August 2013 - Humans aren’t born with an innate fear of heights. Research suggests it’s a learned response as babies gain experience crawling and navigating the world on their own. As we grow, our sense of space and danger is developed through our unique experiences of trial and error.
I’m never going to want to BASE jump or skydive. I don’t like to be right next to floor-to-ceiling windows in tall buildings and even walking or riding over some bridges makes me a little nervous—even more so when looking at numbers from the American Society of Civil Engineers, which show that one in nine bridges in the United States are rated as structurally deficient.
It’s an expensive job to repair all those crumbling, obsolete bridges, and this spring, many Chicago commuters got to experience the headaches caused when a major bridge gets shut down for construction work. Eighty-three percent of the historic 91-year-old Wells Street drawbridge that spans the Chicago River needed replacement because of extensive corrosion and section loss.
The bridge is a fixed trunnion bascule, one of 37 along the Chicago River, and carries cars, buses, bikes and pedestrians on its lower level and the city’s famous elevated train on its upper level. The construction posed a complicated challenge.
“It’s complicated from every point of view you could possibly have,” said Johnny Morcos, bridge project manager for the Chicago Department of Transportation, in a March 6, 2013 article on NPR. “From an engineering point of view, from an urban dwelling point of view, you’re in the heart of the central business district, you’re cutting off CTA transit users, which there are roughly 70,000 users—and you’re working over a river.”
Watching the crews work on the bridge and reading about the intricacies involved in the project sparked the idea for this month’s article on bridges. I commute north into the city from the Near South Side, so the bridge construction didn’t affect my daily routine, but it certainly affected many of the people I know who had to find an alternate route to work during the short period the bridge was closed.
Devising the most efficient way to repair bridges limits the economic impact of closures. If a bridge goes out completely because of a collapse, it can have a significant impact on road users and states’ economies, in addition to the tragic loss of lives. On the day the I-35 W bridge in Minnesota collapsed, 13 people were killed and 145 were injured. The Minnesota DOT’s initial study concluded that road-user costs due to the unavailability of the river crossing would total $400,000 per day. In addition to that, analysis by Minnesota’s Department of Employment and Economic Development in conjunction with the Minnesota DOT estimated the loss to Minnesota’s economy at about $17 million in 2007 and $43 million in 2008.
This month’s cover story discusses the economic impacts of functioning bridges in more detail as well as highlights some material options and construction techniques for building safe, long-lasting structures. MM
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