JMB Realty Corporation

10 & 30 South Wacker

Chicago, IL

Known as “The Gateway to the Loop,” this building consists of twin 49-story office towers connected by a ten-story low-rise building. The low-rise building and the first ten floors of the south tower once served as the home of the Chicago Mercantile Exchange, one of the largest column-free trading facilities in the world at 40,000 square feet. Benesch provided structural engineering services for the building’s innovative design.

To achieve the desired amount of floor space in the office towers without infringing on the trading facilities required a unique structural framing system. This system permitted the top 38 stories of each tower to cantilever 32 feet over the low-rise building. The cantilevered segments (consisting of series of diaphragm walls) are 150 feet wide.

The towers are cast-in-place, conventionally reinforced concrete structures with the 10 South Wacker tower having the distinction of being Chicago’s first all-concrete skyscraper.

Project highlights

  • Unique framing system to allow cantilevered towers
  • Largest column-free trading facility in the world at the time of its construction
  • First all-concrete skyscraper in the City of Chicago