- Bridge Specs: Tower Height = 20′: Span = 105′: Travel Width =5’: Deck = Timber: Mainline = 1-1/4” galvanized structural strand: Suspender Size = 1/2” wire rope: Anchors = Mechanical rock anchors drilled to 12’ (west); Concrete dead man (east)
- Services Performed: Design/Engineering, Fabrication, Demo, Installation.
The Needleton Suspension Bridge is located in the San Juan National Forest next to the historic Durango and Silverton Narrow Gauge Railroad north of Durango, CO. Crossing the Animas River at approximately 8200’ elevation, the Needleton Suspension Bridge allows hikers (and a few remaining cabin owners) access to the Chicago Basin and the Weminuche Wilderness Area. Sahale, LLC was hired by the Forest Service to replace the existing bridge that had become unstable due to age, repeated floods and general deterioration.
The Needleton Bridge posed several challenges. Due to heavy usage of the trail system, Sahale enjoyed a limited construction window to complete the demolition of the old bridge and construction of the new one, with the only access for material and equipment via the narrow gauge railway. From a design standpoint, the key challenge was that the narrow gauge railroad tracks ran perpendicular to the bridge across the natural landing area for backstay cables.
Steve Howell’s fabrication team completed fabrication and staged the bridge to Durango in February 2008. Martin Walz led the installation team, arriving in September 2008 to transfer bridge material and equipment to the site, and begin demolishing the old bridge, including towers and mainlines. The team modified existing abutments, drilled new anchorages on the west side of the river, and excavated the existing anchorages on the east side to establish new connection points.
Thought to be the third bridge at this site, the Needleton Suspension Bridge is a suspended truss design. The 105’ stiffening truss allows for stock travel and heavy snow loading. The modified suspension- stay design permits a relatively steep departure angle on the backstay nearest the railroad track, negating the use of a tower jackleg and giving the rock anchors direct penetration into the surrounding bedrock. This novel design allowed the bridge to be built with no disruption to the railroad schedule or earth disturbance near the tracks.
A rotating four-man Sahale crew lived on-site, renting one of the few A-frame cabins that remain in the area, living and working there except for a four day break at Thanksgiving when the crew took the train into Durango. The crew faced a number of challenges including limited communications with the design team, temperatures that declined from 55 to 9 degrees, icing of the river, and ongoing concerns about train safety. Challenges aside, the crew was captivated by the beautiful setting and looked forward to the daily passing of the classic steam train rumbling through the valley.
Today, when hikers return from the Chicago Basin and the “14’ers”, they cross the Needleton Suspension Bridge and wait at the whistle stop for a steam train headed back down the Animas River Valley to town. This rail line has been in place since 1882; the Needleton Suspension Bridge will keep it company for many more decades.