InfrastructureStructural, regulatory, and human errors contributed to Washington bridge collapse
When an important bridge collapsed on Interstate 5 near Mount Vernon, Washington, in 2013, questions were raised about how such a catastrophic failure could occur. A new analysis outlines the many factors that led to the collapse, as well as steps that transportation departments can take to prevent such accidents on other bridges of similar design.
When an important bridge collapsed on Interstate 5 near Mount Vernon, Washington, in 2013, questions were raised about how such a catastrophic failure could occur. A new analysis by a team of civil engineering faculty at the University of Illinois at Urbana-Champaign outlines the many factors that led to the collapse, as well as steps that transportation departments can take to prevent such accidents on other bridges of similar design.
The analysis by University of Illinois civil engineering professors Tim Stark, Ray Benekohal, Larry Fahnestock and Jim LaFave was published in the American Society of Civil Engineers’ Journal of Performance of Constructed Facilities.
“The bridge repair costs exceeded $15 million, and that doesn’t account for the economic losses that the area felt because they and visitors no longer had access to the interstate,” Stark said. “Even though this accident occurred three years ago, it’s still very important because many bridges have this same design, not only in Washington but in other states.”
U of I says notes that the collapse on 23 May 2013 was precipitated when an oversized trailer clipped the top of the second cross-frame on the bridge. The analysis found several inciting factors, including regulatory ones – the truck had a permit to cross the bridge; structural ones – a minor impact caused a chain reaction that collapsed the bridge; and human error – miscommunication between the drivers of the truck hauling the oversized trailer and its pilot car.
How did an oversized vehicle receive a permit for a bridge with lower clearance than its height? Inaccurate record-keeping, Stark said. The opening of the bridge was curved, so that the clearance over the far lanes was lower than the clearance in the center lanes. However, the Washington Department of Transportation only keeps the maximum clearance in its bridge database, which is used to issue permits for oversized vehicles.
“The key issue in this case is the variable vertical bridge clearance,” Stark said. “Many bridges have a square opening, so the clearance is the same across all lanes. The problem with this bridge was that it curved down over the edge lanes. The oversized trailer was 15 feet 9 inches tall. The database said the bridge was 17 feet 3 inches, which was in the center – almost two feet higher than the edges, which is where the oversized trailer was traveling.”
