Geometric non-linear modelling of partial interaction in composite T-beams in fire

The formulation for partial shear interaction in composite beams was developed over 50 years ago in closed form. This formulation is suitable for many cases encountered in practice, but it does not account for the geometric non-linearity produced by the "P-delta" effect. This effect is important in a compartment in a steel or composite framed building in a fire, where the initially large compressive forces which develop because of restraint against thermal expansion interact non-linearly with the large deflections of the composite floor slab, and a geometrically non-linear formulation must necessarily be invoked to capture the partial interaction behaviour of the composite floor system during a fire. This paper provides an elastic analysis of partial interaction at moderately low levels of temperature, so as to shed light on the significance of the parameters that affect the structural behaviour as well as to provide a precursor for an inelastic analysis to treat catenary action. The differential equations which quantify the problem are derived and solved numerically, and an illustrative example is worked.