Page 28 - COLLAGE

4. CHAPTER

FAILURES AND DISASTERS

The Saint Isaac's Bridge across the Neva River in Saint Petersburg suffered two disasters, one

natural, a gale in 1733, and then a fire in 1916.

Floating bridges can be vulnerable to inclement weather, especially strong winds. The U.S.

state of Washington is home to some of the longest permanent floating bridges in the world,
and two of these failed in part due to strong winds.

In 1979, the longest floating bridge crossing salt water, the Hood Canal Bridge, was subjected
to winds of 80 miles per hour (130 km/h), gusting up to 120 miles per hour (190 km/h). Waves

of 10–15 feet (3.0–4.6 m) battered the sides of the bridge, and within a few hours the
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western ⁄4 mile (1.2 km) of the structure had sunk. It has since been rebuilt.

In 1990, the 1940 Lacey V. Murrow Memorial Bridge was closed for renovations. Specifically,

the sidewalks were being removed to widen the traffic lanes to the standards mandated by
the Interstate Highway System. Engineers realized that jackhammers could not be employed to

remove the sidewalks without risking compromising the structural integrity of the entire bridge.
As such, a unique process called hydro demolition was employed, in which powerful jets of

water are used to blast away concrete, bit by bit. The water used in this process was temporarily
stored in the hollow chambers in the pontoons of the bridge in order to prevent it from

contaminating the lake. During a week of rain and strong winds, the watertight doors were not

closed and the pontoons filled with water from the storm, in addition to the water from the
hydro demolition. The inundated bridge broke apart and sank. The bridge was rebuilt in 1993.

A minor disaster occurs if anchors or connections between the pontoon bridge segments fail.
This may happen because of overloading, extreme weather or flood. The bridge disintegrates

and parts of it start to float away. Many cases are known. When the Lacey V. Murrow Memorial
Bridge sank, it severed the anchor cables of the bridge parallel to it. A powerful tugboat pulled

on that bridge against the wind during a subsequent storm, and prevented further damage.

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