well-defined yield stress and exhibits significant strain hardening at relatively small strains. Nevertheless, design provisions for bolted connections between stainless steel structural members in current international standards are essentially based on the rules for carbon steel with some very limited modifications. As the connections form an essential part of all structural assemblages, a comprehensive understanding of their behaviour is vital for efficient design and consequently better performance of structures. For this reason, an investigation into the behaviour of stainless steel bolted connections has been carried out so as to better understand the response of these structural components. Suitable available test data have been reviewed and replicated using numerical models in order to study the behaviour of lap bolted connections and gusset plate connections in stainless steel under static tensile load. Strain-based criteria were defined to identify three failure modes: net section rupture, bolt shear and bearing failure. The developed FE models were successfully validated against the test results, after which they were employed to meticulously investigate the behaviour of bearing and net section rupture of lap bolted connections, as well as the net section failure of single angles connected to gusset plates. The results demonstrated that the response of stainless steel connections has some different aspects from that of carbon steel. The findings have been used to revise the design rules for net section and bearing capacities in Eurocode 3 Part 1.4. These proposed rules take into account the particular mechanical characteristics of stainless steel and therefore offer an improvement to those currently available.