Innovation Follows Program World population by 1960 was about to burst at the seams. Or so it seemed. Capping the dramatic population increases of the first half of the 20th century, the 1950s' baby boom intensified people’s sense of an earth that was shrinking. Metropolitan centers in particular were pressed for space. Housing was needed         The revolutionary framed-tube structural system was first seen in the construction of the DeWitt-Chestnut Apartments.   for a large number of people — single-family homes were not sufficient — and office space was also wanted for the spiraling numbers of office workers. A healthy economy ensured a sustained demand for office space. High-rise construction offered the perfect solution. Super-tall buildings could provide large amounts of floor area without having to be densely packed, one building upon the next. A portion of each city block that a high rise occupied could be left available for desirable city plazas and parks. Despite these apparent advantages, super-tall building construction faced a critical deterrent: expense. Skyscrapers were simply too costly by modern development standards. A tower reaching as high as the Empire State Building could not be justified in economic terms. It was a generally accepted "fact" of construction that taller buildings cost more to build per square foot of rentable floor area than shorter buildings. A rapid run-up in structure costs resulted from increased wind forces: in order to withstand greater wind effects, a tower's structural framework had to be strengthened and stiffened considerably with increasing building height. Developers, therefore, were dissuaded from building above the thirty-story range by this cost premium. They leaned instead toward constructing bulky, site-consuming edifices. It appeared that conditions in central business districts were bound to worsen, with every building site being completely filled. It was at this critical moment in the development of the modern urban environment that Fazlur Khan entered the profession. Filled with both ambition and optimism, and equipped with solid training in structural engineering, Fazlur Khan was undeterred by the mindset and technological difficulties that hindered tall building design. He recognized that the structural systems utilized for high-rise construction were not on a par with the modern scale of architecture,     In 1960, buildings over 20 stories were still newsworthy; by the close of the decade, people were "living in the sky." Apartments in the John Hancock Center in Chicago are located as high as the 90th floor.     and he took on the challenge of advancing state-of-the-art structural engineering. A decade of revolutionary advances had just begun. Fazlur Khan's earliest contributions to the field — developing the shear wall frame interaction system, the framed-tube structure, and the tube-in-tube structure —         The Onterie Center in Chicago interpreted the trussed-tube structural system for reinforced concrete construction.   led to significant improvement in structural efficiency: they made the construction of tall buildings economically feasible. The framed-tube structure has its columns closely spaced around the perimeter of the building, rather than scattered throughout the footprint, while stiff spandrel beams connect these columns at every floor level. This structural system was first implemented in 1964 in the construction of the DeWitt-Chestnut Apartments in Chicago, a 43-story reinforced concrete tower designed by Fazlur Khan and his colleagues at Skidmore, Owings & Merrill (SOM). Because of its great relative strength and stiffness, the tubular form immediately became a standard in high-rise design. As the reach of tall buildings extended, Fazlur Khan resolved to discover structural systems appropriate for each new scale of architecture. Crafting rational architecture in cooperation with Bruce J. Graham, chief design architect in SOM's Chicago office, he united an exceptionally efficient "trussed-tube" structural system with an articulate, graceful form for Chicago's 100-story John Hancock Center.     Looking up at the Sears Tower, the world's tallest building for over twenty years. The design for this 1450-foot-tall tower introduced the bundled tube structural system, as well as a new vocabulary in architectural form.     A few years later he introduced another groundbreaking structural system, the "bundled tube." This design for Chicago's 110-story Sears Tower was structurally efficient and economic: at 1,450 feet, it provided more space and rose higher than the Empire State Building, yet cost much less per unit area. Equally important, the new structure type was innovative in its potential for versatile formulation of architectural space. Efficient towers no longer had to be box-like; the tube-units could take on various shapes and could be bundled together in different sorts of groupings. When one looks at a text on tall-building design today, one finds these recognizable structure types: the framed tube, the shear wall frame interaction, the trussed tube, the bundled tube, and the composite system (also developed by Fazlur Khan). Though Khan developed structural systems for particular project needs, he based his innovations on fundamental structural principles that allowed them wide application. His developments are among today’s “conventional” systems for skyscraper design.         Saudi Arabia celebrated its new airport terminal in a postage stamp design.   As the building boom in the West came to an abrupt halt in 1974, new demands surfaced that thrust designers into unfamiliar settings. Clients in the Middle East and Asia, for example, were anxious and now financially able to construct housing, offices, and other facilities in large scale. SOM took on this design work, and Fazlur Khan responded to needs and situations as he perceived them. For the immense roof of the Hajj Terminal of the new airport in Jeddah, Saudi Arabia — intended to shelter 80,000 pilgrims at a time, waiting for up to 36 hours — he searched for a coherent scheme that was both efficient and honored the spirit of the Hajj pilgrimage. The fabric roof structure melds a traditional concept, that of the Bedouin tent, with sophisticated technology. Twenty years after the airport's opening, this fabric roof and the space that it creates continue to awe as well as comfort terminal users.