Experimental Testing on Concealed Beam Hanger Mass Timber Connections Considering the Influence of Gap Size and Intumescent Sealants

Abstract This paper investigates the influence of gap size (openings/spaces between two structural members) on mass timber beam-column concealed hanger connections in fire. The presence of an intumescent sealant, and how it can influence the temperature development in a concealed connection with a small gap, is also analysed. The experimental results of sixteen concealed connections manufactured with a proprietary aluminium concealed connector are presented. The connections were exposed with a 0 mm, 3 mm, 6 mm and 10 mm gap to the ISO 834 standard fire for 60 min. Half of the samples in each sample group were protected with an intumescent fire protection sealant. The temperatures in the timber were measured at various locations around the gap and directly at the location of the aluminium bracket. These results show that unprotected 6 mm and 10 mm gaps should be avoided. The intumescent sealant performed well and limited the temperature development in the aluminium bracket significantly. When compared to the bracket temperatures of the 0 mm samples, the increase in temperatures in the unprotected samples (on average at 60-min) ranged between 62 and 258% depending on gap size, while in the protected samples temperatures were limited to between − 4% to 21%. The application of an intumescent fire sealant also improved the predictability of the thermal development in the connections and in the 3 mm gap protected samples the lowest temperatures were recorded.