A risk-based approach for timber building decay prediction

The durability of timber structures subjected to biotic attacks is becoming of increasing concern due to several recent examples of failures caused by early degradation. Therefore, the design process of a timber building cannot prescind from accounting for the possible degradation due to biotic attack, especially in light of the recent spread of high-rise timber buildings. Furthermore, it is of extreme importance that reliable models to foresee possible sources of degradation in existing buildings are made available so that retrofit interventions can be programmed before it is too late. In the work presented herein, the decay due to fungal attack was predicted through a risk-based approach where decision trees were created to address all the possible scenarios where water or moisture can intrude within the construction details that most affect the durability. These decision trees allow to assign a risk class, defined based on a thorough review of the major European standards addressing timber "use-classes". The trees also lead to the selection of a proper prediction function for estimating the decay depth, chosen among suitable functions available in the literature. The proposed methodology was applied to selected case studies where a good correlation was found between the decay level detected onsite and the results from the prediction model. To facilitate the application of the methodology to both the design of new durable timber buildings and the assessment of existing timber structures, an ad hoc software tool named TSafe was developed. In the present paper, due to the length limit, the focus is on the decision trees and the risk classes, while just a brief description of the case study used for the procedure validation is given.