FAZLUR R. KHAN LECTURE 1 Life-Cycle and Sustainability of Civil Infrastructure Systems – Strauss, Frangopol & Bergmeister (Eds) © 2013 Taylor & Francis Group, London, ISBN 978-0-415-62126-7 Fazlur Khan’s legacy: Towers of the future M. Sarkisian Skidmore, Owings & Merrill LLP, San Francisco, USA ABSTRACT: Dr. Khan’s contributions to the design of tall buildings have had a profound impact on the pro- fession. Kahn had a unique understanding of forces, materials, behavior, as well as art, literature, and archi- tecture. Long before there was widespread focus on environmental issues, Kahn’s designs promoted structur- al efficiency and minimizing the use of materials resulting in the least carbon emission impact on the environment. Kahn was interested in the performance of structural systems over an expected life; recognizing a building’s life -cycle and issues of abnormal loading demands, he developed concepts to apply to severe wind environments as well as early concepts of seismic isolation of structures. These system ideas have led to the development of other concepts which have yielded buildings much taller than those considered by Kahn. His ideas have inspired others to expand the possibilities in tall building design, life-cycle engineering and the effects of the structures on the environment. However, the offer was subsequently withdrawn and he went on to become an Executive Engineer with 1 INTRODUCTION the Karachi Development Authority. Because he felt that his technical abilities where not fully uti- Inquisitive as a child, Fazlur Rahman Kahn was in- lized, Kahn returned to SOM in 1960 where he spent terested in form and how forms could be made. He the rest of his career developing arguably some of created objects with mud, clay and sand, and was in- the most important structural designs of the century. terested in mechanical objects, learning that some where fragile and could easily be broken if they did It is interesting that Kahn’s favorite poet was not have the required strength. He was passionate Rabindranath Tagore and that his favorite poem was about literature and poetry and had a special interest the “Tagore Song,” which begins with the Bengali in societies, particularly those related to his family’s lyric “This is your beginning and my end. The flow background and the people of Bangladesh. As a (of life) continues mixing both of us.” So much of young student Kahn was interested in studying phys- what is considered in recent developments of struc- ics but his father encouraged him to focus on apply- tural optimization, efficiency, and life-cycle consid- ing his mathematical skills to his practical and me- erations is based on flow—the flow of forces, mate- chanical interests. rial, and energy. The future of structures is to design for this flow and create structures that behave natu- Several of Kahn’s early works were focused on rally without damage when subjected to extreme the design of bridges. After graduating with a civil loading conditions. engineering degree from the University of Dhaka previously known and the University of Dacca, East Pakistan, he worked as an engineer for the Design 2 FOUR AGES OF THE SKYSCRAPER Division, Communications and Buildings Depart- ment of the Government of East Pakistan. After Renewal and opportunity followed the Great Chica- completing his graduate studies at the University of go Fire on October 9th, 1971, first through Chicago’s Illinois, he began his career at SOM, initially hired World’s Columbian Exposition schedule for com- to design highway and railroad bridges under the di- pletion in 1892 (four centuries after the discovery of rection of the U.S. Air Force Academy. In the late the Americas by Columbus) but finished in 1893 1950’s Kahn returned to his home country to be the with the development of new ideas from Daniel Director of the country’s Building Research Center. Burnham, William Holabird, Louis Sullivan, John 2 Wellborn Root and others. Following the exposi- modernism. Khan strongly opposed this approach to tion, the first skyscraper age as well as the era of the design and considered the designs to be whimsical First Chicago School emerged corresponding with rather than rational. Most importantly he considered the early use of structural steel and advances in the work to be a waste of precious natural resources. structural engineering. The age ushered in the idea of structural frames clad with exterior wall systems Khan’s scathing assessment of post-modernism and vertical transportation through passenger and was summarized in his written address to the Archi- freight elevators. The first skeletal form with a glass tecture Club of Chicago in 1982, accepting his un- and structured façade was designed by William Le precedented election to President of the Club. Khan Baron Jenny, a civil engineer that practiced as an ar- died before the address could be given. Khan wrote chitect and considered the father of the First Chicago “Today it seems the pendulum has swung back again School, through