9. Standard Bank of Johannesburg, S. Africa 1970 Example of tall building with a core tree structure: floors are suspended from cantilevered arms in groups of ten floors.
10. Lake Shore Apartments (steel) Stanhope Building (reinforced concrete) Rigid frame structures
11. 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
12. 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
13. 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 Jardin House (central core)
14. Trussed frame structures Alcoa Building, San Francisco Int’l Financial Ctr, Shenyang Hotel, Barcelona Hearst Building, NYC
15. 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.
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17. 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
18. 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
19. One Shell Plaza Skidmore Owings & Merrill Houston, Texas 1971 52 story office block “tube in tube” structural type. All lightweight concrete. Matt foundation.
40. Sears Tower (Sears & Roebuck Co.) Skidmore Owings & Merrill Chicago, IL 1974 109 stories. Bundled tube structural concept. Height to width ratio 6.4.
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42. 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
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49. “ 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
50. Citicorp Center Hugh Stubbins / Wm. Lemessurier New York City 1977
51. The base of the CitiCorp Center Tower has only a central concrete lift core and four mega-columns coming down to the ground. This creates an open through-block site that has been filled with public space, retail shops and a reconstructed church (St. Peter’s Lutheran) seen in the left foreground of the photo.
52. Engineer William LeMessurier designed the structure of the CitiCorp Tower as a braced perimeter frame with long diagonals on the facades in a chevron pattern (eight floors high) collecting and transferring the floor loads to the center of each face where the mega-columns below are located. These façade trusses collect about 1/2 of the gravity loads and resist the entire wind loads on the building. At the base of the tower, where the chevrons end, a diagonally braced transfer floor is required to transfer the wind shear (resisted by the chevron trusses) to the central concrete core.
53. In the typical floor framing beams run in one direction, girders in the other. Diagonals at the corners are required for stiffening due to the unique chevron vertical structure. Note the doubling of columns at the midpoints of the sides to carry the concentrated vertical loading transferred by the chevrons. The core above the base is steel framed. Below it is reinforced concrete.
55. Bank of the Southwest Helmut Jahn and Wm LeMessurier Houston, Texas 1982 Comparison of types of building structures based on the bending rigidity index (BRI). See Ch.2 Tower and Office p.80
