Salesforce Tower Chicago is the last of a three-tower development situated on what used to be a parking lot right against the Chicago River. Photo by Jeff Yoders for ENR
At 850 ft tall and 1.2 million sq ft, it’s easy to view Salesforce Tower Chicago as a typical office high-rise in the third-largest U.S. city’s central business district, but the glass skin of this latest structure hides design and materials innovations that allowed it to achieve a 27% reduction in concrete production and a 9% reduction in steel used compared with a typical office tower of this size.
The former Wolf Point South—the name was changed to 500,000-sq-ft anchor tenant Salesforce after construction began in April 2020—is the first building in Chicago to measure environmental product declarations to quantify embodied carbon emissions of concrete, steel and other construction materials. Its structural engineer, Magnusson Klemencic Associates (MKA), and the developer responsible for its $800-million construction cost, Hines, have created an Embodied Carbon Reduction Guidebook, a result of MKA’s work on the embodied carbon calculator, with the tower as its first demonstration project.
A Walsh team installs curtain wall at SalesForce Tower in Chicago overlooking the confluence of the Chicago River's three branches. Photo by Jeff Yoders for ENR
Salesforce Tower has belled caissons for its perimeter columns and the podium, and 10 core caissons that go 110 ft deep into bedrock with 6-ft sockets to deal with heavy wind loads and uplift, says Matt Streid, a principal in MKA’s Chicago office. Its original name, Wolf Point South, refers to the Y-shaped confluence of the three branches of the Chicago River. East and west residential towers were previously built in the development that sits on a former Kennedy family-owned parking lot.
The tower has only one true below-grade level, roughly 10 ft below the bottom of the Chicago River, while the first three floors span to the same raised level of downtown Chicago above lower Wacker Drive. The below-grade structure is made of concrete foundation walls and slabs. A city-required riverwalk has a 16-ft cantilever over the river. Streid says that MKA, design architect Pelli Clarke & Partners, Hines and contractor Walsh Group negotiated with the U.S. Army Corps of Engineers to get as far out over the river as they could with the riverwalk because the site was already tight with deliveries coming from a haul road that goes underneath the existing Wolf Point East residential tower.
With limited lay-down area, crews had to coordinate crane picks for materials upon arrival. Photo by Jeff Yoders for ENR
“There has been a paradigm shift in the past 10 to 15 years where people need less space and companies are looking to fit more people and get rid of some of the wasted square footage,” says Sean May, vice president at architect-of-record HKS and the senior project architect on Salesforce Tower.
A typical 5-ft grid was downsized to a 4-ft-9-in. grid, which translates from a traditional 10-ft office to a 9-ft-6-in. office in the tower. Tenants who have signed on are mainly like tech provider Salesforce that utilize open floor plans and use most of their rented space.
From the ground floor (the building’s fourth level), the tower transitions to a steel-framed building with floors supported by W14 steel perimeter columns, Streid says.
Steel erector Danny’s Construction had to place the outrigger in tight spaces due to the geometry of the building and the two neighboring towers. Photo by Jeff Yoders for ENR
Salesforce Tower has a steel-frame composite slab-on-metal deck composition with the typical floors having 3.25-in. lightweight concrete on 3-in. metal deck. The two-story outrigger trusses occur between levels 38 and 40.
“Instead of having a 42-ft-wide core, we effectively have a 120-ft-wide core on these floors,” Streid says.
The building’s core strength varies by floor between 12 KSI and 10 KSI. Using high-strength steel allowed MKA to reduce steel quantities in rebar and structural steel columns.
“Respecting serviceability, how much the building’s drifting, how much it’s accelerating and moving, that’s not a code-dictated provision, so we can be more aggressive,” Streid says. “We use expected concrete strengths in our serviceability models, and there really is a difference, with the actual concrete strengths achieving over 18 KSI. It’s a meaningful uptick. We don’t go all the way to assuming 18 KSI in our models, but we do take advantage of increased material properties to help out. The stiffness controls the building.”
