Finite Element Modelling of the Structural Behaviour of a Novel Cellular Beam Non-composite Steel Structure in Fire

Abstract

A novel cellular beam structure (CBS) intended for two to ten storey office 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 flooring system, which yields an innovative structure with many benefits, including reduced construction time and cost. However, a major obstacle to commercialisation is the unknown fire resistance. Thus, this paper presents a series of non-linear finite element models that simulate the structural behaviour of the CBS under standard and parametric fire conditions. The simulations include single structural elements in isolation and global structure models. Overall, it was found that the CBS performs satisfactorily in a fire, provided that the integrity of the ceiling system can be maintained. However, significant lateral deflections up to 185 mm are predicted in a standard fire, which threatens the integrity of the ceiling. Under parametric fire conditions, a cooling phase suggests that there is negligible permanent deformation after a fire, due to the flexibility 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 deflections, thereby safeguarding the integrity.