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No description available.

This thesis is concerned with the design optimization of single-storey steel portal frame buildings. In the UK, such buildings account for 90% of all single-storey buildings and 50% of all constructional steelwork used. Two different types of steel portal frames are considered: conventional hot-rolled steel portal frames, which can achieve spans of up to 50 m, and cold-formed steel frames, which while less popular in the UK, may be more efficient for spans around 12 m. A real-coded niching genetic algorithm is used for the purposes of the design optimization. By adopting a niching strategy, the diversity of the population is effectively maintained and so increases the probability in searching for the optimum solution in the design space. The efficiency of the real-coded niching genetic algorithm is demonstrated through design examples of both hot-rolled steel and cold-formed steel portal frames. For the design optimization of hot-rolled steel portal frames, the optimization algorithm is used to minimize the material cost of the portal frame, per square m on plan, taking into account both the hot-rolled steel cross-sections and the eaves haunch size. In all cases, a frame spacing of 6 m is adopted. Both ultimate and serviceability limit states are considered, with deflection limits recommended by the Steel Construction Institute. It is shown that serviceability deflections govern for the design of a 50 m span portal frame, where material costs increase by 60% compared to an ultimate limit state design only. For small span frame, i.e., span of 10m, material cost only increases by 19%. For the design optimization of the cold-formed steel portal frame, the same algorithm is applied to minimize the material cost of the main frame members. In addition, frame spacings of both 4 m and 6 m are considered. For the case of a 12 m span frame, with rigid joints, it is shown that the frame design is not sensitive to serviceability deflections and that the frame is 24% cheaper (in terms of material costs per square m) than using hot-rolled steel. When the effects of semi-rigid joints and stressed-skin action are included, it is shown that the cost of members is further reduced by 32%.

The behaviour of joint in global frames subjected to fire is greatly affected by combination of forces and moments, originating from restraint to thermal expansion as well as large vertical deflection of structural members. In order to facilitate the design process of achieving robustness in simple beam-to-column connection, a componentbased model has been developed for fin-plate connections in this research. The new model represents the realistic behaviour of such connections under the influence of combined forces, together with the high rotations which can occur at the ends of beams, during building fires. The key aspect of the component method is that it characterises the force-displacement properties of each active component at any temperature, as a nonlinear "spring". The temperature-dependent characteristics of each individual component in each bolt row are defined, including the failure mechanism of the weakest component, based on experimental and analytical findings. Primary failure modes adopted for fin plate connections are bearing/block shear of the plates and bolt shear. A major additional complication is force reversal in components, which may occur simply because of temperature change, without any physical reversal of displacement. The Massing Rule has been adopted to incorporate the effect of permanent deformations at any temperature when force reversal occurs. To account for the bolt slip phases, force transitions between tensile and compressive quadrants take place only when positive contact between a bolt and the edge of its bolt hole is re-established. The results of high-temperature tests on the fin-plate connections have been used to verifY the model for isolated joints at ambient and elevated temperatures. The developed component model for the fin-plate connection has been extended for the application of moment-resisting beam splice connection, also known as the "column-tree" system. The component-based connection model has also been used to study joint behaviour in structural sub-frame analyses. Incorporating it into non-linear finite element software will enable engineers to generate the global structural interactions for steel and composite structures in fire scenarios, up to and including connection failure. The new connection element has been validated with reasonable agreement with the available experimental data, showing its capability of capturing the key features of the overall connection interaction in a realistic manner, based on the underlying mechanics, coupled with evidence from experimental data.

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No description available.

In this thesis, standard algorithms are used to carry out the optimisation of cold-formed steel purlins such as zed, channel and sigma sections, which are assumed to be simply supported and subjected to a gravity load. For zed, channel and sigma section, the local buckling, distortional buckling and lateral-torsional buckling are considered respectively herein. Currently, the local buckling is based on the BS 5950-5:1998 and EN 1993-1-3:2006. The distortional buckling is calculated by the direct strength method employing the elastic distortional buckling which is calculated by three available approaches such as Hancock (1995), Schafer and Pekoz (1998), Yu (2005). In the optimisation program, the lateral-torsional buckling based on BS 5950-5:1998, AISI and analytical model of Li (2004) are investigated. For the optimisation program, the programming codes are written for optimisation of channel, zed and sigma beam. The full study has been coded into a computer-based analysis program (MATLAB).