Evaluation of dowel bearing strength of fungal-decayed cross-laminated timber

Dowel bearing strength of three cross-laminated timber (CLT) species (Douglas-fir, Norway spruce, spruce pine fir) were periodically assessed through 40 weeks of exposure to two brown rot fungi species (Gloeophyllum trabeum and Rhodonia placenta). Time-dependent regression models were developed to describe the relationship between level of fungal exposure and dowel bearing strength of CLT. Obtained dowel bearing strength values were used to predict the capacity of floor-to-wall CLT connection systems. Predicted strength values were compared with capacity of actual connection systems which were subjected to similar biodeterioration treatments. Significant reductions in the dowel bearing strength of CLT were observed 30 weeks after fungal inoculation. Similar patterns of degradation were observed for both fungi in all three CLT species, but R. placenta was slightly more aggressive than G. trabeum, causing a 16.2 MPa reduction in dowel bearing strength of Douglas-fir after 40 weeks of exposure. Connection capacities estimated using National Design Specification yield models for dowel type fasteners and the dowel bearing strength of fungal-damaged CLT were consistent with observed properties and were within 85% of actual capacity of connections tested, especially in early stages of decay.