Steel design optimization Thesis
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Organisation of the thesis
The thesis consists of ten chapters and three appendices. These can be summarised as follows:
Chapter 1 provides an introduction, raising the problems associated with the analysis and design of steel frame structures. The main features of a design optimization problem are then discussed. The literature review of the design optimisation of steel frameworks is also demonstrated. Finally, the aim of research and overview of the thesis are presented.
Chapter 2 describes in details the design procedure as required by the British Codes of Practice. The chapter ends with describing methods used, in the present study, to represent the charts of the effective length factor of column in sway and non-sway frames into a computer code. Here, analytical solutions are obtained using regression analysis based on Statistical Package for Social Sciences (SPSS) and genetic programming methodology.
Chapter 3 starts with studying the stability concept, historical background about the stability problem of steel frames. It then discusses the methods of analysis, which are used for the determination of the effective buckling length of columns in sway and nonsway frameworks. A FORTRAN code based on the direct method is developed and verified using results from the literature and the finite element package (ANSYS).
In Chapter 4, the stability concept of steel frame structures has been applied where the general forms of the critical buckling load of five frameworks are obtained using the direct method of analysis. The finite element package (ANSYS) is also used to verify the results obtained from these forms. Comparisons have been made between the effective buckling length factor calculated by the more accurate analysis (direct method or finite element method) and that determined by the approach presented by BS 5950.
Finally, four questions are raised, and the answers will be given in the following chapters.
Chapter 5 introduces main features and formulation of the design optimisation problem. It also discusses the most frequently used methods of design optimization. Here, the concept of genetic algorithm is described in detail.
Chapter 6 describes the developed GA, new implementations, tuning of genetic algorithm parameters and comprehensive tests are presented. Different crossover operators are implemented and also tested. Comparisons between results obtained by the developed algorithm and those described in the literature or those obtained when
using the ANSYS optimization methodology are also presented.
Chapter 7 is concerned with assessing the potential of the developed genetic algorithm to the treatment of complicated structural problems. Here, the maximum ratio between the effective buckling length factor determined by the approach presented by BS 5950 and the calculated by using the finite element analysis is investigated. Three problems are formulated and solutions are obtained for different examples.
Chapter 8 presents a genetic algorithm based technique for the design optimization of multi-storey steel frame structures according to BS 5950. In this chapter, it has been proven that the developed genetic algorithm linked to design rules to B S5950 can successfully be incorporated in design optimization in which the structural members are required to be selected from the available catalogue and the design should satisfy a practical design situation. In the formulation of the optimization problem, the objective function is the total weight of the structure and constraints are imposed on the design
criteria as required by the British codes of practice (BS 5950 and BS 6399). The design variables are selected from a catalogue (British Standard BS 4). In addition, to study the effect of the accuracy of determining the effective buckling length on the optimization process and the obtained optimum designs, three approaches for determining its value are considered. Finally, In order to verify the results achieved by applying the developed Fortran code for design optimization, the CSC (1998) software is used.
Chapter 9 extends the study of chapter 8 to the discrete optimum design of threedimensional (3D) steel frame structures using the modified genetic algorithm (GA). Following the design procedure of steel structures to BS 5950, the minimum weight design of 3D steel frame structures is presented where the most unfavourable loading cases are considered. The CSC (1998) software is also used to verify results.
Chapter 10 shows the main achievements, conclusions followed by recommendations for several promising area of further work.
