Performance of Heavy Timber Connections in Fire

In heavy timber construction, connections using bolts, dowels and steel plates are widely used to assemble wood components and transfer loads. From the fire safety point of view, understanding the fire performance of heavy timber connections is particularly important because they are recognized as the weakest link in heavy timber buildings under fire attack. Due to the variety of connection types, geometries and fastener arrangements, and the significant variabilities in the properties of wood and steel at elevated temperatures, the analysis of the fire performance of timber connections is complex.;The modelling part of this research included a three-dimensional finite-element heat transfer model and an analytical structural model for the fire resistance of timber connections. Comparison with test data generated in the experimental program indicated that both thermal and structural models show reasonable agreement with the measured specimen temperatures and fire resistances of the timber connections.;Furthermore, the third part of this research is devoted to developing simplified calculation methods for wood-wood-wood and wood-steel-wood connections using bolts or dowels, and bolted steel-wood-steel connections. Test data found in the literature and the test results generated in this research were used to develop the simplified calculation methods. Comparison between the predictions using the simplified calculation methods and the measured results in fire-resistance tests or modelled results using the heat transfer model and the analytical structural model, shows that the predictions for wood-wood-wood and wood-steel-wood connections are almost always within a +/-15% envelope, and the predictions for steel-wood-steel connections are almost always within a +/-10% envelope.;The experimental part of this research consisted of a series of fire-resistance tests conducted in compliance with CAN/ULC-S101 for wood-steel-wood (WSW) and steel-wood-steel (SWS) bolted timber connections loaded in tension. The effects of wood side member thickness, fastener diameter, number of fasteners, edge distance, load level and type of protection were studied. Results showed that the fire resistances of all tested WSW bolted connections with no protection were less than 45 minutes and the fire resistances of all tested SWS bolted connections with no protection were less than 25 minutes. Specimens with thicker wood side members were found to exhibit better fire resistances. Decreasing the load ratio increased the fire resistance. The results of tests on protected specimens showed that the protection provided by a single-layer of 15.9 mm type X gypsum board increased the fire resistance by more than 30 minutes, whereas a double-layer of 12.7 mm Douglas fir plywood increased the fire resistance by 15 minutes.