This report summarises the findings in a project directed at determining what is known about the fire performance of connections between heavy timber members.
In Canada, where a 45 minute fire-resistance rating is required, the NBCC lists minimum dimensions of solid sawn or glulam columns (loaded in compression), beams (loaded in bending) and trusses (bottom chord loaded in tension) which achieve the rating. Methods for designing connections between solid sawn or glulam members that preserve the 45-minute rating are also provided. Where a one-hour fire resistance rating is required, the NBCC provides equations to calculate the dimensions of glulam columns (loaded in compression) and beams (loaded in bending) which achieve the rating. However, no guidance is given for designing glulam members loaded in tension and no guidance is given on connections between glulam members that preserve the one-hour rating. Furthermore, no guidance is provided for designing solid sawn members (or their connections) when loaded in compression, bending or tension.
In the U.S.A., the minimum cross-sectional dimensions of glulam and solid-sawn timber beams and columns that achieve a 1-hour rating can be calculated from the same simple formulae provided in NBCC. As an alternative, a more advanced mechanics-based method can be used to calculate minimum cross-sectional dimensions of glulam and solid-sawn timber loaded in bending, compression and tension. Where a 1-hour fire-resistance rating is required, connectors and fasteners must be protected from fire exposure by wood, fire-rated gypsum board, or any coating approved for the required fire-resistance time. This approach does not account for any inherent fire resistance of the connection but rather requires it be protected by wood, fire-rated gypsum board or a coating that can provide the entire 1-hour rating.
In Europe, guidance is provided on how to design wooden structures and their connections to achieve fire resistance ratings up to one hour. Extensive guidance is given for connections consisting of two structural members spliced together with side plates of wood or steel and held together with dowel-type fasteners (nails, bolts, dowels and screws). Unprotected wood-to-wood connections of this sort, designed in compliance with ambient (non-fire) design standards, have an inherent fire resistance rating of at least 15 minutes. The fire-resistance rating can be increased to 30 minutes or even 60 minutes by the application of wood, wood-based or gypsum board panels with thickness calculated using simple formulas. As an alternative, a fire-resistance rating up to 60 minutes can be achieved using connections with internal steel plates.
There is currently no guidance provided to designers in Canada on how to design a connection between heavy timber members that can ensure a 1-hour rating. As this seems inappropriate, it is strongly recommended that Canadian building code committees be approached and requested to adopt either the approach taken in the USA or the one in Europe.