A white hard-hat on his head, the earnest look of a professor on his face, Bill Baker has a ready metaphor to reveal the hidden structural logic behind Chicago's unprecedented reach into the sky. Mimicking the cores of concrete that shoot up the center of today's supertall skyscrapers, Baker stands like a soldier at attention, his feet touching. The silolike cores are too thin to single-handedly brace the towers against howling winds, he says. So Baker extends his left arm and puts it on the shoulder of a colleague standing with him in front of Donald Trump's ever-growing skyscraper on the Chicago River's north bank.The new thinking will give Chicago two companions to the existing spires, as well as the world's tallest residential building.
Chicago offers something that no other city can: a chance to view the present generation directly alongside the previous generation -- Sears Tower, the Aon Center and the John Hancock Center. That trio of giants, which was based on the structural concept of a "framed tube," redefined the skyline's silhouette between 1969 and 1974.Prior to which time such Industrial Age classics as the Wrigley Building, Tribune Tower, the Intercontinental Hotel, and the Board of Trade defined the skyline.
The article goes on to note that designers have taken into account the lessons learned from the World Trade Center collapse, both in providing emergency exit and in strengthening the structure.