Behaviour Of Composite Floors Research Articles

Behaviour of composite floors with different sizes of edge beams in fire

Novel experimental results and extensive numerical studies on three one-quarter scale composite floor assemblies tested in fire are presented. The purpose is to investigate the effect of bending stiffness of protected edge beams on the fire behaviour of the assemblies. The focus of the paper is on the behaviour of interior panels with both rotational and inplane restraints along the four edges. Test results showed that tensile membrane action was mobilised at a deflection equal to about 1.0 of the slab thickness irrespective of the bending stiffness of the edge beams. An increase of the edge beam bending stiffness could help to reduce the slab deflection initially. However, as temperature increased cracks in the slab over the protected main or secondary edge beams developed, the composite slab-beam action was weakened and the benefit associated with a greater stiffness of the edge beams was lost. Subsequent part of the paper describes the distribution and development of membrane stresses in the slab and the steel beams in fire. It is noteworthy that due to composite action of protected edge beams and slab, the neutral axis across a section rises and falls within the steel web during the fire duration. However, at the slab centre above the unprotected intermediate secondary beams, no clear tensile region can be found.

The effect of eccentricity on the free vibration of composite floors

The paper investigates the effect of neutral axis locations of a composite section on the dynamic behaviour of composite floors. It is demonstrated that for a composite section the second moment of area of the section in respect to any assumed location of the neutral axis is always larger than the true value of the second moment of area of the section. The relative errors in the calculation of the second moment of a composite section between the actual location of the neutral axis and four other possible assumed locations of the neutral axis are examined. The calculated natural frequencies of several stiffened plates using the assumed locations of the neutral axis are compared with the available measured natural frequencies and numerical results. Finally, the effect of the assumed locations of the neutral axis on the dynamic characteristics of a real composite floor is assessed. It is concluded that the predicted natural frequencies are not sensitive to the assumed locations of the neutral axis, but disregard of the eccentricity in calculation will lead to underestimation, at least, of the fundamental natural frequency of a composite floor and will alter the orders of mode shapes.