The overall objective of this research is to develop a methodology that will foster the design of fire-safe buildings of wood or hybrid construction. This project aims to develop a design methodology (i.e., calculation methods) which will allow the calculation of the fire-resistance of CLT assemblies/construction. The methodology will take into account the thickness and number of laminations and their orientation, the species and strength properties of the laminations, the load imposed on the panel, and any additional fire protection such as gypsum board or plywood. This will provide manufacturers and designers a methodology to predict the fire-resistance of panels for use in various applications.
In order to establish calculation methods a series of experimental tests has been undertaken. To date, two CLT fire-resistance tests have been conducted at the NRC fire laboratory where the panels were subject to standard CAN/ULC-S101 fire exposure. Both 3-ply CLT assemblies consisted of 38 x 89 mm black spruce boards, where the two outer longitudinal plies consisted of SPF 1650Fb-1.5E machine stress-rated (MSR) lumber, and the inner transverse ply was SPF No.3/stud. Each panel was protected with two layers of 12.7 mm CGC Sheetrock® FireCode® Core Type X gypsum board. Thermocouples were placed behind each layer of gypsum board and embedded at 19-mm increments into the panels to a depth of 76 mm.
The first test was a floor assembly, where a load of 2.7 kPa was applied. The test was ended after 77 minutes due to equipment concerns from the laboratory staff, therefore structural failure was not reached. The greatest measured char depth in the panel was 11.2 mm. The maximum deflection of the floor was 32.1 mm.
The second test was a wall assembly, which failed due to buckling after 106 minutes when subjected to 333 kN/m. From one data point a charring rate of 0.4 mm/min was calculated. The maximum deflection of the wall was 55.3 mm. From the thermocouple data, it was determined that the two layers of gypsum delayed the onset of charring in both the floor and wall tests by approximately 60 minutes.
So far the proposed calculation methods have proved to be conservative in predicting the time to structural failure and charring rates.
Due to the difficulty of sourcing CLT assemblies to test, six additional full-scale fire resistance tests are to be completed in 2011-2012. The current test plan includes testing two more wall assemblies and four more floor assemblies. Tentatively, the next set of floor tests to be completed will be on a 5 ply unprotected assembly with the only difference between them being the type of adhesive used. Similarly, a 5-ply unprotected wall assembly will be tested. A composite floor assembly consisting of CLT with a concrete toping is also planned to be tested. This leaves one wall and one floor test to be finalized allowing for investigation of any questions raised in the tests identified above.