A New Rubric for SEI: Eminent Structural Engineers

The SEI Editorial Board is working continually to improve examples that inspire all engineers. The idea is that papers our Journal. In recent issues we have focussed on preparing will present a personal interpretation or discussion of how well-balanced issues treating a single common theme that the work of the featured individual influenced structural combine a range of Structures, Reports, and Science and Tech- engineering developments or other engineers. Furthermore, it nology papers. We believe that this has been well received by is our hope that the authors of these papers will be able to you, our readers, and we hope to continue this in the future. draw on a personal relationship with, and be in a position to The Editorial Board has also discussed the introduction of include personal anecdotes that illustrate the professional new rubrics for SEI, in addition to those mentioned above, as facets of, the featured individual. a way of increasing the attractiveness of the Journal. We have We are very pleased that the first paper to be published in tried, for example, to encourage readers to submit discussions the new rubric more than satisfies the aims, ideas and hopes of published papers. We hope, with your help, to be able to presented above. It presents the life and work of Dr. Fazlur publish such papers in the near future. R. Khan, one of the most eminent structural engineers of re- This issue marks the beginning of a new rubric; Eminent cent times, and it is written by his daughter, Yasmin Sabina Structural Engineers. This rubric has been created with the Khan. We hope that you enjoy it. aims of increasing awareness of our structural engineering heritage through a better understanding of the work of emi- Simon F. Bailey nent structural engineers and promoting good engineering Chair, SEI Editorial Board

Dr Fazlur R. Khan (1929–1982)

Yasmin Sabina Khan, Struct. Eng., Brookline, MA, USA

Introduction

The structural systems for high rise de- matician and educator, he acquired a sign that Fazlur R. Khan (Fig. 1) initi- thorough grounding in mathematics ated in the 1960s and 1970s provide a and analytical thought in his youth; basis for design still today. Responsible he also discovered a joy for learning for some of the world’s tallest struc- that would endure throughout his life. tures – notably, Chicago’s 110-story Following undergraduate studies in en- Sears Tower, the tallest building in the gineering, he received Fulbright and United States since its completion in Pakistan government scholarships, which 1974 (Fig. 2) – Khan established a se- together supported three years of post- ries of efficient structural systems that graduate studies at the University of significantly expanded the range of al- Illinois in the United States. Working ternatives for building construction at an unusual pace, he earned two mas- and secured a new standard for design. ter’s degrees and a doctorate in this These structural types, which include period. He considered the experience the trussed tube, the bundled tube, essential to his career; his professors and the composite system, also offered reinforced his attitude toward inquiry logical frameworks as core ideas for and strengthened his confidence in in- architectural design and enabled Khan, novative thinking. In addition to gain- through his ideas for structures, to ing a firm understanding of materials shape building architecture. and principles, he fostered an intuitive comprehension of structural behavior. Fig. 1: Fazlur Khan, c. 1980 “I put myself in the place of the whole Personal Background (Stuart Rodgers Photographers) building,” he would later explain, and “visualize the stresses and twisting a Fazlur Khan was born in Dhaka, building undergoes” [1]. Bangladesh (then Dacca, British India) on 3 April, 1929. The son of a mathe-

Structural Engineering International 3/2004 Eminent Structural Engineers 245 the 43-story Chestnut-DeWitt Apart- ments in Chicago; combining an interi- or tube with a perimeter tube he creat- ed the tube-in-tube system for a 50-sto- ry concrete office building, One Shell Plaza in Houston – while working on this project he also formulated an in- fluential load history method for analy- sis of inelastic deformation, consequent of his study of creep and shrinkage movement. When confronted with the problem of a 100-story structure for the John Hancock Center in Chicago, he refined the tube system to develop a stiff trussed tube, which is clearly ex- pressed in the building architecture (Fig. 3), and for the 442 m Sears Tower he stiffened an exterior tube with inte- rior cross-diaphragms, forming the bundled tube. In 1968, reflecting a re- markable openness of mind for the time, he employed a composite structur- al system in a 50-story office tower, One Shell Square in New Orleans, eliminating the barrier to mixed mate- rial use in future high rise design. When developers raised their sights to Fig. 2: 442 m Sears Tower introduced the the 600–700 m range in the early 1980s, bundled tube system (Ezra Stoller © Esto) he again searched for a structural sys- tem appropriate to the building scale. Innovative Approach to Design The solution he arrived at was a tele- High Rise Buildings In 1961, when Khan began to work on tall buildings as a young engineer at Skidmore, Owings & Merrill (SOM), the main structural systems known to designers were the beam-column frame and the shear wall or shear truss.These systems were effective for buildings up to 20 to 30 stories, but their application in taller structures resulted in dispro- portionate cost increases for increas- Fig. 4: Ideas for a superframe, Khan’s ing height. Contemplating how to re- pocket notebook, 1981 duce unit area costs, he perceived that a tall building tends toward vertical scoping superframe (Fig. 4) with one cantilever behavior and that the geom- or more wind portals incorporated into etry of the structural frame can con- the structure. He aimed to avoid re- tribute to lateral resistance. By design- liance on supplemental damping de- ing the structure to minimize shear rack- vices, which required regular mainte- ing at each floor level, thereby causing nance and incurred additional construc- cantilever action to be predominant, tion cost, and intuitively perceived the efficient use of structural material could beneficial effect of portals or façade re- be achieved. liefs on cross-wind response. Over the course of the decade he de- veloped a series of structural systems Light Weight Structures based on this understanding of can- tilever action. He was convinced that Fazlur Khan’s influence extends as well different building scales required dif- to light weight roof structures. In the ferent structural systems and he took mid-1970s he utilized a cable-stayed sys- pleasure in crafting structures to meet tem to create a large unencumbered the needs of his projects. Khan first im- space at Baxter International head- plemented his concept for a perimeter quarters outside of Chicago, thus vali- cantilever tube structure in the framed Fig. 3: Chicago’s John Hancock Center, dating this structural type for build- tube, which he developed in 1962 for completed in 1970 (Ezra Stoller © Esto) ings. When the design team on an air-

