100-story John Hancock Center in Chicago: a case study of the design process
Autor(en): Kahn, Fazlur R.
Objekttyp: Article
Zeitschrift: IABSE journal = Journal AIPC = IVBH Journal
Band (Jahr): 6 (1982)
Heft J-16: 100-story John Hancock Center in Chicago: a case study of the design process
PDF erstellt am: 30.09.2021
Persistenter Link: http://doi.org/10.5169/seals-26292
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http://www.e-periodica.ch IABSE PERIODICA 3/1982 IABSE JOURNAL J-16/82 27
100-Story John Hancock Center in Chicago — A Case Study of the Design Process
Le Centre John Hancock, 100 etages, ä Chicago — Un cas pratique du Processus de projet
Das John Hancock Center mit 100 Stockwerken in Chicago Eine Fallstudie über den Entwurfsprozess
Fazlur R. KHAN Born in Dacca, March 27, 1982 Bangladesh, Dr. Khan (1930- t 1982) received his Partner Former of Bachelor of Engineering Skidmore, Owings & Merrill degree from the Chicago, IL, USA University of Dacca. He studied at the University of Illinois, Cham- paign-Urbana, where he earned Master and Doctor of Structural Engineering degrees. In 1955, Dr. Khan joined the firm of Skidmore, Owings & Merrill and was made a general partner in Charge of structural engineering in 1970.
SUMMARY This paper is a continuation of the discussion about the interaction between architect and structural engineer which was initiated by two contributions in the last Journal J-15/82. The author, late Dr. Fazlur R. Khan, describes his positive experience with an early and close collaboration between architect and engineer during the design process and its fruitful influences on the architectural and structural characteristics of a high-rise building.
RESUME Cet article fait suite ä la discussion sur la collaboration entre l'architecte et l'ingenieur civil, qui a ete introduite par deux contributions dans le dernier Journal J-15/82. L'auteur, feu Dr. Fazlur R. Khan, decrit ses experiences positives d'une collaboration etroite et continue entre l'architecte et l'ingenieur des le debut du projet. II souligne les influences positives de cette collaboration sur les caracteristiques architecturales et structurales d'un bätiment de 100 etages.
ZUSAMMENFASSUNG Dieser Beitrag ist als Fortsetzung der Diskussion über die Zusammenarbeit zwischen Architekt und Ingenieur gedacht, die in der letzten Ausgabe des Journals J-15/82 eingeleitet wurde. Der Verfasser, der verstorbene Dr. Fazlur R. Khan, schildert in diesem Artikel seine positiven Erfahrungen mit einer frühzeitigen und intensiven Zusammenarbeit zwischen Architekt und Ingenieur beim Entwurf eines 100stöckigen Hochhauses. 28 IABSE JOURNAL J-16/82 IABSE PERIODICA 3/1982
1. INTRODUCTION
The design process of any major building, in order to produce a successful result, must be multi-disciplinary in nature. The idea of the architect drawing up a nice sketch representing his Vision of a building may have some possible validity for a minor structure such as a residential building or for a small commercial project, but would result in an utter architectural disaster for any major building requiring complex interaction between various planning, environmental, structural and functional disciplines.-The 100 story John Hancock Center in Chicago (Figure 1) is certainly a good example of such a complex multi-use project. In looking back fifteen years one can now objectively discuss and elab- orate on the various aspects and nuances of the design process of this major building which in fact could not be done as openly at the time of the actual designing of the building.
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If the commercial, parking, office and apartment could be all put together in one building, then the large percentage of the site could be left open for ground level use by the public. The impact of the project at the ground level would be much less overpowering and in fact, would contribute to more human interaction so lacking in many of the recent projects. In spite of initial concern about large structural diagonal members crossing through Windows in the office, commercial and apartment, the design team was finally convinced that the structural-architectural interaction could be taken to füll advantage by creating an architectural expression of strength and elegance evoking the spirit of the rational Chicago School of Architecture. 2. BUILDING SHAPE An efficient floor plan of a commercial or office building should be large, in the order of 25,000 square feet or more, whereas an efficient apartment building floor plan generally should be much smaller. More significantly, an office floor plan needs a lease-span of more than forty feet which means the width of the building can be more than 160 feet. An apartment floor plan on the other hand, cannot effectively use a large distance between the core and exterior wall (lease-span) simply because every apartment room is expected to have an exterior view and direct open exterior Ventilation. Because of this reason, if there were no structural constraints, the Volumetrie form of the building would have been a wide office building that narrows down at the upper floors to a width acceptable for an apartment building. This means that while an office building could be wider than 150 feet at the base, an apartment building connot be planned with that width, but can have a realistic maximum width of perhaps not more than 125 feet. Schematically this would create an elevation showing stepping off where the apartment floors begin at the upper floors. But the structural system of the trussed tube structure requires a continuity of the four exterior walls throughout the height of the building (Figure 3). This structural requirement initiated a number of studies of the building slowly tapering upwards so that at the first apartment floor level the building width is reduced to an acceptable dimension for efficient apartment layout. Dozens of such shapes were studied with the help of a Computer program which defined the exterior geometry in each case and computed the individual floor areas as well as the total floor area in the building to match the program requirements. The final shape selected had the base dimension of 160 feet by 260 feet tapering upwards to 100 feet by 160 feet at the top floor level. This double tapered truncated pyramid shape was a Joint structural- architectural desicison satisfying both structural efficiency as well as architectural aesthetics of the form. The structural-architectural interaction in devising the form and shape of the building is another example of the close working relationship between the architect and engineer as a team rather than a preconceived design by an architect where the engineer has to simply solve the problem given to him. In the beginning of the project the most important consideration for accepting this diagonally braced truss tube was its efficiency and economy. It had to meet a budget originally established to reflect the competitive traditional construction Systems for the traditional two-tower Solution. Fortunately on the basis of previous experience gained with Mike Sasaki's thesis, the author could realis- tically commit to a maximum of 30 pounds of structural steel per square foot for this 100 story building. Normally, a 30 pound per square foot budget would be set for a traditional frame building of only 30 to 40 stories. 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