COVINGTON, Ky. - A bridge that is both fracture critical and structurally deficient connects Covington and Cincinnati.
It's not the Brent Spence, but the Roebling Suspension Bridge.
The Brent Spence Bridge gets all the attention because a replacement structure is badly needed. It is classified as functionally obsolete, but not structurally deficient.
What do those terms mean?
Under Federal Highway Administration classifications, a structurally deficient bridge suffers from either poor design or physical decay that requires limits on the weight or spacing of vehicles allowed to travel on it. A functionally obsolete bridge is a span that is either too narrow or carries more traffic than it was designed to handle. A bridge can be classified as either structurally deficient or functionally obsolete, but not both.
Out of Ohio's nearly 14,000 bridges, 6,381 bridges are either structurally deficient or functionally obsolete, according to the 2011 National Bridge Inventory.
Kentucky has 4,257 deficient bridges, while Indiana has 3,939. In all, roughly one out of every four bridges in the Tri-State can be classified as either structurally deficient or functionally obsolete.
Such bridges can also be considered fracture critical.
A fracture critical bridge is a steel structure with no redundancy. The failure of a single piece of steel could cause the entire bridge to fail.
The I-35W bridge in Minneapolis was both fracture critical and structurally deficient. When it collapsed in 2007, 13 people were killed.
The Silver Bridge connecting Gallipolis, Ohio and Point Pleasant, West Virginia was also a fracture critical bridge. A small, unseen crack in a single steel eye bar caused the entire bridge to fall into the Ohio River in 1967. Because the failure occurred during rush hour when the bridge was packed with vehicles, 46 people were killed in the collapse.
"It's always in the back of your mind, you know, is this bridge safe?" said Cindy Cherry. She lost her mother and her sister in the Miamitown Bridge collapse in 1989.
The temporary span across the Great Miami River was not designed to handle the lateral forces created by flood waters. Helen Zorn, 52, and her daughter Terry Siemon, 27, were driving across the bridge when it suddenly gave way. Their bodies were pulled from the river days later.
"That it didn't have to happen is what's so troubling," Cherry said.
Ironically the temporary bridge was erected because the old Miamitown Bridge was deemed unsafe as both a fracture critical and structurally deficient structure. It was demolished once the temporary bridge was completed right next to it.
Saveourbridges.com analyzed data from the 2009 National Bridge Inventory to map the 7,980 bridges in the US that are both fracture critical and structurally deficient. Remember, that means the bridge is in poor condition and it could fall down if only one steel member fails.
That brings us back to the Roebling Suspension Bridge. It has stood majestically as the icon of Cincinnati since its twin towers were constructed in 1865, the year President Lincoln was assassinated. Experts say the Roebling Bridge should outlive us all, just as it has outlived its original builders.
But the suspension bridge is both fracture critical and structurally deficient. Annual inspections have uncovered cracks in the steel and other defects that have required temporary weight limits and repairs.
Construction crews are nearly finished demolishing what's left of the most dangerous section of the Sixth Street Viaduct, and a replacement structure has already begun to take shape.
The I-Team used the map from saveourbridges.com to investigate about a dozen Tri-State bridges, expecting to find a series of dangerous spans in desperate need of replacement. Instead we found that since the time the data was collected in 2009, most of the worst bridges in our area have either been replaced, closed or are in the process of reconstruction.
The Ohio Department of Transportation inspects every bridge, every year. ODOT is currently building several replacement bridges in the southwest part of the state.
The new Jeremiah Morrow Bridge on I-71 is being constructed between the northbound and southbound lanes of the existing bridge. %page_break%Opened in 1964, Ohio's highest bridge is strikingly similar in design to the I-35W bridge that failed in Minnesota. It is fracture critical and nearing the end of its projected service life, but the old Jeremiah Morrow is not considered structurally deficient.
The new bridge is a marvel of engineering.
"It has concrete and steel components in it," said ODOT engineer Brandon Collett. "So if anything were to go wrong with it, there's other redundant systems within the structure itself that will keep anything from becoming catastrophic."
Project engineer Dan Mendel added, "that concrete is actually protecting the structure itself."
What that means is the concrete box girder serves as its own counterbalance during construction, and steel tendons that run through tubes inside the structure are tightened to constantly compress the bridge. Steel is strongest in tension and concrete is strongest in compression, so post-tensioning keeps the bridge in a state of equilibrium.
In short, the new 239-foot high I-71 span over the Little Miami River will be much safer than the fracture critical bridge its replacing.
TRAGEDY + HARDSHIP = SAFER BRIDGES
Why the sudden boom in bridge replacement? The 2007 collapse of the I-35W bridge in Minneapolis raised awareness of the nation's aging infrastructure, while the recession created a trillion-dollar stimulus to fund "shovel ready" construction projects.
In other words, tragedy and hardship came together at a time when the average age of bridges in America approached their projected life-span of 50 years. That created both the demand for safer bridges, and the supply of money to replace them.