The effects of radial cracks on the fire performance of heritage timber

Heritage timber buildings are found worldwide and their irreplaceable nature makes them of high value. A common occurrence on heritage timber members is radial shrinkage cracks resulting from changing moisture contents over time. There is little information available that can be used to assess the fire performance of heritage timber members (which has unique differences from contemporary timber), and to the author's awareness, no information regarding how the presence of radial cracks affects the fire performance and char depth of a timber member. The purpose of this study is to provide an evaluation of the effects of radial cracking on the fire performance of timber members, including its effect on char depth, time to ignition, and residual strength. Full-scale heritage Pine timber members were procured from a 115-year-old building undergoing demolition and then subjected to a pool fire. Cracked samples were also extracted from the members and tested in a Cone Calorimeter apparatus relative to solid samples. It was found that the presence of cracks did allow for deeper charring with the full-scale tests showing 64% greater char depth in the cracked region and the Cone Calorimeter tests showing 29% greater char depth on the cracked samples. Four-point bending tests of the full-scale members subjected to a pool fire showed that the effect of the fire exposure and the cracks did not significantly impact the capacity of the members (7.2% difference) but reduced the stiffness as the ultimate deflection increased by 43%. These results can help to inform practitioners who encounter heritage timber members to more accurately assess the fire performance of the member, such that they can make informed decisions on the level of fire protection required. The study also provides methodologies for the collection of heritage timber test materials.