Charter Bank, S. Africa. Example of tall building with a core tree structure: floors are suspended from cantilevered arms in groups of ten floors.
Lake Shore Apartments (steel) Stanhope Building (reinforced concrete) Rigid frame structures
A rigid or semi-rigid frame will deform under lateral loads in two ways: a) cantilever bending and b) shear sway distortion The combination of these represents the actual behavior of the frame structure. Stiffening the frame with x-bracing, for example, will cause more cantilever bending and less shear sway
Core and frame systems provide adequate stiffness up to 30-40 stories. Generally cores are at the center of the building, both for practical reasons (daylight) and to resist shear forces more effectively. If not centered, they are usually symmetrically located. Core and frame structures
Examples of tall buildings with cores in various positions. From left to right: Knights of Columbus Building (core at four corners), Inland Steel (core on one side), PSFS (core on one side), and AT&T (central core)
First Wisconsin Center Skidmore Owings & Merrill Milwaukee, Wisconsin 1974 An example of a steel frame with a belt truss and outrigger system at the 15th and 41st floors, and a transfer truss at the 3rd level. Note that the outrigger trusses are in the direction of the wind only indicating that wind resistance in the longi- tudinal direction is provided only by the stiffness of the frame. Diagrams illustrate the effect of belt truss and outriggers in stiffening a core-frame structure. On the right, the bending moment decreases in response to increasing stiffness provided by the belt trusses.
The research on tall buildings at IIT (Illinois Institute of Technology) under Mies van der Rohe and Fazlur Khan of SOM led to new concepts on how tall buildings might efficiently resist lateral forces. Myron Goldsmith’s thesis project proposes a super structural frame, detached from the envelope, and capable of resisting all the lateral forces at the perimeter of the building where it can do so more effectively. Myron Goldsmith Superframe 80+ story high rise
The Chestnut-Dewitt apartment building (Chicago, 1961-65) and the Brunswick Building (Chicago, 1962-66) were the starting points for Fazlur Khan and SOM’s application of the concept of a framed tube structure for high rise buildings. Chestnut-Dewitt Apartment Building Brunswick Building framed tube tube in tube
One Shell Plaza Skidmore Owings & Merrill Houston, Texas 1971 52 story office block “tube in tube” structural type. All lightweight concrete. Matt foundation.
Alcoa Building (Truss frame) Skidmore Owings & Merrill San Francisco, CA ca 1965
Fazlur Khan’s structural systems classification Type 1 Shear Frames: semi-rigid and rigid Type 2 Interacting Systems: frame with shear truss, frame with shear belt & outrigger trusses Type 3 Partial Tubular Systems: end channel frame with interior shear trusses Type 4 Tubular Systems: exterior framed tube, bundled frame tube, exterior diagonalized tube
“ There is more fun than anything else in doing a more elegant solution for an ordinary 75-story building. We have a long way to go to make the skyscraper what it really can be, and it doesn’t have to be super-tall to do this. There are ways to open up space, to make it more economical and to face the problems of fire and transportation and pedestrian joy at the bottom. These are much more interesting problems.” William LeMessurier Engineering News Record November 3, 1983