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).