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Wednesday, 19 June 2013 13:22

Inspectors’ job is to determine which bridges are holding up

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fr bridgesDelvin Adams stood at the top a ladder leaning against the underbelly of a bridge near Harmon Den in Haywood County, banging the rustiest looking metal beam with a hammer.

 

Adams, a bridge inspector with the N.C. Department of Transportation, cleared the debris from the steel beam holding up Interstate 40, and as he slapped it again with the hammer, bits of rust tumbled onto the road below. Adams called down to fellow inspector Joe Huntsinger that the beam was half an inch thick, and Huntsinger marked it down in his notes. The beam, one of several that holds up the Interstate 40 bridge, was originally seven-eighths of an inch.

“You look for rust that is starting to eat away at the steel,” Adams said. 

Based on its condition, the Harmon Den bridge will be placed on a list of structures in need of fixing within the next two years, Adams added.

“It looks bad, but it’s not that bad yet,” Adams said.

In other words, it’s not dire. DOT will just need to weld a metal plate onto part of the beam to strengthen it. However, had the rust left the metal beam “paper thin,” the inspectors would have immediately filled out a priority report, which lets the department heads know that work must be done on the structure within 30 days.

“That is something that is critical,” Adams said.

A mixture of age, weathering and road salt all contribute to the natural oxidation of metal. It’s DOT’s job to monitor and inspect bridges across the state and make sure they are safe.

“Our job is to catch any problem before it gets bad,” Huntsinger said. “We look for everything.” 

Aging and unsafe infrastructure once again found a prominent place in the national spotlight recently after a bridge in Washington state collapsed. The National Transportation Safety Board, an independent federal agency that investigates transportation-related incidents, called the collapse a warning for the nation.

The point of inspections is to, hopefully, prevent bridges from giving way. North Carolina has 13,778 bridges, and each is inspected on a biannual basis, according to statistics from DOT.

Bridges are ranked on a zero-to-nine scale after each inspection. No bridge is ever given a nine however. Each newly constructed bridge is awarded an eight. If a structure is given a five, it is “getting bad,” Adams said. “You get twos and threes, it’s about ready to be shut down.”

DOT workers must take classes on how to rate infrastructure to ensure relative consistency among all inspectors. The state DOT currently employs 44 bridge inspectors.

Of the state’s nearly 13,800 bridges, 5,656 are marked as structurally deficient or functionally obsolete. Structurally deficient bridges are deemed in relatively poor condition or do not meet the minimum load-carrying requirements, which is 40 tons. Bridges are considered functionally obsolete if they are too narrow, have inadequate under-clearances, have insufficient load-carrying capacity or are poorly aligned with the roadway.

“The thing is that when you think about that a third of the time you are driving on an inadequate bridge, that is a little frightening it seems to me,” said Michael Smith, head of the Construction Management Department at Western Carolina University. Smith has studied how decrepit infrastructure is harming the U.S.’s ability to compete in the global trade market.

But like other Americans, that doesn’t keep him from crossing bridges when he comes to them.

“After a while, you quit worrying about things,” Smith said.

Adams, who has 37 years experience in inspections, isn’t concerned either, but for a different reason.

“None of them are really that bad,” Adams said.

 

Skating along

A single bridge inspection can take anywhere from a couple of hours to a couple of days depending mostly on the size of the bridge. Bridges that are fracture critical receive more attention.

Although they are not inherently dangerous, fracture-critical bridges, such as the Washington state bridge, only have two metal support beams and therefore are only one bad beam away from failure. Fracture-critical bridges were built in the post-WWII infrastructure boom.

“That was an easy way to design a bridge. It was cheap,” Adams said.

In government, redundancies are frowned upon, but not in architecture.

“We tend to think of redundancy as a bad thing, but in design, redundancy is hardly negative,” Smith said.

Bridges, and roads for that matter, in the U.S. were built in the 1950s and 1960s. They were expected to last about 50 years. The average age of U.S. bridges is 47 years today, Smith said, and not enough has been done to replace the declining infrastructure.

“They invested a heck of a lot in infrastructure post-WWII, and we have been skating on that. We have been riding on that investment ever since,” he said.

As the country’s infrastructure declines, it will negatively impact the U.S.’s trading ability, Smith said. People can’t move goods from place to place without infrastructure.

“The reality is, in order to have a vital economy, you need to trade beyond your immediate region,” Smith said. “We have known this for a long time, and we keep forgetting it.”

Each year, the World Economic Forum, an independent international organization, ranks countries in order of global competitiveness based on 12 pillars, including infrastructure, well-functioning public and private institutions, and good health and primary education. The U.S., which ranked first in 2009, has continued to slip further down the totem pole each year since. This year, it placed seventh.

To Smith, the primary reason for the U.S.’s slip is aging infrastructure — something that could be improved if the government is willing to make the investment. 

“I don’t think we should pave the world,” Smith said “But the truth is we need wise infrastructure.”

However, Adams argued that old is not always bad. When Hurricane Katrina hit New Orleans in 2005, the Maestri Bridge, which was built in the 1920s, fared well, while the Twin Span Bridge, which was constructed 40 years later, sustained extensive damage.

 

 

Bridge conditions by county

The North Carolina Department of Transportation keeps a list showing how many bridges it is responsible for in each county. It also states how many are deemed structurally deficient or functionally obsolete.

Structurally deficient bridges are deemed in relatively poor condition or do not meet the minimum load-carrying requirements, which is 40 tons. Bridges considered functionally obsolete are too narrow, have inadequate under-clearances, have insufficient load-carrying capacity or are poorly aligned with the roadway.

Haywood County

Total bridges 287

Structurally deficient 84

Functionally obsolete 54

Jackson County

Total bridges 216

Structurally deficient 42

Functionally obsolete 75

Macon County

Total bridges 204

Structurally deficient 69

Functionally obsolete 54

Swain County

Total bridges 95

Structurally deficient 16

Functionally obsolete 20

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