Grand Coulee Bridge - Grand Coulee, WA
Posted by: Groundspeak Premium Member T0SHEA
N 47° 57.917 W 118° 59.053
11T E 351890 N 5314346
Quick Description: Part of the Grand Coulee Dam project, which was, in turn, the beginning of the Columbia Basin project, this truss bridge was a PWA project.
Location: Washington, United States
Date Posted: 5/29/2018 8:41:01 PM
Waymark Code: WMYCJG
Published By: Groundspeak Premium Member Geojeepsters
Views: 0

Long Description:
The largest single water reclamation project ever undertaken by the U.S., the Columbia Basin Project was instituted to irrigate 1,029,000 acres of arable crop land, of which 671,000 has been irrigated to date. The completion of the Grand Coulee Dam in 1941 was the first step in implementing the project, which entailed the construction of more dams, bridges, pumping stations and canals in northwestern Washington.

The Coulee Dam Bridge, of cantilever steel through truss construction, was built as part of the Coulee Dam project, built to be stronger than a normal vehicle bridge to allow the passage of heavy construction vehicles and equipment.

Some Statistics:

  • Main Span Length - 550 Feet (167.64 Meters)
  • Structure Length - 1089 Feet (331.93 Meters)
  • Roadway Width - 20.3 Feet (6.19 Meters)
  • Spans - 3 Main Spans and 4 Approach Spans
  • Pier Height - 150 feet high (45.71 Meters)

The bridge was one of many PWA and WPA projects built in Washington state:

“The Bridge was built from 1934-1935 and at the height of its construction it gave the more than 7000 workers on the Grand Coulee Dam passage to their homes in Mason City. The Bridge itself is just a bit north of the dam that shares its name. The bridge is part of the roadway Washington 155. Now it is mainly for everyday traffic but when it was originally built it was for the sole purpose of aiding in the help in the construction of the Grand Coulee Dam. The Cantilever Truss Bridge was meant to be able to hold the weight of some massive machinery. Maybe one of the most important things that the bridge did was it enabled the dam that it was supporting to be completed before schedule.”
From the Living New Deal

Grand Coulee Bridge

In late 1934, the Bureau of Reclamation began the construction of a 950 foot through cantilever steel truss across the Columbia River near the site of the Grand Coulee Dam. The bridge was designed by the Washington Department of Highways for the Columbia Basin Commission to serve a dual purpose. It would be used to transport heavy equipment across the Columbia during the construction of the dam, and after the dam's completion, it would be used as a permanent highway structure on State Route 155. Consequently, the flooring and floor framing which carries a 20 foot wide roadway, curb to curb, and two 4 foot sidewalks, was built to handle H-20 loadings rather than the standard H-15.

The structure consists of two 200 foot anchor arms, two 175 foot riveted cantilever trusses, and one 200 foot Warren truss suspended span. The approach spans were composed of four concrete T-beams. Approximately 300 tons of structural carbon and silicon steel were used. Pin-connected links support the four corners of the suspended span in order to allow for the changes in length due to the live load and temperature. Transverse movement in the suspended span is prevented by a shear lock in the bottom lateral system.

The steel structure is supported by monolithic concrete piers that are 150 feet high, and are resting securely on bedrock. However, during the erection of the structure, the foundation was not so secure - as the structure neared completion, the east pier tilted nine inches from its original position. It was believed that this movement was caused by a deposit of fine glacial material which lay beneath the 20 or 30 foot surface layer of gravel, that often slides when disturbed. As an emergency measure, a 50-ton jack was placed in the gap between the cantilever arms. Cables were welded to the anchor arms and trusses, and secured to deadmen on shore which consisted of two 72 foot long steel girders As soon as the jack was in place, the tilting of the pier ceased. It was fortunate that the movement of the pier was parallel to the bridge center line, and did not cause distortion of the steel framing. Although the piers were finally taken down to a firm foundation through the construction of pneumatic caissons, the emergency remedies delayed the bridge contract for several months.

The Grand Coulee Bridge was one of two 550 foot cantilever trusses designed by the highway department in 1935. Its straightforward Warren truss suspended span, and the minimal bracing over the piers reflects the refinement and progressive simplification of the cantilever truss form in the 20th century. The Grand Coulee Bridge even represents a departure in form from the cantilever structures built in Washington during the previous decade. The bridge is significant in its role as a major transportation link in the construction of the Grand Coulee Dam.
From the NRHP (HAER) Inventory Form

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Project type: Bridge

Date built or created: 1934-1935

Location: Spanning the Columbia River

City: Grand Coulee

Condition: Good upkeep with a little wear and tear

Website for additional information: [Web Link]

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