Kootenai Falls Swinging Bridge

Kootenai Falls Swinging Bridge

Hovering 35 feet above the raging rapids of Kootenai River in northwestern Montana, Kootenai Falls Swinging Bridge presents an incredible tourism destination and a major attraction to the Libby and Troy communities. After parking directly off Highway 2, a short trail provides passage to the Swinging Bridge and breathtaking Kootenai Falls.

Managed by the US Forest Service, the bridge was originally built in 1937 by the Civilian Conservation Corps, to provide access for firefighters to the north side of the river. After a decade of use, the original structure was swept away by the surging Kootenai River in the spring of 1948. The Swinging Bridge was rebuilt at a higher elevation in 1950 with upgraded features, such as concrete foundations on the stair towers. As is customary with simple suspension bridges, regular inspection and maintenance was required, with the most recent timber deck replacement completed in 2016 by the Forest Service.

The popularity and use of the Kootenai Falls Swinging Bridge has steadily increased and the Forest Service determined that significant rehabilitation or replacement would be required to maintain a safe structure. Structural evaluation of the bridge in the 1990s led to the limitation of five people on the bridge at one time, which temporarily ensured the safety of visitors prior to a permanent fix.

The Forest Service enlisted Morrison-Maierle to develop options for rehabilitation and replacement of the Swinging Bridge in the fall of 2016. Viable options for the budget, site conditions, access, and owner preferences included bridge saddle and deck replacement; or bridge saddle, decking, and stair replacement; or bridge saddle, decking, stairs, deadman anchor, and cable replacement; or full replacement of the entire structure with an upgraded swinging suspension bridge.

In order to provide a safe and enjoyable experience for the growing number of tourists and reduce the routine maintenance required, the Forest Service decided to construct a new Swinging Bridge. The challenge then became creating a new, safe, robust bridge that would provide the same thrilling experience and similar look as the old bridge.

Access was one of the biggest challenges of this project. With no roads on either side to accommodate equipment, as well as a weight limited existing structure, all materials and equipment had to be flown in with a helicopter or hiked down the steep, quarter mile pedestrian trail to the bridge. Therefore, the team had to make sure the project materials were simple, efficient, highly functional and lightweight. This construction approach allowed for very minor impacts to the surrounding environment, due to the limited use of machinery and overall minimalistic nature of the project.

Weight management was also key to the design process. The design incorporated high-capacity micropiles that were light, compact and required little grout to anchor the bridge on either side. The tower pieces were also designed with weight in mind as they also needed to be transported via helicopter. The main cables were light enough to be maneuverable, while robust enough to provide a 378,000 pound tensile capacity for large snow and pedestrian loading.
In order to improve the safety and functionality of the bridge, Morrison-Maierle redesigned the swinging bridge by placing the main load bearing cables above the deck, rather than at the bottom like the two previous bridges. This design provides a useful handrail for users, as well as allows the floor to move freely, intensifying the swinging nature of the bridge.

This project was completed two months ahead of schedule which allowed for more visitation time for this popular tourist destination.