PTI JOURNAL | December 2015 3

CASE STUDIES CASE STUDIES

ONE ELEVEN

The high-rise building located at 111 W. Wacker Drive in downtown Chicago, IL, was formerly known as the “Water-view.” The structure was originally designed as an 89-story luxury hotel located along the Chicago River. The construc-tion of the conventionally-reinforced building progressed until the 27th floor, when it was shelved due to financing issues. In 2012, the hotel was redesigned as a 60-story resi-dential apartment building and renamed “OneEleven.”

What separates this high-rise tower from others is the 60 in. (1520 mm) transfer deck located on the 30th floor. The original design called for a 72 in. (1830 mm) conventionally-reinforced slab with the post-tensioned (PT) floors above. The PT supplier and concrete contractor redesigned it into a 60 in. (1520 mm) thick slab using PT to replace roughly 372 tons (337 metric tons) of rein-forcing bar. The redesign saved around $380,000 from the cost of the transfer deck (excluding costs of other vertical elements). The reduced dead load of the slab also helped eliminate the reshoring requirements. The 12 in. (305 mm) building height reduction funneled into lower costs for all vertical elements and lower operational energy costs. A flat-plate was used in lieu of large beams and transfer girders to reduce forming costs.

Fig. 1—Draped PT in 60 in. (1524 mm) transfer deck.

Location: Chicago, ILSubmitted by: AMSYSCO, Inc.Owner: Related MidwestArchitect: A.Epstein & SonsEngineer(s): Halvorson & PartnersContractor: Lend-LeasePT Supplier: AMSYSCO, Inc.Other Contributors: Adjustable Forms Inc.

The transfer mat was placed in two lifts (20 in. and 40 in. [508 and 1016 mm] lifts) for a total of roughly 2250 yd3 (1720 m3) of 6000 psi (41.4 MPa) concrete. One of the placements lasted 17 hours and had an increased degree of complexity due to being placed mid-air. In total, there was 60 tons (54.4 metric tons) of unbonded PT (gross weight) used in the transfer deck.

The use of unbonded PT in the original design was also used to reduce the high-rise building height by at least 1 in. (25 mm) per floor as compared to mildly-reinforced concrete. PT helped make a stalled project more economical due to the reduction in material costs (concrete columns/walls, MEP piping, elevators/stairs, and curtain-wall).