Effective properties of spray-applied fire-resistive material for resistance to cracking and delamination from steel structures

This paper presents a study on quantifying the effective properties of spray-applied fire-resistive material (SFRM) to mitigate delamination of fire insulation from steel structures. The crack development in SFRM, its propagation and then delamination is investigated for two types of structural elements; a flimsy steel truss chord, and a beam-column assembly in a moment-resisting frame insulated with three types of SFRM widely utilized in steel construction. In the truss chord, the strain ductility of steel at which delamination initiates and propagates is studied, while in the beam-column assembly, the extent of delamination over the plastic hinge region developed on the beam is monitored. A fracture mechanics-based numerical model is employed to undertake parametric studies to determine effective parameters of SFRM for minimizing delamination. In the sensitivity study, the material properties of SFRM applied on steel members are varied over a wide range. Results from the sensitivity study indicate that the elastic modulus of fire insulation (E), thickness of insulation (t) and interfacial fracture energy (G_c) are the crucial factors that govern the delamination of SFRM from the steel surface. Subsequently, results from an additional set of parametric studies, carried out on a beam-column assembly, also infer that delamination of SFRM occurs over the plastic hinge region and is mainly governed by the critical factors of E, t and G_c. Results from these studies indicate that all three governing factors play a critical role in determining the extent of delamination and such delamination can be overcome if the interface fracture energy in normal mode is enhanced to 350 J/m².