Better Bridges: Bridge Inventory 2009 State of Bridges
Like Pennsylvania, Oklahoma also expects to be able to lower its number of SD/FO bridges within the coming year. Bob Rusch, bridge division engineer for the Oklahoma Department of Transportation, says this is the fourth consecutive year the number of bridge projects in the state’s eight-year Construction Work Plan has increased and represents the largest increase in bridge work ever incorporated into the plan.
“The department’s Federal Fiscal Years 2010 -2017 Construction Work Plan enumerates priorities for highway and bridge construction during the next eight years and includes more than $4 billion in improvements to the state’s bridges and highways,” Rusch says. “The plan continues the agency’s focus on bridges with an increase of more than 100 bridges over last year’s plan for a total of more than 560.” In addition, he adds, “The department is also continuing to make strides in our State Bridge rehabilitation Program which provides significant repairs to existing bridges.”
The actual number of bridges doesn’t always paint the most accurate picture of deficiency or obsolesence. A state with fewer bridges could have a higher percentage of bridges that are SD/FO, but the numbers of SD/FO bridges could actually be relatively low.
The highest percentage of SD/FO bridges in the nation – 55percent – is in the District of Columbia. By percentage, Rhode Island** comes in second with 53 percent SD/FO bridges, followed by Pennsylvania at 39 percent, Hawaii at 38 percent and New York at 37 percent.
Regardless of what the official statistics show about the number of bridges that are SD and FO, some bridge engineers say that we should look at the square footage of SD and FO bridges to get a true picture of the situation. Ray Mumphrey, highway bridge program manager with the Louisiana Department of Transportation, says that while the number of SD/FO bridges may have decreased, the square footage may actually be increasing. “It may look like we’re making progress [in the nation] with the number of deficient bridges, however larger bridges are becoming deficient which increases the square footage of deficient bridges,” Mumphrey says. “There are a lot of interstate [bridges] becoming deficient, although the numbers of deficient structures may have gone down.”
Adds John Jones, M.S., P.E., Bridge Manuals, Modeling and Policy Engineer with the Kansas Department of Transportation (KDOT): “In all cases, square footage is the best indicator of [their] status.”
Clearance and capacity concerns
Even after the August 2007 collapse of I-35W Mississippi River Bridge in Minnesota, bridge needs are still not being seen as “critical,” says Dan Holderman, P.E., a bridge management engineer with the North Carolina Department of Transportation. “Even after the I-35W collapse, [there is still] very little emphasis on bridges and other infrastructure.”
Investigators found that the Minneapolis bridge, which killed 13 people when it collapsed into the Mississippi River failed because of a flaw in its design, when it announced its findings on Jan. 14, 2008. The designers had specified a metal plate that was too thin to serve as a junction of several girders, investigators say, according to a New York Times report immediately following the findings.
The bridge, which was designed in the 1960s, lasted 40 years. However, like most other bridges, the Times reported, it gradually gained weight during that period, as workers installed concrete structures to separate eastbound and westbound lanes and made other changes, adding strain to the weak spot.
This is when the bridge problem becomes more than a structural issue. It also becomes a capacity and a clearance issue. Although bridges can be functionally obsolete (e.g. geometrically deficiencies such as waterway openings, width, clearance issues, etc.) they are still considered safe to the motoring public even if they aren’t up to the standards – such as the current-day recommended width – for modern-day standards and commerce.
“We have so many oversize and overweight vehicles that go through Indiana, [and] we have to route vehicles all over the place because of structurally deficient, low-capacity or low-clearance bridges,” said Bill Dittrich, state bridge inspection engineer for the Indiana Department of Transportation. “In the early to mid 1980s, we [the state of Indiana] didn’t allow permitted vehicles on our interstate highways. Now, we are letting trucks go over them.”
Mike Clements, Georgia Department of Transportation state bridge engineer, says that’s part of the problem in his state, too. “Increased weight limits” is Georgia’s major cause of bridge damage, he says.
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