The John Hancock Center in Chicago, Illinois is an amazing structuralengineering achievement.The leadengineer on the project, Fazlur Kahn, developed a system of redistributing thevertical and horizontal loads by using exterior cross bracing (Figure1).He also designed the tower to taper(the floor area gets smaller as the building gets taller) which reduces the horizontal(wind) loading on the building (Figure 2). In addition, Chicago is in a low seismic zone, so the major lateral forces actingon the building would be wind. With these reductions in load, Kahn was able to achieve smaller beam andgirder sizes (approximately 30 psf).

Figure 2: Taper of JohnHancock Center

Insurance products are issued by: John Hancock Life Insurance Company (U.S.A.), Boston, MA 02116 (not licensed in New York) and John Hancock Life Insurance Company of New York, Valhalla, NY 10595. Vitality is the provider of the John Hancock Vitality Program in connection with policies issued by John Hancock. The John Hancock Center is a 100-story, 1,128-foot (343.7 m) supertall skyscraper at 875 North Michigan Avenue, Chicago, Illinois, United States.It was constructed under the supervision of Skidmore, Owings and Merrill, with chief designer Bruce Graham and structural engineer Fazlur Khan. When the building topped out on May 6, 1968, it was the second tallest building in the world and the.

John Hancock Center
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Vital Statistics:
Location: Chicago, Illinois, USA
Completion Date: 1969
Height: 1,127 feet
Stories: 100
Materials: Steel
Facing Materials: Aluminum, glass
Engineer(s): Skidmore, Owings & Merrill

Today, the John Hancock Center in Chicago, Illinois, is affectionately known as 'Big John,' but it was not always this way. Located on North Michigan Avenue along Chicago's 'Magnificent Mile,' the skyscraper was controversial from the start for its enormous bulk and dark metal exterior. Eventually, it was celebrated for its very brashness, and today it remains one of Chicago's best-loved icons.

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Currently, the John Hancock Center is the twelfth tallest building in the world. But to keep such a tall building standing in the 'Windy City,' engineers had to make the enormous structure super stiff. How did they do it? The John Hancock Center is actually a super-tall steel tube. Steel columns and beams are concentrated in the skyscraper's perimeter, and five enormous diagonal braces on the exterior walls of the skyscraper give it extra strength in the wind. The skyscraper also rises from 40,000 square feet at the base to 18,000 square feet at the summit. This tapered design provides additional structural stability against wind forces.

In order to reach the whopping height of 1,127, engineers knew that the enormous 384-million-pound tower needed caissons to prevent it from sinking into the soft ground. Today, the John Hancock Center rests on several caissons that extend down to bedrock. One of the caissons actually reaches 191 feet below the ground -- the deepest ever sunk in Chicago!

Here's how this skyscraper stacks up against the biggest skyscrapers in the world.
(height, in feet)

John Hancock Center 1,127'

Fast Facts:

• The diagonals completely block the view from two windows on each floor. Ironically, a rental agent has transformed these 'blocked' windows into something of a status symbol -- it actually costs more money to rent from these rooms!
• In 1997, the John Hancock Center was remodeled, and half of the 94th floor's southern windows were replaced with screens. Tourists can visit the 'Skywalk,' as it is called, and breathe the outside air and hear the noise of the city below.
• Offices occupy the lower floors of the 100-story skyscraper, and apartments are located on the upper floors of the building. Additional facilities include restaurants, health clubs, a swimming pool, and even an ice-skating rink.