CNA Center vs Aon Center

Comparing the CNA Center and the Aon Center is interesting because they both stand in Chicago, IL, and were completed just one year apart, but they were designed by different architects.

This offers a unique glimpse at how rival designers approached projects in the same city during the same era.

The Aon Center is clearly the larger tower of the two, both in terms of height and number of floors. It rises to 1135ft (346m) with 83 floors above ground, while the CNA Center reaches 600ft (183m) with 44 floors above ground.

Aon Center also offers more total built-up area, a total fo 3,599,965 sqf (334,448m²), which is about 2,299,966 sqf (213,674m²) more than what the CNA Center offers.

Of course, each project may have faced different briefs or regulatory constraints, which we don't really know about and could also explain the outcome.

Both the CNA Center and the Aon Center were designed in line with the aesthetic conventions of the International Style style.

Both buildings were completed when the International Style style was already past its peak. This makes them feel like late echoes of the movement, more reflective of continuity or nostalgia than of cutting-edge design at the time.

Both the CNA Center and the Aon Center were designed to serve as commercial towers, and that has remained their main use since their completion, serving similar roles in the urban fabric.

The Aon Center also provides 679 parking spaces.

The two towers rely on different structural systems, reflecting distinct engineering strategies.

The CNA Center uses a Frame structural system, which relies on a regular grid of columns and beams to sustain its weight, while the Aon Center uses a Framed Tube In Tube system, that combines a strong central core with a perimeter tube of columns.

Yet, when it comes to their facade, they both employed the same solution, a Curtain Wall facade.

A curtain wall is a non-load-bearing facade hung from the structural frame. It is anchored to floor slabs and transfers only its own weight and wind loads, allowing for sleek, glassy exteriors.