Suspension Trail Bridge Using Sustainable Materials, Montana

Construction of the 27,5 m suspension pedestrian bridge over Rattlesnake Creek near Missoula, Montana, did not sacrifice aesthetics, or spare innovation, in providing a valuable link in the city's trail system. Engineers reviewed historic US Forest Service trail suspension-bridge construction, relying on the proven technology to construct a bridge with small-diameter wood (smallwood), salvaged from bug-killed lodgepole pine, and other sustainable design materials. With its lathe-turned native smallwood and subtle arch, the bridge, built with grants including US Forest Service funds, is in harmony with its rustic environment. Most of the bridge is constructed of reused materials. A running surface made of recycled tires covers a composite deck made of waste plastic and sawdust. The 150 mm diameter smallwood members were cut from wasting lodgepole pines and used for floorbeams and braces. Half-rounds were used for the lattice-patterned stiffening trusses that form the bridge's sides. Many ravaged lodgepole pines are salvageable, giving the wood potential as an economical, abundant construction material ideal for trail bridges. Lodgepole pine smallwood is now used in building construction, but the Rattlesnake project was the first bridge built with this locally recycled material. Across the heavily wooded American Northwest, pine bark beetles have killed large areas of lodgepole pines. These standing dead trees are mostly left to waste. There is a tremendous opportunity to develop this resource for constructing buildings and bridges. Smallwood, a 150 to 230 mm material officially known as small-diameter roundwood, is well suited for making joists and intermediate members. Friends of Missoula Parks, a nonprofit group, received a grant from the US Forest Service (USFS) to promote the use of smallwood in constructing a pedestrian bridge over Rattlesnake Creek in a forest near Missoula, Montana.