A plaza between the two towers will mark the end of Water Street. It will feature public art and spaces for residents and guests.
Image courtesy of Related Midwest

Designing for Wind

Work on the project has required navigating complex logistics, reusing parts of the existing site, overcoming engineering hurdles and tackling one of the greatest challenges of tall buildings: conquering the wind.

“As architects and engineers, we know that architectural form is the single most influential factor in wind performance,” says Brad Young, senior associate principal and project engineer at SOM, which designed the structure. “We focused on the upper half of the tower where wind forces are strongest. That’s where the setbacks occur, and they ended up being a win-win. They create terraces and reduce wind effects.”

The stepped massing on the towers’ eastern facades were refined through extensive wind tunnel testing that enabled engineers to observe how the air moves across the site, particularly the strong currents that sweep in from the west and southwest along the river.

“We saw a kind of wind cavern effect,” Young notes. “After initial testing, we refined the form. Even subtle adjustments had a big impact.”

The adjustments allowed the team to pursue the unconventional goal of eliminating the need for a tuned mass damper, a common feature in supertall buildings to counteract sway.

The towers’ tapered form and cascading terraces will help break up wind patterns and reduce pressure on the facade.
Image courtesy of Related Midwest

“Dampers cost money, take up valuable space near the top of the building and require long-term maintenance,” Young says. “Our approach was to avoid them if we could by using architectural form and structural systems instead.”

The solution came in the form of a continuous belt and outrigger system, which can be compared to suspenders holding up pants. The system entails reinforced concrete walls extending from the building’s central core to its perimeter, tying the structure together and increasing stiffness. There is a primary belt wall at Level 44, and a secondary belt wall near the top completes the system.

“The architecture and structure work together, which allows us to control motion without a damper,” Young says.

“The belt wall at Level 44 is incredibly complex,” adds Don Biernacki, executive vice president of Related Midwest and president of LR Contracting Co., which is developing the project. “You’re talking about a massive horizontal structure 44 stories in the air along the lakefront.”

The numbers illustrate the scale: 400 cu yd of concrete placed in two operations, 150,000 lb of reinforcing steel and 12,000 sq ft of formwork. The work also required 24 precisely located openings to allow for future curtain wall installation.

“Everything had to be sequenced perfectly,” Biernacki says. “It’s like a symphony. Each trade has its moment and, if something is off, the whole thing can fall out of sync.”

Vertical construction advances with a tower crane and bright yellow climbing formwork that encases floors while a concrete pump works to form the building’s core.
Image courtesy of Related Midwest

Months of Preparation

Even before any structure could rise, the team had to deal with the history of the site that was previously excavated for The Spire. Transforming that long-vacant hole required engineering ingenuity and environmental expertise.

The team chose to use as much of the existing foundation as possible.

“There were twenty 10-foot-diameter rock caissons already in place,” Young notes. “We positioned the building’s core directly over them to take advantage of what was there.”

But first it was necessary to pump out “over 20 million gallons of water,” says Rich Goodwin, senior superintendent for Related Midwest.

Other caissons already on the site were incorporated into the design to reduce both the cost and the environmental impact.

“It was a strategic decision. Everybody bought into it early,” Young says.

The project has used elements of the existing foundation of The Spire, a project that was abandoned in 2008.
Images courtesy of Related Midwest

Precision Through Technology

As construction advanced, maintaining accuracy was especially critical because of the dense reinforcement and embedded systems within each concrete slab.

“We relied heavily on technology,” says Nosa C. Ehimwenman, president and CEO of Bowa Construction, the co-general contractor. “BIM and VDC coordination started even before we got on site.”

The team used digital models to plan every detail, from rebar placement to mechanical systems, but drone verification was crucial to keeping the project on schedule and preventing rework.

“We used drone technology to scan each slab before pouring,” Ehimwenman says. “It compares what’s built to the model. If something is off, even slightly, we fix it before the concrete goes in.”

The process helped the team maintain an aggressive construction schedule.

The team did three-day pours—a swift pace to achieve in a constrained urban site. Bordered by water, residential buildings and major roadways, the pours required careful logistical planning.

“We directed most of the traffic off of Lake Shore Drive to minimize disruption to neighbors,” Goodwin says. “It’s all about communication—with the city, with residents, with everyone.”

Work is progressing on the tight urban site, which is bordered by water, roadways and residential buildings.
Image courtesy of Related Midwest

Collaboration on a Crowded Site

More than 260 workers have been on site at peak construction of the North Tower. Daily huddles and weekly foreman meetings keep everyone working in unison.

“We break things down into long-term goals, weekly plans and daily tasks,” Goodwin says. “And we keep communication open. If one trade falls behind, others step up.”

That collaboration extended to another of the project’s most difficult challenges—installing the curtain wall around the belt wall.

“We designed 3-foot by 3-foot box-outs in the belt wall,” Goodwin says. “That allows future access for installing the facade.”

The openings required additional reinforcement but ensure that the building’s exterior can be completed without compromising the structure.

As the North Tower rises, certain work is held off until portions are under glass to better ensure worker safety.
Image courtesy of Related Midwest

Against the Wind

While the design mitigates wind effects on the structure, wind remained a constant challenge.

“You can have a calm day at ground level, but it’s too windy to work up top,” Goodwin says. “We always say, ‘Every day is a windy day.’”

The team sequenced work to reduce wind exposure.

“We intentionally held off on certain work until it’s behind glass,” Goodwin says. “It goes against instinct, but it’s safer.”

“We’ve logged over 1.5 million worker hours with fewer than 10 incidents,” Ehimwenman says. “That speaks to the planning and culture on this project.”

For Ehimwenman’s firm, which is the minority contractor, the project is a milestone.

“To work on a high-rise of this magnitude, at this location, it’s the honor of a lifetime,” he says.

Situated at the juncture of the Chicago River and Lake Michigan, 400 Lake Shore Drive will offer residents panoramic views of the city.
Image courtesy of Related Midwest

Recalling History

The site itself, near the settlement of Jean-Baptiste Pointe DuSable, a Black man who established the first permanent settlement in the area in the late 1770s to early 1780s, adds another layer of significance to the project.

“This building stands for more than just architecture,” Biernacki says. “It’s being built by a diverse team, including a minority general contractor and community-based businesses.”

The team says integrating architecture and engineering—rather than turning to mechanical solutions like dampers—and a collaborative approach from design through execution set the project apart.

“We wanted the building to solve the [wind] problem,” Young says. “And we proved that it could.”

“This is a gateway to the city, and it reflects what Chicago is about,” Biernacki adds.