Evaluation of Zero-Strength Layer Depths for Timber Members of Floor Assemblies with Heat Resistant Cavity Insulations

Fire resistance of timber members can be evaluated by an analytical design model known as Effective Cross-Section Method (ECSM). In this method, the residual cross-section in fire conditions is evaluated by decreasing the original cross-section by a notional charring depth and a so-called zero-strength layer. The ECSM for timber frame assemblies (TFA) exposed to standard fire conditions has been already presented. This design model considers the fire protection provided by claddings and cavity insulations, for which design values for zero-strength layers are still missing. In this paper, zero-strength layer depths for different set-ups of TFA are determined by means of a series of thermo-mechanical simulations. Model-scale furnace experiments were performed in order to validate the simulations. The study presents an analysis of the parameters that influence zero-strength layer depths for load-bearing members of timber frame assemblies exposed to the standard time-temperature fire curve.