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The work presented in this thesis is concerned with the investigation of the dynamic behaviour of magnetorheological elastomers (MREs) and smart sandwich structures. An extensive review, covering existing smart materials and their applications, has highlighted that smart materials and structures can be applied to large scale structures. Comprehensive experimental tests have been carried out in order to gain knowledge and data on the dynamic shear properties and behaviour of stiffness change of MRE and MRE cored adaptive sandwich beam structures depending on magnetic fields. Dynamic shear property tests with different curing stages have been enhanced to obtain various properties. The new developed forced vibration test rig enabled forced vibration tests of MRE embedded sandwich beam with various aspects such as different magnetic field strength, various oscillations of force amplitudes, boundary conditions and damping effects under localised magnetic fields to be made. In parallel to these experimental investigations, a new theoretical model was developed by combining the magnetisation effects on iron particles in terms of the curing times. In addition, a new macro scale modelling approach for rubber like materials (nonlinear behaving materials) was made by adopting FEA analysis to obtain the optimum volume of pores and size of iron particles to enhance the performance of MREs. A higher order sandwich beam theory is extended to include damping properties of MRE. It has been demonstrated that a higher order sandwich beam theory appears to be the most versatile and accurate modelling method for a sandwich beam with an MRE core material. The results from higher order theory have been combined with a power flow analysis for the smart floating sandwich raft vibration isolation system. Finally, an experimental study was performed to illustrate the control capabilities of MRE adaptive vibration absorber for a propeller shaft in real time. From this research work, a better understanding of the dynamic behaviour of MRE embedded sandwich beam has been acquired.

X-ray Computer Tomography (CT) is well suited to the inspection of Fibre-Reinforced-Plastic (FRP) composite materials. However, a range of limitations currently restrict its uptake. The aim of the present research was to develop advanced inspection procedures that overcome these limitations and increase the scope of composite structures that can be inspected by industrial cone beam CT. Region of Interest (ROI) CT inspection of FRP laminated panels was investigated and two data completion methods developed to overcome reconstruction errors caused by truncated projection data. These allow accurate, highly magnified regions to be reconstructed on objects that extend beyond the Field-of-View (FOV) of the detector. The first method extended the truncated projection data using a cosine signal tailing off to zero attenuation. This method removed the strong 'glowing' artefacts but an inherent error existed across the reconstructed ROI. This did not affect the defect detectability of the inspection but was viewed as problematic for applications requiring accurate density measurements. The second method used prior knowledge of the test object so that a model could be created to estimate the missing data. This technique removed errors associated with ROI reconstruction thus significantly improving the accuracy. Techniques for extending the FOV were developed and applied to the inspection of FRP wind turbine blades; over 1.5X larger than the conventional scanning FOV. Two data completion methods were developed requiring an asymmetrically positioned detector. The first was based on the cosine tailing technique and the second used fan beam ray redundancy properties to estimate the missing data. Both produced accurate reconstructions for the 'offset' projection data, demonstrating that it was possible to approximately double the FOV. The cosine tailing method was found to be the more reliable. A dual energy image CT technique was developed to extend the optimum dynamic range and improve defect detectability for multi-density objects. This was applied to FRP composite/Titanium lap joints showing improved detectability of both volumetric and planar defects within the low density FRP. The dual energy procedure was validated using statistical performance measures on a specially fabricated multi-density phantom. The results showed a significant improvement in the detail SNR when compared to conventional CT scans.

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.

This thesis focused on the mechanisms involved in negative thermal expansion of 2D/3D lattice structures. The effects of varying the constituent materials and geometry were explored. The lattices had geometries similar to those found in light-weight structures in many transport applications, including aerospace and spacecraft. One specific case was to determine how to reduce the coefficient of thermal expansivity (CTE) of such structures to near zero, by using two constituent materials with contrasting CTEs, without incurring penalties in terms of other elastic and failure properties, mass and manufacturability. The lattice geometries able to exhibit altered CTE were explored, and penalties in terms of other elastic properties were quantified. The results were scale-independent and so were generic to all such lattices. Analytical prediction and generic relationships between the geometries of the lattices and their performance were proposed. Experimental validation of the model predictions was undertaken using physical samples. The thermomechanical properties were simulated by commercial finite element method (FEM) codes (Ansys 11, Ansys, Inc.). Ansys parametric design language was adopted to generate large sets of solutions to be evaluated against chosen criteria. Results show small or, in some cases, no penalties to be paid in terms of stiffness and mass for implementing dual-material lattices with near-zero CTE. Such lattices may compete favourably with high-cost and high-density materials (e.g. Invar) and the manufacture of dual-material lattices can be by standard processes or alternative new process such as Additive Layer Manufacturing (ALM). An example of truss core sandwich application for aerospace application was modelled by FEM. Applications as cores in sandwich panels might be the first route by which the ALM manufacturing process is required to develop dual-material capability.

Cold formed steel (CFS) sigma sections are commonly used as purlins in the construction of modern industrial and residential buildings due to their excellent strength-to-weight ratio. This thesis reports investigations on the structural behaviour of CFS sigma purlins in three different parts of modern roof systems. In the first investigation, the pre-buckling, buckling, post-buckling and post-failure behaviour of continuous CFS sigma purlins near internal supports was studied by experimental and numerical methods. In the second investigation, the moment-rotation response as well as the moment resistance of the sleeve connection of sigma purlins was studied by laboratory tests. Engineering models were developed to predict the behaviour of this connection and a good correlation was observed with the experimental data. In the third investigation, the flexural stiffness and moment resistance of CFS sigma purlins fastened to roof sheeting with large screw spacing was studied experimentally. The purlin-sheeting assemblies were subjected to both downward and uplift loadings, from which different behavioural aspects such as flexural stiffness, failure modes and ultimate load were examined. Test results are utilized to develop design proposals for sigma purlins that codes or standards have not yet covered.

