SUMMARYUnderstanding structural behaviour of buildings during a fire is accepted as being essential to make full use of the recently introduced performance-based design codes. However, currently the behaviour of buildings during the cooling phase of a fire is poorly understood. Evidence from full-scale tests and real fires has shown that collapse of buildings can occur during the cooling stage of the fire, which can compromise the safety of firefighters and the public in the proximity of the building. This joint project between Manchester and Edinburgh University, will investigate the behaviour of cooling steel-concrete composite structures to gain an understanding of their behaviour and the underlying mechanics. The project includes testing of composite slabs, subject to different axial restraint conditions and natural fire scenarios, to obtain a unique understanding of forces generated within the structure during the cooling stage of a fire. Working in parallel to the experimental phase of the project, existing numerical models will be extended to simulate structural behaviour during the cooling phase. Once validated, the numerical models will allow an understanding of the behaviour of complete structures during the full duration of the fire, significantly advancing the current modelling capabilities which concentrate on the behaviour up to the fire's estimated maximum temperature. The results from the complex models, together with the experimental results, will allow simple design rules to be developed to ensure that buildings do not collapse during the cooling stage of the fire, thus ensuring the required level of safety for both firefighters and the public.