Heat transfer analysis of the composite slab in the Cardington frame fire tests

The structural modelling of the Cardington Frame fire tests as part of the Department of Environment, Transport and Regions funded Partners in Technology project has highlighted the importance of the temperature evolution both temporally and spatially in determining the structural response. Restrained thermal expansion/contraction and thermal bowing are the main driving force behind almost all the structural phenomena witnessed in the tests.

The four British Steel fire tests carried out on the 8-storey composite steel and concrete building at Cardington have provided a wealth of information about the temperatures in the fire atmosphere and the protected and unprotected steel. Unfortunately, there is considerably less information on the temperatures attained in the concrete slab. In Tests 1–3, the temperatures through the depth of the slab have been recorded only at a few points and in terms of the structural modelling this has been just about adequate. There were no temperatures recorded in the slab in Test 4 (Office demonstration test).

The finite element, adaptive heat transfer program HADAPT has been used to model the heat transfer to the composite steel and concrete slab. HADAPT is a 2D adaptive heat transfer code capable of carrying out a nonlinear, transient, thermal analysis. The code models moisture evaporation from the pores of the concrete by assuming a phase change in the region of 100°C. The measured concrete temperatures in Tests 1–3 have been used to calibrate the model which has then been used to predict the slab temperatures in Test 4.