Building regulations require that key building assemblies exhibit sufficient fire-resistance to allow time for occupants to escape and to minimize property losses. The intent is to compartmentalize the structure to prevent the spread of fire and smoke, and to ensure structural adequacy to prevent or delay collapse. The fire-resistance rating of a building assembly has traditionally been assessed by subjecting a replicate of the assembly to the standard fire-resistance test, (ULC S101 in Canada, ASTM E119 in the USA and ISO 834 in most other countries).
Massive wood elements such as solid sawn timbers, glued laminated timber (glulam) and structural composite lumber (SCL) can provide excellent fire-resistance. This is due to the inherent nature of thick timber members to char slowly when exposed to fire allowing massive wood systems to maintain significant structural resistance for extended durations when exposed to fire. Calculating the fire-resistance of massive wood elements can be relatively simple because of the essentially constant and predictable rate of charring during the standard fire exposure. Charred wood is assumed to no longer provide any strength and stiffness; therefore the remaining (or reduced) cross-section must be capable of carrying the load.
This report presents two (2) mechanics-based design procedures as alternative design methods to conducting fire-resistance tests in compliance with ULC S101 or to using Appendix D-2.11 of the NBCC, which is limited to glulam members stressed in bending or axial compression. The procedures are applicable to solid sawn timber, glulam or SCL structural members and aim at developing a suitable calculation method that would provide accurate fire-resistance predictions when compared to test data. The long-term objective is to provide recommendations for incorporating either method into CSA O86 and/or NBCC.
The comparisons between the proposed methodologies and the experimental data for beams, columns and tension members show good agreement. While further refinement of these methods is possible, these comparisons suggest that the use of the CSA O86 equations and a load combination for rare events adequately address fire-resistance design of massive wood members.
A series of 3 cross-laminated timber (CLT) fire-resistance tests were conducted in accordance with ULC S101 standard as required in the National Building Code of Canada.
The first two tests were 3-ply wall assemblies which were 105 mm thick, one unprotected and the other protected with an intumescent coating, FLAMEBLOC® GS 200, on the exposed surface. The walls were loaded to 295 kN/m (20 250 lb./ft.). The unprotected assembly failed structurally after 32 minutes, and the protected assembly failed after 25 minutes.
The third test consisted of a 175 mm thick 5-ply CLT floor assembly which used wood I-joists, resilient channels, insulation and 15.9 mm ( in.) Type X gypsum board protection. A uniform load of 5.07 kPa (106 lb./ft²) was applied. The floor assembly failed after 138 min due to integrity.