Structural Intelligence

Meet the engineers behind some of the world’s most ambitious buildings.

Photo © Finn MacLeod | SOM

Are engineers the unsung heroes of architecture? Certainly, without their contributions, ​the skyscrapers that define skylines around the world would simply not be possible​. But their work goes far beyond supertall feats of virtuosity like the Burj Khalifa. Engineers collaborate with architectural design teams on projects at all scales — from interior renovations to urban master plans — bringing their deep expertise and a rigorous approach to solving problems. William F. Baker and Mark Sarkisian, the leaders of SOM’s Structural Engineering Practice, speak about how architects and engineers work together in this interview, originally published on Architizer.

Mark Sarkisian (left), SOM Structural and Seismic Engineering Partner, and William F. Baker, SOM Structural and Civil Engineering Partner. Photo © Cody Pickens

What role have models traditionally played in SOM’s design process?

William F. Baker: Models have always played an integral role in the design process at SOM: A model helps the design team to understand the project in ways that drawings or even rendering cannot. If you walk through our offices, you will see models everywhere. They are not static representations of an idea, but something the team modifies and “plays” with to refine the design.

There’s a tactile, visual element that inspires new ways of seeing and understanding the project. Models help the team work out how buildings can be detailed and built. A major aspect of SOM’s design philosophy is structural clarity. In the Utzøn Center exhibition in Aalborg, Denmark, we only modeled the structure to demonstrate that we strive for buildings where the architecture is the structure and the structure is the architecture.

How have new model-making technologies like 3D printing changed SOM’s design process? Has it encouraged new forms or strategies that would have otherwise been difficult to illustrate or grasp?

Baker: Our model shop has all the latest tools. Tools such as 3D printing can make model-making faster and more accurate. At SOM, we aim to use these tools to facilitate the exploration of the design, not to enable willful form-making. Some firms are more about form, but that is not for us. Even for a firm like SOM, where we value simplicity and clarity, models are immensely helpful in understanding a design. We also use a range of materials to explore large and small elements of structural systems. My office is full of pinups and component samples.

3D-printed models show four iterations of the design for Tianjin CTF Finance Centre. Photo © SOM

Given how sophisticated digital structural testing and building information modeling have become, do physical models still play a role in testing engineering concepts?

Baker: At SOM, we actually have a wind tunnel in our Chicago office to test models of tall buildings; it’s hugely helpful in the conceptual design. Seemingly small changes in the shape of a tower can have a major effect on how it moves and responds to forces that act upon it. In the past, we had to rely only on our experience to evaluate competing concepts for a tower.

A wind tunnel in SOM’s Chicago office allows teams to test conceptual skyscraper designs. Photo © SOM

At times, we have avoided a scheme because we had no basis for evaluating a novel shape, and we could not take the risk. Now, we use the wind tunnel for many of our tall building competitions and for the refinement of a tower during the concept and schematic design phases. The wind behavior of a tall tower can have a huge effect on the cost, embodied carbon and structural member sizes of a tower.

Are there any structural clichés that SOM tries to avoid?

Baker: I don’t like to see fake structure elements used as “decoration.” Buildings should be honest. Nothing is more honest than an appropriate structure clearly expressed.

Are there any signature structural innovations of which the firm is particularly proud?

Mark Sarkisian: We’re proud of quite a few innovations that have been realized over the past 50-plus years. SOM partner Fazlur Khan’s tube structural systems — framed, bundled, braced, tube-in-tube — are now ubiquitous: The John Hancock Center and the Willis Tower are groundbreaking examples that the Chicago team sees on their commutes every day. SOM has also been an inventor, or early adopter, of numerous other innovations that have enabled structures at a range of scales, including the supertall Burj Khalifa in Dubai. Core and outrigger, bundled core, buttressed core, stayed-mast, supercore, Michell truss bracing, pin-fuse joints, and precast corewalls are a few examples. Our recent work on timber construction has garnered a lot of attention, as well.