246 Eminent Structural Engineers Structural Engineering International 3/2004 port project for Jeddah, Saudi Arabia, perimeter tube with cross-diaphragms sought a light weight solution for the to lessen the effect of shear lag – this immense, 430 000 m2 Hajj Terminal, he system was not initiated until 1969, resolved to design a tensile structure however, when he developed the mod- unhampered by the level of labor-inten- ular, or bundled, tube for the Sears sive field construction associated with Tower. Likewise, he offered a scheme cable net structures and developed the for a trussed tube in concrete several cable-membrane tensile structure, in years before he had the opportunity to which the fabric membrane serves as realize it in the Onterie Center design both enclosure and structural element. for Chicago. While researching SOM projects for a Ability for Critical Judgment book on my father [2], I came across numerous examples of his application His enthusiasm for structural concepts of load tests and other practical, though and efficient systems, which inspired sometimes unconventional, methods to colleagues to share in his excitement verify progressive design. Supplement- for innovation, was complemented by ing theory with experiment allowed a judicious temperament and the abili- him to venture into nascent structural ty to assume responsibility for imple- materials and systems, such as pre- menting new techniques. Khan’s deci- stressed concrete in the 1950s and Fig. 5: Fazlur Khan and Bruce Graham, 1965 sion to use lightweight aggregate con- (K & S Photographics – courtesy of Skidmore, Owings composite floor framing in the 1960s. crete for the entire structure of One & Merrill LLP) When he needed to evaluate building Shell Plaza, for example, preceded the sway for the John Hancock Center, but American Concrete Institute’s publi- ance in the years since Khan’s practice, could not commission extensive mo- cation of guidelines for its use as a but in the 1970s he was considered tion-simulator tests, he made use of the structural material. Despite the prob- “perhaps the number-one illustration” rotating floor of an exhibit at Chica- lems encountered in earlier applica- of a teamwork doctrine [3]. Through go’s Museum of Science and Industry. tions of lightweight concrete, he was example of his work, along with his He had recognized the potential test- certain that, with strict quality control manner of working with others, he pro- ing apparatus during a family visit one during mixing and placement, a high moted the partnership of engineers weekend; holding my hand as we viewed quality structural material could be and architects in conceiving building the exhibit he felt a jerk that drew his at- obtained. His confidence and integrity schemes. tention to the rotating mechanism. By convinced the developer, Gerald D. putting together a simple study with a Hines, to approve the progressive de- few volunteer subjects he evaluated Conclusion sign approach. people’s perceptions to motion, ob- His eagerness for progress in engineer- taining results that were surprisingly Fazlur Khan’s endeavors were marked ing did not distract him from concerns close to those of subsequent experi- by a passionate ambition for progress of structural performance and critical ments. He continued to devise practi- in engineering.At the same time, Khan structural issues. During construction cal studies in this manner throughout greatly appreciated the larger setting of the John Hancock Center a difficult his career. of design, notably its functional, aes- situation arose that forced him to as- thetic, and social aspects. It was indeed sess the nature of an inexplicable col- Collaboration in Design a broad perspective of design objec- umn movement measurement. Fully tives that directed his development of aware that costly construction delays Committed to interdisciplinary collab- new structural systems. might threaten the viability of the pro- oration, he established a level of com- Vigorously pursuing advances in mate- ject, he discounted consensus in the munication with colleagues that at once rial use and structural technique, he in- field that the measurement was erro- provided an important depth to his vigorated the engineering profession neous and halted erection of the steel work and enabled him to participate as and established many of the conven- frame to commence a caisson investi- an equal partner in design. He was tional methods available to designers gation. His judgment proved wise when convinced that intellectual exchange today. He expressed his ideas for struc- a dismaying 4,2 m long void was found stimulates creativity and enlarges the tural action in systems that were not in one concrete shaft. scope of design ideas; he was also only efficient but also visually coher- determined that a “building’s natural ent, and thereby gained a leading role strength should be expressed” [1]. Dur- Practical Commitment to Progress for engineering in architectural design. ing the 1960s he worked closely with Bruce J. Graham, the chief design ar- Khan was an active participant in pro- chitect in SOM’s Chicago office, who fessional associations and worked to References shared with him an interest in structur- organize new ones, such as the Chicago [1] KIELAR, R. M. Construction’s Man of the al clarity and logic and provided vital Committee on High Rise Buildings and Year: Fazlur R. Khan. Engineering News Record, support for the realization of his ideas. the Council on Tall Buildings and Ur- Vol. 188, 10 February 1972, pp. 23, 21. Together they created the bold sky- ban Habitat. He was known for his scraper designs that celebrate the van- [2] KHAN, Y. S. Engineering Architecture: The generosity in terms of time and talent. Vision of Fazlur R. Khan. New York, W.W. Nor- guard structural systems (Fig. 5). He was also open with his thoughts for ton & Company, 2004. structural systems: as early as 1966 he The benefit of communication to cre- [3] Structures, Professional Matters Are Focus. shared his idea for stiffening a large ative activity has gained wide accept- Civil Engineering–ASCE,Vol. 44, June 1974, p. 80.

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