Structural Optimisation in Building Design Practice: Case-Studies in Topology Optimisation of Bracing Systems

Year: 2007
Author: Baldock, Robert
Supervisor: Prof. Kristina Shea
Institution: University of Cambridge
Page(s): 1-165


This thesis aims to contribute to the reduction of the significant gap between the stateof-the-art of structural design optimisation in research and its practical application in the building industry. The research has focused on structural topology optimisation, investigating three distinct methods through the common example of bracing design for lateral stability of steel building frameworks. The research objective has been aided by collaboration with structural designers at Arup. It is shown how Evolutionary Structural Optimisation can be adapted to improve applicability to practical bracing design problems by considering symmetry constraints, rules for element removal and addition, as well as the definition of element groups to enable inclusion of aesthetic requirements. Size optimisation is added in the optimisation method to improve global optimality of solutions. A modified Pattern Search algorithm is developed, suitable for the parameterised, grid-based, topological design problem of a live, freeform tower design project. The alternative objectives of minimising bracing member piece count or bracing volume are considered alongside an efficient simultaneous size and topology optimisation approach, through integration of an Optimality Criteria method. A range of alternative optimised designs, suitable for assessment according to unmodelled criteria, are generated by stochastic search, parametric studies and changes in the initial design. This study is significant in highlighting practical issues in the application of structural optimisation in the building industry. A Genetic Programming formulation is presented, using design modification operators as modular "programmes", and shown to be capable of synthesising a range of novel, optimally-directed designs. The method developed consistently finds the global optimum for a small 2D planar test problem, generates high-performance designs for larger scale tasks and shows the potential to generate designs meeting user-defined aesthetic requirements. The research and results presented contribute to establishing a structural optimisation toolbox for design practice, demonstrating necessary method extensions and considerations and practical results that are directly applicable to building projects.

Keywords: structural topology optimisation, structural design practice, bracingdesign, Evolutionary Structural Optimisation, Pattern Search, Optimality Criteria, Genetic Programming, computer-aided design, large-scale structural size optimisation

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