I didn't see this posted here. If it was I'm sorry about the double posting. If you haven't seen the videos, they're a must.
http://www.chicagotribune.com/entertainment/chi-070817tall-story,0,6407755.story
How to build today's supertalls
Elegance, not machismo, is behind Chicago's unprecedented reach for the sky
By Blair Kamin | Tribune architecture critic
August 18, 2007
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.
http://www.chicagotribune.com/entertainment/chi-070817tall-story,0,6407755.story