December 6, 2017
by Chris Phares
Built on a desirable, but long-vacant parcel of land in downtown Chicago, 150 North Riverside has been hailed as one of the most spectacular engineering feats in the Windy City’s history. Rising from a site constrained by seven active railroads, two bordering and elevated roadways, and the Chicago River, the project team turned the prohibitive site into a gleaming look-into-the-future-possibility of urban construction.
This article examines the many design, engineering, and construction components of this now-iconic building, which has changed Chicago’s landscape.
Site challenges and solutions
The sliver of land where 150 North Riverside was built sat vacant for decades. The lot, which is only 26 m (85 ft) across at its widest point, sits adjacent to the Chicago River—seven active railroad tracks ran directly through the site, as well as three elevated roadways border its north, south, and west sides. Anyone who wanted to build on the eastern third had to leave at least 9 m (30 ft) for a city-mandated Riverwalk.
Chicago-based Riverside Investment and Development purchased the lot and two adjacent parcels, which consisted largely of air rights above Amtrak rail lines. This facilitated the construction of an overbuild, ultimately destined to house a hidden parking level topped by a green plaza, but utilized during the construction by contractors.
The team had to construct the building’s foundation within an incredibly narrow space—caused by active uncovered railroad tracks and the Chicago River—leading to its signature silhouette.
From concept to completion, every phase of the project posed significant design and execution challenges. However, innovative thinking by everyone on the project team brought the building to fruition.
To best utilize the available space onsite, the team constructed the office tower to cantilever and flare to its maximum width at the eighth floor, using a transfer truss spanning four stories, 31 m (104 ft) above the building’s plaza. The narrow foundation freed up the majority of the site for public use, including a 27-m (90-ft) tall glass-enclosed lobby and a public park over the now-covered train tracks, an amphitheater, and the Riverwalk.
Chicago-based Goettsch Partners designed the office floors to cantilever out from the central core. The building is constructed with a smaller base for its first seven stories, and then extends to the full size of the office floor space. Featuring a small building footprint, this design allows for a dramatic, light-filled lobby while providing efficient, column-free office floors above. Emulating the river, which the tower overlooks, vertical mullions undulate along the building’s east and west façades.
To construct the slim foundation, the team worked to install the second-largest mat foundation in Chicago history—16 of the 3-m (10-ft) caissons were placed 33 m (110 ft) into the bedrock with 2312 m3 (3024 cy) of concrete over the course of 19 hours, although the caissons took substantially longer. The result is a new tower with an extremely slender base—49 m (162 ft) long and 14 m (47 ft) wide, which rises to a total height of 229 m (752 ft).
Utilizing the river
Once the foundation was complete, the team turned their focus to erecting steel and placing concrete, including enclosing the active rail lines to create a public plaza. The team used 9-m (30-ft) tall, cast-in-place concrete walls and precast concrete bulb tees to cover the tracks. The site was too crowded to support a land-based crane with a reasonable reach, as there was limited site access, buildings, and elevated roadways nearby. A tower crane also could not lift the bulb tees, requiring as much as 58,059 kg (128,000 lb) of lifting capacity. With no space for a crane onsite, the project team turned the adjacent Chicago River from a challenge to an asset and designed a floating platform system to employ the use of a massive barge-mounted crane.
All this river-related activity required cooperation from the city, the Coast Guard, the U.S. Army Corps of Engineers (USACE), and the Metropolitan Water Reclamation District.
With a maximum 91 m (300 ft) of boom and 598,742 kg (660 tons) of lifting capacity, the 907,184-kg (2 million-lb) crane setup distributed groundbearing pressure evenly across the barge’s 31 interlocking sections. Anchored by four spuds driven into the riverbed, the barge allowed the team to pick up the bulb tees over the rising building core and set them up to 6 m (20 ft) away on the site’s west side, without taking up space on the jobsite. The project team used the crane to install nearly 200 bulb-tee girders, weighing as much as 40,823 kg (90,000 lb), to support the tower’s new pedestrian plaza. To top out the superstructure, the team poured 42,050 m3 (55,000 cy) of concrete, placed 10.8 million kg (12,000 tons) of rebar, and erected 9 million kg (10,000 tons) of steel.
After the foundation was completed, the project team utilized some of the world’s highest-strength steel and largest-rolled shaped steel—W36x925—to bring the building to life and achieve the necessary strength and stiffness in the structure. In addition to using 482-MPa (70-ksi) rolled shapes for the first time in the United States, the fabricators pre-fitted the steel for the transfer truss in the shop itself to confirm every single bolt hole aligned, with no welding or reaming of bolt holes on the entire transfer system. The team preplanned every step to prevent any issues in the steel truss and concrete core connection for constructing level floors.
To connect everything properly, the project team sequenced the work in a very particular fashion. The biggest sequencing component was the building’s signature lobby, which features a 25-m (85-ft) tall glass wall hung from the tip of the transfer truss at Level 8.
The team ran two independent schedule paths from the project to ensure the tower and plaza construction met at the correct point in time and the tower’s structure did not get in the way of the crown.
