Numerical Modelling of Timber Connections Considering the Influence of Gap Size and Intumescent Sealants

This paper presents the development of finite element models for timber connections with gaps under fire conditions which are subsequently validated using experimental data. Fourteen models are developed for concealed steel-to-timber connection configurations with gap sizes of 0, 3, 6 and ¹0 mm exposed to ISO 834 standard fire for 120 min. Half of the models consider protection of the gap with an intumescent fire protection sealant, with two finite element models being developed for each configuration—protected and unprotected. A detailed calibration exercise was performed, and it was found that due to the timber's flaming combustion and changing characteristics, the radiative heat transfer in the gaps increased. The radiation onto the exposed surface of the recessed steel components, based on calculated values only, was consistently underpredicted. The impact of the density of the timber and how it affects the thermal development around and inside the gap are shown to be important, and an increase in gap width does not necessarily lead to higher convective heat transfer in the gap. The presence of the intumescent fire sealant in the gap blocked radiation, and it appeared to have reduced the convective heat transfer. The paper concludes with a simplified and generalised engineering model to conservatively calculate temperatures in connections for timber gaps up to 10 mm in width.