Design optimisation of multi-story steel structures with single and multi-objective functions using three optimisation techniques

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Alkhadashi, AEM, 2022. Design optimisation of multi-story steel structures with single and multi-objective functions using three optimisation techniques. PhD, Nottingham Trent University.

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Abstract

Undoubtedly, the best design of any structure aims at the most economical and environmentally balanced solution without impairing its function and structural integrity. To achieve this, structural designers often engaged in design optimisation. In this study, single and multi-objective stochastic search methods are proposed for optimum design of two and three-dimensional multi-story structures with three, six, and nine stories. The optimality objectives are the structure weight and embodied energy as well as calculating the cost and embodied carbon of the resulting optimum options. Three optimality algorithms developed in MATLAB, namely, Genetic Algorithms (GA), Particle Swarm Optimisation (PSO) and Harmony Search Algorithm (HSA), were used for structural optimisation to compare the effectiveness of the algorithms. Two life cycle stages were considered, production and construction stages which include three boundaries: materials, transportation, and erection. In the formulation of the optimum design problem, 107 universal beams "UKB" and 64 columns "UKC" sections were considered for the discrete design variables. The imposed behavioural constraints in the optimum design process were set according to the provision of EC3.

This research developed optimisation models for evaluation of embodied energy, embodied carbon and cost for steel structures to assist designers, during the initial stages, to evaluate design decisions against their energy consumption and carbon impacts. The study shows that the integration of the analysis, design and optimisation methods employed in MATLAB can be effective in obtaining prompt optimum results during the decision-making stage.

Overall, this research demonstrates that the three methods (i.e GA, PSO and HAS) are very useful tools in improving the structural performance of buildings and are effective in reducing the structural weight and embodied energy. Although, a critical observation of the optimised designs shows that the results obtained via HSA are generally better solutions in comparison with those derived from GA and PSO. The total weight and embodied energy for HSA are, on average, 3% and 5% less than that of GA and PSO respectively, when applied to single objective problems. Whereas, when the weight and embodied energy functions are taken as a multi-objective, HSA showed an average difference of 16% and 7% less than that of GA and PSO respectively, and this difference increases in larger structures. Overall, the resulting embodied energy was directly linear to weight. In addition to this, extensive optimum design charts were produced to enable designers in obtaining prompt optimum results during the decision-making stage. The research suggests areas for further investigation and provides recommendations based on the study findings and conclusions.

The results show that combining analysis, design, and optimization methods in MATLAB can be effective in obtaining prompt optimal results during the decision-making stage, with solutions obtained in less than 12 minutes for up to nine-story three-dimensional design problems.

Item Type:	Thesis
Creators:	Alkhadashi, A.E.M.
Date:	August 2022
Rights:	I certify that: The copyright of this dissertation rests with Nottingham Trent University. No information derived from this dissertation shall be published without prior consent of the University. The submission of this work for assessment confirms that the work is mine alone and that all other sources have been acknowledge consistent with regulation of the University.
Divisions:	Schools > School of Architecture, Design and the Built Environment
Record created by:	Linda Sullivan
Date Added:	25 Apr 2023 10:19
Last Modified:	25 Apr 2023 10:19
URI:	https://irep.ntu.ac.uk/id/eprint/48828