Masters Degrees (Civil Engineering)

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Browsing Masters Degrees (Civil Engineering) by Author "Aucamp, Herman"

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    The optimisation of web-tapered portal frame buildings
    (Stellenbosch : Stellenbosch University, 2017-03) Aucamp, Herman; Van der Klashorst, Etienne; Stellenbosch University. Faculty of Engineerng. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Web-tapered members are widely advocated as a cost-effective alternative to conventional structural sections for portal frames. These non-prismatic members improve the distribution of internal stresses throughout a frame, which leads to substantial weight savings and increases the clear spans achievable. Web-tapered portal frames constitute a well-established practice in many countries. However, this construction technique is rarely seen in South Africa, despite its potential. Some software developers have developed automated design packages for structures with webtapered members that produce cost-effective buildings and expedite the design process. However, the principles that govern the design of web-tapered members are unclear as none of the major international steel design specifications have adequate provisions for non-prismatic steel members. Design Guide 25 for the design of portal frames using web-tapered members was published by the Metal Building Manufacturers Association and the American Institute of Steel Construction. This guide utilises the concept of an equivalent prismatic member to allow the design to be done using AISC 360. In this study, a new approach is developed for the design of web-tapered members, based on SANS 10162-1 but utilising the equivalent prismatic member concept from Design Guide 25. This new approach was validated against the results of full non-linear analyses, with imperfections taken into account, in the finite element software Abaqus and found to yield safe results. The proposed design approach was subsequently incorporated into a structural optimisation procedure specifically developed to obtain the lightest possible structure for multiple load combinations. The optimisation procedure uses a genetic algorithm in search of an optimum solution when using doubly symmetric, welded sections that are either prismatic or web-tapered. The results show a weight reduction of up to 17% for span lengths of 50 m when comparing web-tapered portal frames with prismatic ones. These results were also compared to designs produced by a commercial software package for web-tapered frames that reduced frame weights by 38% from what can be achieved with prismatic sections.