Humidity impact on timber connection strength
Authors
Dominika Malkowska and Eleni Toumpanaki
Abstract
The effects of climate change in several regions of the world include increased rainfall, which can lead to moisture ingress into buildings. This issue is particularly problematic for timber structures and timber based external wall insulation systems due to potential defects in waterproofing that can lead to direct contact with water, which can cause timber decay and a decrease in strength, as moisture becomes trapped between permeable and impermeable surfaces, e.g. within a timber frame wall panel. While the effect of moisture on timber strength properties is well known, its impact on timber connections is less studied. Timber connections usually involve dowel-type fasteners, creating a tight-fit joint where any expansion of wood due to increased moisture content is hindered by the fastener holding the members together. This study examined the effect of moisture on the strength of timber connections, particularly focusing on the additional stresses in the connection, caused by hindered expansion of wood in two scenarios: 1) timber with high moisture content and 2) timber subjected to cyclic changes in moisture content. The experimental tests indicated that there is no effect of additional stress build-up in such connections on the withdrawal strength, although an instance of screw brittle failure observed during testing requires further studies. The cyclic changes in hygrothermal conditions were found to significantly affect embedment strength of OSB.
Published date
June 2025
Notes
Published in ‘Proceedings from the 14th World Conference on Timber Engineering June 22 June 26, 2025’ edited by Kelly Rischmiller.