Floating Bridges - Pushing the Limits: New Adventures in Engineering - page 26

spanned by a cable-stayed bridge, a bridge type that was promoted in the mid-1950s by Homer Had-
ley, who called it a “tied-cantilever,” and that was just being introduced in Europe. But Hadley was
again ahead of his time, for it was to be another two decades before a cable-stayed bridge would be
built in America. Perhaps fittingly, the first such bridge in the contiguous United States was erected
(in 1978) over the Columbia River, between Pasco and Kennewick, in Washington, where Hadley
left his mark as an engineer. Locally, the Pasco-Kennewick Bridge is known simply as the “cable
bridge.”
A significant floating bridge was put into service in 2000 in Osaka, Japan, and it solves the prob-
lem of maintaining a wide shipping channel in an unusual way, even for a floating structure. The
floating portion of the bridge, which is more than 1,200 feet long (with a clear span of more than
850 feet), looks not unlike a conventional steel span supported near its extremes on two massive
piers. The bridge is in fact supported on two hollow-steel pontoons. When a ship wants to pass,
which is not expected to be often, the entire bridge is rotated to the side of the channel. A smaller
and much older floating bridge operating on a similar principle is located in Willemstad, Curaçao,
in the Netherlands Antilles. Known as the “Floating Lady” and the “swinging old lady,” this bridge
dates from 1888 and still opens about six times a day. Since 1996, another modest floating bridge
has provided a convenient means for pedestrians to walk between Canary Wharf and the West India
Quay in London's Docklands, on the Isle of Dogs. Though spanning less than three hundred feet,
this elegantly designed structure is a model for how attractive a floating bridge can be.
Currently, the technology of floating bridges is being combined on the drawing board with that
of offshore oil and gas exploration, in which it is not uncommon to tether massive drilling rigs in
water depths of more than one thousand feet. Among bridge proposals that rest on floating found-
ations are those designed to cross the fifteen-mile-wide Strait of Georgia, near Vancouver, British
Columbia; the sixteen-mile-wide Strait of Gibraltar; and between pairs of Hawaiian islands, where
water depths can exceed two thousand feet. Such ambitious crossings are likely to be among those
discussed in the coming decades, but like Homer Hadley's first Seattle floating bridge, they are not
likely to be realized until the right combination of circumstances—technical, economic, and polit-
ical—arises.