The APA (The Engineered Wood Association) provides a technical note titled “Calculating Fire Resistance of Glulam Beams and Columns,” which describes the natural fire resistance of glulam beams and columns and provides fire endurance calculation methods.
In the presence of fire, the outer portion of a glulam member becomes charred. This layer of charred wood then functions as an insulator, helping to protect the undamaged interior of the member from the heat. The rate of advancement of this insulating char layer into the remaining, undamaged portion of the member has been well documented (approximately 0.025 inches or 0.6 mm per minute) and forms the theoretical basis of the equations used to predict fire endurance.
The document provides two analytical methods for calculating the fire resistance of glulam beams and columns. Both ways are based on a similar fire performance database and result in a comparable result, except that Method A is limited to a maximum fire resistance of two hours, while Method B is limited to a maximum fire resistance of one hour.