Hood Canal Bridge - History - Design, Fabrication, and Construction

Design, Fabrication, and Construction

The design and planning process for the Hood Canal Bridge took nearly a decade amid criticism from some engineers throughout that time. Critics questioned the use of floating pontoons over salt water, especially at a location where tide fluctuations vary as much as eighteen feet and the funneling effect of the Hood Canal might magnify the intensity of winds and tides. The depth of the water, however, made construction of support columns for other bridge types prohibitively expensive. The water depth below the pontoons ranges from 80 to 340 feet (24 to 104 m). In its marine environment, the bridge is exposed to tide swings of 16.5 feet (5 m).

The pontoons for the bridge were fabricated in the Duwamish Waterway in Seattle, Washington. During fabrication two of the pontoons sank. When they were attached for the first time, and then towed into place and anchored, sea conditions in the Hood Canal were too severe and the pontoons were returned to a nearby bay until a better method of attaching could be devised. The architects and the contractor decided the design was faulty. A new contractor was hired and the design modified. It was decided to use a large rubber dam between each of the two pontoons as they were attached, clean the concrete surfaces of all marine growth, epoxy, and tension them with a number of cables welded to a variety of attachment points. This system seemed to work from when the bridge opened in 1961 until the disaster of 1979.

The east approach span weighs more than 3,800 tons (3,400 tonnes) and the west approach span weighs more than 1,000 tons (907 tonnes)