The Sears (ahem, Willis) Tower and Chicago’s Skyline

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We’ve celebrated the skyscrapers of Chicago before – in our very first Building Types of Chicago post, in fact – and today we talk about a specific example.  The Willis (or, Sears) tower was not only the tallest in the world for many years … it also served as a structural model for its taller, younger cousins.  It has anchored the Chicago skyline and the concept of healthy downtown business districts, from its construction to this day.  Today, hats off to the Fill-in-the-blank Tower!

A Sears Tower by any other name would … Not Smell Any Different

The official website willistower.com somewhat coyly describes the building as “the Willis Tower (formerly known as the Sears Tower)” whereas Wikipedia is a little more straightforward in its first sentence “built and still commonly referred to as Sears Tower.”  As a Chicago resident and child of the Chicagoland suburbs (albeit someone who does not work in the loop), I’ve never heard anyone say “Willis Tower” without either pausing or throat clearing.  If the name sticks for its full 15 year lease people may be getting used to it just about in time for the next change.  Or maybe not.

Constructing the (then) world’s tallest building

Constructing a structure to stick up 1500 feet in the air is a lot like constructing a bridge that extends 1500 feet from a support on only one end.  Building a skyscraper is NOT EASY.

sears willis tower diagramTall buildings in the windy city encounter huge wind forces – but for people on the top floors swaying like the end of a metronome, or hearing loud wind noises, makes them uncomfortable.  At the same time they enjoy both windows at the exterior of the building and a minimum of interior walls and columns.

For the (then) Sears tower, architect Bruce Graham of SOM and engineer Fazlur Rahman Khan designed a system of “bundled tubes.”

This concept divided the big square of the building footprint into nine smaller squares and then wrapped each one in a grid work of structure, leaving the floor in the middle open and uninterrupted.  The nine (and 7 and 5 and 2) tubes are “belted” together by huge trusses that occur at the areas with air vent louvers.

Two of those tubes only go up 50 stories, two more stop at the 66th floor and three more finish at floor 90, leaving only the center and north segments to go all the way up to floor 108.

This slimming effect reduces the amount of wind force on the top of the building and also makes for smaller areas of floor for rental – Sears only anticipated occupying the lower portion of the building and renting out higher (smaller) floors to other businesses.

This structural concept has since been used again and again in the world’s super tall structures.  The Burj Khalifa in Dubai (currently the tallest artificial structure) shares both the design architect (SOM) and the structural concept (bundled tubes).

Building Downtown Businesses

Regardless of what we call it, the Willis Tower is more than just a tall building.  When it was first envisioned, it was a vote of confidence in the city of Chicago and a strong statement of the power of keeping businesses downtown.  The location was chosen with an eye to maximizing people moving – close to the terminus of several Metra lines, Chicago loop routes and the adjacent highway spaghetti bowl.

Sears was serious about bringing its employees into the city.  To construct on that site they had to purchase not only the 15 buildings that already occupied the spot but a street that cut it in half.  Sears bought Quincy Street from the city of Chicago and then tore it out.

The commitment to keeping businesses downtown ebbed in popularity during the intervening decades, with more and more corporations taking their headquarters (and employees) out to the suburbs where land seemed more plentiful and cheap.  Sears itself relocated its HQ out to Hoffman Estates starting in 1992.  The infrastructure of Chicago’s loop remained.

And now it is filling up again and even expanding as companies new and old shift their central headquarters back into the city.  Google, Motorola and most recently Kraft Heintz are just a few of the big name companies moving major corporate centers to the Chicago center (if not the loop).  These moves are often linked to job cuts and reductions in size of corporate headquarters but from an urban perspective it remains a good thing.  More people, more transit, more interest in urban affairs.

Note: This trend is not just limited to Chicago.  Citylab highlights how Panasonic’s decision to move their corporate headquarters from suburban NJ to downtown Newark shifted their employee commute stats from 88% solo car trips to 35% and from 4% to 57% transit users.  We can’t stop cheering about this trend.

So, the Tower-with-Two-Names is a visual symbol of the city, a landmark of the midwest, an object lesson in structural engineering and a catalyst of urban planning.  Not bad for a modern day ziggurat.  We salute you!