Darrell Sapp, Post-Gazette The former IBM Building, now housing the United Steelworkers, is partly supported by its diamond-latticework steel frame.

Architect: Curtis & Davis, New Orleans
Engineers: John Skilling and Leslie Robertson, Seattle
Built: 1961-63

When the IBM Building opened in 1963, Joseph Watterson, writing in the American Institute of Architects Journal, called it "the only fine and daring piece of new architecture ... in the downtown area."

It came from the Big Easy and the Big Apple, where a New Orleans firm with a New York office and an international practice was designing buildings for IBM in the early 1960s. Mobile, Trenton and Shreveport got conventional steel-and-glass boxes, one to three stories tall. But the Pittsburgh office was a high-rise building and an architectural and engineering breakthrough, with diamond-patterned walls that act as both skin and skeleton.

"The chief reason for the building's fame is its virtually unprecedented structure," wrote Interiors magazine in a 1967 feature on Nathaniel Curtis and Arthur Davis' work. "The building is supported by a central core and its four lattice-covered exterior truss walls, each of which has only two points of support. The system is particularly acclaimed for its efficient use of steel (five different types are combined) and the enormous benefits for the interior spaces."

The column-free interior made it an early model of open-space planning, and it was the forerunner of all tall buildings with concrete cores and load-bearing, external frames, including New York's World Trade Center. The Twin Towers and the IBM Building had the same Seattle-based engineers, John Skilling and Leslie Robertson.

The test of its integrity came in 1962, when nine of its 13 stories were complete and it was time to remove the wooden supports and see if the building would stand on its A-framed pylons.

"It was a sight to buckle the knees of strong men and make stress analysts tremble under the strain," the Pittsburgh Press reported. But when workmen knocked out the props, "the thing just stood there."

Architectural historian James D. Van Trump viewed it with some amusement. "There is no doubt that it is a really engaging 'stunt,' like one of those old vaudeville 'turns' in which a whole pyramid of acrobats is supported on the shoulders of one man. ... We might conceive of the building as a great ornamental lantern that might be any size you please, with its present dimensions merely fortuitous. Is this the Pharos of the future? -- Lighten our darkness, we beseech thee, O IBM, and by thy great mercy defend us from all perils and dangers of the night!"

Today the building still wows us and is that rarest of birds, a modern office tower that's fun to look at. But the podium on which the building and its plaza sit creates a wrap-around concrete wall that makes for a bleak streetscape at the southwest corner of Stanwix Street and Boulevard of the Allies. And the plaza's large reflecting pool and its rubble-stone bottom, alas, have vanished, replaced by a perfunctory lawn.