The ability to predict the temperatures in protected steel structures is of vital importance for the progress of fire safety engineering. Existing methods are limited in several respects, typically being computationally restricted and limited to examination of the performance of specific components. This thesis investigates a generalised CFDbased methodology for thermal analysis of structural members in fire, developed to overcome these limitations. A novel methodology has been developed, known as GeniSTELA (Generalised Solid ThErmal Analysis), which computes a “steel temperature field” parameter in each computational cell. The approach is based on a simplified 1D model for heat transfer, together with appropriate corrections for 2D and 3D effects, to provide a quasi- 3D solution with a reasonable computational cost. GeniSTELA has been implemented as a submodel within the SOFIE RANS CFD code. The basic operation of the model has been verified and results compared to the empirical methods in EC3, indicating a satisfactory performance. The role of the surface temperature prediction has been examined and demonstrated to be important for certain cases, justifying its inclusion in the generalised method. Validation of the model is undertaken with respect to standard testing in fire resistance furnaces, examining the fire ratings of different practical protection systems, and the BRE large compartment fire tests, which looked at protected steel indicatives in full-scale post-flashover fires; in both cases, a satisfactory agreement is achieved. Model sensitivities are reported which reveal the expected strong dependencies on certain properties of thermal protection materials.

A new concept in composite construction has been developed at the University of Salford, involving the use of fibre-reinforced cement channels, combined structurally with partially prestressed composite concrete T-beams. The British Standards Institution Code of Practice, CP110: 1972, "The Structural Use of Concrete", permits the use of Class 2 and Class 3 (partially prestressed) concrete members in structural design'. The limiting design criteria for such members are usually the limit'states of deflection and cracking and therefore, an improvement in their flexural behaviour would be beneficial. This improvement may be brought about by the addition of fibre-reinforcement, in the form of two or three dimensionally randomly distributed fibres. The Code of Practice, CP110: 1972, does hot, however, give any guidance on the use of fibres in structural members and it is also apl. arent that the methods outlined in the code for the calculation of the limit states are limited and can be improved. The flexural behaviour of twenty-two partially prestressed composite concrete T-beams was investigated. Each beam consisted of a precast partially prestressed X-joist web, combined with a cast-insitu lightweight aggregate concrete flange. Alkali-resistant glass fibrereinforced cement channels were placed at the soffits of six beams and steel fibre-reinforced concrete was used in the webs of two beams. The T-beams were subjected toshort-term, long-term and fatigue loading and their structural performance was considered in terms of strength, cracking and deformation. Theoretical relationships are derived between the applied moment and the depths of the neutral axes of stress and bending, enabling a design equation relating applied moment to the steel stress to be developed. Subsequently, design equations for the calculation of the limit states of deflection and cracking are developed, which are directly applicable to both conventional and fibre-reinforced structural members. The use of a fibre-reinforced cement channel as an integral structural part of a concrete member results in many important advantages when compared with conventional concrete members and the test results show that they considerably improve the structural performance of the partially prestressed composite concrete T-beams.

Cellular beams (CBs) have become increasingly popular in the UK and other countries over the recent years. However, the research into the behaviour of these beams has not advanced at the same rate. There is still no robust codified guidance available to design cellular beams and cellular composite beams at ambient and elevated temperatures. Meanwhile, numerical simulation approaches, such as Finite Element (FE) analysis, have enabled the researchers to advance their investigations into various behavioural aspects of these beams. In this research, the developed numerical models using the ABAQUS package were able to predict, to a high accuracy, the failure mode and failure load (temperature) of CBs and cellular composite beams at ambient and elevated temperatures.Within the investigations on cellular beams, it was found that predicting the correct failure mode by FE models can be extremely sensitive to the maximum load increment allowed in the software (for elastic-perfectly plastic stress-strain relationship for steel material) and also to the applied boundary conditions. In particular, slight changes in the boundary conditions applied to the top flange of the beam, can change the failure mode from web post buckling to Vierendeel mechanism. The buckling resistance of the web post of cellular composite beams was found to be sensitive to the amplitude of web imperfections at ambient temperature. However, the ultimate resistance of these beams was not affected by the amplitude of web imperfections at elevated temperature. This suggests that the 'Strut' model used in current design method to estimate the buckling resistance of the web post is not reasonable at elevated temperature and needs to be modified. The failure of cellular composite beams under a uniform distributed load (UDL) and at elevated temperatures, was governed by distorsional buckling before the development of web post buckling. Adding full-height web stiffeners to the beam in such cases improved their loading resistance at ambient temperature by up to 15% and prevented the occurrence of distorsional buckling at elevated temperature. Increasing the end-restraints decreased the deflections of CBs which are governed by catenary action at elevated temperature. However, this also critically promoted the occurrence of web post buckling which could be due to the P-∆ effects and instabilities resulting from the restrained expansion of the beam.Asymmetric beams showed a higher sensitivity and vulnerability to the magnitude of the load ratio than symmetric sections. This suggests a more prudent approach for the fire design of asymmetric beams as opposed to symmetric beams.