The world's tallest concrete building makes its home at 311 South Wacker Drive, Chicago. The 70-story tower rises 967 feet high and just so happens to be right across the street from the Sears Tower, the world's tallest steel-frame building. The view from the street in front of the tower allows observers to notice the flame-finished rose granite below the Gothic-styled glass section at the top and the polished banding weaving through the tower's strong vertical planes. The building's floor plan - six-sided at ground level - changes as it rises.
The building core rests on an 8-foot-thick concrete mat that is supported by 92-foot-long cassions socketed into bedrock. The tower columns are supported by similar cassions. The building has a shear wall and interactive frame structural system to resist lateral loads. Top down construction was chosen as the construction method because it allowed work on the tower to begin at the same time that construction was going on for the three below-grade parking levels. All the tower concrete was pumped, although conveyors deposited the mix for the 8,000-yard continuous pour of the mat foundation. To complete the building, the ready mix supplier delivered 110,000 cubic yards of concrete. As many as 10 different concrete mixes were used, most of them high strength. Superplasticizing admixtures were used throughout the structure to improve workability and placeability.