The role of transfer beams on the global structural fire response of tall steel framed buildings

摘要

In buildings where columns are not continuous along their height loads are often transferred via transfer beams. As a result, these beams can be subjected to larger shear forces and bending moments in comparison to conventional beams. Transfer beams are typical in modern construction, especially for high-rise buildings; commonly arising to achieve architectural features. Nonetheless, the research on their behaviour in fire is limited. In this paper, a case study of a building modelled with deep and shallow transfer beams is examined with the finite element analysis software LS-DYNA. Two sub models are investigated: a three storey model; and a seven storey model, which includes the upper structure of the building. For the three storey sub-model, a potential collapse mechanism is presented that is associated with the deep transfer beams. The results show that the increasing beam deflections in a fire event can lead to inwards pull-in of columns and deflection of non-fire affected storeys under both single-storey fires and multi-storey fires. The inclusion of the upper structure in the analysis through the seven storey sub-model has shown that adequate load redistribution between the columns, bracing and beams on the upper storeys of the structure can assist in preventing the mechanism from occurring although a trend for runaway failure is still observed. Shallow beams were found to be vulnerable only when subjected to multi-storey fires. The single element idealization that is adopted in design guidance would not be able to necessarily capture these collapse mechanisms. Therefore, care should be taken by designers when assessing the expected fire performance of structures with transfer beams that support a large number of stories or have the potential to be exposed to multi-storey fires.