Pontoon Bridge - Disasters

Disasters

Floating bridges can be vulnerable to inclement weather, especially 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. Waves of 10–15 feet (3.0–4.6 m) battered the sides of the bridge, and within a few hours the western 3⁄₄ miles (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 hydrodemolition 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 (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 hydrodemolition. 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.