Web openings are increasingly used in load bearing cold-formed steel members, such as wall studs or floor joints, to facilitate services in buildings. In such members, web crippling can occur at points of concentrated loads, which will be influenced by the size and position of the openings. Due to the improvement of cold-formed techniques, the material thickness and strength of channel section is increased but research on the cold-formed steel members with web openings is limited. Therefore, the behaviour and design of cold-formed steel channel members with web openings are investigated in this study. Both experimental tests and non-linear elasto-plastic finite element analysis (FEA) are used to investigate the effect of circular web openings on web crippling behaviour of cold-formed steel channel-sections with circular web openings under interior-one-flange (IOF) and end-one-flange (EOF) loading condition; the cases of both flanges unfastened and flanges fastened are considered. In the case of the tests with web openings, the holes are located either centred above the bearing plates or with a horizontal clear distance to the near edge of the bearing plate. Good agreement between the experimental tests and non-linear finite element models was obtained. The finite element models were then used in a parametric study to investigate the effect of cross-section sizes and web holes on the web crippling strengths of channel sections. The web crippling strengths of cold-formed steel channel sections without holes from experimental and numerical investigations were compared with the current design strengths from British Standard, Eurocode and North American Specification (NAS). Only the NAS provides design strengths for the case of circular holes with a horizontal clear distance to the near edge of bearing plates and only for the case of flanges fastened to the bearing plates. However, NAS design code has limitations and also failed to predict the web crippling strengths of cold-formed channel-sections with holes. Therefore, new design strength reduction factor equations for cold-formed steel channel-sections need to be proposed. An extensive statistical analysis of web crippling for cold-formed steel channel-sections with web holes was carried out, including 135 test results and 1463 numerical results. In addition, design recommendations in the form of web crippling strength reduction factors were proposed. Reliability analysis was performed to evaluate the reliability of the proposed strength reduction factors. It was shown that the proposed strength reduction factors agree well with the experimental and finite element results.

In aircraft design, considerations to aeroelastic interactions are necessary to define permitted operating conditions which are safe. Limit cycle oscillations (LCO) are an example of unwanted and potentially dangerous wing behaviour. These are constant amplitude structural vibrations, driven by the interaction between a wing and the surrounding airflow. The present work is concerned with the numerical analysis of LCOs. More specifically, addressing the lack of comprehensive stochastic analyses of these highly nonlinear phenomena by utilising techniques which improve efficiency and support high complexity. This will allow simulation to be used more extensively in the aircraft design process which will enable safety factors to be rationalised thus improving aircraft performance. The cost of LCO simulation is reduced by implementing a High-Dimensional Harmonic Balance-based (HDHB) formulation. This method showed excellent agreement with the corresponding time-marching models and efficiency gains surpassed one order of magnitude. An objective of this work is to implement HDHB to problems with nonlinearities in both structural and flow field characteristics. Polynomial Chaos Expansions (PCE) are employed for the propagation of parametric uncertainties, offering large efficiency gains in comparison to Monte Carlo methods. Bifurcations uncovered in the stochastic analysis were handled well by the PCE by partitioning the parameter space along the discontinuity. Stochastic model updating, also enabled by the efficiency of the HDHB method, is explored to tackle the difficulties in establishing sources of nonlinearities within aeroelastic problems. A Bayesian inference technique is used to perform the parameter estimations of elusory structural characteristics for the purpose of model calibration. Parameter values were able to be identified with high accuracy using sparse observational data. This work has shown that the HDHB method provides an attractive alternative to timemarching methods. In addition, when combined with PCE, the stochastic analysis of highly complex LCOs is realisable.

Fibre reinforced polymer (FRP) strengthening materials offer an opportunity to increase existing concrete slab capacities and service lifetimes. Most previous research in this area has focussed on using glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP), with relatively little on using basalt fibre reinforced polymer (BFRP) as a strengthening material. Previous research has also tended to focus on strengthening simply supported elements and has not considered the beneficial influence of the in-plane lateral restraint imparted from the reinforced concrete building frame. Furthermore, by installing FRPs using the near surface mounted (NSM) technique, disturbance to the existing structure can be minimised. This research considered both the beneficial effects of compressive arching action (CMA) and FRP strengthening on test slabs constructed from normal strength concrete with span-to-depth ratios of 20 and 15 and 0.15% steel reinforcement. 0.10% BFRP and CFRP was used in strengthened slabs, which were compared with unstrengthened control samples. The bond strength of BFRP and CFRP bars was also investigated over a range of bond lengths with two adhesive thicknesses using an articulated beam arrangement in order to establish optimum bond characteristics. Finally, nonlinear finite element analysis (NLFEA) slab models were developed and validated against experimental test results. The research showed that CMA effects occurred in all in-plane restrained slabs, including those strengthened with FRP bars, and that increases in capacity due to arching and FRP strengthening were cumulative but generally separate in nature. Relationships were also established to allow practicing engineers to estimate in-plane restraint stiffness. Comparisons were also made between slab capacity predictions obtained using the Queen’s University of Belfast (QUB) Arching Theory, NLFEA modelling and current design code approaches. These showed that QUB Arching Theory and NLFEA methods were reliable and that current code methods are highly conservative in comparison with other approaches.

