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January 22, 2018
Project: 150 North Riverside
Client: Riverside Investment & Development Co., Goettsch Partners
The waterfront site that is now home to Chicago’s newest 54-story high-rise was once considered so restraining that developers had avoided it for almost a century.
Compressed between the Chicago River to the east, seven active Amtrak rail lines to the west, and city bridge viaducts to the north and south, the site offered only 8,500 square feet of buildable area. Despite the property’s drawbacks, Magnusson Klemencic Associates offered an innovative structural solution that maximized the tiny footprint while delivering not only a 1.25 million-square-foot office tower, but also a 1.5-acre outdoor public park and river walk for the owner, Riverside
Investment & Development Co. Goettsch Partners was the architect.
The site’s constraining features, further complicated by a 30-foot setback at the river for Chicago’s Riverwalk, left only a sliver of land for the tower’s base. MKA solved the problem by using a razor-thin concrete central building core structural system that allows the 750-tall tower to rise from a base that’s just 39 feet wide.
To achieve this feat, MKA employed a number of technical innovations. For the tower support system, MKA created eight four-story, sloping steel-transfer systems to channel the loads from the tower above to its narrow base, and out of Amtak’s air space. These form the building’s distinctive tapered base and make way for the light-filled lobby.
The structure also used the largest rolled steel sections produced in the world, and steel that is 40 percent stronger than conventional steel shapes.
To deal with an unprecedented blade core height-to-width slenderness of over 19-to-1 (three times narrower than traditional building designs), MKA employed 12 water-filled tanks at the top of the building to minimize building motion under strong winds.
Holding 160,000 gallons of water, the wave action in the tanks not only calms the building during wind events, but also serves as city-approved fire protection storage tanks to help supply the building’s sprinkler system. This dual-use is a first for the city of Chicago.
MKA developed a precast, prestressed concrete lid structure designed to conform to strict Amtrak requirements for train operations, and with no temporary construction shoring needed. Once completed, the lid was designed as a critical staging area for the contractor before its ultimate use as a park.
To support the building at its base and deal with the highly magnified loads caused by the narrow core, MKA designed 16 massive concrete caissons that were drilled 110 feet deep and socketed 6 feet into solid bedrock, literally anchoring the building to the earth to resist uplift. The caissons support a 10-foot-thick concrete foundation mat. This hybrid caisson/mat solution used half the number of support piles as a conventional building.
To support the lid structure and the precisely coordinated concrete crash walls at the track level, MKA designed high-capacity micropiles — one-third the diameter of traditional piles used in Chicago — creating the highest capacity-to-diameter ratio of any piling ever used in the city. More than 100 micropiles were strategically placed within Amtrak’s infrastructure.
A nearly 100-foot-high glass fin wall — the tallest tension-only, glass fin wall in the world — hangs from the structure above like a curtain. MKA met all the challenges associated with deflection control, wind-load transfer and construction tolerances. The glass wall creates a light-filled lobby space and increases sunlight in the outdoor park.