Local Angle: Both spans of I-5 Bridge called 'fracture critical'; others in area appear worse
Both spans of the Interstate 5 Bridge are considered "fracture critical" by the Oregon Department of Transportation; if one crucial part of bridge sustains a big enough blow, the bridge could collapse. It's a designation the Columbia River bridge shares with many bridges in both Oregon and Washington.
ODOT categorizes it as a bridge without safety redundancies or backups that would prevent it from collapsing if part of a bridge truss is damaged or removed.
Although both spans of the I-5 Bridge over the Columbia River are fracture critical, they are not considered "structurally deficient," a label given to 89 Oregon bridges that require truck weight restrictions because a crucial part of the bridge is in poor condition.
ODOT spokesman Don Hamilton said that the bridge would be "very vulnerable" to even a moderate earthquake, and it is likely to collapse in the 9.0 Cascadia subduction zone earthquake expected to occur within the next 200 years. The I-5 Bridge is built on wooden pilings that are embedded in the riverbed's soil, but they do not extend into the sturdier bedrock under that soil, he said.
By comparison, the Glenn Jackson Bridge over the Columbia River on Interstate 205 is expected to be damaged, but not necessarily collapse, during a 9.0 Cascadia quake, Hamilton said.
Dozens of state bridges have problems
SEATTLE — Dozens of bridges in Washington are both in disrepair and at risk of collapse if hit hard enough in the wrong place.
An Associated Press analysis identified about state 50 bridges as structurally deficient and fracture-critical.
The Skagit River bridge that collapsed in May was a fracture-critical bridge, but it was actually not in disrepair like some of its peers.
While some of the bridges identified by the AP are small spans in low-travel areas, others are prominent. They include an Interstate 5 bridge that carries northbound drivers over the East Fork of the Lewis River, another I-5 span over the Stillaguamish River, and a Capitol Boulevard bridge in Olympia that carries many government workers over I-5 and into the city.
The span over the East Fork was built in 1936, and officials hope to replace it in the coming 10 to 15 years. Because of age, corrosion and metal fatigue caused by vibration, the state has restricted weight on the bridge. Washington state Department of Transportation spokeswoman Heidi Sause said the bridge wasn’t built for the wear — bigger loads and more traffic — that is now common.
“This is a bridge that we pay close attention to and we monitor very carefully,” Sause said.
AP’s analysis looked at 607,380 bridges in the most recent federal National Bridge Inventory. It found 7,795 were both structurally deficient and fracture-critical.
— Mike Baker
WASHINGTON — Motorists coming off the Frederick Douglass Memorial Bridge into Washington are treated to a postcard-perfect view of the U.S. Capitol. The bridge itself, however, is about as ugly as it gets: The steel underpinnings have thinned since the structure was built in 1950, and the span is pocked with rust and crumbling concrete.
District of Columbia officials were so worried about a catastrophic failure that they shored up the horizontal beams to prevent the bridge from falling into the Anacostia River.
And safety concerns about the Douglass bridge, which is used by more than 70,000 vehicles daily, are far from unique.
An Associated Press analysis of 607,380 bridges in the most recent federal National Bridge Inventory showed that 65,605 were classified as "structurally deficient" and 20,808 as "fracture-critical." Of those, 7,795 were both -- a combination of red flags that experts say indicate significant disrepair and similar risk of collapse.
A bridge is deemed fracture-critical when it doesn't have redundant protections and is at risk of collapse if a single, vital component fails. A bridge is structurally deficient when it is in need of rehabilitation or replacement because at least one major component of the span has advanced deterioration or other problems that lead inspectors to deem its condition poor or worse.
Engineers say the bridges are safe. And despite the ominous sounding classifications, officials say that even bridges that are structurally deficient and fracture-critical are not about to collapse.
Together, the bridges that fit both criteria carry more than 29 million drivers a day, and many were built more than 60 years ago. Those bridges are located in all 50 states, plus Puerto Rico and the District of Columbia, and include the Brooklyn Bridge in New York, a bridge on the New Jersey highway that leads to the Lincoln Tunnel, and the Main Avenue Bridge in Cleveland.
The number of bridges nationwide that are both structurally deficient and fracture-critical has been fairly constant for a number of years, experts say. But both lists fluctuate frequently, especially at the state level, since repairs can move a bridge out of the deficient categories while spans that grow more dilapidated can be put on the lists. There are occasional data-entry errors. There also is considerable lag time between when state transportation officials report data to the federal government and when updates are made to the National Bridge Inventory.
Many fracture-critical bridges were erected in the 1950s to 1970s during construction of the interstate highway system because they were relatively cheap and easy to build. Now they have exceeded their designed life expectancy but are still carrying traffic -- often more cars and trucks than they were originally expected to handle. The Interstate 5 bridge in Washington that collapsed in May was fracture-critical.
Cities and states would like to replace the aging and vulnerable bridges, but few have the money; nationally, it is a multibillion-dollar problem. As a result, highway engineers are juggling repairs and retrofits in an effort to stay ahead of the deterioration.
There are thousands of inspectors across the country "in the field every day to determine the safety of the nation's bridges," Victor Mendez, head of the Federal Highway Administration, said in a statement. "If a bridge is found to be unsafe, immediate action is taken."
At the same time, all that is required to collapse a fracture-critical bridge is a single unanticipated event that damages a critical portion of the structure.
"It's kind of like trying to predict where an earthquake is going to hit or where a tornado is going to touch down," said Kelley Rehm, bridges program manager for the American Association of State Highway and Transportation Officials.
Signs of age are clear. The Douglass bridge, also known as the South Capitol Street Bridge, was designed to last 50 years. It's now 13 years past that. The district's transportation department has inserted "catcher beams" below the bridge's main horizontal beams to keep the bridge from falling into the river, should a main component fail.
Alesia Tisdall, who drove over the bridge every day for 15 years but now crosses it only occasionally, said she found its "bounce" unnerving. "You'd look at the person sitting next to you like, `Did you feel that bounce?' And they'd be looking back at you like they were thinking the same thing."
Peter Vanderzee, CEO of Lifespan Technologies of Alpharetta, Ga., which uses special sensors to monitor bridges for stress, said steel fatigue is a problem in the older bridges. He compared steel bridges to a paper clip that's opened and bent back and forth until it breaks.
"In a bridge system, it may take millions of cycles before it breaks. But many of these bridges have seen millions of cycles of loading and unloading."
While the Skagit span was not structurally deficient, the I-35W bridge that collapsed in Minneapolis in 2007 had received that designation. The bridge fell during rush hour, killing 13 people and injuring more than 100. The National Transportation Safety Board concluded that the cause of the collapse was an error by the bridge's designers, not the deficiencies found by inspectors. A gusset plate, a fracture-critical component of the bridge, was too thin.
Congressional interest in fixing bridges rose after the 2007 collapse in Minneapolis, but efforts to add billions of extra federal dollars specifically for repair and replacement of deficient and obsolete bridges foundered. A sweeping transportation law enacted last year eliminated a dedicated bridge fund that had been around for more than three decades. Now, bridge repairs or replacements must compete with other types of highway projects for federal aid.