Launch Slideshow

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Building a 100-year bridge

Building a 100-year bridge

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    Rebuilding Upper and Lower Wacker Drive in Chicago, workers place high-performance concrete on a 2,800-square-foot upper deck placement. The white plastic ducts house post-tensioning cables. Specifications call for a 100-year service life. Photos: Joe Nasvik

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    A worker sets up the form superstructure.

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    A worker puts the finishing touches on a beam form. Notice the close truss spacing for the deck spanning a traffic lane below.

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    Testing and quality control are seen as vital to the project's success. Flood Testing Laboratories represented McHugh Construction, making sure ready-mix trucks met specifications before unloading.

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    The top 2 inches of the deck is latex-modified concrete to provide an impermeable surface that resists chloride. This layer is intended to be sacrificial and will be replaced as needed.

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    The high-performance concrete used on this project included silica fume. Because slight amounts of water loss in silica-fume concrete results in cracking, curing blankets were placed and saturated shortly after the concrete was placed.

By Joe Nasvik

PROJECT PARTICIPANTS:

OWNER: CHICAGO DOT
DOT FUNDING: Federal Highway Administration and Illinois DOT
Architect: Site Design Group, Chicago
ENGINEER OF RECORD: ALFRED BENESCH, CHICAGO
GENERAL CONTRACTOR: James McHugh Construction, Chicago
READY-MIX PRODUCER: Ozinga Ready-Mix Concrete, Chicago
POST-TENSION REINFORCEMENT SUPPLIER: Dywidag Systems International, Bolingbrook, Ill.
LATEX-MODIFIED CONCRETE CONTRACTOR: Henry Frerk, Chicago
TESTING: FLOOD TESTING LABORATORIES, CHICAGO

Running along the Chicago River as it curves south toward St. Louis, Chicago's dual-level Wacker Drive is used by 300,000 vehicles and pedestrians every day. The top level is for local traffic; the bottom level for through-traffic and trucks servicing buildings along the street. Originally built in 1926, the east-west portion was demolished and rebuilt in 2002 and 2003. Many of that project's specifications carried over to reconstruction of the north-south portion, which began in the fall of 2010 and continues today. These include:

  • Considered a bridge deck, Upper Wacker Drive must be designed and built for a minimum 100-year service life and resist chemical assault from deicers.
  • The deck should have no cracks during its service life.
  • Pedestrian access to all building entrances must continue throughout construction, including demolition, even though the deck extends to the building walls on both sides.
  • The vertical clearance for Lower Wacker Drive must increase from 12 feet 6 inches to 13 feet 9 inches to allow for truck access.
  • Brett Szabo, senior project manager for McHugh Construction of Chicago, says there were additional challenges:

  • Although most of the east-west reconstruction had buildings on one side and the Chicago River on the other, the north-south portion has buildings on both sides, including the Opera House, Mercantile Exchange, and the Willis (formerly Sears) Tower — 18 skyscrapers along the project's entire length.
  • To maintain access to all building loading docks and underground parking, traffic on the lower level continue during construction; thus, upper deck forming operations must proceed with live traffic beneath.
  • The concrete superstructure for the upper deck is built first, at 13 inches thick, then topped with 2 inches of latex-modified concrete to get the final profile and elevation.
  • Funding for the $54 million project is shared between the Federal Highway Administration (FHWA), the Illinois DOT (IDOT ), and the Chicago DOT (CDOT).

    A total of 15 segments — separate 200 x140-foot concrete placements — are planned to complete the construction in mid-2012. As the project progresses, each segment is completed and turned over for public use.

    The overall length is 2,900 feet over seven intersections. This construction used 55,000 cubic yards of high-performance concrete , 2½ million feet of post-tensioning (PT) strand, and almost 7 million pounds of epoxy-coated reinforcing steel bars (all rebar on the project is epoxy-coated).

    Historical Wacker Drive

    In 1909, Daniel Burnham and Edward Bennett produced a long-range plan for the development of the City of Chicago that included Wacker Drive: a two-level street alongside the Chicago River circling two-thirds of the downtown Loop. Construction on the east-west portion of the street didn't begin until 1924; the north-south section wasn't built until the 1950s.

    For the initial two-year project completed in 1926, workers installed 598 caissons to a depth of 95 feet below the surface to support the 5,700-foot length of the upper deck. More than 1 million pounds of reinforcing steel and 116,000 cubic yards of concrete were used for the columns and deck with a thickness as great as 3 feet.