wood protection by design

itself. In Europe several decay models were developed during the last decade (Brischke
and Thelandersson 2014). The models suggested so far differ in experimental data
source and prevailing decay types considered. Within the DuraTB project a logistic
dose-response model has been selected using basically wood moisture content and
temperature as input and fungal decay as output variables. The model is based on field
tests data, where white and soft rot fungi were the predominant decay organisms. In
contrary, brown rot fungi are the most prominent hazard for Norway spruce glulam if
exposed to the weather as intended in this project. Hence, the existing model needed
verification to predict brown rot decay and thus performance of timber elements. As
shown in Fig. 4 brown rot preceded clearly faster than white and soft rot at a given
dosage and thus at given time. Furthermore, wood exposed to shade tended to decay
slower which might be caused by the formation of biofilms consisting of algae and other
non-degrading organisms. Further field test data from running trials at different
locations in Europe will be used to further validate and improve the model if needed.
Mean decay rating [0-4]
4
y = 4*EXP*(-EXP(1.564-(0.0054*x)))
R² = 0.8681
3
2
1
Brown rot - No shade
Brown rot - Shade
White and soft rot
0
0 200 400 600 800 1000 1200 1400
Dose
Fig. 4. Preliminary model for brown rot decay in different softwoods with clear
differentiation between unshaded and shaded conditions. Grey diamonds indicating
white and soft rot decay in earlier field tests. Mean decay rating and dose calculated
according to Brischke and Thelandersson (2014) based on wood MC and temperature.
Besides wood moisture content and temperature, and thus besides the ambient climatic
conditions, the formation of cracks might have a significant effect on durability. Cracks
serve as entry ports for both, moisture and fungal spores. Since the dimension and tree
ring orientation of a wooden element can have a significant impact on its dimensional
changes and thus on the formation of cracks, this potential influence parameter was
examined separately. Specimens of different size were exposed above ground for five
years and monitored with respect to moisture and fungal decay. In summary, a clear
effect of component dimension was neither found on moisture content nor on decay
development. However, it was confirmed that cracks can serve as starting point for
fungal decay, but alternative ways of infection must not be neglected (Fig. 5).