Bridges provide drivers with a safe passage over water, roadways, train tracks and other obstacles using materials such as wood, steel, iron, concrete, cement and more. But building or fixing one of these connections can be time consuming and costly.
This month Senate Transportation Chairman Willie Simmons announced that over the course of a week federal inspectors had closed more than 100 bridges on local roads in the state of Mississippi. A bill that was introduced this year in the state would have raised transportation money through an internet sales tax. Projections showed that collections could have generated an annual revenue of between $50 million and $175 million for needed repairs. The bill was not approved, but a House bond bill that would let the state borrow $50 million for repairs is still hanging on.
For the second time in a row, America’s infrastructure has earned a grade of D+ from the American Society of Civil Engineers (ASCE). ASCE issues these report cards every four years, grading the state of U.S. bridges, dams, parks, airports, railroads and other vital links.
The United States has 614,837 bridges, of which almost 40 percent are at 50 years or older. According to ASCE, on average there were 188 million trips across structurally deficient bridges daily in 2016.The term “structurally deficient” does not mean a bridge is about to fall down, but indicates one in need of repair or rebuilding. Further deterioration could mean a bridge must be limited to certain load levels or closed.
In steel bridges, localized structural damage produces a weakened condition called fatigue. Repetitive loading from years of passing traffic then causes cracks to develop. Most older steel bridges suffer from fatigue and eventual cracking because when they were designed codes in place did not adequately address this problem, or because they are carrying loads heavier than they were originally designed to hold.
Fatigue crack growth generally can be managed through regular repairs without compromising the bridge’s performance. However, if cracks are not repaired, they can grow quickly, which could lead to catastrophic failure. This means it is critically important to evaluate rates of crack growth, and to understand how rapid crack growth can affect the integrity of bridges.
A study performed by the American Road and Transportation Builders Association found that 8.4 percent of Illinois’ 26,704 bridges are structurally deficient, which means that one or more key elements, such as the bridge deck or its foundation, is in poor or worse condition, according to federal standards. Illinois, which has the third-highest number of bridges in the country after Texas and Ohio, ranks sixth in number of structurally deficient bridges.
For Chicago bridges on Illinois’ top 10 list, the city’s transportation department plans repairs to the bridges at Wilson and Lawrence this summer, including structural repair of the concrete. Work is expected to take about six to eight months.
Among the state bridges on the list, repairs are being planned by the Illinois Department of Transportation and construction could begin on I-290 over Salt Creek in Addison as early as 2018, on I-55 at Lemont and Joliet roads in Will County in 2019 and on I-53 over Kirchoff Road in Rolling Meadows in 2021.
New methods of building and repairing structurally deficient bridges has cut down on expense and time spent re-routing traffic. In Wayne County, Ind., contractors plan to use the accelerated bridge construction method called a slide-in bridge to replace the twin three-span bridges carrying eastbound and westbound Interstate 70 traffic over State Road 121/New Paris Pike.
The new bridge deck will be built on temporary supports adjacent to the existing bridge. Once the new portion of the bridge is completed, four-lane traffic would be decreased to two lanes, barriers would be set up, the existing portion of the bridge will be demolished and the new bridge will slide laterally into place. The same method would take place for the two lanes on the other side of the bridge. Construction is anticipated to begin in early April 2017 and finish before June of 2018.
Another time-saving bridge is a prefabricated one. The Arizona Department of Transportation (ADOT) will install the state’s first prefabricated bridge on old Route 66. The 110-foot-long bridge will be transported in sections from Phoenix, where it is being manufactured, to the bridge site in Mohave County. The support structure is already in place and bridge installation is expected to take place this month.
This reduces traffic restrictions and closures to days instead of weeks or months. According to ADOT, this initiative saves an estimated $2.6 million in road user impacts to traditional bridge construction methods. That includes work zone delays and a costly, long-term detour to commuters, businesses and visitors who depend on the Oatman Highway corridor. The total cost of the bridge project is $1.8 million.
Seattle, Wash., will be the first bridge in the world with a new type of column that flexes during an earthquake and then snaps back to its original position. The Washington State Department of Transportation is building an offramp from Highway 99 to South Dearborn Street that has a flexible column that can withstand so little damage during an earthquake that it can be used after the quake has settled.
The project is based on research performed at the University of Nevada, Reno. But the bridge’s safety feature comes at a price. Shape-memory rods cost 90 times more than conventional rebar and the bendable concrete is four times more expensive than ordinary concrete. However, the materials are only used in the tops of the columns that are most vulnerable to earthquakes, so the innovations added only about 5 percent to the overall cost.
Iowa and Illinois are teaming up and seeking bids on the Interstate 74 bridge project. The Iowa Department of Transportation is seeking bids on three contracts that are worth about $400 million for the project. The new bridge will be built east of the existing one, with two spans of four lanes and full shoulders. A recreation trail and an overlook are also part of the design. The bids will be opened April 25 with work expected to begin in the summer.
The Illinois Department of Transportation is preparing a similar process for the their portion of the bridge. The first will be work on the new bridge viaduct with a mandatory pre-bid meeting on the $120 million project, expected in the coming weeks, so the candidates can ask questions and learn more about the work. The bids will be opened in June with construction expected to start in August.