Teal River Bridge
Chequamegon National Forest
Sawyer County, WI
County Highway S
The Teal River bridge, constructed in 1989, of southern pine and red (Norway) pine, is a single span structure 32 1/2 ft. in length and 24 ft. in width. It utilized glued laminated timber, horizontally laminated, for the first time in a stress laminated design and with two species for the best economical design. The 3-span 90 ft. long Richland Center Bridge, Richland County, WI, was built in 1991 using all red pine.
The moisture content of wood at the time of installation and in-service is a primary consideration in the design of all timber bridges. Changes in moisture content influence wood dimensions, stiffness, and strength. Many timber bridges in the past 10 years have used wood of high moisture content, 24-28% at time of construction and often beyond 30%. The equilibrium moisture content in service is not beyond 18-20%.
As the wood loses moisture content to 20% or less, shrinkage beneath deck asphalt surfacing leads to that wearing surface cracking and deteriorating. The solution is proper wood moisture content initially. The use of a top deck surface of lumber plank (also called wearing surface) is not a proper solution. These planks will eventually dry on the top, stay wet on their lower surface, causing upward cupping and fastening failures. Deck panels beneath the plank will remain wet on top and dry below and cup in the opposite direction.
Preservatively treated wood is to be used for all timber bridges.