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首页> 美国政府科技报告 >Moisture Content Variations of Nail-Laminated Bridges in Northern Climate
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Moisture Content Variations of Nail-Laminated Bridges in Northern Climate

机译：北方气候中钉扎层桥的含水率变化

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Timber in nail-laminated and stress-laminated bridges is often installed with211u001emoisture contents (MC) near the fiber saturation point. Post-installation 211u001emoisture loss induces shrinkage in the timber components, which results in 211u001eloosening of component fasteners. This research project sought to establish the 211u001eequilibrium moisture content (EMC) of timber bridges in Minnesota. Researchers 211u001etook seasonal MC measurements on six nail-laminated timber bridges to determine 211u001eannual MC variations and moisture gradients in individual bridge components: 211u001ethree bridges from northern Minnesota in St. Louis County and three from southern 211u001eMinnesota in Sibley County. An electrical resistance meter measured moisture 211u001econtent, with oven-dry and toluene distillation methods of MC determination as 211u001econtrols. The study found the average MC of bridge components in St. Louis County 211u001ewas 2 percent-11 percent higher than bridge components in Sibley. The study 211u001edetermined the average MC at a three-inch depth on three of the major bridge 211u001ecomponents as: deck laminations 18 percent (Sibley) to 28 percent (St. Louis), 211u001etransverse stiffener beams 14 percent (Sibley) to 18 percent (St. Louis), and 211u001edeck supports 17 percent (Sibley) to 27 percent (St. Louis). The results indicate 211u001ethat the regional microclimate may greatly affect MC. Results from this reseach 211u001ewill allow MC specifications to be determined before bridge installation, helping 211u001eminimize post-installation moisture-related problems and optimize design 211u001ecalculations. In addition, results will provide necessary data for ongoing 211u001eresearch on transverse load-sharing characteristics of longitudinally nail-211u001elaminated timber bridges. Finally, this information will provide a basis for 211u001einspecting MC in timber bridges.

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