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Introduction

The structural systems for high rise de-sign that Fazlur R. Khan (Fig. 1) initi-ated in the 1960s and 1970s provide abasis for design still today. Responsiblefor some of the world’s tallest struc-tures – notably, Chicago’s 110-storySears Tower, the tallest building in theUnited States since its completion in1974 (Fig. 2) – Khan established a se-

ries of efficient structural systems thatsignificantly expanded the range of al-ternatives for building constructionand secured a new standard for design.These structural types, which includethe trussed tube, the bundled tube,and the composite system, also offeredlogical frameworks as core ideas forarchitectural design and enabled Khan,through his ideas for structures, toshape building architecture.

Personal BackgroundFazlur Khan was born in Dhaka,Bangladesh (then Dacca, British India)on 3 April, 1929. The son of a mathe-

matician and educator, he acquired athorough grounding in mathematicsand analytical thought in his youth;he also discovered a joy for learningthat would endure throughout his life.Following undergraduate studies in en-gineering, he received Fulbright andPakistan government scholarships, whichtogether supported three years of post-

graduate studies at the University of Illinois in the United States. Workingat an unusual pace, he earned two mas-ter’s degrees and a doctorate in thisperiod. He considered the experienceessential to his career; his professorsreinforced his attitude toward inquiryand strengthened his confidence in in-novative thinking. In addition to gain-ing a firm understanding of materialsand principles, he fostered an intuitivecomprehension of structural behavior.“I put myself in the place of the whole

building,” he would later explain, and“visualize the stresses and twisting abuilding undergoes” [1].

The SEI Editorial Board is working continually to improve

our Journal. In recent issues we have focussed on preparingwell-balanced issues treating a single common theme that combine a range of Structures, Reports,and Science and Tech-nology papers. We believe that this has been well received by

 you, our readers, and we hope to continue this in the future.The Editorial Board has also discussed the introduction of new rubrics for SEI, in addition to those mentioned above, asa way of increasing the attractiveness of the Journal.We havetried, for example, to encourage readers to submit discussionsof published papers. We hope, with your help, to be able to

 publish such papers in the near future.

This issue marks the beginning of a new rubric; Eminent Structural Engineers. This rubric has been created with theaims of increasing awareness of our structural engineeringheritage through a better understanding of the work of emi-nent structural engineers and promoting good engineering

examples that inspire all engineers. The idea is that papers

will present a personal interpretation or discussion of howthe work of the featured individual influenced structural engineering developments or other engineers. Furthermore, it is our hope that the authors of these papers will be able todraw on a personal relationship with, and be in a position toinclude personal anecdotes that illustrate the professional 

 facets of, the featured individual.

We are very pleased that the first paper to be published inthe new rubric more than satisfies the aims, ideas and hopes

 presented above. It presents the life and work of Dr. Fazlur R. Khan, one of the most eminent structural engineers of re-cent times, and it is written by his daughter, Yasmin SabinaKhan.We hope that you enjoy it.

Simon F. BaileyChair, SEI Editorial Board

A New Rubric for SEI: Eminent Structural Engineers

Dr Fazlur R. Khan (1929–1982)Yasmin Sabina Khan, Struct. Eng., Brookline, MA,USA

Fig. 1: Fazlur Khan, c.1980

(Stuart Rodgers Photographers)

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246 Eminent Structural Engineers Structural Engineering International 3/2004

Innovative Approach to Design

 High Rise Buildings

In 1961, when Khan began to work ontall buildings as a young engineer at

Skidmore, Owings & Merrill (SOM),the main structural systems known todesigners were the beam-column frameand the shear wall or shear truss.Thesesystems were effective for buildings upto 20 to 30 stories, but their applicationin taller structures resulted in dispro-portionate cost increases for increas-ing height. Contemplating how to re-duce unit area costs, he perceived thata tall building tends toward verticalcantilever behavior and that the geom-etry of the structural frame can con-

tribute to lateral resistance. By design-ing the structure to minimize shear rack-ing at each floor level, thereby causingcantilever action to be predominant,efficient use of structural material couldbe achieved.

Over the course of the decade he de-veloped a series of structural systemsbased on this understanding of can-tilever action. He was convinced thatdifferent building scales required dif-ferent structural systems and he took

pleasure in crafting structures to meetthe needs of his projects.Khan first im-plemented his concept for a perimetercantilever tube structure in the framedtube, which he developed in 1962 for

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 ShellPlaza in Houston – while working onthis project he also formulated an in-fluential load history method for analy-sis of inelastic deformation, consequentof his study of creep and shrinkage

movement. When confronted with theproblem of a 100-story structure forthe John Hancock Center in Chicago,he refined the tube system to developa stiff trussed tube, which is clearly ex-pressed in the building architecture(Fig. 3), and for the 442 m Sears Towerhe stiffened an exterior tube with inte-rior cross-diaphragms, forming thebundled tube. In 1968, reflecting a re-markable openness of mind for thetime, 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 tothe 600–700 m range in the early 1980s,he again searched for a structural sys-tem appropriate to the building scale.The solution he arrived at was a tele-

scoping superframe (Fig. 4) with oneor more wind portals incorporated intothe structure. He aimed to avoid re-liance on supplemental damping de-vices, which required regular mainte-nance and incurred additional construc-tion cost, and intuitively perceived thebeneficial effect of portals or façade re-liefs on cross-wind response.

