The slim floor system is widely used in the construction of composite steel-concrete structures. This system leads to several and well known advantages, such as the high load carrying capacity in spite of the small thickness, the ease in developing floor and frame layouts especially with semi-rigid connections. In this paper, an innovative slim floor beam is presented which is connected with two collaborating slabs. The purpose of the added concrete slabs is to reach a faster erection of semi prefabricated slabs and a longer fire resisting time of the system. Moreover, the composite effect produces a significant service load increase too. In the paper the geometrical details of the system are fully discussed, by presenting the industrial production process; then the attention is focused on the experimental results obtained with six beams loaded until failure in monotonic four point bending tests. Finally, the interpretation of the test results is used to set up design rules for the proposed system.
The very encouraging results are a substantial step towards the development of new powerful composite solutions able to show extended load and fire resistance.