Models show the structural systems for 100 Mount Street (Michell truss bracing), John Hancock Center (braced tube), and 111 Main Street (core with suspended floors). Photos © SOM

Our culture is a big part of driving these sorts of innovations forward and encouraging more widespread acceptance of new structural concepts. We have an internal working group we call the Research Gang that convenes to think up new solutions and test them. We are able to experiment and quickly iterate on our designs alongside our colleagues in a variety of disciplines. That sort of collaboration and willingness to facilitate rigorous experimentation is an enduring quality of our practice that we are very proud of.

In a recent test, SOM’s innovative timber-concrete composite system withstood more than 80,000 pounds of pressure. This result marks an important step toward using timber, a renewable resource, for high-rise construction. Photo © SOM

How much is the firm trying to create unique, one-off buildings, and how much are you trying to innovate new typologies and technologies that could be widely reused?

Sarkisian: Every structure is unique because of its physical and cultural context and the needs of the site and the client. A concept can take on many forms. We have created tubular towers of many shapes, braced buildings, a variety of topologies; the list goes on. It is natural that we never do the same building twice.

When do engineers enter the design process for supertall projects? How much does engineering drive the design?

Baker: SOM has always been an interdisciplinary firm, so the relationship between engineering and design is symbiotic. When we start on a project, we’re all there and can examine the constraints and opportunities together. Throughout the process, it’s not one discipline informing the other — it’s an open, active dialogue across the entire team.

“The right structural concept can be the difference between a design that moves forward and one that is never realized.”

This process applies to all projects, not just supertall projects. Some of the most important projects we have done are not at all tall: Exchange House, the Air Force Academy Cadet Chapel, and the Hajj Terminal, for example. When a project comes in the office, we try to have all the disciplines present for the initial meeting, before there is any scheme. These initial brainstorming sessions include planning, interiors, MEP, sustainable engineering, civil engineering, structural engineering, and architecture. It is this process that keeps the firm moving forward in creating new and substantive architecture.

London’s Exchange House was built on a platform above active rail tracks. Engineered like a bridge, the building’s structural design enabled train service to continue below during construction. Photo © John Davies
With its exposed steel frame, the completed building expresses the engineering solution that made its construction possible. Photo © Richard Waite

How important is location and geography in driving the engineering of a tall project? Have any structural concepts been a reaction to unique regional constraints?

Sarkisian: Design is the search for constraints. The constraints of location should be manifested in the design. This can be in the form of the local construction technology, the foundation conditions, wind conditions, the seismic condition, the climatic issues of temperature, sunlight, air quality, etc. All of these can show up in the structure and architecture. One of the more interesting problems is when a location has both high wind and high seismic. For wind, you want high stiffness; for seismic, you want a soft structure and high ductility. How can you satisfy both? We are doing a lot of research in this area, in both structural topology and devices such as the pin-fuse connection.

SOM’s Pin-Fuse Seismic System is designed to protect buildings in earthquake-prone regions. These devices operate mechanically during an earthquake, allowing the building to respond flexibly when subjected to extreme ground movement. Images © SOM

How do you think about the value of an innovative structural concept, and how do you communicate that value to the client?

Sarkisian: The right structural concept can be the difference between a design that moves forward and one that is never realized. On the commercial side, successful clients understand that and listen. It also shows up in the cost and the speed of construction. On the design side, structural innovations move architecture forward. They create new design opportunities that can lead to new architecture. The designs of many of our most famous buildings are based on structural innovations.

Are structural engineers the unsung heroes of supertall architecture?

Baker: I once heard that mathematicians are among the most contented people. The beauty of an elegant proof is profound. I think structural engineers are often so pleased by an elegant structure that outside acclaim is not needed. The downside of not being focused on being known to the public is that many students aren’t aware of what can be achieved as a structural engineer. For this reason, structural engineers need to make more of an effort to display their contributions to architecture.

The bold structural design of Poly International Plaza is making waves far beyond the Beijing business district it anchors: The project took five awards at the 2017 Architectural Engineering Institute (AEI) Conference. Photos © Bruce Damonte

To learn more about how engineers and architects collaborate, explore an exhibition that puts structural design on display…

…and catch a glimpse of skyscraper designs that remain on the drawing board.