Membrane Action of Floor Slabs in Fire (Part 1): Load-Bearing Fire Tests of a Composite Flooring System Composed of Rc Slabs and an Unprotected Steel Beam

This is the authors' abstract. We don't add key points for this paper.

In this paper, the results of load-bearing fire test are introduced that targets a composite flooring system composed of a flat RC slab and an unprotected beam. When the unprotected steel beam applied as a secondary beam is exposed to fire, it loses strength at an early stage of fire. On the other hand, for flat RC slabs supported in 2 ways, when deflection increases, membrane stress occurs within the cross section of the slab, and as a result the load bearing capacity of the slab is improved due to this membrane action. In RC slabs in which two-tier reinforcements are arranged, when subjected to fire heating, the temperature at the upper-side reinforcement becomes lower than that at the lower-side reinforcement, and thus the tensile strength at the upper-side reinforcement is kept to a high level for a long time. As a result, it is forecast that the retention of strength by the slab due to the membrane action during fire will become more conspicuous. In order to understand these behaviors, a load-bearing fire test was carried out by means of standard fire heating in accordance with ISO 834, targeting a composite flooring system composed of a two-tier reinforcement-arranged flat RC slab and an unprotected steel beam. The following will summarize the results of the tests.