Aon Center

skyscraper
international-style
IL
Chicago

About the Aon Center in Chicago
Architect and team
Architectural style
Spaces and uses
Structure and materials

The Aon Center is an International Style skyscraper designed by Edward Durell Stone, in association with Perkins & Will Partnership, and built between 1970 and 1973, for a reported $120 million dollars, in Chicago, IL.

Aon Center is not the only name you might know this building by though. It is common for companies to want to attach their names to iconic buildings when they move in, or for the general public to come up with nicknames, and this one is no exception. The Aon Center is also known, or has been known as, Standard Oil Building, or Amoco Building.

Its precise street address is 200 E.Randolph Street, Chicago, IL. You can also find it on the map here.

Although this building is unrelated to the Twin Towers in NYC, many have highlighted the similarities between both projects. The structure type of choice in both cases was a "framed tube-in-tube", which naturally creates narrow windows and, depending on the materials used, the distinctive vertical stripes which both projects share.

The building underwent a major restoration between 1990 and 1992.

Building's timeline

Construction begins

1970

Construction completed

1973

Restoration

1992

years ago

2024

1990 to 1992 - During this $80 million restoration, the carrara marble cladding panels of the building were replaced with granite panels.

Architect and team

Edward Durell Stone was the architecture firm in charge of the architectural design, in association with Perkins & Will Partnership.

That being said, architecture is a complex discipline involving many professionals from different fields, without whom this building would have not been possible. We will surely be leaving out a lot of names here, but here is a list of the people we do know also played their part in making the Aon Center a reality:

Perkins & Will in charge of Structural Engineering
Turner Construction as the Main Contractor
Otis as the company in charge of the elevators system
Standard Oil Company of Indiana as the Main Developer

Architectural Style

The Aon Center can be categorized as an International Style building.

The international style originated in Europe in the early 20th century, and made its way to the US a couple of decades later when the rise of the Nazi regime forced figures such as Walter Gropius, Marcel Breuer, or Mies van der Rohe to flee Europe.

The International Style emerged as a response to the prevailing historicism and ornate architecture styles of the late 19th century, which according to a younger generation of architects didn't represent the new materials and construction techniques that were on the rise at the time.

Architecture in the early 20th century US was marked by the adoption of steel structures, modern construction techniques, and the rise of the skyscraper. As it turns out, this combination of circumstances created the perfect ecosystem for the International Style to flourish, becoming the to-go style for skyscraper designs during the mid-20th century, when American cities were growing fast.

The International Style’s legacy can not only be found in numerous iconic buildings across all major American cities, but also incorporated in contemporary architecture, which still puts a big emphasis on functionality and minimalism.

Spaces & Uses

The Aon Center reaches an architectural height of 1135ft (346m), 1188ft (362m) if you count the antenna, with the last accesible floor being 1076ft (328m) off the gorund. It has a total of 88 floors, 83 above ground and 5 basements, served by 50 elevators.

In regards to parking space, the building has a total of 679 spots available, which roughly equals 8 spots per floor (above ground).

Ever since opening its doors to the public in 1973, the Aon Center has mainly been used as Commercial space.

1188ft (362m)

1135ft (346m)

1076ft (328m)

5 basements

Materials & Structure

The Aon Center uses a framed tube-in-tube structure , with steel columns and concrete slabs.

A framed tube-in-tube structure uses a central core, known as inner tube, which usually holds stairs, lifts and installations, and a perimeter of columns around it, which form the exterior tube. The interior tube is tipically more massive (often made of reinforced concrete), and the exterior tube is "lighter" (made of steel or concrete columns). Both tubes are conencted via horizontal elements which make up the floors and also transmit any horizontal froces from the facade to the core.

The facade of the building is load bearing. This is a direct consequence of the integration of the exterior "tube" into the facade, something which most framed tube-in-tube buildings do in order to liberate the interior space from structural elements and achieve a more flexible interior.

So the facade of the builing is techinically load-bearing, yes, however, in between the load-bearing colums we find a curtain-wall type of facade, which by itself would not be cosnidered load-bearing.

From an aesthetic point of view, the facade features a curtain wall consisting of 15 vertical bands of windows with dark glass and metal frames on each side, embedded in white Carrara marble triangular pillars, which are part of the building's structure. So yes, the facade is both structural, and a curtain wall.

Over time and due to weather conditions, the Carrara marble cladding deteriorated and had to be replaced with granite of the same color.

The facade transfers horizontal wind loads to the main building structure through connections in the floors or columns..