The Thermomechanical Response of Structural Timber in Real Fire Exposures

Timber is commonly found as a building material in both historic structures with significant heritage value, as well as in contemporary structures that are becoming increasingly taller. Although widely used, uncertainty remains regarding timbers fire performance. There is little available information specific to heritage timber, and data is still lacking regarding the degradation of contemporary timber beyond the char layer. Moreover, there is an architectural desire to build more complex timber structures, which often feature open-plan spaces, a configuration for which there exists little information regarding the fire performance of combustible structures as well as very little design guidance. In order to facilitate the conservation of historic timber buildings and the creation of innovative contemporary timber buildings, there needs to be a stronger understanding of the thermomechanical response of structural timber to real fire exposures. A series of small- and large-scale experiments were performed, to assess the thermomechanical performance of both heritage and contemporary engineered timbers, as well as encapsulation materials meant to improve timbers fire performance. Experimental setups used for assessment considered radiant panels in the Cone Calorimeter and Lateral Ignition and Flame Spread Apparatuses to evaluate and compare metrics such as flame spread, charring rate, and time to ignition. Further, pool fires were used to create a larger scale thermal exposure in the assessment of characteristics such as charring, adhesive strength loss, and material degradation. Lastly, finite element analysis software LS DYNA was used to create a model of a timber ceiling exposed to a well ventilated, open plan fire, in order to understand experimental data collection needs to facilitate future design methodologies for timber structures. Contributions to the state-of-the-art include developments into a mechanism that may cause gypsum board encapsulation failure, highlighting relative differences between heritage and contemporary timbers fire performance (including charring rate, flame spread, and ignition time), and analysing adhesive degradation in contemporary engineered timbers (Glued Laminated Timber and Laminated Veneer Lumber). The thermal model also allowed for identification of experimental data sets were recommended for collection, which may eventually contribute towards developing design methodologies for open plan well ventilated timber structures.