The Science Behind Strong Bridges

A highway bridge carrying I-35 West traffic over the Mississippi River collapsed during rush hour on Wednesday night. Guests discuss the current status of the recovery efforts in Minneapolis and the health of the United States' infrastructure.

Lowell Greimann, professor emeritus, Department of Civil, Construction, & Environmental Engineering, Iowa State University

Study Answers Question of Why Bridges Collapse

Tacoma Narrows suspension bridge in Puget Sound, Washington state, vibrates violently. i i

hide captionNov. 7, 1940: The Tacoma Narrows suspension bridge in Puget Sound in Washington state vibrates violently just before its collapse due to hurricane-force winds causing a violent oscillating motion known as "flutter."

Keystone/Getty Images
Tacoma Narrows suspension bridge in Puget Sound, Washington state, vibrates violently.

Nov. 7, 1940: The Tacoma Narrows suspension bridge in Puget Sound in Washington state vibrates violently just before its collapse due to hurricane-force winds causing a violent oscillating motion known as "flutter."

Keystone/Getty Images

Notable Bridge Disasters

2007: A truck packed with passengers and merchandise overloads a bridge in the West Africa's Republic of Guinea, causing it to collapse, killing 65 people.

2006: Bridge collapse in Quebec, Canada kills five.

2005: A flood washes away a rail bridge in India, killing 114.

2005: A highway bridge under construction in southern Spain collapses, killing six.

2002: A barge hits a 500-foot section of a bridge spanning the Arkansas River in Webbers Falls, causing it to collapse, killing 14 people.

2001: A bridge collapses in Lisbon, Portugal, causing a tour bus to plunge into a river, killing more than 50.

1994: The Seongsu Bridge collapses in Seoul, South Korea, killing 32.

1987: A bridge on the New York State Thruway near Amsterdam, New York, gives way, killing 10. Together with the 1983 Mianus River bridge accident, it prompts major efforts to reduce U.S. bridge failures.

1983: Rusty pins fail, causing 100 feet of I-95 to fall into the Mianus River in Connecticut, killing 3.

1980: The Sunshine Skyway Bridge in Tampa Bay collapses, killing 35 people. A ship hit the bridge during a storm.

1967: The Silver Bridge over the Ohio River connecting Point Pleasant, West Virginia, to Kanauga, Ohio, collapsed December 15, 1967, during evening rush hour. Forty-six people died. The accident prompted major reforms in government efforts to inspect and maintain bridges in the United States.

1876: A railroad bridge falls into the Ashtabula River in Ohio, killing 92. The designers later commit suicide.

Compiled from news reports and historical accounts

Mother Nature is hard on bridges.

That's the main message from scientists who conducted a massive study of why bridges fail in the United States. The researchers say floods were responsible for more than half of recent bridge failures; fewer bridges were toppled or disabled by factors such as overloading, deterioration, or design flaws.

The 2005 study by Kumalasari Wardhana and Fabian Hadipriono of Ohio State University looked at 503 U.S. bridges that had failed between 1989 and 2000. The failed bridges included everything from spans designed to carry pedestrians over roadways to floating pontoon bridges across lakes. "Failure" was defined as anything from collapse to damage so serious the bridge had to be closed.

Overall, they found that 53% of the failures came during floods, when raging waters undermine bridge footings or batter the structures with debris. The great floods of 1993 were particularly hard on bridges across the Midwest. Earthquakes brought down another 3% of the bridges.

A collision with a car or a boat was the second leading cause of bridge failure, bringing down about 12%. Fourteen bridges were felled by a collision with a car or truck, while ships and barges toppled 10. Three bridges failed after collisions with trains.

"Overloading" took third place in the survey. Roughly 10% of the bridges failed after too many people or cars crowded on to the span. The study notes that 107 people were injured after a walkway collapsed at an auto racetrack in North Carolina.

Deterioration and design flaws – potential factors in the collapse of the Interstate 35 West bridge in Minnesota — were responsible for about 9% of the failures. Twenty bridges, for instance, failed due to corroded steel or related deterioration.

The study, which appeared in the Journal of Performance of Constructed Facilities, notes that some bridges are particularly plagued by problems.

The Evergreen Point Floating Bridge on Lake Washington, Washington had an 11-year run of bad luck. The pontoon bridge's deck cracked open in 1989, then again in 1991. Then, eight years later, strong winds split the bridge in two. In 2000, it was damaged by a collision.

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