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Bridge along CTA’s Purple Line replaced in Evanston — in just 55 hours

A worker carts bundles bottled water back crew working installatian overpass bridge corner Chicago Ave. Greenleaf St. Friday June 8

A worker carts bundles of bottled water back to a crew working on the installation of an overpass bridge at the corner of Chicago Ave. and Greenleaf St. Friday, June 8, 2012, in Evanston. | John J. Kim~Sun-Times

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Updated: July 11, 2012 6:09AM

If you ride the Purple Line Monday morning, and glance out your train window as you pass Greenleaf Avenue in Evanston, rest assured you are not seeing things.

The bridge you crossed Friday afternoon — the crumbling 103-year-old span with rusty rebar poking out of its stained concrete — is indeed gone, replaced by a spanking new through-girder steel bridge designed to last a century.

Installing it, incredibly, was a long weekend’s work — scheduled to take 55½ hours, between the time the Purple Line shuts down at 8:30 p.m. Friday, until it reopens 4 a.m. Monday, if all goes according to plan.

Of course it took months of preparation to get the work done so fast, the first of three bridges to be replaced in June in Evanston, part of a $10.3 million Chicago Transit Authority project that will increase speeds on the Purple Line, notorious for having to slow in too many spots for aging track.

And if South Siders, whose Red Line is going to be out of service for five months for repairs next year, are tempted to cast an envious eye, if not voice outrage, over the speed of this project, remember that replacing a few bridges is nowhere near the scope of redoing track bed.

“The work on the Purple Line and the south Red Line are very different,” said CTA spokeswoman Molly Sullivan. “The south Red Line work involves replacing the entire railroad, in its entirety, from the ground up along a 10-mile stretch. The roll-ins are . . . not comparable to the Red Line at all.”

“Roll-in” is the operative word. Up until a few decades ago, in order not to shut down, the CTA would have built a new bridge next to the old, then shifted the track over.

But thanks to advances in the technology of moving very heavy objects, the bridges can be built nearby and rolled into place.

The three bridges, each weighing nearly 400,000 pounds, were fabricated at Prospect Steel in Little Rock, Ark., of U.S. steel, then disassembled and shipped up in pieces.

Since April, Evanstonians have watched the steel bridges put together at three locations: the parking lot of the Jewel at Chicago and Greenleaf; the south lane of Grove Avenue, and at Dempster.

Jewel was surprisingly open to the idea of the CTA building a bridge in its parking lot.

“They were very gracious — they gave up a lot of parking space,” said Jim Harper, chief engineer at the CTA.

Of course they get something back — since the tracks border their parking lot, the new 200-foot retaining wall the CTA put in as part of the project replaced a decaying wall.

The weekend process was a delight for fans of heavy equipment.

“I just think this is so cool,” said Chuck Cole, an Evanston resident who watched until midnight Friday and returned Saturday. “It’s just fantastic to me that someone can coordinate this stuff, so it all comes off like clockwork.”

First the bridge was demolished, then a 350-ton crane sets two pre-cast concrete abutment decks — what the bridge sits upon — atop 85-foot deep caissons, two flanking the track north of Greenleaf, and two south. The caissons were poured last fall, using heavy-duty, 6,000 PSI concrete, forming piles four feet wide and belled at the bottom to help distribute the load.

Then two bright red Goldhofer trailers — self-propelled platforms bristling with 360-degree rotating wheels — were slipped under the new bridge and jacked it up off its squat I-beam supports.

At 4:45 p.m. Saturday, it began to slowly crawl across the Jewel parking lot, watched by several dozen residents in the bright 90-degree sun as, over several hours, it was swung toward its goal, inch by inch.

The city of Evanston was so excited about the new viaducts, it showed a live feed of the bridge installation on its website.

“We’re remarkably happy,” said Eric Palmer, Evanston spokesman. The old bridges are “not exactly the most sightly things. They’re deteriorating. They pose a hazard to pedestrians. Big chunks of cement fall.”

The other two bridges, at Dempster and Grove, will be installed the weekend of June 23, if all goes according to plan.

After that, Palmer said, the city will try to get Metra to replace some of their aging viaducts, which parallel the CTA tracks.

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