The elliptical hollow section (EHS) is the most recent addition to the steel hollow section (SHS) family, providing an alternative hollow section solution, for architects and structural design engineers. However, despite the extensive interest in their use on the basis of both architectural attraction and structural efficiency, a complete absence of fire resistance data and design guidance is restraining applications. This experimental and numerical analysis investigation has studied, for the first time, the structural performance of steel columns with elliptical hollow section, when subjected to extreme temperatures, represented by the hydrocarbon fire curve. A total of 12 unfilled, unprotected pin-ended elliptical hollow section steel columns were tested in a two part experimental programme. Two different sections were tested, 250 x 125 x 8.0 mm and 200 x 100 x 8.0 mm with slenderness Az = 40.1 and Az = 50.8, namely EHS-A and EHS-B respectively. The first stage tested six columns, three of each slenderness, unrestrained and under three different loading levels (al. = 0.3, 0.45, 0.6). These f irst tests demonstrated the unique local and overall buckling failure modes of the EHS co lumns under compressive loads and elevated temperatures, while recording invaluable load-displacement data, paralleled with steel temperature profiles. The second stage of the experimental program applied axial restraint against the EHS columns thermal expansion. As columns are rarely used in isolation, the application of an axial restraint represents a more rea listic column boundary condition found in construction. This study il lustrates that the additional axial forces present when restraint is applied, will accelerate the failure rates of the EHS columns. The recorded experimental data and the fin ite element method (FEM) was utilised to quantitatively express the performance of the EHS columns. The calibrated model demonstrated that a very good numerical approximation solution was obtained, on careful consideration to the thermal expansion coefficient and geometric imperfection of the column. Using the FEM model, a comprehensive parametric analysis was performed, which provided a platform to aid in the development of the critical buckling stress equation and validation of design guidance. A proposed theoretical formula for stub columns in compression under elevated temperatures is also presented. The thesis concludes that the current Eurocode method for determining the critical temperature of steel hollow sections is deemed safe for unprotected elliptical hollow section steel columns under uniform compression.

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The load-carrying capacity of slender columns is limited by global instability. However, through the addition of strategically placed cross-arms and external prestressed cables, buckling displacements can be inhibited and the load-carrying capacity considerably enhanced. Such systems, known as prestressed stayed columns offer efficient and lightweight structural solutions. Previous research on prestressed stayed columns has been largely analytical and numerical studies. To the knowledge of the author, experimental investigations into the antisymmetric and interactive modes of buckling in stayed columns have not been attempted hitherto. In addition, although some previous studies have attempted to investigate the optimum prestressing configuration of stayed columns for design purposes, generic design guidance for this type of structural component has been lacking. Therefore, the primary aim of the current study is to conduct experimental and numerical investigations into the possible buckling and post-buckling behaviour and to develop an efficient design method for these structural components. A full scale experimental investigation has been conducted with a total of 18 test specimens to demonstrate the critical modes of buckling (symmetric and antisymmetric) with interactive post-buckling. This has also investigated the imperfection sensitivity of the stayed columns. Nonlinear finite element (FE) modelling was conducted in parallel with the experiments. These models were utilized, after successful validation against the experimental results, to investigate the sensitivity of the stayed system to the variation of key parameters. Subsequently, an efficient design method for prestressed stayed columns has been developed, including design charts and equations relating the resistance of the stayed column system to the level of the initial prestress in the cables for varying cross-arm lengths and global imperfection levels. Structural reliability analysis, using the procedures in Annex D of EN 1990, was conducted to evaluate the design safety factor. Worked examples of the proposed design method are also presented to demonstrate the developed procedure for diiferent key cases. It is shown that a straightforward yet rational design method has been formulated.

The use of hollow section columns in steel construction is presently hindered by the lack of adequate connection technologies. Due to access constraints, standard bolting techniques are difficult to achieve, if not impossible without welding. As an alternative to welding, blind-bolting techniques were developed to provide desirable bolted configurations, allowing hollow column frames to be erected in the same way as open profile column frames. But the current blind-bolting techniques are restricted to the construction of simple connections because of their difficulties in achieving sufficient tensile stiffness. More recently, a novel anchored blind-bolt, labelled the Extended Hollo-bolt (EHB), has been developed at the University of Nottingham; as a modification of the standard Hollo-bolt. For the proposed connection technology, its potential in providing moment-resistance has been assessed successfully. However, the existing data related to the performance of this novel connector in tension is insufficient to permit its design. This work investigates the performance of the EHB blind-bolt under tension loading and focuses on determining, and modelling the stiffness of this novel technology in such a way to enable its application within the component method approach. An extensive experimental programme was devised to collect sufficient component characteristic data to enable the development of an EHB component model. This covered data deals with the overall response of the connector and the individual responses of its contributing elements. A total of 51 experimental pull-out tests and 20 pre-load tests have been performed. The force-displacement behaviour of the investigated joint component was determined under monotonic pull-out testing, where remote video gauge techniques have been adopted to capture the full non-linear response of the component, alongside traditional techniques to confirm the reliability of the data. The test matrix varies the grade and size of the component's internal bolt, the strength of concrete, and the depth of its mechanical anchorage. From the pull-out tests it was identified that the EHB component can ultimately develop the full tensile capacity of its internal bolt. This ultimate failure mode is confirmed for the range of parameters that was covered in this study. Increasing concrete strength had the most enhancing effect on the response of the component. A secondary programme was related to the measurement of pre-load that is induced in the internal bolt of the EHB component at its tightening stage; where pre-load was monitored over a five day period. The test matrix varies the grade and size of its internal bolt, and also considers various bolt batches. It was concluded that the relative level of component pre-load to ultimate strength increased only in the case where higher bolt grades were used. To model the tension behaviour of the EHB component, a mechanical model was developed that is based on an assembly of the component's different sources of deformation. The component model employs idealised springs with tetra-linear characteristics for the elongation of Its Internal bolt element, and springs with tri-linear characteristics for the slip of its expanding sleeves and mechanical anchorage elements. By comparing the predictions of the component model with relevant experimental data, the component model has been shown to be capable of describing the EHB component response with reasonable accuracy; capturing its tensile stiffness and its yielding trend. The accuracy of the component model has also been assessed in exclusion of pre-load effects. It was found that if the level of pre-load Is excluded from the assembly process, this can have highly undesirable effects on the predictions of the component's response. The findings of the supplementary pre-load testing programme assisted greatly in the accuracy of the component model by providing the necessary levels of pre-load. The proposed component model has demonstrated that the behaviour of the EHB component can be modelled by the component method approach; by employing Idealised models for the behaviour of its contributing elements. The validated component model is considered to simulate the tension behaviour of the novel anchored blind-bolt with sufficient fidelity that it can be considered as a benchmark for further studies.