The 2,000-foot, corkscrew-designed Chicago Spire may well be one of the most impressive engineering feats of 2007. Here’s why.

Contractors broke ground on the Chicago Spire project in June. Situated on a 2.2-acre site where the Chicago River meets Lake Michigan, the Chicago Spire will build on the city’s significant architectural legacy.

Among its many engineering achievements, the Chicago Spire has a base-to-height ratio approaching one to 10, making it the most slender super-tall building in the world, according to Shelbourne Development Group, Inc.

When it is completed in 2011, it will not only be North America’s tallest building — surpassing Chicago’s own Sears Tower (1,450 ft. tall) and New York City’s forthcoming Freedom Tower (planned to be 1,776 ft. tall) — it will also be the tallest residential building in the world, standing at 2,000 ft. (610 m). Further, the current design will surpass the height of the CN Tower in Toronto to become North America’s tallest freestanding structure and will also shatter the record for the longest continual elevator lift by 500 ft.

Some local people refer to the structure as Chicago’s “drill bit.” In various media coverage, the building has been compared not only to a drill bit, but also a blade of grass, a tall twisting tree and a lighthouse, according to ChicagoArchitecture.info. Moreover, as Architecture Magazine has pointed out, “many critics have noted [the dome-like roof] gives the entire tower the unfortunate form of a sex toy.”

Computer rendering of the Chicago Spire. This is the current design as of Sept. 26, 2007.
Credit: Santiago Calatrava – Shelbourne Development Group, Inc.

It will also include a relatively unique design feature: a twisting exterior designed to deflect wind. The seven-sided corkscrew design will reduce wind gusts at street level by directing most of the wind upward along the channels.

In rectangular buildings, a fluid wind flow puts pressure on the windward face of the building, while as air moves around it, a suction is applied to the leeward face. This often causes a sway in tall buildings which can be counteracted, at least partially, by stiffening the structure or by using a dynamic wind damper, according to the Mario Salvadori book Why Buildings Stand Up.

Although the curved design — which is similar to that of Sweden’s Turning Torso — will not completely negate wind forces, a tapering concrete core and about a dozen shear walls emanating from it are installed to counteract the wind forces.

Each of the building’s floors is anchored to a central column but offset. Each floor rotates on average 2.44 degrees from the one below, with a total rotation of 360 degrees as it reaches its 2,000 ft. height. The result is, in fact, very similar to a drill bit.

The building is designed to be made primarily out of concrete, and the spire rests on 34 caissons that are being drilled 110 ft. into the bedrock.

In addition, the Chicago Spire will incorporate world-class sustainable engineering practices to earn “gold” certification from the United States Green Building Council upon completion. Green touches include intelligent building and management systems, waste storage and recycling management, a cooling system that draws water from the Chicago River, cisterns for collecting rainwater for landscaping, monitored outdoor air delivery and ornithologically sensitive glass to prevent migratory-bird collisions.

According to a recent announcement from Popular Science, when the Chicago Spire is completed, residents near of its 150 floors will be able to see the curvature of the planet.

Imagine living with that window view!