Structural fire comparison of char depth and explicit temperature thermal damage models

Char depths in fire damaged timber are often used as a substitute to infer equivalent fire resistance for tests without structural load applied. However, the thermal profile in mass timber can differ markedly between compartment fires with a cooling phase and fixed duration standard furnace tests. This technical note evaluates publicly available temperature and charring data from a fully developed open plan mass timber fire test to compare structural capacity throughout the fire based on two thermal damage models. The first method uses measured char depth and an assumed zero-strength layer, while the second method utilises the measured temperature profile. Both damage models were applied to the same structural calculations. The results show that, in absence of sprinkler or fire service intervention, structural capacity reduction is more severe when actual temperatures are considered. These outcomes are of interest to interpret data from fire tests with respect to fire resistance.