These buildings are both in Chicago, Illinois, USA. Khan’s pioneering idea of using tubular design meant the use of exterior perimeters (consisted of closely located exterior columns or braced frames or shear walls) joined at their edges to form a tube in a building structure.
The tubes are used as a lateral system to resist wind forces and seismic forces through cantilevering from the foundation below. The tubular systems are much better than other framing systems since the tubular system’s lateral resistance and stability are much stronger and there is a decrease in construction materials used since there is little need to include large support columns at the interior of buildings. The tubular system’s strength made it possible to build higher rise buildings, revolutionizing construction of skyscrapers. More interior space is also created from tubular systems, since there is no need for space for core walls in centers of the structure. If your project ever required you to construct and design skyscrapers, this is a very efficient method of doing so.
There are different types of tubular systems. One type is the framed tube. Closely spaced exterior columns formed the perimeter of the structure in the shape of a tube. More interior space is created since only a few interior columns were needed and there is no need for bracing and shear walls for lateral resistance.
Another type is the trussed tube. Cross bracings are constructed on the exterior of the tube for lateral resistance. Not only are the columns bundled closely at the exterior for lateral stability, these bracings provide extra stability. The John Hancock Center has a trussed tube structural system. It only needed 145kg of steel per square meter, which is 61 kg of steel per square meter less than that of the Empire State Building.
We should always carry an open mind and explore opportunities that are quite different than original and traditional ideas. Khans’ tubular structures made designing and constructing skyscrapers much safer and efficient. If Khan never thought of tubular structure, it will be a world filled with rectangular buildings with high rises up to 20 stories high.