The optimisation of web-tapered portal frame buildings

Aucamp, Herman (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

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.

AFRIKAANSE OPSOMMING: Elemente met tapse webbe word wyd gepropageer as ’n ekonomiese alternatief vir konvensionele struktuurelemente in portaalrame. Die gebruik van hierdie varie¨erende struktuurdele verbeter die verspreiding van interne spanning regdeur ’n raam. Hierdie proses lei tot ’n aansienlike gewigsbesparing en langer moontlike spanwydtes. Tapse web portaalrame is ’n gevestigde bedryf in baie lande; tog word hierdie konstruksietegniek selde in Suid-Afrika gesien, ten spyte van die voordele wat dit bied. Sommige sagteware-ontwikkelaars bemark geoutomatiseerde ontwerppakkette vir die ontwerp van kostedoeltreffende, tapse web strukture. Die beginsels wat die ontwerp van elemente met tapse webbe bepaal is egter nie duidelik omskryf nie, aangesien geen van die internasionale staalontwerpspesifikasies voldoende voorsiening maak vir tapse web strukture nie. DG25, vir die ontwerp van portaalrame met tapse webbe, is onlangs gesamentlik deur MBMA en AISC gepubliseer. Hierdie gids maak gebruik van die konsep van ’n ekwivalente prismatiese stuktuurdeel vir die ontwerp van tapse web elemente, met behulp van AISC 360. Tydens hierdie studie is ’n nuwe benadering ontwikkel vir die ontwerp van tapse web strukture. Dit word baseer op SANS 10162-1, maar gebruik die ekwivalente prismatiese element konsep uit DG25. Die akkuraatheid van hierdie nuwe benadering is bevestig deur ’n reeks eindige element analises in die sagteware Abaqus, met inagneming van nie-lineˆere materiaal en geometriese gedrag, asook imperfeksies. Daar is bevind dat die voorgestelde ontwerpmetode ’n veilige oplossing bied vir tapse web elemente. ’n Strukturele optimaliseringprogram is ook ontwikkel, gebaseer op die voorgestelde ontwerpmetode, om die ligste moontlike portaaalraam te verkry onder die invloed van verskeie laskombinasies. Die optimale oplossing word gevind deur die gebruik van ’n genetiese algoritme, en is in staat om dubbele simmetriese, gesweisde struktuurdele in beide prismatiese ´of tapse web portaalrame te ontwerp. Die resultate dui op ’n vermindering van tot 17% vir 50 m spanwydtes. Hierdie resultate is ook vergelyk met ontwerpe met ’n kommersi¨ele sagtewarepakket, doelgemaak vir tapse web portaalrame. ’n Totale gewigsbesparing van 38% staal is gevind in vergelyking met die konvensionele portaalrame.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101099
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