191 N. Wacker Drive, Chicago

Development Team
DEVELOPER: Hines/National Office Partners, Chicago
GENERAL CONTRACTOR: Clark Construction Group, Chicago
DESIGN ARCHITECT: Kohn Pedersen Fox Associates, New York
ARCHITECT OF RECORD: Kendall/Heaton Associates, Houston
STRUCTURAL ENGINEER: Thornton-Tomasetti Engineers, Chicago
MEP ENGINEER: Cosentini Associates, Chicago
STEEL FABRICATOR: SMI-Owen Steel Co., Columbia, S.C.
STEEL ERECTOR: Abate Irwin, Eighty-Four, Pa.
CONCRETE: James McHugh Construction Co., Chicago
CURTAIN WALL: Antamex International, Concord, Ontario, Canada
PLUMBING: Great Lakes Heating and Plumbing, Chicago
ELECTRICAL: F.E. Moran, Northbrook, Ill.

The 191 N. Wacker Drive building is a 40-story, 910,000-sq.-ft. office located in Chicago's West Loop. The $125 million structure features a glass exterior and lantern at its top.

The design takes into account the context of the surrounding area. For example, 191 N. Wacker Drive is clad in a unitized curtain wall system of aluminum mullions and blue-tinted glass - similar to the 333 W. Wacker building next door.

Because a portion of the rebuilt Wacker Drive clips a corner of the property, the City of Chicago asked for and effected an easement. Consequently, the design team had to build the office floors to the property line yet kept the base outside the easement.

The solution was to place seven concrete columns that lean into the property as they go down. This step-back was achieved with a corbel - a series of projections, each stepped progressively farther forward with height. The slope begins on the third floor and continues through the eighth.

Because the lean weakens the stability of the lateral system, the core walls are flanked with two concrete shear walls.

Building Has Steel Frames

The Chicago office of Houston-based Hines, the developer, wanted to keep the building height down to reduce costs.

Consequently, the floor-to-floor height is 13 ft. W-18 steel beams achieved the desired height economically.

A problem arose. The lateral span from the core to the perimeter is 48 ft., a distance that exceeds the 40-ft. maximum of the beams.

To close the 8-ft. gap, steel frames come into play. Those selected resemble two-branch steel trees. A 26-ft.-high column forms the "trunk" and two 8-ft.-long beams form the "branches."

The truck was positioned 40 ft. from the perimeter so that the 8-ft.-long branches close the distance to the core.

The logistics of the site presented problems. To the north lies the Chicago Transit Authority's Green Line elevated track, which limited the amount of staging room. On the east is a neighboring building, making only 9 ft. of space available. An alley on the south was required to stay open. And Wacker Drive, which itself was undergoing reconstruction, is on the west.

As a result, a tower crane sat inside the structure on a pad spanning two grade beams within the core. The rigidity of the structure supported the crane.

The jury commented, "This is a timeless, elegant and simple classic. The design is beautiful, and the team that built this must be very proud."

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