Service life of timber structures in outdoor conditions is predominantly affected by the climatic conditions in terms of moisture and temperature over time. On the one hand, the two parameters moisture content and temperature determine the exposure-induced dosage that can lead to fungal infestation and subsequent decay. On the other hand, the material resistance of wood stands in opposition to exposure and is itself affected by the inherent protective properties of wood and its ability to take up and release water in liquid or vaporous form. Other factors such as design details, in-use conditions, and maintenance are only indirectly affecting the service life of wooden structures and can be accounted for through the aforementioned parameters. In recent years a couple of dose-response models have been developed within the Swedish national research project ‘WoodBuild’ and the European WoodWisdomNet project ‘Durable Timber Bridges (DuraTB)’ to predict fungal decay of wood. They have the potential to serve as instrument for design and performance prediction of timber structures. Several logistic decay models were applied and compared with respect to their feasibility to quantify direct and indirect decay influencing factors such as climate on macro, meso and micro level, topography, and design details. A factorization approach is presented based on dose-response relationship between wood material climate and responding fungal decay, where onset of decay is defined as limit state. The concept does also allow for quantifying the material resistance of untreated, modified and preservative treated wood using factors based on laboratory and field durability tests as well as short term tests for capillary water uptake, adsorption and desorption dynamics.

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