The Fillmore Street bridge over Monument Creek is becoming famous. But as Charlie Sheen taught us, fame has its drawbacks.
In a June 2009 column, I introduced you to the bridge, which is 288 feet long and five lanes wide and sits just east of Interstate 25.
Of course, I wrote about it in my June 28, 2009, blog.
Since then, it’s fame has grown from coast to coast. It has been featured in discussions by engineers at Stanford University in California and at the Northeast Bridge Preservation Conference in Hartford, Conn.
The Fillmore Street bridge even has its own video on You Tube.
But all its buzz is not necessarily a good thing. Engineers are talking about it because of its rocker bearings.
Rocker bearings are stubby, steel supports — like big shoe boxes — rounded on top and bottom.
Several of the Fillmore bridge bearings are tilted at alarming angles.
The bearing are sandwiched between the top of 38-foot-tall concrete bridge piers and the hortizontal steel beams of the bridge.
Folks called me in 2009, scared the bridge might fall based on what they saw underneath as they traveled the Pikes Peak Greenway trail.
So I called Dan Krueger, a senior civil engineer in Colorado Springs’ engineering department.
Krueger told me when the bridge was built in 1961, rocker bearings were used to allow slight rotatation to compensate for movement in a bridge.
The Fillmore bridge slopes from west to east and flexes, like most bridges, from thermal forces each day. It expands in the sun and contracts as it cools, especially in summer.
He said the city took ownership of the bridge in 2007 from the Colorado Department of Transportation and had been inspecting it every three months. He said the bridge was stable and safe.
I took a few photos, posted them on my blog and went back to harassing homeowners associations.
Then I received an email in December from a structural and forensic engineer in New York. She wanted permission to use my photos in her research proposal to study bridge rocker bearings. The Fillmore bridge rocker bearings caught her attention.
She told me the Fillmore rocker bearings were the subject of discussion in engineering circles. I learned our little bridge was discussed at engineering conferences from California to Connecticut. (They even used my photos.)
I found references on the Web, even the You Tube video, and learned the city had put the bridge under intense scrutiny.
So I called Krueger back and learned that in 2009 the city hired Structure Inspection and Monitoring Inc., or SIM, of San Jose, Calif., to install sophisticated sensors to determine the stability of the bridge and learn why its bearings tilted.
The good news: experts say the bridge is safe.
“If the bridge was unsafe, we would close it,” Krueger said. “It’s open and we’re watching it.”
But he acknowledged the bridge is puzzling.
“The bridge does have some issues but it appears to be stablized,” Krueger said. “There are some head-scratcher things about the structure.”
Like why the rocker bearings tilted. And why the bridge seems to have slid against the east abutment.
Spencer Graves, president of SIM, said he’s studied a year’s worth of data and agrees with Krueger’s assessment.
“It seems to be quite safe,” Graves said. “It’s not dangerous. The city is taking responsible action. The prudent thing is to monitor.”
Graves believes a 38-foot-tall concrete pier which rises from Monument Creek moved in a flood sometime since the bridge was widened in 1971.
And, he said, he believes saturation of manmade hill at the west end caused it to slump, causing the bridge to shift.
His company installed an array of sensors and probes on the bridge and is conducting intense monitoring of the bridge to determine if it is moving.
Krueger said the question of movement is the key.
“We have to establish whether the bridge is moving or not,” he said. “That’s why the equipment has been installed. To answer that question.
“If it’s moving, then we need to get something in the hopper to fix it.”
He understands why people who see the bridge are worried.
“There are some odd things that are worthy of concern and watching and monitoring, which is what we’re doing.”
But he believes it is not moving more than any other bridge.
“It is anchored on the west abutment,” Krueger said. “And it rests against the east abutment only in summer. A gap opens in winter, which is good.”
It means the bridge is expanding and contracting as designed. Not moving freely and premanently lodged against the east end.
That flexing explains why the expansion joint at the east end was a chronic problem for street crews.
It constantly needed to be patched as the bridge moved back and forth.
Krueger said the new information has allowed the city to address the joint with a more weather-proof solution to minimize the constant cracking.
Below I’ve posted photos explaining some of the impressive technology employed by Graves’ SIMS group to monitor the bridge.
After a year of monitoring to establish a baseline of data, the city now will spend another year watching it to determine if it is acting up and in need of an expensive repair or even more expensive replacement.
It would cost upwards of $2 million to replace.
The problem is that the bridge scored an 85.6 sufficiency rating on its 2010 inspection. It needs to score a 50-80 rating to qualify for fedreal bridge rehabilitation funds. And it must score below 50 to qualify for federal bridge replacement funds.
So any work done now would be funded solely by Colorado Springs taxpayers. And nobody wants to buy a new bridge if they don’t have to.
Of course, no one wants the bridge to end up like Charlie Sheen, either.