The Interstate 70 bridges over the Kansas River, a fracture

It’s all about trusting a set of eyes.

Inspectors for counties and the Kansas Department of Transportation crawl, climb and creep over bridges all across the state to ensure that problems don’t develop that lead to catastrophic failures like Wednesday’s deadly bridge collapse in Minneapolis.

That means they’re looking for the tiniest of details: a discoloring of paint that indicates a stress point; hairline cracks in steel or concrete; and, yes, even large concentrations of bird droppings, which are a corrosive.

Despite the low-tech methods, Kansas transportation leaders sought to assure motorists that the state’s bridge system was safe.

“It is safe to travel across the bridges on the state highway system in Kansas,” Deb Miller, secretary of KDOT, said Thursday. “If we thought there was any bridge on the state highway system that carried any risk of collapse, we would close that bridge immediately.”

Kaw concerns

There are two very large, busy bridges in Lawrence that inspectors crawl around on more than others. Those are the Kansas Turnpike bridges that cross the Kansas River between the East Lawrence and West Lawrence interchanges.

Each is similar to the bridge that collapsed in Minnesota. Both sets of bridges are classified as “fracture critical.” It is a scary-sounding engineering term that means that it takes only one significant piece of the bridge to fail for the entire bridge to collapse.

Danny Mahnke – the lead bridge inspector for HNTB Corp., which does the inspection for the Kansas Turnpike Authority – confirmed the bridges’ design makes them fracture critical. But, he said, as a result, the bridges get inspected every year. The federal inspection standard for bridges is every two years.

Work to replace the Kaw bridges – there are technically two, one eastbound, one westbound – is scheduled to begin in 2008. Mahnke said the 51-year old bridges need to be replaced because “there’s a lot of deterioration” in some of the steel elements.

Miller, who also is on the KTA, said the bridges are still safe to travel.

“We look at the data related to that bridge, and absolutely it is safe,” Miller said.

Improvements in bridge design are expected to make the new bridges more stable and less susceptible to a sudden failure. The $140 million project – which is equal to the cost to build the entire turnpike in the 1950s – is expected to be completed in late summer 2011.

High-tech methods

In addition to the annual routine inspection, the two turnpike bridges receive a more detailed inspection of its truss system every two years, and the underwater portion of the bridge is inspected every five years.

All the checks are visual inspections. There are other higher-tech methods for inspecting bridges. Some bridge designs – not necessarily the turnpike bridges – lend themselves to ultrasound testing. That involves shooting sound waves into the bridge to detect cracks. There’s also magnetic particle testing, which involves placing fine, magnetic dust on steel structures to help identify cracks that are difficult for the naked eye to see. But those tests are almost always the exception, not the rule, when it comes to Kansas bridge inspections.

Matt Bond, a former bridge designer for KDOT, said the state’s inspection methods are in line with industry norms.

“I would say we have a really good bridge inspection program,” said Bond, who is now the stormwater engineer for the city of Lawrence. “I would say that what happened (in Minnesota), most likely won’t happen here. It is really, really uncommon to have something happen as sudden as this.”

Others in Douglas County also were expressing optimism in the state of Kansas’ bridges. Keith Browning, Douglas County director of public works, is responsible for inspecting 161 bridges that are on county and township roads. The county is mandated to follow the same inspection procedures that the state uses.

“I absolutely feel like we are in a good position to catch problems before they happen,” Browning said. “But that said, things do happen. I’m sure the people in Minnesota were confident, too.”