The Elbert Files: An exercise in problem solving
Friday, October 04, 2013 7:00 AM
Years ago, I spent a memorable night on the 82nd floor of Chicago’s John Hancock Center. Arriving after sunset and looking down, I saw only clouds. Even more mind-bending was the fact that the land beneath the 100-story tower had once been a swamp.
That swamp and the Great Chicago Fire of 1871 played significant roles in the creation of the Hancock Center and every other modern skyscraper, according to Thomas Leslie, Iowa State University’s Pickard Chilton Professor of Architecture.
Leslie’s new book, “Chicago Skyscrapers, 1871-1934,” is a history of the explosion in tall-building technology that occurred between the Chicago fire and the Great Depression, and the role that Windy City architects, engineers and developers played in that evolution.
The 1871 fire is widely credited with spurring development of fire-resistant building materials. Less well known is the role that Chicago’s soil played in the evolution of tall buildings. Leslie has described Chicago’s “jelly-cake” soil as “the worst soil in the world for building a skyscraper.”
“Chicago rested upon a hundred-foot-thick layer of waterlogged clay that frustrated attempts to build on bedrock below,” Leslie wrote. A hardpan clay crust that was 2 to 10 feet deep covered most of the jelly-cake, and the city’s earliest tall buildings were erected with the realization that their weight would cause them to sink between 6 and 12 inches.
The trick for early builders was estimating how much a building would sink. Chicago’s 1872 city hall was an early victim.
It began to lean as soon as it was completed and wound up tilting so much that it had to be torn down in 1885. The Auditorium, which opened in 1889 at Congress Boulevard and Michigan Avenue, was another example. It still stands today, but because it has sunk, visitors step down into its lobby, Leslie explained.
Chicago builders “had to work within the bearing capacity of the hardpan until a feasible method of drilling to bedrock emerged” decades later, Leslie wrote.
The jelly-cake soil led to experiments with materials that were lighter and stronger than traditional timber and stone, and Chicago’s architects were among the first to use cast iron and steel.
They were also the first to devise ways for spreading weight, Leslie said.
One method developed in the 1880s was called “spread grillage.” Parallel steel beams were used to spread the weight of columns over larger areas. The idea was to float the weight on steel grills, which served as “lily pads” for the foundation.
By the end of the 19th century, Chicago’s builders were in a competition with their New York counterparts to see who could erect the tallest buildings.
New York had the advantage of bedrock that was close to the surface, but Chicago had the advantage of larger lot sizes with up to 150 feet of street frontage, compared with 25 feet of frontage in New York.
“Chicago architects had room to create well-ordered, regular buildings, while New York architects continually dealt with small, irregular lots that prevented any really organized solutions from emerging,” Leslie said.
Concerns about weight resulted in less ornamentation on Chicago buildings, which evolved into leaner, cleaner lines that became known as the Chicago Style of architecture.
Chicago architects pioneered in the development of lighter-weight curtain walls with more windows that could bring in more daylight, which was a prized commodity in the pre-electric age.
“In hindsight the poor soil was a great advantage, in that it forced really innovative solutions that replaced heavy masonry, making buildings more efficient,” Leslie said.
So, the next time you find yourself on the top floors of Des Moines’ Ruan Center or 801 Grand, think about the swamp and fire in Chicago where it all started.
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