Council on Tall Buildings and Urban Habitat

Grid Up to the Sky
Milena Todorovic and Etienne Serveau

Honorable Mention
Site: Chicago, USA
University of Illinois at Urbana Champaign
Competition: CTBUH 2nd Annual Student Competition - 2012 Reimagining Tall

Building overall
Building restaurant
Sky gardens
Hotel pool
Concept study
Building section
Groundfloor plan
Building diagrams

Grid Up to the Sky
The main idea behind this skyscraper was to create an aesthetically dominating form that will become a recognizable symbol of Chicago. The concept came from the city itself and its rich architecture legacy. The tower is located in a Streeterville (North Cityfront Plaza) neighborhood that includes some of Chicago’s tallest skyscrapers and famous historical and cultural venues. It was a challenge to represent Chicago’s historical context through contemporary materials and principles. Rigid street grid, steel- frame construction and views to the Michigan Lake are prime conceptual elements that shaped this tower. The diagrid structure emphasizes the three-dimensionality of the street grid and variable movement of the Chicago River.

The tower was deliberately challenged with some less sustainable but more practically real problems. Issues like accommodating wind power, ensure quality views from the tower and activating the river walk inspire the tower's elegant and expressive form. The diagrid structure contributed to the building’s harmonious relationship with the ground and created a new public space along the river walk. It also gave free column exterior and aesthetically dominate and expressive form.
The tower shape is composed from fifty 30’x30’ floors that are mutually rotated by 2 degree. Experiments showed that by increasing the number of polygon sides the drag coefficient of the tower decreases and eventually approach to that of a circular tower. The results demonstrate a substantial reduction in the wind drag while the radius is increased. The wind drags are reduced when the tower is twisted properly.

Tower program is constituted of retail/ commercial base, below grade parking and services, hotel and hotel amenities, residential condominiums and private amenities.

There are two possible structural systems for the Tower:  Fiber concrete ultra-high performance (BFUHP, BCV, Ductal) with Reinforced concrete construction method and Composite steel construction method. First has high mechanical resistance, tightness of material, reduction of material quantity, is sustainable against pollution, freezing and aging with a self protection. Second is a low cost and easy to dissemble for future repairs. This tower is example how the flexible attitude toward principles of construction can reduce need for complex sustainable systems.