When constructing an 858-foot tower on Chicago’s lakefront, you need to design a structural system that can handle wind. The North Tower at 400 Lake Shore Drive, a 72-story building that will house 635 rental residences, sits at the confluence of Lake Michigan’s shoreline winds and the Chicago River’s wind corridor.
To stand strong in these conditions, Related Midwest, LR Contracting Company and architects Skidmore, Owings & Merrill (SOM) have implemented an innovative belt and outrigger wall system that balances form with function. The goal is to confuse the wind and stabilize the building, without the need for mechanical dampers or blow-through floors required by some supertall towers.
Architecture as Aerodynamics
What truly sets 400 Lake Shore apart is how its architectural design actively contributes to wind resistance. The building’s cascading terraces aren’t just aesthetic; they are aerodynamic strategy. Based on extensive testing in SOM’s high-tech wind tunnel, the tower’s stepped design has been carefully cleaved apart and staggered along the north and south faces of the building, with steps on each edge purposefully misaligned.
This intentional asymmetry serves a critical function to break up wind vortices. When wind hits a conventional rectangular tower, it can form spiral patterns (vortices) that amplify the building’s movement. The misaligned steps at 400 Lake Shore disrupt these patterns, essentially confusing the wind and preventing it from establishing pressure. Even the bay window curtain walls add texture that further disrupts air flow across the façade.
The building’s placement and orientation reinforce these advantages. Angled toward the cityscape with terraces stepping down the eastern façade, the tower presents a disruptive profile to the winds traveling up Lake Michigan’s shore and funneling through the Chicago River.
What Makes the Structural System Different
The belt and outrigger system amplifies what the architecture sets in motion. While using these systems isn't new — it's considered best practice for tall, slender residential towers — 400 Lake Shore's approach is notable:
Continuous outriggers: Instead of limiting outrigger walls to just a few mechanical floors (the typical approach), 400 Lake Shore runs them on every single floor from the foundation up to Level 44, or about 60% of the building's height. That's a much more comprehensive use of the system than most towers employ.
The primary belt wall at Level 44: This horizontal concrete band wraps around the building's north and south faces. The scale is staggering, as it required 400 cubic yards of concrete (delivered in two massive pours of 200 cubic yards each), 150,000 pounds of rebar (enough to fill six semi-trucks), and 12,000 square feet of wall forms. The on-site construction teams, including LR Contracting Company, BOWA and Goebel Forming, coordinated 24 access openings — two per bay — to accommodate future window installation. This belt ties multiple perimeter columns together in one move, and where the outrigger walls intersect it, the core suddenly connects to an entire line of façade columns instead of just a few. A secondary belt wall at Level 72: Near the top of the tower, a second, smaller belt wall ties the system together at the uppermost stepped section, ensuring the entire structure works as one coordinated unit.
Tailored to the architecture: Coordinating the structural system with the building’s staggered, stepped design — rather than a simple rectangular shaft — requires precise engineering integration. The structure and architecture don’t just coexist; they collaborate.
The Result: Wind Resistance Without Compromise
The synergy between stepped architecture and robust structural engineering allows 400 Lake Shore to achieve what many supertall buildings cannot: excellent wind performance without mechanical dampers or open blow-through floors that disrupt the façade. This is an especially notable achievement for what will be one of Chicago’s tallest towers, rising on one of its most prominent sites.
The structural team also is reusing the deep foundations left behind by the never-completed Chicago Spire project, further improving building performance while reducing concrete usage.
When complete, 400 Lake Shore's North Tower will be known as much for its distinctive stepped form as for the sweeping lake, river, and city views visible from within—all framed by reimagined bay window curtain walls that echo Lake Michigan's rippling surface. But it’s the under-the-hood harmony between form and structure that makes such impressive vistas possible.