Almost all deliveries to Salesforce Tower’s site had to go through a tunnel underneath Wolf Point East directly north of the site. Photo by Jeff Yoders for ENR
The outriggers extend to seven 65-KSI perimeter columns that perform like ski poles stabilizing the central core, but only at the main cross walls of the building. A belt-truss, also at floors 38-40, distributes the load evenly between the outriggers and the intermediate columns in between.
The specialty concrete mixes and simply using less material achieved a 27% concrete savings on the building’s embodied carbon, but MKA and HKS were able to cut down on the project’s steel frame by specifying A913 Grade 65 high-strength steel. The Nucor Aeos high-strength steel in Salesforce Tower’s columns and members is made of 90% recycled material. Streid says 65 KSI is MKA’s new baseline and using the Aeos steel reduced the column sizes and enclosures by 30% from 50 KSI steel and saved one to three hours of preheat time to help achieve a 9% reduction in steel on the project.
“Using a higher strength steel allows you to keep a smaller section size, reducing its embodied carbon,” says Elliot Wilm, project manager for general contractor Walsh.
It was still a project that used a lot of steel from both suppliers who make the product: Nucor and ArcelorMittal. The belt truss, outriggers and associated tie plates alone totaled 675 tons, says Colin Gilbert, project manager for steel fabricator Cives. Placing those tie plates was difficult inside the core form framing because of the tighter geometry of the slimmed-down tower, especially at level 40.
“The tie plates were 24 in. deep, and the distance between the core form framing and the core wall form itself was 30 in.,” says Carl Hultman, senior project manager at steel erector Danny’s Construction.
Accounting for the depth of the lift, there were only 4 in. of vertical clearance remaining to place the tie plates. Hultman says Danny’s chose rigging points close together so that they could fit the end of a plate in and then let the center of it move further past its final location to allow enough room to swing the opposite end of the tie plate where it needed to be. The tie plates could then be lowered and final position adjustments made, then welded in place to their supports within the concrete form. Extensive surveying and tight erection tolerances allowed the final bolted connections of the outriggers to fit up seamlessly. Cives created a 3D model for all of the structural steel to plan delivery and installation, while general contractor Walsh coordinated the entire project in a Navisworks model that incorporated the MKA and HKS design models.
A belt truss at floors 38-40 and outriggers that begin at the 40th floor allow Salesforce Tower Chicago to remain stable against wind and shear forces right along the Chicago River. Schematic engineering illustration courtesy of Magnusson Klemencic Associates
Michael Izzo, Hines’ vice president of carbon strategy, says the real estate market and Hines itself have already been influenced by the lessons learned on Salesforce Tower using the Embodied Carbon Reduction Guidebook.
“It’s been felt in our future projects within the area and even with concrete manufacturers, really looking at their offerings and going through all their cement mixes to see how they can reduce their embodied carbon, even bringing portland limestone cement to the table,” Izzo says.
Salesforce Tower has belled caissons for its perimeter columns and the podium, and 10 core caissons that go 110 ft deep into bedrock with 6-ft sockets to deal with heavy wind loads and uplift. Schematic engineering illustration courtesy of Magnusson Klemencic Associates
Izzo notes that all of Hines’ new developments will use the guide to reduce embodied carbon and the Conceptual Construction Group, the team within Hines to develop the guide with MKA, is helping to push implementation on day-to-day activities with design and construction teams. Some other projects already utilizing the guide include Oak Brook in Oak Brook, Ill., and 555 Greenwich in New York.
“Operational carbon is very easy to see because you see it in energy reduction,” Izzo says. “Embodied carbon is a fairly new topic, the data transparency isn’t there. We know it’s a big problem, and I think it’s about stewardship and realizing that technology will get us there.”
Salesforce Tower is expected to be completed in 2023.
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