Browsing by Author "Kloos, Michael"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
- ItemAn investigation into the structural behaviour of a novel cellular beam structure in fire(Stellenbosch : Stellenbosch University, 2017-12) Kloos, Michael; Walls, Richard Shaun; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: The Southern African Institute of Steel Construction (SAISC) has developed a novel cellular beam structure (CBS), which has been specifically designed for the construction of two to ten storey office blocks. The concept is based on the factory production of modules, which can be transported to site and quickly erected, thereby reducing construction time and cost. The modules consist of cellular steel beams and a ceiling board system, thus avoiding any wet trade, and remaining lightweight. The modularity allows for architectural freedom, as multiple configurations are possible. Furthermore, modules can later be added, or even re-used in another structure. However, the primary challenge hindering the commercialisation of this system is its unknown fire resistance. In South Africa, and worldwide, all structures require a fire rating, and thus an investigation into the fire resistance of the CBS has been carried out in this thesis to assist in bringing the system to production. As part of a larger project, this thesis focuses on the structural behaviour of the CBS under fire conditions, with an emphasis on numerical modelling. With the unconventional layout of the structure, standard fire design methods do not necessarily apply, or conversely could result in an over-conservative and costly specification of passive fire protection. Thus, a rational/performance-based approach has been developed, in which non-linear finite element (FE) models developed in Abaqus are used to characterise the behaviour of the CBS. Non-linear FE modelling procedures are required to model the CBS, as the material properties, geometry, structural loads and temperatures change over the course of a fire. The models developed have been validated based on three case studies in the literature. The CBS is then investigated using a total of 18 single element models consisting of isolated elements, and 9 global structure models. Three different time-temperature fire scenarios are considered: (a) a standard fire with the fire-rated ceiling remaining in place, (b) a standard fire with the ceiling failing, leading to significantly hotter beam temperatures, and (c) a parametric fire. This allowed the CBS to be tested under a variety of boundary conditions, thermal loads and possible fire scenarios. Overall, the models indicate that the CBS performs well under fire conditions. The structure is able to deffect and expand as the steel heats up, which reduces the internal forces. An ultimate failure mode, which could cause a collapse, is only detected under conservative conditions that are unlikely to occur. The models developed are used to predict the maximum vertical and lateral defections of the steel members. The vertical deflections were found to be relatively small in terms of typical fire deflections, with a maximum predicted value of 35 mm (span/229) under the standard fire with the ceiling in place (the primary design scenario). However, a maximum lateral deflection of 185 mm is anticipated, which will require careful detailing considerations. Under parametric fire conditions, negligible permanent deformation is predicted by the global structure models once the steel returns to ambient temperature. Ultimately, design recommendations are made to increase the fire resistance. Firstly, steel end connections should be designed to provide negligible moment restraint, and to allow free thermal expansion using slotted bolt holes. Secondly, if the ceiling system is designed to accommodate the predicted deflections, the integrity of the entire system is protected and the chance of a structural failure is significantly reduced.