Among the tall buildings of Pittsburgh, the United Steelworkers Building stands out not for its height (only 13 stories) but for its dramatic diamond-lattice façade.
The diamond grid is more than just decorative. The steel exterior walls represent the building's supporting structure; they serve as a load-bearing exoskeleton.
Designed by the architectural firm Curtis and Davis and constructed in the early 1960s, this structure (then known as the IBM Building) was one of the first to have its load-bearing frame visible on the outside—a style regarded then as daring and innovative.
The design is a modern adaptation of a wooden framing scheme for covered bridges, patented in 1820 by U.S. architect Ithiel Town. His lattice trusses, made from diagonally positioned planks, replaced the heavy timbers required for more traditional, rectilinear bridge designs.
Photos by I. Peterson