Completion 16: Grand Plaza
Cost: $140 million

The 1.7 million-sq.-ft. Grand Plaza apartment in Chicago's River North neighborhood has two edifices, the 56-story East Tower and the 37-story West Tower.

Ensuring the lateral stability of the East Tower was a major concern. Because drift from Lake Michigan's unrelenting winds could cause problems such as shattered windows, stiffening measures were employed to reinforce the tower.

Two 12-in.-thick outrigger walls on each floor from level 10 through 37 connect the concrete elevator core to the concrete perimeter walls. They stretch from the southwest to the northeast axis. One outrigger wall reaches from the southwest corner of the perimeter to the southwest corner of the core, and the other from the northeast corner of the core to the northeast corner of the perimeter.

The design helps to maximize the resistance to overturning.

The East Tower shares a nine-story base - sometimes called a podium or pedestal - with the West Tower. Because the podium holds parking spaces and drive aisles, the outrigger walls could not be used as stiffening devices there.

As a result, 18-ft.-long, 3-ft.-wide, 5-ft.-high outrigger beams span from the core walls to the perimeter walls for further stiffening. The concrete beams, two per level, are located in the floor slabs of the second, third and ninth floors. The substantial floor-to-floor height - 18 ft. in the first and second levels - afforded the space for the beams.

Takes Up City Block

Grand Plaza is huge. It fills a city block, bordered by Ohio, State and Dearborn streets and Grand Avenue, and the development holds 15 million lbs. of rebar, about 160,000 cu. yds. of concrete and 19 elevators.

Work was phased to reflect the major segments of the structure.

The 1,000-space parking garage on floors three through eight was finished first. The 100,000-sq.-ft. retail space on floors one and two was completed next.
Work on the 764 apartments was completed last.

Grand Plaza is a city within a city. Amenities include an outdoor running track, swimming pool, putting greens, athletic facility, cyber cafe, library and meeting room with kitchen.

Fifteen transfer beams were installed below grade to parcel pressure from one column line to multiple caissons.

Above grade, 13 floors have transfer beams; seven are in the East Tower, the taller of the two buildings.

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