Experimental analysis on the structural continuity effect in steel decking concrete slabs subjected to fire

Abstract

Composite steel decking concrete slabs are an important structural member in building construction. Nevertheless, the behavior of these slabs in case of fire are not yet well characterized and the corresponding fire design methods need improvements. Several parameters that affect the behavior of these slabs in case of fire and that are not taken into account in the fire design at the moment have to be included. One of these parameters, is the continuity effect between slab panels. This study evaluated the structural performance of continuous steel decking concrete slabs subjected to fire. For this purpose, 8 real-scale slabs, with 2.56 × 4.60 m, were subjected to the ISO 834 standard fire curve for a duration of 180 min. The structural continuity of the slab, and thus the induced hogging moment, was studied by introducing at mid-span a thermally-protected intermediate beam. In these tests the following parameters were registered: temperature distribution in the cross-section; temperatures in the unexposed slab’s surface (thermal insulation); mid-span deflections; concrete cracking occurrence; longitudinal elongation of the rebars and relative slip between the steel decking and the concrete. It was observed that the composite behavior of the slab was lost at nearly 5 min of fire exposure, the structural continuity at 10 min and the membrane effect at a time between 30 and 50 min, depending of the slab’s characteristics. The negative rebars didn’t show an effectiveness in the structural continuity of the slab. The steel decking did not have a great contribution in the loadbearing capacity of the slab because it loses resistance and detaches from the concrete in the first minutes of the fire. However, embossments in the web can enhance the shear strength between the steel deking and the concrete and improve the composite action of the slab in case of fire. This research demonstrated the need of further research on the adhesion of the steel decking to the concrete in this type of slabs in case of fire.