Early in his career at SOM, Iyengar cut his teeth on high-rise buildings, working under the direction of renowned structural engineer, the late Fazlur Khan, ENR’s Man of the Year in 1972. This included Chicago’s the 1,128-ft-tall John Hancock Center, now called 875 North Michigan Avenue. The tower, which opened in 1970, sports a structurally efficient diagonally braced perimeter frame. Iyengar also worked with Khan on the 1,451-ft-tall Sears Tower, now named Willis Tower. The Sears Tower, which premiered an efficient bundled tube structure, was the tallest building in the world when it opened in 1973.

“It was my impression that because of his engineering rigor, Hal did a lot of the heavy lifting for Faz,” says Baker.

ENR Newsmaker

After Khan died of a massive heart attack in 1982, Iyengar, named a general partner in 1975, continued to innovate. Among the SOM engineering projects he led are the north building of the McCormick Place convention center, which has a cable-stayed roof; the Broadgate Exchange House in London, a 10-story building that is also a bridge for it spans railroad tracks using 106-ft-tall architecturally expressed arches; and architect Frank O. Gehry’s Guggenheim Museum Bilbao in Spain. For that project, Iyengar, who served as a structural design consultant to SOM, was named an ENR Newsmaker (ENR 1/5/1998 p. 60).

The museum, described in ENR as a tumble of intersecting curves, was the first to use 3D parametric modeling and high-tech fabrication methods on such a grand scale. After convincing Gehry to switch to a steel instead of a concrete structure, Iyengar and the SOM team developed a highly regular grid steel frame, with straight members generating the curves.

Because the steel could be mass produced, the building could be built with a rapid prototype approach. For design and fabrication, an unbroken electronic chain started with a solids model in Gehry’s office, which was translated into a 3D structural wireframe. This model was fed into a steel detailing program, which also drove fabrication machines that produced the straight steel members.

For the London building, with its four tied parabolic arches, Iyengar said, “We needed a clear span across the tracks,” because there was no room at track level for conventional foundations or columns. He added, “We also wanted to pick up the architectural themes of the historic train station.”

Clearing the Tracks

The building, located directly above Liverpool Street Station, was among Iyengar’s most innovative. To clear the tracks, which required a 78-meter clear span structure, SOM used three different systems: an X-braced truss system, a 10-story catenary suspension system and the parabolic arch.

Iyengar was born on May 6, 1934 in Mysore, India. In 1955, he earned a bachelor’s of engineering at the University of Mysore and, in 1957, a master’s of science in hydraulic and civil engineering at the Indian Institute of Science in Bangalore. In 1959, he earned a master’s of science in structural engineering at the University of Illinois at Urbana-Champaign.

He was active in the profession and produced at least 13 research projects. He was a member of many groups, including the American Society of Civil Engineers (ASCE), the American Concrete Institute, the American Institute of Steel Construction (AISC) and the Structural Stability Research Council.

In 2006, Iyengar won the 2006 Fazlur Khan Medal for lifetime achievement from the Council on Tall Buildings and Urban Habitat. He also received lifetime achievement awards from ASCE, in 1995, and AISC, in 2000.