At the confluence of the Chicago River and Lake Michigan, a long-stalled construction site in the city of Big Shoulders is being transformed into an ambitious new development: 400 Lake Shore Drive, a complex that the developer says will reshape the skyline while showcasing new ways to design and build supertall buildings.
The first of two planned towers rises on land that was once the site of The Spire, a massive residential tower that was never built due to the financial crisis of 2008. Each is expected to be nearly 900 feet tall. They will house rental apartments, some designated as affordable housing, and offer panoramic city, lake and river views from a mix of studios, one-, two- and three-bedroom units.
A square between the two towers will mark the end of Carrer de l’Aigua. It will have public art and spaces for residents and guests.
Image courtesy of Related Midwest
Design for the wind
Work on the project has required navigating complex logistics, reusing parts of the existing site, overcoming engineering obstacles and tackling one of the biggest challenges of tall buildings: conquering the wind.
“As architects and engineers, we know that architectural form is the most influential factor in wind performance,” says Brad Young, senior associate director and project engineer at SOM, which designed the structure. “We focused on the top half of the tower, where the wind forces are strongest. That’s where the setbacks occur, and they ended up winning there. They create terraces and reduce the effects of the wind.”
The stepped mass on the eastern facades of the towers was perfected through extensive wind tunnel testing that allowed engineers to observe how air moves across the site, particularly the strong currents that sweep in from the west and southwest along the river.
“We saw a sort of wind cavern effect,” Young notes. “After initial testing, we refined the form. Even subtle adjustments made a big impact.”
The adjustments allowed the team to pursue the unconventional goal of eliminating the need for a tight mass damper, a common feature in supertall buildings to counteract sway.
The tapered shape of the towers and cascading terraces will help break up wind patterns and reduce pressure on the facade.
Image courtesy of Related Midwest
“Shock absorbers cost money, take up valuable space on top of the building and require long-term maintenance,” says Young. “Our approach was to avoid them if we could by using architectural forms and structural systems.”
The solution came in the form of a continuous stabilizer and belt system, which can be compared to suspenders that hold trousers. The system consists of reinforced concrete walls that extend from the central core of the building to its perimeter, uniting the structure and increasing rigidity. There is a main belt wall at level 44 and a secondary belt wall near the top completes the system.
“The architecture and structure work together, allowing us to control motion without a damper,” says Young.
“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 edge of the lake.”
The numbers illustrate the scale: 400 cubic yards of concrete placed in two operations, 150,000 pounds of reinforcing steel and 12,000 square feet of formwork. The work also required 24 precisely located openings to allow for future curtain wall installation.
“Everything had to be sequenced perfectly,” says Biernacki. “It’s like a symphony. Every trade has its timing, and if something doesn’t work, everything can be out of sync.”
Vertical construction progresses with a tower crane and bright yellow climbing formwork enclosing the floors while a concrete pump works to form the core of the building.
Image courtesy of Related Midwest
Months of preparation
Even before any structures could go up, the team had to deal with the history of the site that was pre-excavated for The Spire. The transformation of this vacant hole required engineering ingenuity and environmental expertise.
The team chose to use as much of the existing base as possible.
“There were already twenty 10-foot-diameter rock caissons,” Young notes. “We placed the core of the building directly over them to take advantage of what was there.”
But first it was necessary to pump “more than 20 million gallons of water,” says Rich Goodwin, senior superintendent for Related Midwest.
Other caissons already on site were incorporated into the design to reduce both cost and environmental impact.
“It was a strategic decision. Everyone bought into it early on,” says Young.
The project has used elements from the existing foundation of The Spire, a project that was abandoned in 2008.
Images courtesy of Related Midwest
Precision through technology
As construction progressed, maintaining accuracy was especially critical due to 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 general contractor. “The BIM and VDC coordination started even before we got to the site.”
The team used digital models to plan every detail, from bar placement to mechanical systems, but drone verification was crucial to keeping the project on schedule and avoiding rework.
“We used drone technology to scan each slab before pouring,” says Ehimwenman. “Compare what’s built to the model. If something is wrong, 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 fast pace to achieve in a limited urban location. Bordered by water, residential buildings and major roads, the dumps required careful logistical planning.
“We’ve directed most of the traffic off Lake Shore Drive to minimize disruption to neighbors,” Goodwin says. “Everything is a matter of communication: with the city, with the residents, with everyone.”
Work is progressing in the narrow urban precinct, which is bordered by water, roads and residential buildings.
Image courtesy of Related Midwest
Collaboration in a crowded place
More than 260 workers have been on site during the peak construction of the North Tower. Daily meetings and weekly foremen’s 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, the others step up.”
This 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 boxes on the belt wall,” Goodwin says. “This allows future access to install the facade.”
The openings required additional reinforcement but ensured that the exterior of the building could be completed without compromising the structure.
As the North Tower is erected, some work is interrupted until the parts are under glass to better ensure the safety of the workers.
Image courtesy of Related Midwest
Against the Wind
Although the design mitigates the effects of wind 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 there,” Goodwin says. “We always say, ‘Every day is a windy day.’
The team sequenced the work to reduce wind exposure.
“We’ve intentionally held back certain works until they’re behind glass,” says Goodwin. “It’s counterintuitive, but it’s safer.”
“We’ve logged over 1.5 million man hours with less than 10 incidents,” says Ehimwenman. “That speaks to the planning and culture of this project.”
For Ehimwenman’s company, which is the minority contractor, the project is a milestone.
“Working in a skyscraper of this magnitude, in this place, is the honor of a lifetime,” he says.
Located at the confluence of the Chicago River and Lake Michigan, 400 Lake Shore Drive will offer residents panoramic views of the city.
Image courtesy of Related Midwest
Remembering 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 is more than just architecture,” says Biernacki. “It’s being built by a diverse team, including a minority general contractor and community-based businesses.”
The team says the integration of architecture and engineering, rather than turning to mechanical solutions such as shock absorbers, and a collaborative approach from design to execution set the project apart.
“We wanted the building to resolve [wind] problem,” says Young. “And we showed that it could.”
“This is a gateway to the city and reflects what Chicago is all about,” adds Biernacki.
