Willis, Aon Trump and Hancock Skyscraper

Chicago Building Types: the Skyscraper

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This post is part of a series of studies of classic Chicago Building Types.  Each city has its history of materials, wealth, population shifts and popularity, as well as its hopes and fears, written in its buildings. Don’t miss our studies of Chicago BungalowsWorker CottagesCourtyard Apartment Buildings, Residential Hotels, Greystone FlatsFour-Plus-One Apartments, and Fire Cottages.  We’ll be making an ongoing study of several of Chicago’s common building forms and how they came to fill the city around us. 

THE SKYSCRAPER: Chicago’s Iconic Center

How ever much the people who live in the North, West and South sides may feel that high rise living/working does not define their Chicago, our skyline is the face we present to the world.  Almost any plane trip to or from the city shows off our most impressive side and approaches by car (or via the lake) each give an impressive “HERE IT IS” moment when the loop high rises come into view.  Only 29 thousand of Chicago’s 2.7 million residents live in the loop but all of us find occasion to engage with it, even if only by admiring its skyline from our own home ground.

RACE TO THE TOP

Chicago is home to several of the worlds tallest buildings.  The Willis (oh, give us a break, the Sears) tower is currently ranked 12th, Trump Tower 16th, the Aon Center 37th and the John Hancock 40th.   As with any competition, there has been disagreement about the rules.  Dissent over the definition of “tallest building” after the building of the Petronas Towers in 1998 (which either did or did not take the title of “tallest” from our own Sears tower) actually led to the development of four different categories – height to architectural top (which includes spires but not antennae), hight to top occupied floor, height to top of roof and height to tip.

I’m reminded of the competing towers of Lucca, a walled city in Tuscany, where after one powerful family’s tower was topped by a rival across the city, the first family planted trees on their roof in order to re-gain their pre-eminence in height.

lucca's tallest

OUR (MULTI) STORIED HISTORY

The claim of tallest building is a hard (impossible?) one to hold on to but Chicago is not likely to lose the stake in high rise history provided by William Le Baron Jenney’s Home Insurance Building – the precursor of the modern skyscraper.

home insurance building

Although it appears to be a conventional masonry building the Home Insurance Building actually incorporated both a cast iron and structural steel framing system (the building was already under construction using iron, when Jenny decided to switch to steel at the 7th floor).  The metal skeleton (although hidden, fire-protected and re-inforced inside masonry walls) which supported the building’s weight, was the key concept used in the construction of modern high rise buildings.  It was demolished in 1931 but its legacy remains in the city which reaches for the sky all around it.  For more, check Donald L Miller’s City of the Century (1996) pages 339 – 341.

HOW SKYSCRAPERS WORK: THE TRIUMPH OF ENGINEERING

The process of hiking our daily life half a mile into the sky requires not a few amazing feats of engineering.

Carrying loads to the ground

Making a building so tall requires enormous structural loads – the weight of so many floors of human activity, stuff and, well, floor.  All that load travels from roof on down, through supporting columns, which can become very big, and to the footing, where it has to be evenly distributed and not sink or shift.  The ideal high rise design then is as light weight as possible.

Not tipping over

At the same time tall buildings encounter dramatic wind forces making them effectively a cantilever which goes straight up from the ground.  Since people really don’t like swinging on a pendulum in the wind, tall buildings need to be very rigidly constructed to prevent movement.   The above mentioned weight consideration (as well as a general preference for windows) means we can’t just make solid exterior walls.  Ingenious systems of bracing (like the X diagonals on the Hancock building) stiffen the building with a minimum of material used.

Keeping their cool

Managing the mechanical requirements of such a tall building is a challenge.  Single family homes generally place an AC condensor unit in the side yard, commercial buildings several stories high keep their mechanical equipment on the roof, but a skyscraper usually needs the equivalent of several floors devoted entirely to HVAC for each zone, often siting part of the system in the top of the building (far from ground level view) and disguising another half or two thirds of the system at intervals lower down in the building.

Getting up there

Elevator systems must be designed to quickly and efficiently carry people and goods up and down.  Some buildings  divide elevator lobbies into zones by height (and prestige), others use a “sky lobby” system which rushes people up to a mid point and then switches them to a different stack of elevators to choose individual destinations on upper floors.  Complex computer systems are used to determine the most efficient pattern for pickups and drop offs as different floors are accessed.

WHO IS UP THERE IN THE SKY

The loop may be known more for work and play rather than home and hearth, a lot of people live in the sky over Chicago.  For example, the Hancock Center is a city in a building with 6 floors of retail space on Michigan Avenue, surmounted  by office space, a 44th floor grocery store, a pool, a post office,  a voting station (the building is its own electoral precinct) and 702 residences.  Learn more crazy Hancock facts here.

QUESTIONS

At the end of his chapter on Skyscrapers in the classic pean to engineering Why Buildings Stand Up, Mario Salvatori asks:

“Are skyscrapers a blessing for the densely populated ares of our modern metropolises or are they a dehumanizing fruit for technology for technology’s sake”

The question of the sustainability of high rise building (both environmentally and socially) is still open to a lot of debate.

Do you love it or leave it?  What’s your favorite part of Chicago’s skyline?