Maximum Space From A Tight Fit

Innovative design, engineering, and construction practices combined to deliver the one-of-a-kind 150 North Riverside tower.

Cutting-edge design and construction combined to produce the 150 North Riverside building, a 54-story office tower that sits on a 39-ft.-wide base.

By Chris Phares, Clark Construction

Inspiration, vision, and creativity can turn even the most daunting challenge into an opportunity. That is exactly what happened when a two-acre site in downtown Chicago was considered too problematic to develop. It took decades for the right developer and design and construction team to embrace the opportunity and turn a vacant sliver of land along the Chicago River into a trophy-class office space. How they did it is a glimpse into the future of urban construction.

The site for what is now 150 North Riverside sat vacant for decades. Situated on a narrow plot, and surrounded by the Chicago River to the east, active Amtrak rail lines to the west, and Lake and Randolph Street viaducts to the north and south, the parcel of land was laden with complexities. The tracks, combined with city easement and Riverwalk requirements, absorbed more than 75% of the property, leaving a buildable site that measured only 39 ft. wide. But Riverside knew that this parcel had all of the key locational attributes that are expected for a Class A office building. For example, the site is two blocks from Chicago’s busiest commuter rail station, offers convenient access to all forms of public transportation, and provides easy access to the expressways.

Riverside Investment & Development, Chicago (riversideid.com) personnel selected Chicago-based Goettsch Partners (gpchicago.com) to design the building. The firm’s previous work creating unique, bold designs was one factor that helped win the project. Structural engineering work was performed by Magnusson Klemencic Associates, Chicago (mka.com). The resulting gravity-defying design takes advantage of the open riverfront site with projections and setbacks that distinguish the building from nearby structures.

Before anything could move forward, Riverside had to purchase the parcel and structure a unique acquisition of two adjacent parcels of largely air rights above the rail lines. This now three-parcel site allowed the design team to create the 54-story office tower directly on the riverfront, in conjunction with a surrounding public park and Riverwalk.

Riverside’s plan was to build a publicly accessible, open-space plaza above the rail tracks to the west, and place the building as close to the river as possible on the east. This meant they needed to negotiate air rights with Amtrak and get approval from the City of Chicago. In addition, the closest existing building is a condominium tower only 120 ft. away. Convincing local residents, and their alderman, to approve the project was also necessary. Over the course of 18 months, the alderman arranged several meetings with Riverside, residential neighbors, and community organizations to understand their concerns and conduct a dialogue focused on site infrastructure and community benefits.

After almost a dozen proposal iterations, Riverside presented a plan that addressed the alderman’s concerns and residents’ requested changes: accessibility, maximizing open green space, reducing the amount of hardscape, providing public access to the river, and managing traffic and infrastructure needs. While the building design evolved numerous times in the five years prior to construction, the defining shape of the tower remained the same because no other solution would have worked as well or made the same bold statement.

Every phase of the project—from concept to completion—posed significant design and construction challenges. However, innovative thinking and a singular focus on delivering the best possible result from the entire team brought this iconic building to fruition. Profiling these details illustrates how the final product is an intensely collaborative and visionary solution to these challenges.

The lobby, designed to be just as bold as the building’s overall design and construction, uses an 85-ft.-tall glass wall that showcases 150 Media Stream, a one-of-a-kind cultural landmark in the form of a 3,000-sq.-ft. digital-art installation.

Design and Engineering

The building’s base is dramatically smaller than the rest of the tower. The 752-ft. tower rises on a 39-ft.-wide base, which slopes outward at an angle for the first eight stories, then widens to nearly the full width of the site. To accomplish this feat, Clark Construction Group, Chicago (clarkconstruction.com), designed a core-supported structure—a massive central concrete “spine” that holds the elevator core and also transfers the load of the upper floors down to the foundations. Caissons were drilled more than 110 ft. below grade and sunk 10 ft. into bedrock to provide a stable foundation.

Placed between the tracks and the river, the tower occupies less than 25% of its two-acre site. This narrow building footprint allows more than 75% of the property to be unenclosed outdoor space, vastly increasing the pedestrian experience on and surrounding the site. The park and plaza provide more than 1,000 lineal ft. of seating, multiple assembly/event spaces, and 360 ft. of Riverwalk frontage. The Riverwalk component addresses a key element in Mayor Rahm Emanuel’s vision for a Chicago that knits together different parts of the city and provides an aesthetically pleasing connection to boats and water taxis.

Vertical mullions (fins), emulating the river, undulate along the building’s east and west facades to help activate them with an ever-changing pattern of light and shadow. The fins also provide solar shading and minimize cooling loads during summer months, particularly on the building’s west elevation. The narrow north and south faces are divided into three vertical planes that accentuate the slenderness of the tower, with the center plane recessed to create additional corner offices.

