Vol.:(0123456789) 1 3 International Journal of Steel Structures https://doi.org/10.1007/s13296-019-00215-5 Finite Element Modelling of the Structural Behaviour of a Novel Cellular Beam Non‑composite Steel Structure in Fire M. Kloos 1  · R. S. Walls 1 Received: 6 June 2018 / Accepted: 12 February 2019 © Korean Society of Steel Construction 2019 Abstract A novel cellular beam structure (CBS) intended for two to ten storey ofce buildings has been developed by the Southern African Institute of Steel Construction (SAISC) which consists of prefabricated modules comprising of cellular steel beams encased in a multi-layered fooring system, which yields an innovative structure with many benefts, including reduced construction time and cost. However, a major obstacle to commercialisation is the unknown fre resistance. Thus, this paper presents a series of non-linear fnite element models that simulate the structural behaviour of the CBS under standard and parametric fre conditions. The simulations include single structural elements in isolation and global structure models. Overall, it was found that the CBS performs satisfactorily in a fre, provided that the integrity of the ceiling system can be maintained. However, signifcant lateral defections up to 185 mm are predicted in a standard fre, which threatens the integrity of the ceiling. Under parametric fre conditions, a cooling phase suggests that there is negligible permanent defor- mation after a fre, due to the fexibility of the structure. Ultimately the results are used to make recommendations that: (a) steel end connections are designed to provide negligible moment restraint (b) slotted bolt holes are provided to allow free thermal expansion, and (c) the ceiling system is carefully detailed to accommodate the predicted lateral defections, thereby safeguarding the integrity. Keywords Structural fre engineering · Cellular beams · ABAQUS · Finite element analysis · Fire loading 1 Introduction All structures require a fre rating, which typically quantifes the fre resistance of the structure in relation to the ISO 834 standard fre curve (SABS 2011). This ensures that struc- tures are protected from the natural hazard of fre. Within this setting the SAISC has developed a novel lightweight structure (Figs. 1, 2, 3) that makes use of cellular steel beams and a fooring system made up of fbre-cement and fre- resistant boards (Fig. 6). The design allows the prefabrica- tion of modular units, that are lightweight, easy to transport and quick to erect on site, thereby reducing the construc- tion time and cost. However, the unknown fre resistance remains a barrier to the commercialisation of the Cellular Beam Structure (CBS). Cellular beams have been specifed primarily to facilitate the placing of services without the need for any additional false fooring. Yet there are comparatively few studies of cellular beams at elevated temperatures where no composite behaviour is considered (as in the case of the CBS). How- ever, one such study by Najaf and Wang (2016) suggests that the same general failure mechanisms are observed as for ambient conditions (Kuchta and Maślak 2015; Kerdal and Nethercott 1984), with only one additional mechanism being detected. A structural analysis is greatly complicated during a fre as material properties, geometry, structural loads and temperatures change over the course of a fre (Gillie 2009). Furthermore, due to the unconventional layout of the CBS, standard fre design methods do not necessarily apply, or conversely could result in an over-conservative and costly specifcation. Thus, a performance-based approach has been developed, in which a series of non-linear fnite element (FE) models are used to characterise the behaviour of the CBS. FE models have been used extensively worldwide to investigate steel structures in fre, with studies on buckling Online ISSN 2093-6311 Print ISSN 1598-2351 * R. S. Walls rwalls@sun.ac.za 1 Department of Civil Engineering, Stellenbosch University, c/o Banhoek & Joubert Street, Matieland, Private Bag X1, Stellenbosch 7602, South Africa