As the $21 million Paseo Bridge rehabilitation project nears completion in Kansas City, two University of Missouri-Rolla researchers are sharing their findings on why the bridge cracked in the first place.
Dr. Genda Chen, associate professor of civil, architectural and environmental engineering, and Dr. Lokesh Dharani, Curators’ Professor of mechanical and aerospace engineering, have spent the last two years examining why a vertical strut in the 51-year-old Kansas City bridge fractured and figuring out how it could have been prevented.
The bridge was closed for 10 days in January 2003 after an 8-inch gap between the approach and the main span of the suspension bridge was discovered.
The steel strut cracked after debris, such as sand and salt, gathered inside a lower link housing, clogging it and preventing the bridge from flexing with traffic.
“Many people thought the low temperature was to blame, as the temperature was recorded to have hit 9 below zero, but the low temperature was a secondary reason,” Chen says. “Simulation results indicated that the strut would never have fractured even at low temperatures and with a 0.005-inch initial defect if the pin in the lower link was free to rotate.”
Simple maintenance, such as greasing the 11-inch pins or sealing the housings, could have prevented the strut’s failure, Chen says; however the bridge’s design kept the lower link pins inaccessible to inspections, and allowed debris to drop into the housings. The current rehabilitation project includes cleaning out the bridge’s pivot points.
Another option Chen recommends would be to install a device to remotely monitor the rotation of all four vertical struts and alert officials if one became mechanically frozen. “You don’t have to send people to the bridge every time, so it’s very economic, but there are still concerns of reliability and maintenance of these devices,” Chen adds.