Improvements in the structural performance of glulam timber beams by the inclusion of reinforcing materials can improve both the service performance and ultimate capacity. In recent years research focusing on the addition of fibre reinforced polymers to strengthen members has yielded positive results. However, the FRP material is still a relatively expensive material and its full potential has not been realised in the combination with structural timber. The primary aim of this research is to evaluate the feasibility of strengthening timber beams by the addition of a post-tensioned basalt fibre reinforced polymer rod. This will be achieved through the experimental testing of a combination of unreinforced and post-tensioned GL28 timber beams, with both unbonded and bonded Basalt Fibre Reinforced Polymer (BFRP) rods being utilized as the post-tensioning tendon. It is intended that experimental and analytical research will begin to assess the viability of using this timber composite in construction scenarios.

This Thesis describes the numerical simulation of fluid-structure interaction (FSI) problems. A finite-volume based stress analysis code was developed and coupled to an existing in-house CFD code to form a general purpose FSI solver capable of being used with the advanced turbulence and near-wall models developed within the research group. The code has been used to study a number of physiological flows in the present work, although the general nature of the solver allows it to be used for other applications also. By using the same numerical method, implemented in a consistent manner, for both fluid and solid domains, the inefficiencies associated with using separate packages for the fluid and solid were avoided. Separate packages typically store information in different data structures; some form of software interface is required to transfer information between the two packages. This additional software layer, which is called during each FSI iteration, causes a considerable overhead. By using a single numerical mesh across both domains, the inaccuracies associated with boundary interpolation were also avoided. Typically, separate packages use meshes which do not conform at their common boundary. In order to find nodal values of the fluid pressure, say, at the solid nodes, some form of interpolation is necessary. The interpolation leads to the introduction of truncation errors. These improvements allow for more accurate and efficient FSI simulations, particularly transient cases, to be performed. The solid solver was verified against analytical solutions for a number of test cases, including: planar stress distribution in a square plate with a circular hole in the centre; axisymmetric stress in a thick walled cylinder under internal pressure, and unsteady displacement of a cantilevered beam under free vibration. Before coupled analyses were performed, the flow solver was also validated through a number of rigid walled test cases, including steady flow through a stenosed tube and unsteady flow through an aneurysm. Many physiological flows are difficult to capture due to flow separation and early transition to turbulence. The use of a low-Reynolds number k-ε turbulence model was successful at capturing the flow field over a range of physiologically relevant flow rates. Once the solid body and flow solvers had been validated in isolation, they were coupled together and applied to a number of physiological flows, namely: steady flow through an initially straight tube with a compliant wall; steady flow through a compliant stenosis, and unsteady flow through a compliant aneurysm. The results from all three test cases showed good agreement with the available experimental and numerical data in terms of wall deformation. The solid body solver also proved itself to be capable of producing high quality numerical meshes for use in other simulations. The fluid mesh was considered to be a solid body with arbitrary material properties; the required deformation was specified as prescribed displacement boundary conditions. The main benefit of this method, compared to simple elliptical grid generation methods, is that near-wall grid spacing was preserved throughout the coupled simulation.

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The objective of my thesis is to enhance the understanding of compressive membrane action (arching action) in concrete slabs with special relevance to composite bridge deck slabs. Compressive membrane action is a common structural phenomenon in laterally restrained concrete slabs and enhances the loading capacity of laterally restrained slabs due to in-plane thrust derived from the restraint offered by the boundary conditions. The aim of this research is to establish the behaviour of bridge deck slabs using the nonlinear finite element method and experimental tests. More and more bridges built in the past 50 years employed composite structures with decks constructed of reinforced concrete and supported by longitudinal steel girders. A series of third scale composite steel-concrete bridge deck models were built for the experimental models. The design parameters ofthe concrete strength, the steel beam size and reinforcement percentages were varied in the models. The target of the· experimental tests was to find out the influence of these design parameters had on compressive membrane action. Commercial finite element packages were adopted to simulate the compressive membrane action in the concrete slabs using nonlinear numerical analysis. The accuracy of simulation results. Because punching failure is a common failure mode in this structural type and is difficult to be simulated in FEA, failure criteria based on implicit and explicit analysis were established to capture the limit loads for the numerical analysis. Furthermore, the research proposed the most suitable simulation method to be used and modelled compressive membrane action in concrete slabs, including the type of element and solution method to be adopted. At last, a modified theoretical model based on QUB model (Taylor et al 2003) for the prediction of ultimate loads of bridge decks was proposed.