Power lift to stack 34 floors on existing urban mall

This story first appeared Jan. 23 on Power Construction's own website.

Located in the heart of Chicago’s Loop, famed Block 37 is in the midst of a major vertical expansion. The unique project involves adding 34 new floors, the most in the city’s history, on top of a fully-operating, four-story, retail mall across the street from Macy’s on State St. With 690 apartments, Block 37 is also Chicago’s largest rental project currently in construction.

Constructing a high-rise building on top of an occupied building in a dense commercial district is the project’s fundamental challenge. Besides myriad logistical issues that must be managed daily, the most visible aspect of this expansion is the dual structural support design of steel trusses with a concrete mat slab. Each system supports roughly one-third of the buildings weight and transfers the load around the retail mall to the caisson foundations below.

Four jumbo steel trusses, each about three stories in height, were manufactured in Luxembourg and shipped in pieces overseas by boat to Chicago. These 120-ton trusses were then assembled on Randolph Street (adjacent to the site) and lifted into place. The crowning touch is a 30-ft-wide-X-9-ft-tall steel girder, weighing 30 tons. This plate girder supports a 282-ft-tall, 18-in-thick concrete sheer wall that stabilizes the tower once completed. The mat slab is a 5-ft-6-in-thick slab of steel-reinforced concrete that was poured in-place using two concrete placing booms simultaneously.

Now that the critical structural supports and non-typical floors have been erected, the remainder of the 435-ft-tall tower will have a new concrete floor added every four days. Occupancy is scheduled for July 2016.

Key to the planning of such a complex, fast-paced project is the use of state-of-the-art, computer technology, aka building information modeling (BIM). This detailed, 3D-computer model is then used by the entire team of contractors and designers to figure out precise dimensions and locations of each element of the project. The team also uses the latest iPad tablets in lieu of paper drawings, to coordinate, manage, and communicate project details.

Power Construction is managing the design and construction, in collaboration with the architectural firm of Solomon Cordwell Buenz, and structural engineer, Thornton Tomasetti.

Much more to come on this project...