Instead of one tube, a building consists of several tubes tied together to resist the lateral forces. Such buildings have interior columns along the perimeters of the tubes when they fall within the building envelope. Notable examples include Willis Tower and One Magnificent Mile.
Willis Tower, completed in 1973, introduced the bundled tube structural design and was the world's tallest building until 1998
The bundle tube design was not only highly efficient in economic terms, but it was also "innovative in its potential for versatile formulation of architectural space. Efficient towers no longer had to be box-like; the tube-units could take on various shapes and could be bundled together in different sorts of groupings."[8] The bundled tube structure meant that "buildings no longer need be boxlike in appearance: they could become sculpture.