Lobby Blurs Boundaries

How a high-rise building meets the ground can be more important than how it meets the sky. While the enclosed building occupies 25% of the site, the all-glass lobby creates a space that seeks to blur the boundaries between indoor and outdoor spaces.

To make the lobby equally as bold as the building’s overall design and construction, the design uses an 85-ft.-tall glass wall that hangs from the tip of the transfer truss at level eight. This glass wall showcases 150 Media Stream, a one-of-a-kind cultural landmark in the form of a 3,000-sq.-ft. digital-art installation. With content directed by a full-time curator, the piece displays artwork in collaboration with local and nationally renowned institutions, such as the Chicago History Museum, the Hyde Park Arts Center, the University of Illinois at Chicago, the School of the Art Institute of Chicago, the University of Chicago, and world-renowned new-media artists.

The 150 North Riverside tower (center with the green roof) sits on a 39-ft.-wide site, hemmed in by railroad tracks and the Chicago River.

Above the lobby

For design continuity, the building core is clad with the same granite on the interior and exterior. All non-structural surfaces are glazed and the west wall of the lobby is enclosed with a 90-ft.-high glass wall, suspended from the structure above and supported by 2 1/2-ft.-deep glass mullions.

The Chicago River played a significant role in design and construction. The building’s curtainwall enclosure references its location on the river, where the water is sometimes very smooth and highly reflective and, at other times, provides a wave-like texture. The system is composed of 8,500 individual units for a total of 540,000 sq. ft. of glass.

To ensure the building is fully isolated from the noise and vibrations of the nearby Amtrak and commuter trains and the “L” train system, 4-ft.-thick concrete core and crash walls were constructed at the west edge of the parcel. The public areas above the tracks are supported by roughly 1-ft.-thick concrete slabs and precast concrete which, in turn, is supported by foundation elements that bear on bedrock. To meet these acoustic requirements, the team performed comprehensive acoustical testing of the curtainwall system. The tests, the first of their kind, validated design criteria and ensured the curtainwall attained a sound-transmission-class (STC) rating of 43.

One component that was not challenging was incorporating sustainability. The growth and development of our communities has a large impact on our natural environment. To that end, sustainability is a tenet that guided work on 150 North Riverside, which was designed and constructed for LEED Gold Core and Shell certification and exceeds all local code requirements for energy and efficiency. Specifically, eco-friendly features include a 100% green roof, high-efficiency plumbing and mechanical systems, a high-performance floor-to-ceiling curtainwall system, open floor plates, lobbies with significant natural daylight, and use of low-VOC, non-emitting construction materials.

The tower foundation is supported by 16 fully reinforced caissons, each 10 ft. dia. and drilled 6 ft. into bedrock.

Public Open Space

It is extremely rewarding to see a long-vacant parcel develop into an iconic structure and vibrant public space. Wolff Landscape Architects, Chicago (wolfflandscape.com), were retained to design the public space because of their experience with landscapes on structures and with the complex Chicago entitlements process. This experience was invaluable in navigating a process that requires all projects along the river be treated as “waterway planned developments” that must be reviewed and approved by the 42nd Ward Alderman, the Department of Housing and Economic Development, and the Chicago Plan Commission.

Wolff architects developed a design that divided the building’s public open space into three different zones: the entry plaza, the riverfront promenade, and the elevated park. The landscaped park and riverfront promenade hide parking and provide 24/7-accessible green space for tenants and passersby.

The tower’s 45-ft. setback from the river made possible 1 1/2 acres of public space around the building. The plaza is wide at the street to invite visitors into the site. It then narrows between the Riverwalk and the park, and expands again to provide direct access to the building’s main entry. The 300-linear-ft. Riverwalk has a continuous walkway, overlooks that bring pedestrians to the water’s edge, benches facing the river, a landscape buffer between the building and the Riverwalk, and a terraced seating area facing the river. The park is a green and passive space intended to be a respite from the busy, dense urban surroundings. Access from the plaza to the park is by direct steps and a switchback-sloped sidewalk, eliminating the need for an ADA ramp.

The overall construction approach was driven by a culture of integration and Lean principles. Onsite leadership created a collaborative environment that pushed the limits of teamwork to optimize the process and minimize waste of materials, time, and effort. The interests of all stakeholders were aligned to “what’s best for the project.” The resulting structure has been recognized with several awards, including the 2017 Chicago Innovation Award, the Chicago Commercial Real Estate Awards 2017 Development of the Year, and the Chicago Building Congress 2017 Merit Award Finalist for New Construction Over $55 Million.

Chris Phares is a project executive with Clark Construction Group, Chicago. His 17 years in the construction industry include extensive experience in design-build, sustainability, commercial construction, and urban development. Contact him at 312-258-5484 or chris.phares@clarkchicago.com.

There was no space for an on-site crane to build the tower. The solution was a floating platform system that allowed use of a massive barge-mounted Manitowoc 888 Ringer crane.

