Fire Performance of Hybrid Timber Connections

Wood is being widely used as a construction material; however, the use of wood has been restricted by building codes because it is combustible. Hybrid building systems involve the use of heavy timber in combination with other materials. A hybrid timber connection is considered as the weakest link in this construction system particularly under fire exposure. Analysis of hybrid timber connections is complicated because the behavior and properties of the different materials are different under fire exposure.This study aims at investigating the effect of different parameters on the fire performance of hybrid connections between a glulam beam and a steel column by conducting full scale tests and finite element modeling. The experimental part of this research consisted of a series of full-scale tests conducted in compliance with CAN/ULC-S101. Three different types of connections were investigated, Concealed shear tabs, Exposed shear tabs with 2 and 4 bolts and Seated connections with one bolt and without a bolt. Two sizes of bolts 12.7 mm and 19.1 mm were used and each connection was tested for three load ratios 30%, 60% and 100%.Test results showed that the Seated connection without a bolt outperformed the Exposed and Concealed connections. It was noticed that at 100% load ratio the failure times for all connections were less than 40 minutes. Lowering the load ratio from 100% to 30% increased the failure time by 50 to 72%. Increasing the bolt size reduced the failure time by 20 to 48 %. Reducing the number of bolts from 4 to 2 increased the failure time by 10 to 86% and removing the bolt from the Seated connection increased the failure time by 50 to 125%. The final failure mode was always brittle / splitting of wood, even when ductile failure (yielding of bolts or crushing of wood) was the governing mode in ambient design. Three empirical formulas are proposed by the author to calculate the failure time for design purposes for the three different connections.