Equilibrium Moisture Content of Wood in Minnesota Timber Bridges

Principal Investigator:

Timothy Larson, Assistant Professor, Wood & Paper Science

Project Summary:

Often timber bridge construction utilizes material near fiber saturation point (FSP), or approximately 30% moisture content (MC). After installation, bridge components will drop in MC until equilibrium moisture content (EMC) is attained. Variations of MC beneath FSP cause dimensional changes in the timber bridge components. It is therefore important to know timber bridge EMC and MC fluctuation because shrinkage of deck laminations may cause a loss of transverse load transfer in stress-laminated and nail-laminated decks and thus reduce the deck lateral stability. This study will use oven-dry moisture determination methods, electric resistance moisture meters and toluene distillation methods to develop a moisture content profile of timber bridge wood components. The study will involve two sets of 5 timber bridges, one in northern Minnesota and the other in central Minnesota. In addition, the study will incorporate all available stress-laminated timber bridges. Sampling will be repeated 4 times over the course of a year in order to develop a MC variation pattern. The results from this study will provide a basis for predicting the EMC and MC variation of Minnesota timber bridges. This information will help to enhance and further the understanding of stress- laminated and nail-laminated timber bridges by specifying the moisture content of the bridge material. Also, knowledge of the EMC will assist with the understanding and retrofit of existing bridges.

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