SIX FOOT WALLS.

SIX FOOT WALLS. This article by Blair Kamin, the architectural critic of the Chicago Tribune, describes the changes in skyscraper construction which have taken place in Chicago in the last 125 years. The new skyscrapers, including the Chicago Spire (which I posted on here), are being built with a “core and outrigger” structure. The central core is connected to structural columns at the perimeter by steel or concrete arms. From 1969 to 1974, in the John Hancock building among others, Chicago architects pioneered the use of the “framed tube”, which featured a load-bearing core, but with the outer shell bearing a large part of the load. The first curtain-wall building, in which the internal frame supported curtain walls (which hung like curtains and bore no weight), was built in Chicago by William Le Baron Jenney in 1885. Before that, skyscrapers relied on load-bearing walls. The Monadnock Building, a favorite of mine, was built after Jenney’s in 1891 and reached seventeen stories. Part of it had load-bearing walls. They were six feet thick. The walls of the “outriggers” reaching out to the columns in one of the new buildings will be five and a half feet thick.