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Form Follows Function: The Beauty of Structural Shells with SOM Engineer Toby Mitchell

This article is part of our coverage of the Chicago Architecture Biennial, a curated series of design exhibits across the Windy City that make up North America’s largest architecture festival.

The exhibit “SOM: engineering X [art + architecture],” presented the poetry of structural excellence. Highlights included a series of over 30 tower models, videos, sketches, historical photos and structural shell models. The display illustrated the connection between the beauty and functionality of well-executed structural engineering.

We caught up with SOM’s Toby Mitchell, one of the exhibit’s main contributors, whose work focuses on high-performing structural shells. Mitchell received his Ph.D. in structural engineering from U.C. Berkley, and on top of his day-to-day duties at SOM’s Chicago office, he’s also a member of the SOM research group, working to implement new technologies.

HD Architectural: Why do shell structures matter? Can you discuss the inspiration that set you on this journey of researching structural shells?

Toby Mitchell: Shells have stiffness because of their shape, so they’re very efficient and can achieve very light and delicate structures. This is important from an ecological perspective, since they use so much less material than conventional structures. However, my interest in studying them was prompted simply by the fact that they look cool.

HD Architectural: And, how are you applying this in your SOM work as well as your research there?

Toby Mitchell: It gets incorporated into the design of roofs and canopies that are part of larger sites. We don’t do a lot of stadium roofs, per se, but we do a lot of developments that have atriums, concourses, or other features where a skylight or canopy should be a design centerpiece.

HD Architectural: How do you use your findings to communicate with and guide architectural and building services teams? What is the workflow process like there (can you give an example)?

Toby Mitchell: Usually it starts with a discussion of the top-level goals of the project. Is it a roof that has to keep out the elements, or is it just providing shade? Where are the entrances and exits? Where can the structure touch the ground and where should it be open? Is there a material in mind?

Once this discussion gives us a picture of what we want in the abstract, I try to pick out a tool from our computational toolbox that fits the design intent, or sometimes I build a new one for that project. Depending on the project and design team, I may propose a particular design option myself, or I might be training the architectural designers to use the tools we’ve selected to achieve their design goals.

We caught up with SOM’s Toby Mitchell, one of the exhibit’s main contributors, whose work focuses on high-performing structural shells.

HD Architectural: Tell us some of your favorite projects you’ve worked on at SOM.

Toby Mitchell: My favorite ones have been the most collaborative. It’s not always comfortable to be talking to your architectural counterparts continuously through the design, but it leads to better results than each discipline heading back to their desks after a meeting, and then only talking again at the next meeting. The best ones were where I was at the design architects’ desks three or more times a day for weeks on end walking through the exact details of how the structural and architectural designs can be integrated and continuously refining the design. This is generally greeted with some funny looks at the beginning (“you’re here again?”), but by the end there’s a recognition that we had achieved something special.

HD Architectural: Since this is tied to the Chicago Biennial, how did you opt to work for SOM’s Chicago office and what makes Chicago such a strong architecture city?

Toby Mitchell: SOM’s Chicago office maintains a great two-way conversation between the architects and engineers. This enables a lot of interesting design opportunities that wouldn’t be available in a more compartmentalized firm. Chicago itself has a storied tradition of technically focused architecture thanks to its strong modernist roots, and this helps keep the different disciplines focused on a high level of design integration.

HD Architectural: What are your favorite examples of inspiring architecture and structural engineering in Chicago?

Toby Mitchell: I’m a big fan of the Garfield Park Conservatory. It’s a beautiful space not just because of the vegetation, but because of the classic, delicate steelwork. A hundred years ago when it was built, structural steel was an expensive, relatively new and exotic material. So, the builders had to be very economical with it, I think, and the result was a very light filigree structure that lets in a huge amount of natural light and that seems to disappear when you’re inside the space. In a certain sense, the modern cheapness of steel is the enemy of good design; it lets people be lazy rather than work to achieve the lightest possible structure!

HD Architectural: What do you appreciate about the Chicago Biennial and participating in SOM’s engineering X [art + architecture] exhibit?

Toby Mitchell: The important thing about the Biennial is that it’s focused on presenting architecture to a wide public audience. The SOM exhibit was put together with that in mind. You don’t need to be an expert or even an architecture aficionado to get something out of it.

We really focused on giving people a window into the top-level concepts, the general philosophy of how engineering and architecture come together. More than that, we gave people a lot of cool physical models and videos and images to look at! The visual presentation of the exhibit is the thing I think I’m the most proud of. It looks great!

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