The objective of this study is to identify an appropriate FE model for determining the dynamic characteristics of a long-span flat concrete floor. The Cardington concrete building was selected for the study because it represents a popular form of concrete construction. The natural frequencies of the floors were measured. Several FE models of the floor are considered and the models are refined based on the comparison between numerical predictions and dynamic measurements. It is concluded that a floorcolumn model provides the most appropriate representation of the actual structure.