 Light Weight Structures

Fazlur Khan’s influence extends as wellto light weight roof structures. In themid-1970s he utilized a cable-stayed sys-

tem to create a large unencumberedspace at Baxter International head-quarters outside of Chicago, thus vali-dating this structural type for build-ings. When the design team on an air-

Fig. 2: 442 m Sears Tower introduced thebundled tube system (Ezra Stoller © Esto)

Fig. 3: Chicago’s John Hancock Center,

completed in 1970 (Ezra Stoller © Esto)

Fig. 4: Ideas for a superframe, Khan’s

 pocket notebook, 1981

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Structural Engineering International 3/2004 Eminent Structural Engineers 247

port project for Jeddah, Saudi Arabia,sought a light weight solution for theimmense, 430000 m2 Hajj Terminal, heresolved to design a tensile structureunhampered by the level of labor-inten-sive field construction associated withcable net structures and developed thecable-membrane tensile structure, inwhich the fabric membrane serves asboth enclosure and structural element.

 Ability for Critical Judgment 

His enthusiasm for structural conceptsand efficient systems, which inspiredcolleagues to share in his excitementfor innovation, was complemented bya judicious temperament and the abili-ty to assume responsibility for imple-menting new techniques. Khan’s deci-sion to use lightweight aggregate con-crete for the entire structure of OneShell Plaza, for example, preceded the

American Concrete Institute’s publi-cation of guidelines for its use as astructural material. Despite the prob-lems encountered in earlier applica-tions of lightweight concrete, he wascertain that, with strict quality controlduring mixing and placement, a highquality structural material could beobtained. His confidence and integrityconvinced the developer, Gerald D.Hines, to approve the progressive de-sign approach.

His eagerness for progress in engineer-ing did not distract him from concernsof structural performance and criticalstructural issues. During constructionof the John Hancock Center a difficultsituation arose that forced him to as-sess the nature of an inexplicable col-umn movement measurement. Fullyaware that costly construction delaysmight threaten the viability of the pro-  ject, he discounted consensus in thefield that the measurement was erro-neous and halted erection of the steel

frame to commence a caisson investi-gation. His judgment proved wise whena dismaying 4,2 m long void was foundin one concrete shaft.

Practical Commitment to Progress

Khan was an active participant in pro-fessional associations and worked toorganize new ones, such as the ChicagoCommittee on High Rise Buildings andthe Council on Tall Buildings and Ur-

ban Habitat. He was known for hisgenerosity in terms of time and talent.He was also open with his thoughts forstructural systems: as early as 1966 heshared his idea for stiffening a large

perimeter tube with cross-diaphragmsto lessen the effect of shear lag – thissystem was not initiated until 1969,however, when he developed the mod-ular, or bundled, tube for the SearsTower. Likewise, he offered a schemefor a trussed tube in concrete severalyears before he had the opportunity torealize it in the Onterie Center designfor Chicago.

While researching SOM projects for abook on my father [2], I came acrossnumerous examples of his applicationof load tests and other practical, thoughsometimes unconventional, methods toverify progressive design. Supplement-ing theory with experiment allowedhim to venture into nascent structuralmaterials and systems, such as pre-stressed concrete in the 1950s andcomposite floor framing in the 1960s.When he needed to evaluate buildingsway for the John Hancock Center, butcould not commission extensive mo-tion-simulator tests, he made use of therotating floor of an exhibit at Chica-go’s Museum of Science and Industry.He had recognized the potential test-ing apparatus during a family visit oneweekend; holding my hand as we viewedthe exhibit he felt a jerk that drew his at-tention to the rotating mechanism. Byputting together a simple study with afew volunteer subjects he evaluatedpeople’s perceptions to motion, ob-

taining results that were surprisinglyclose to those of subsequent experi-ments. He continued to devise practi-cal studies in this manner throughouthis career.

Collaboration in Design

Committed to interdisciplinary collab-oration, he established a level of com-munication with colleagues that at onceprovided an important depth to hiswork and enabled him to participate as

an equal partner in design. He wasconvinced that intellectual exchangestimulates creativity and enlarges thescope of design ideas; he was alsodetermined that a “building’s naturalstrength should be expressed” [1]. Dur-ing the 1960s he worked closely withBruce J. Graham, the chief design ar-chitect in SOM’s Chicago office, whoshared with him an interest in structur-al clarity and logic and provided vitalsupport for the realization of his ideas.Together they created the bold sky-

scraper designs that celebrate the van-guard structural systems (Fig. 5).

The benefit of communication to cre-ative activity has gained wide accept-

ance in the years since Khan’s practice,but in the 1970s he was considered“perhaps the number-one illustration”of a teamwork doctrine [3]. Throughexample of his work, along with hismanner of working with others,he pro-moted the partnership of engineersand architects in conceiving buildingschemes.

Conclusion

Fazlur Khan’s endeavors were markedby a passionate ambition for progressin engineering.At the same time, Khangreatly appreciated the larger settingof design, notably its functional, aes-thetic, and social aspects. It was indeeda broad perspective of design objec-tives that directed his development of new structural systems.

Vigorously pursuing advances in mate-rial use and structural technique, he in-vigorated the engineering professionand established many of the conven-tional methods available to designerstoday. He expressed his ideas for struc-tural action in systems that were notonly efficient but also visually coher-ent, and thereby gained a leading rolefor engineering in architectural design.

References

[1] KIELAR, R. M. Construction’s Man of the

Year: Fazlur R. Khan. Engineering News Record,Vol. 188, 10 February 1972, pp. 23, 21.

[2] KHAN, Y. S. Engineering Architecture: TheVision of Fazlur R. Khan. New York,W. W. Nor-ton & Company, 2004.

[3] Structures, Professional Matters Are Focus.

Civil Engineering–ASCE,Vol. 44, June 1974,p.80.

Fig. 5: Fazlur Khan and Bruce Graham, 1965(K & S Photographics – courtesy of Skidmore, Owings

& Merrill LLP)