Crews rebuilding the Chicago Skyway have had too much work to do to enjoy the views from the partly elevated thoroughfare.

The $250 million project began in 2001, but there's still a large amount of construction under way on the 8-mi.-long highway on the city's Southeast Side, said Kevin Fitzpatrick, vice president and construction manager for Chicago-based Alfred Benesch & Co., the construction manager.

The redo of the eastbound lanes has been completed, and the project is now focused on $100 million in active contracts on the westbound lanes and affiliated work. Chicago-based Walsh Construction Co., Chicago-based F.H. Paschen/SN Nielsen Inc. and Glendale Heights, Ill.-based Dunnet Bay Construction are the general contractors.

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Labor includes temporarily shoring and jacking the Skyway so that most of the piers supporting the approximately 3.5 mi. of elevated structure can be replaced. Along with the pier replacement, old bridge decks have to be removed and new ones installed. Structural steel members forming the high bridge that spans the Calumet River must be removed and replaced.

An entirely new interchange was installed at 92nd Street - an element completed in July partly in anticipation of increased traffic to the Solo Cup factory under construction on the site of the razed United States Steel Corp. South Works plant nearby. This included the construction of a retaining wall with caissons only 15 ft. from the Norfolk Southern railroad track.

New lanes were added to the 104th Street exit ramp and the 105th Street entrance ramp. An entrance ramp was added at 84th Street in case the existing one near the toll plaza at 87th Street is eliminated in the future to allow for the widening of the toll plaza.

The Skyway project is expected to be complete in November, just in time for Thanksgiving Day. Some clean-up work will likely continue into the early part of 2005.

Overhaul Needed

Tom Powers, chief bridge engineer and deputy commissioner for the Chicago Department of Transportation's Bureau of Bridges and Transit, said the Skyway is being upgraded because detailed inspections in the late 1990s revealed inadequacies.

The Skyway, which originally opened in 1958 as the Calumet Skyway, showed corrosion, warping or cracks in components, loads nearing design capacity, excessive maintenance costs and other problems. The project is intended to upgrade the Skyway for 50 years.

Other key project elements include the installation of 28 surveillance cameras, landscaping and the reduction of bridge structure.

About 1,700 lin. ft. of bridge deck was removed between 75th and 79th streets and about 3,000 lin. ft. at the 106th Street viaduct, Powers said. Fill placed below the structure will carry the roadway.

"We eliminated a mile of structure by placing retained earth fill and thereby reducing long-term maintenance costs," Powers added.

Keeping Traffic Going

The project's unique elements required smart planning.

For instance, the Skyway gradually inclines and reaches its apex on the high bridge, and some of the construction is taking place at an elevation of about 80 to 100 ft., Fitzpatrick said. Further adding to the complexity is that traffic has continued to flow.

About 90,000 vehicles navigate the four-lane thoroughfare every day.
A primary objective was to have the least impact on traffic while also finishing the work with reasonable promptness.

Closing two lanes over three phases was considered, but work could have dragged on for two additional years, Fitzpatrick said. Instead, officials elected to shut one lane over two phases.

A movable zipper wall - concrete barriers linked with pins at project start - was used and allowed three lanes of traffic to remain open.

In the morning when traffic headed downtown is heaviest, two westbound lanes and one eastbound lane are open. At noon, a specially equipped vehicle is driven through the zipper wall's full 15,000-ft. length to shift the wall so that two Indiana-bound lanes are open.

The switchover takes about 45 minutes to an hour and is repeated at 8:30 p.m. for the rush hour the following morning.

"That wall enabled the Skyway to handle the traffic," Fitzpatrick said. "You couldn't have done it with one lane in each direction because there is too much traffic."

The entire Skyway is occasionally shut for short periods for especially delicate activities.

Recently, there was a 15-minute closing at midnight so the thoroughfare could be jacked from its temporary shoring. Then, new bearings were inserted between the bottom of the roadway decks and the substructure.

Informing Motorists

The zipper wall and careful timing of work were initiatives that could relieve only a portion of the congestion.

An "extensive" outreach sought to keep the public informed, said Maria Castaneda, a CDOT media representative.

Pamphlets were handed to motorists to inform them of major activities that might tie up traffic. Electronic message boards suggested alternative routes when traffic backed up on the Skyway or even the Dan Ryan Expressway that the tollway feeds. Local aldermen were told about the project so they could keep their constituents abreast of activities.

Onsite personnel monitored traffic flow and passed information to radio stations that update traffic, including WBBM-AM and its "Shadow Traffic" report. Newspaper reporters from Illinois and Indiana were allowed access to key personnel so that the project could be explained.

"We also have an intensive traffic information system during the weekend" to help inform motorists going to events such as a Chicago Bears game or a downtown festival, Castaneda said.

Steeling the Project

Replacing structural steel members in the high bridge corridor was an important element, and more than 4.5 million lbs. of steel were installed.

About 50 floor beams that run perpendicular to the roadway and underneath the deck are being replaced under the current contract, as well as most of the associated steel stringers extending from the beams and parallel with the roadway.

This element feeds off work on previous contracts. Last year, floor beam sections were replaced under the eastbound lanes with a splicing plate, and the replacements this year extend from the splicing plate and under the westbound lanes. The steel was lifted with cranes on the bridge.

The floor beams attach to trusses on the bridge's sides, and some bottom chords needed replacement. Because the chords are under stress, temporary tension rods were placed to maintain the tautness.

"Then you're able to cut the bottom chord and replace it and slowly take the load off those tension rods and put stress back into the structural members," Fitzpatrick said.

Other materials played an important role in the project, too, because most of the 42 steel piers are being replaced, and each new one is formed with cast-in-place concrete reinforced with steel.

On top of the bridge, pneumatic hammers were used to break the existing decks, and the pieces were pulled back with loaders to a working platform. The existing decks had previously varied between 5.5 and 7 in. in thickness, but the replacements will be 8-in.-thick, high-performance concrete with a 2-in. latex overlay.

"In 10 to 20 years, we'll go in and mill off this latex, and the slab will still be in good shape," CDOT's Powers said. "It's denser and resistant to the infiltration of chlorides."