Testing timber columns for resistance until fire burnout: Role of thermal wave, smoldering, and active suppression

This paper presents a numerical and experimental study on stability until burnout of glued-laminated timber columns in compartment fires. In a previously reported experimental study, six 3.7 m long, 280 x 280 mm² timber columns designed for 60 min of standard fire resistance failed to survive various compartment fires, with four of the six columns failing due to thermal wave penetration into the cross section during the decay phase of the fire.

Here, six additional compartment fire tests are conducted, supported by numerical simulations, to investigate the design of timber columns for burnout resistance. A finite element model is used to design the size of the columns to mitigate the effect of the thermal wave. Five tests on columns up to 400 x 400 mm² show that increasing the section size at constant loading enhances fire endurance, but the columns later failed due to local smoldering. While failure in the smaller columns was driven by the thermal wave and occurred within two hours of ignition, failure in the larger columns was caused by smoldering and occurred more than 10 h after ignition.

In a sixth test, on a 280 x 280 mm² column, water-based fire suppression was used 35 min after ignition. The column remained stable until burnout, showing that early fire suppression may prevent failure of timber columns by addressing both the thermal wave and smoldering mechanisms.