Innovative Engineering And Construction Solutions Solve Site Challenges

From the start, everyone involved with 150 North Riverside knew the construction challenges of building on this tiny parcel of land were going to be significant. The project required innovative problem solving and collaboration. The team of engineers, led by Magnusson Klemencic Associates (MKA, Chicago), and craft-workers, headed by Clark Construction Group, Chicago, provided significant knowledge and experience in building on challenging sites.

Extensive planning occurred in the very early stage of the project’s life cycle. In the design and construction phases, numerous operational tasks were performed with a variety of precedence. For example, experience from a nearby job taught the team that digging belled caissons can produce a lot of messy spoils that must be removed. They also require a big rig that takes time to demobilize. Since pile driving at 150 North Riverside could only be done from 1:00 a.m. to 5:00 a.m. to avoid clashing with nearby train service, belled caissons were ruled out as a structural option. Clark personnel, working with engineering firm MKA and geotechnical consultant GEI Consultants Inc., Madison, WI (geiconsultants.com), redesigned the foundations to a 9 1/2-in.-dia. “micropile” system. This made it possible to use a smaller rig that produced no spoils and could be quickly maneuvered in and out of the rail yard.

GEI experts knew they had to limit the total number of piles and that the piles needed to be as strong as possible. They also recommended minimizing the number of digs. The initial 400-kip micropiles were re-engineered to increase the strength. Over the course of nearly four months, more than 100, 600-kip micropiles—the highest-capacity piles ever installed in Chicago—were sunk between the tracks.

For the tower foundation, MKA designed 16 fully reinforced caissons, each 10 ft. dia. They were drilled 6 ft. into bedrock. The team also pre-planned the foundation-reinforcement design so that a floor could be added to the building midway through construction at the developer’s request.

Foundation and Core

Because this project has a smaller footprint than normal, the core resisting the lateral loads and the foundation carrying the gravity loads were both increased. To do this, the core was elongated and the walls thickened to 4 ft. The walls were constructed of 12-ksi reinforced concrete, with specifications defined for strength and stiffness. This massive concentrated load was carried on a reinforced-concrete mat, 150-ft. long x 40-ft. wide x 10-ft. thick.

The mat caps 16 caissons, each a 10-ft.-dia. steel tube filled with concrete extending 110 ft. deep and socketed 5 ft. into bedrock. These are the largest caissons in Chicago, carrying gravity loads of 28 million lb. The caissons also resist lateral loads by vertically cantilevering above the Chicago River.

Using the River

While the architectural design used the Chicago River for inspiration, the waterway also provided construction solutions. Once the foundation was completed, the focus turned to erecting steel and placing concrete, including enclosing the active rail lines to create a public plaza. The team used 30-ft.-tall, cast-in-place concrete walls and precast concrete bulb tees to cover the tracks. Due to limited site access, adjacent buildings, and neighboring elevated roadways, the site was too crowded to support a land-based crane with a reasonable reach. A tower crane could not lift the bulb tees, which required as much as 128,000 lb. of lifting capacity. With no space for a crane on site, a floating platform system was developed that allowed use of a massive barge-mounted Manitowoc 888 Ringer crane. This required close coordination with the U.S. Coast Guard, the Army Corps of Engineers, and the Metropolitan Water Reclamation District.

The Clark team sequenced the work to ensure that structural elements were properly installed, with a particular focus on the progression of work in the building’s signature lobby. For the tower and plaza construction to meet at the correct point in time so that the tower didn’t block the barge crane, the team used two independent schedule paths to get both aspects to coalesce simultaneously.

Loading symmetry is of particular issue with core-supported buildings. In this instance, imparting equal and opposite reactions to efficiently transfer dead loads from perimeter to core, it was necessary to have tension members located at level eight and compression members at level four. Site constraints required that only the west elevation incorporate the cantilevering beams to transfer loads to the core. Perimeter columns on the east elevation could have extended to grade level, but achieving the balance required to maintain an upright structure would have needed heroic levels of engineering.

Tanks Manage Drifts

Like so many other aspects of this project, the drift and acceleration standards were also a challenge. MKA introduced tuned mass dampers at the top of the building. The dampers house some 200,000 gal. of water in 12 concrete tanks stacked in two layers of six. The inertia of the water in the tank creates a balancing liquid force against the structure to keep the narrow building from drifting. As the building drifts over, the water in the tank has inertia and wants to stay in one place, i.e., it creates a balancing liquid force against the building. As the building moves one way, the water stays and pushes up against the opposing wall and helps push the building back. The water tanks also serve as city-approved fire-protection water.

Using tanks to manage drift is the first time this has been done in the world. While tanks have been used to manage acceleration numerous times, they have not been used to manage drifts and keep cladding joints from getting overstressed due to story drift.

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