A.Brad Douglas, director of engineering at the American Forest & Paper Association, responds: Large solid-sawn and glulam timbers provide a substantial degree of fire endurance. The superior fire performance of large timbers can be attributed to the charring effect of wood. As wood members are exposed to fire, an insulating char layer is formed that protects the core. Thus, beams and columns can be designed so that a sufficient cross-section of wood remains to sustain the design loads for the required duration of fire exposure.

A fire test conducted in 1961 at the Southwest Research Institute compared the fire endurance of a 7x21-inch glulam timber with a W16x40 steel beam. Both beams spanned approximately 43.5 feet and were loaded to full design load (approximately 12,450 lb.). After about 30 minutes, the steel beam deflected more than 35 inches and collapsed into the...

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