Gorge Inn Suspension Bridge, 2000

Seattle City Light, Newhalem, WA


Satellite view of Bridge Location. (resolution not high enough to see bridge.) View Larger Map

Collapsed bridge showing buckled top chords near mid-span and upriver mainline lying across bridge.  Note collapsed tower at far end.

USE:  Pedestrian

SPAN:  250'

TRAVEL WIDTH:  6'

TOWERS:  29' Tall D-Fir Framed Bents w/ 12" x 14" Legs

ANCHORS:  Concrete Deadmen with 2-1/4 Steel Anchor Rods"

MAINLINES:  1-3/4" Bridge Strand

Truss sag toward river; note collapsed tower, and absence of upriver mainline..

 

 

The Gorge Inn Suspension Bridge crosses the upper Skagit River at the small town of Newhalem, WA, in the heart of the North Cascades.  Newhalem is a small company town that began as a remote propectors camp over a century ago and later became the administrative hub for development of a hydroelectric complex owned and operated by the City of Seattle.  Under the direction of public power visionary James D. Ross, three dams were built in the rugged Skagit River drainage early in the 20th Century that remain anchors of the Seattle City Light generation system today.  At Newhalem, site of the Gorge Powerhouse, Seattle City Light continues to administer the town for the purpose of maintaining the hydroelectric complex.  The last public services available to travellers before crossing Washington's North Cascade Highway eastbound are located at Newhalem, and the National Park Service built the North Cascade National Park Visitor Center at Newhalem, across the Skagit River from town center.  The Gorge Inn Suspension Bridge was built in 1969 by Seattle City Light and connects Newhalem Town Center to the National Park Visitor Center by trail.

Gorge Inn Suspension Bridge is a stiffened pedestrian suspension bridge utilizing a welded truss of 4" x 6" tubular steel and bolted 3" x 3" angle iron.  The classic lines and combination of steel and timber components of this attractive light duty suspension bridge are reminiscent of cable bridges erected in remote areas of the West since the early part of the last century.  Unfortunately the use of timber as a structural component in cable bridge design has limitations, particularly as regards the anticipated useful life of the bridge. In October 2000, the north side timber tower collapsed with the bridge carrying 30 or more pedestrians.  Despite the bridge deck dropping more than 10 feet there were miraculously no injuries or fatalities, and the remaining tower together with the stiffened truss prevented total collapse of the bridge into the river.  The photos you see above shows the bent and buckled truss after the collapse and the stabilization repair implemented by Sahale (below). 

Stabilizing the bridge involved installation of temporary towers, mainlines and suspenders.  The objective was to temporarily support the truss over the winter, while a plan for permanent repair could be developed and implemented.  Sahale designed an interim system having tower and mainline geometry that will permit installation of permanent new towers (presumably of steel) and reinstallation of the original mainlines and suspenders while the temporary system remains in place.  The temporary steel towers are approximately 25' tall and are constructed of W8 x 30 beams 4" x 4" x 3/8" angle.  The temporary mainlines are 1-3/8" steel IWRC wire rope with spelter socket attachment via an 8" x 8" x 1" angle fitting to the original anchor rods.  The temporary susView of stabilized bridge from the tower top.  Note pinch at chord buckles near midspan.penders are 4" heavy ratchet straps.  The factor of safety for the temporary system is slightly over 2, with snow load equivalent to 4' snow depth.  Later in 2001, Sahale completed a permanent repair and structural upgrade including installation of new towers, replacement of damaged floor beams and truss members, and fitting of a new redesigned sway brace system.

 

Stabilized bridge after early season snowfall.