the Leiter Building (1879), and later towards architecture that is unrelated to technology in the Home Insurance Building (1885), which is and does not consciously represent the logic of considered the world’s first skyscraper. Jenny, Sul- structure. Nostalgia for the thirties and even earlier livan, and Root, among others, designed structures times has hit a large segment of the architectural that where utilitarian, economical, and free of exces- profession; in many cases façade making has be- sive ornamentation. Root’s Monadnock Building come the predominant occupation. It is apparent completed in 1891 was the tallest in the world at the that postmodernism in architecture is very much the time with 16 stories of load bearing masonry. It is result of the architect’s lack of interest in the reality still the tallest load bearing masonry building in the of materials and structural possibilities: the logic of world and an excellent example of a structural re- structure has become irrelevant once again. This at- sponse to force flow through gradually increasing titude in architecture suits many engineers because widths and depths of the masonry walls as the build- of their overspecialization in engineering schools ing meets its foundations. which treat the solution of the problem as the ulti- mate goal, and not the critical development of the The second skyscraper age was one that used steel problem itself.” construction to new heights while seeking aesthetic inspiration from classic historic models including style and ornamentation from Greek and Roman 3 FIBER AND FLOW monuments. Especially in New York City, corpo- rate owned skyscrapers became a symbol of strength Khan believed that a building’s architectural expres- and prosperity. The Chrysler, Empire State, and sion should emulate the simplicity and elegance of Rockefeller Center Buildings are important symbols the structural form and exhibit the integrity of its of this period. natural strength. Perhaps his most important ac- complishment was the development of the tubular After a sharp decline in construction in the period frame. Based on the concept of force flow and rec- leading up to and following World War II, construc- ognizing that the most efficient structures should be tion of tall buildings began again in the late 1950’s. composed of conceived fibers subjected only to ten- The third skyscraper age and the formation of the sion and compression where the perimeter of the Second Chicago School were dominated by Europe- structure was used to resist lateral and gravity loads an architects such as Mies van der Rohe and Le while reducing bending in structural components. Corbusier. Heavier masonry facades were replaced Khan’s idea was to eliminate the use of redundant with metal and glass, and art deco aesthetics were materials typically required for additional mullions replaced with the International Style which empha- for windows at the exterior wall, to remove interior sized the expression of structure by exposing it on frames that made the use of space less efficient, and the exterior of the building. Myron Goldsmith, a perhaps most importantly, reduce the overall quanti- student of Mies became an important contributor to ty of material required to resist load. this modernist movement. Khan was holistically and conceptually driven by the modernist move- With this design approach, Khan’s goal was to de- ment. sign a structure to resist gravity loads and proportion it to not require any additional material for imposed Many buildings designed in the late 1970’s lacked lateral loads due to wind or seismic conditions. His a particular style and recalled ornamentation from aspiration was to have as little impact on the envi- earlier buildings designed during the second age of ronment as possible. the skyscraper. The fourth age of the skyscraper ig- nored the environment and loaded structures with Khan recognized that the most efficient tubular decorative elements and extravagant finishes. form was one that consisted of a completely solid Sculptural imagery and monumental expression shell at the perimeter of the structure. In this in- dominated architectural practices bored with 3 stance all fibers within the shell would be either sub- Khan identified and struggled with the concept of jected to axial tension or compression. shear lag where the greater the tension and compres- sion participation of columns on the leeward and windward faces of a structure in a three dimensional structure, the greater the efficiency. The shear lag is attributed to the shear racking of the web frames in a tubular structure where practical limitation of spandrel girder depths and column spacing creates flexibility in girders. Therefore, high stresses in web cannot be adequately transferred to flange frames where greater engagement leads to greater efficien- cy. Figure 1. Dr. Fazlur Khan’s Conceptual Tube System He also recognized the practicality of the tall building and the need for views and light within in- terior spaces.