Computer simulation of a full-scale structural fire test

A computer analysis is being developed whose objective is to predict the response of steel framed buildings to fire conditions. This is now capable of analysing 3-dimensional structures, including a representation of the restraint to thermal expansion provided by concrete floor slabs. The analysis has been used to model the first of the fire tests conducted on the full-scale eight-storey composite test frame at Cardington, which took place on 19 January 1995. In this test a 9m secondary composite beam was heated to steel temperatures in excess of 800°C. A comparison is here made between the main deflections predicted by the analysis for various modelling assumptions, and those actually measured during the test. The major problems in setting up a model of the affected region of the structure concern the ways in which the concrete slabs, and other restraining structure surrounding this region, are treated in the model. The ways in which different assumed boundary conditions to the 3-dimensional subframe affect the predictions are shown. The analytical and test results are basically in good agreement, indicating that the analysis can predict response accurately, provided that material properties are known, that heating schemes are predictable, and that the model provides a good representation of the restraint from surrounding structure. A comparison is also made between the actual behaviour and that which would be predicted for an isolated heated member. This comparison indicates that the development of design methods for fire safety of structures needs to be steered away from its traditional emphasis on isolated member behaviour, and towards concepts based on local and overall survival of the structure when the interaction of the heated zone and the cooler surrounding structure is taken into account.