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Development of Cost-Competitive Timber Bridge Designs for Long-Term Performance

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Status:  Complete
Report Date:  08/03/2020


Timber bridges can last 70 years or more with proper design, location, inspection and maintenance. Local Road Research Board research shows that timber-based bridge superstructures can be built in days or weeks compared to weeks or months with concrete or steel bridges. Timber bridges can dramatically shorten needed construction detours and can be built in winter, which is generally avoided with concrete projects. Best-suited to rural sites with straight approaches, timber-based bridges that include innovative elements like metal flashing and treated wood pile caps in combination with waterproofed deck surfaces offer excellent durability and eye-catching detail at costs similar to concrete and steel bridges. Investigators studied recent research, interviewed Minnesota manufacturers, and interviewed and surveyed county engineers in Minnesota and Iowa. They studied design and construction practices and costs of timber bridges being built near Babbitt in St. Louis County and in Dayton in northern Hennepin County before developing design guidelines that meet national bridge standards and specifications. Timber-based designs can be cost-competitive with concrete or steel bridges, and can help local agencies quickly erect bridges, meet green building goals and achieve aesthetic benefits.

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