A Side Streets reader, Jordan Strub, asked me if I’d ever noticed the Fillmore Street bridge.
Specifically, he was curious about the underside of the bridge that carries Fillmore Street over Monument Creek just east of the interchange with Interstate 25.
Here’s a look from www.FlashEarth.com:
Here’s a photo of the bridge taken by Side Streets reader Jordan Strub:
In the photo, piers 2 and 3 are visible. And one of the tilting rocker bearing can be seen at the end of pier 3. The photo is looking south from the Pikes Peak Greenway trail.
Here’s a closer look at the pier and its rocker bearings:
Here’s an even closer look:
There are 18 rocker bearings on the two piers and they are in various stages of tilting. The worst are at 10 degrees on pier 3 while those on pier 2 measure at 5 degrees.
Engineers with the Colorado Department of Transportation say the rocker bearings don’t need to be reset until the tilting reaches 15 degrees. Below is a view from the south.
Resetting them is not eash. The bridge must be jacked up and the rockers placed precisely between the pier and girder to safely transfer the weight of the bridge.
For you hard-core engineer-wanna-be types, here is a blueprint showing a rocker bearing on the right. This is from the CDOT Web site.
CDOT bridge expert Jeff Anderson said the Fillmore Street bridge was built in 1961 and widened in 1971 and was known as bridge No. I-17-P. It was state-owned until 2007 when the city took ownership in a swap for Powers Boulevard.
While it was CDOT property, it was inspected every two years — like every bridge in the state, Anderson said. In it’s last state inspection on Nov. 29, 2006, the bridge was given an 83 sufficiency rating on a scale of 0-100. The deck rated a 6. The superstructure a 7 on a 0-10 scale.
“That structure was still in good shape,” Anderson said, despite the tilting rocker bearings. Bridges must fall to a 50 sufficiency rating and be structurally deficient or functionally obsolete before they are replaced.
Anderson attributed the tilting rockers to natural movement in the bridge. He said it shifted east, flush against the abutment. And pier 3 moved west during a flood years ago.
Here’s a look at the east abutment. There is no gap. In fact, the railing above are smashed together.
Want to see what happens when rocker bearings fail?
Here’s a photo from July 2005 when a rocker bearing supporting a ramp on Interstate 787 in Albany, N.Y., failed.
The following is an excerpt from the August 3, 2005 edition of the Albany Times Union www.timesunion.com).
“A routine bridge inspection nearly two years ago found serious problems with the bearings supporting a section of elevated highway that ruptured and dropped 2 feet last week.
Yet, state transportation officials said they made no plans to fix the problems with the Empire State Plaza ramp before the next planned inspection this fall.
The overall rating on the 24-section ramp that links Interstate 787 northbound with the plaza was set at 5, or generally “good,” on a scale of 1 to 7 in the November 2003 inspection report. A set of bearings atop the concrete pier where the break occurred, however, received a rating of just 2.
“One of DOT’s top engineers said it’s now clear that the poorly rated rocker bearings, steel supports designed to accommodate weather-related expansions and contractions of bridge sections, could have been a factor.
“There were some low-rated bearing elements that may have had something to do with this,” said George Christian, the chief structural engineer for the state Department of Transportation.
“The set of poorly rated bearings was on the section of the ramp that remained atop the pier, sliding toward the section that tumbled from its bearings and nearly fell off. The group of bearings was rated so poorly because they were tipped at an unusually extreme angle, Christian said.
“It was tilted, definitely, more than we would have expected it to be tilted for the conditions at the time of the inspection,” he said.”
Here’s the full text of my Side Streets column that appeared in the June 28, 2009, Gazette:
Jordan Strub was riding his bicycle on the Pikes Peak Greenway trail when he looked up at the bridge carrying Fillmore Street high over the trail and Monument Creek.
Between the horizontal steel girders of the bridge and the vertical concrete piers that rise from the creek bed is a series of stubby, rectangular steel supports – sort of like big shoe boxes – rounded on top and bottom.
Strub noticed that many of the supports are no longer standing straight up and down. In fact, several are tilted at alarming angles.
He wondered if it was an optical illusion because of the slanting bridge, which is lower on the east and rises to meet the west abutment.
He wondered if the bridge, built in 1961 and widened in 1971, had been moving.
He wondered if the bridge was safe.
“I wondered ‘does anyone else ever notice things like this?’ ” said Strub.
Turns out, they do. A number of people besides Strub have seen the twisting, tilting rockers and contacted the city over the years.
But Strub had trouble reaching city engineers, so he contacted Side Streets – or, in this case, Side Bridges – and we got answers.
“The bridge is stable and fine,” said Dan Krueger, a senior civil engineer in Colorado Springs’ engineering department.
He explained that the tipping steel shoeboxes are called rocker bearings or panels. They were designed to rotate to compensate for movement in the bridge.
In this case, Krueger said, the bridge slid east over the years and pier 3 shifted west in a flood years ago, causing the rockers to twist and tilt.
Rockers were common on bridges of the era, although they were abandoned by engineers decades ago in favor of sliding teflon-coated steel plates and thick slabs of neoprene.
Until 2007, the bridge was owned, inspected regularly and maintained by the Colorado Department of Transportation. It noted the rocking rockers as early as 1998, said Jeff Anderson, who manages the CDOT’s bridge inspection program.
“They look funny when they start to tilt,” he said.
Funny? Scary might be a better word.
Anderson said CDOT experts measured the rockers on pier 3 at a 10-degree slant. Pier 2 rockers tilt just 5 degrees. Rockers must reach 15 degrees before CDOT recommends taking action.
“It’s safe,” Anderson said.
So why not pull them out and straighten them up?
“You have to jack up the bridge and reset the rockers to vertical,” Anderson said. “It’s not really very easy.”
At one time, CDOT hoped to rebuild the Fillmore and Interstate 25 interchange and replace the bridge. But the money ran out so it sits.
Despite CDOT’s assurance the rockers have not moved in years, city experts do a visual check every 90 days, and survey crews verify its stability every six months.
“We’re just keeping an eye on it,” Krueger said. “We will monitor it indefinitely.”