Nicholas Isyumov Snippet A

Wind engineer Dr. Nicholas Isyumov talks about his work on the Sears Building – now the Willis Tower – in Chicago during the late '60s. It was to be the tallest building in the world, taller than New York's World Trade Center. The World Trade Center was sensitive to cross-wind dynamic excitations due to vortex shedding. The Sears Building had a more irregular shape – only two of the nine modules extended to the full building height – so vortex shedding was mitigated but significant wind-induced torques were possible. These combined drag, cross-wind, and torsional loadings eventually were codified.