How Fazlur Rahman Khan engineered the modern skyscraper

Fazlur Rahman Khan (1929–1982) transformed the way skyscrapers are designed, making it possible to build taller, lighter and more efficient buildings.

Before his innovations, skyscrapers relied on heavy internal steel frames. For example, the 102-storey Empire State Building (1931) required around 210 kg of steel per square metre (about 50 lb per sq ft), making such structures expensive and material-intensive. Khan's tubular structural systems dramatically reduced steel use while improving strength, allowing the construction of the modern supertall skyscraper.

Born in Bhandarikandi village near Dhaka, then part of British India (now Bangladesh), Khan studied at colleges in Dhaka and Calcutta before receiving a Fulbright Scholarship to the United States. There, he earned master's degrees in structural engineering and theoretical and applied mathematics from the University of Illinois Urbana-Champaign. He later joined the Chicago office of the architecture firm Skidmore, Owings & Merrill (SOM), where he spent almost his entire professional career.

A brief return to Pakistan in 1957 ended when he became frustrated with bureaucratic restrictions and rejoined SOM in 1960. Although trained as a structural engineer, Khan believed engineering and architecture should work together. Colleagues remembered his ability to simplify complex engineering problems and communicate technical ideas clearly to architects, clients and students.

His approach focused not only on structural efficiency but also on aesthetics, culture and improving urban life. Khan's breakthrough came with the development of the tubular structural system. Instead of relying mainly on interior columns, the system shifted much of the building's strength to its exterior walls. This made buildings stiffer against wind loads, reduced steel consumption and created large, open interior spaces.

The concept was first applied in the 43-storey Chestnut-DeWitt Apartments in Chicago (completed in 1965). His best-known early achievement was the 100-storey John Hancock Center (now 875 North Michigan Avenue), completed in 1969. Designed with architect Bruce Graham, it became one of the world's first mixed-use supertall buildings, combining offices, homes and commercial spaces in a single tower.

Its distinctive X-shaped exterior braces became an architectural landmark. The building used only about 29 lb of steel per square foot compared with the Empire State Building's 50 lb, demonstrating the efficiency of Khan's design. Khan later refined the concept with the bundled tube system, most famously used in the 110-storey Sears Tower (now Willis Tower), completed in 1974.

Rather than pursuing height for its own sake, Khan designed the building to provide maximum usable office space while preserving open public areas at ground level. The Sears Tower remained the world's tallest building for nearly 25 years. Alongside his professional work, Khan taught architecture at the Illinois Institute of Technology, where he encouraged students to develop practical, buildable designs. He also played a key role in introducing computer technology to SOM during the early 1960s, strengthening the firm's research capabilities. Beyond engineering, Khan was deeply engaged with culture and public service.

During Bangladesh's Liberation War in 1971, he helped organise humanitarian relief for refugees and co-founded the Bangladesh Emergency Welfare Appeal and the Bangladesh Defense League, which advocated for international support for Bangladesh. Khan also designed the award-winning Hajj Terminal at King Abdulaziz International Airport in Jeddah, completed in 1981.

Its cable-supported fabric roof, inspired by Bedouin tents, was one of the world's largest tensile structures at the time. Khan died of a heart attack in Jeddah in 1982 at the age of 52. His influence continues through landmark buildings such as the Burj Khalifa and Shanghai Tower, which build upon the structural principles he pioneered. In 1998, Chicago honoured his contributions by naming a street leading to the Willis Tower Fazlur R. Khan Way.