Three-dimensional analysis of composite steel-framed buildings in fire

A three-dimensional, nonlinear finite-element procedure for modeling compos ite and steel-framed building behavior in fire is presented. In this approa ch, composite steel-framed buildings are modeled as an assembly of finite b eam-column, spring, and slab elements. The beam-columns are represented by two-noded line elements. The cross section of the element is divided into a number of segments to allow consideration of temperature, stress, and stra in through the cross section. A two-noded spring element of zero length is used to model the characteristics of steel member connections. The slabs ar e modeled by using a layered flat shell element based on Mindlin/Reissner t heory, in which each layer can have a different temperature and material pr operties. Predictions from the model are compared with experimental results , both from isolated element tests and from a major full-scale fire test pe rformed in the experimental composite building at Cardington. The model is clearly capable of predicting the response of composite steel-framed buildi ngs in fire with reasonable accuracy. The procedure has been found to have good computational stability, which is very important in the context of pro blems incorporating very large deformations.