To meet drift and acceleration standards, Magnusson Klemencic Associates, a structural engineering firm, introduced tuned mass dampers, housing some 757,082 L (200,000 gal) of water in 12 concrete tanks stacked in two layers of six, at the building’s top. The inertia of the water in the tank creates a balancing liquid force against the structure in order to keep the narrow building from drifting.
While tanks have been used to manage accelerations in the past, this is one of the world’s first cases in which tanks manage drifts to keep the cladding joints from overstressing from story drift. The water tanks also serve as city-approved fire protection water.
The project team continued to work toward the highest quality of construction when placing the curtain wall façade. The system comprised 8500 individual units for a total of 50,167 m2 (540,000 sf) of glass. To meet the project’s demanding acoustic requirements, the team implemented comprehensive acoustical testing of the curtain wall system. The tests, the first of their kind, validated design criteria and ensured the curtain wall obtained a sound transmission class (STC) rating of 43 STC.
The challenging design and implementation process at 150 North Riverside denotes the team’s critical quality control process and collaboration, which kept the project on schedule while minimizing impact on the surrounding community.
Glass fins, rippling waves
The all-glass lobby creates a space, blurring the boundaries between indoors and outdoors. The remaining portions of the building, spandrel panels included, are clad in approximately 30 percent reflective glazing and the finish is neutral—it is basically gray, but ‘reads’ as blue on sunny days.
The façade incorporates undulating glass fins at each vertical mullion in the unitized curtain wall system. Projecting from 152 to 431 mm (6 to 17 in.), the fins are an allusion to the rippling of windswept water, with the inspiration coming from the adjacent river’s waves.
More pragmatically, the fins also promote solar shading and minimize cooling loads during summer months, particularly on the building’s west elevation.
Prior to the completion of the track overbuild (plaza over the trains), vehicle entry was limited to a single-lane access road—owned by Amtrak—that ran along the train tracks. The entrance to this road was several blocks away from the project site and required coordination and scheduling with Amtrak to avoid any impact to the trains or Amtrak’s operations. Pedestrian access was through temporary stair towers leading from the elevator roadways down the project site.
However, when the track overbuild construction was completed, this all changed. The site joined the adjacent roadway structures at the same elevation, so pedestrians simply walked through the gate onto the project site. Vehicle traffic drove off of the elevated, adjacent roadways and onto the site, across the elevated sidewalk, utilizing temporary engineered driveway entrances.
Sustainability is a key principle in 150 North Riverside’s design. The building was constructed to achieve Leadership in Energy and Environmental Design (LEED) Gold for the rating system’s Core and Shell (C&S) program. Environmentally responsible features include high-efficiency plumbing and mechanical systems, a high- performance floor-to-ceiling curtain wall assembly, open floor plates, and lobbies with significant natural daylight, as well as use of low-volatile organic compounds (VOC) and non-emitting materials.
The tower is also home to 150 Media Stream—a new media installation in the building’s lobby representing the convergence of art, architecture, and technology in showcasing digital works from a rotation of distinguished artists and cultural institutions.
Impact on the community
In delivering 150 North Riverside, the team transformed a vacant lot with uncovered rail lines into a public green space contributing to the beauty of downtown Chicago. Creating an elevated park and plaza, the project team covered the rail lines and improved the acoustic and aesthetic experience for the surrounding neighborhood, including the adjacent condominium building.
The small building footprint, public park, and Riverwalk connection all serve to impact the community in positive ways. Additionally, the office building has already contracted out more than 80 percent of its leasable space, adding to the thriving business community in downtown Chicago.
Throughout the project’s execution, the team avoided negatively impacting the neighborhood while continuing their efforts to provide new and luxurious public spaces along the city’s riverfront.
Maneuvering around the several transportation corridors surrounding the site, the team worked around the clock to prevent impediments to public transportation. For public safety and transportation purposes, the project team completed crane lifts from 1 to 5 a.m. when the trains were not running.
When using the barge-based crane, the team performed a balancing act to prevent water traffic interference. To utilize a barge big enough to accommodate the crane’s size and weight, without stopping water traffic, Chicago Steel Construction was able to customize the barge to a size that met both the crane’s and the U.S. Coast Guard’s demands. It also mitigated much of the traffic issues, keeping the crane at a far enough distance and not impeding pedestrians or cars.
This building helped solve a site constraint, which precluded development on one of the most prominent sites in Chicago for close to 80 years. To repair the urban fabric and make the 111,483-m2 (1.2 million-sf) tower possible, Riverside Investment formed a team of architects, structural engineers, and construction workers with an extensive knowledge set and collective experience in building on challenging sites.
While the building, with its many details, changed numerous times since it was first conceived five years ago, the tower’s basic shape remained unchanged since the very beginning. There is perhaps no other new building in Chicago causing more people to tilt their heads and look up.
The collaborating project team includes Chicago-based Clark Construction Group (general contractor), Cosentini Associates (mechanical/electrical/plumbing [MEP] consultant), Wolff Landscape Architecture, and One Lux Studio (lighting design).
Chris Phares is a project executive with Clark Construction Group. He has worked in the construction industry for 17 years and has extensive experience in design-build, sustainability, commercial construction, and urban development. Phares lives in Chicago. He can be reached at firstname.lastname@example.org.
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