Until the summer of 1997, the two-story attached parking garage of Park Place Tower, a residential high-rise in Chicago, contained only 600 parking stalls for the residents of the tower's 900 deluxe apartments. Because parking was in such great demand, a plan was devised to add 70 parking stalls on the roof deck of the garage and to install an interior roof-deck ramp directly above the existing ramp linking the garage's first and second levels.
The 155,000-square-foot garage was built in 1969. The first floor is a concrete slab on grade, and the second-level parking deck and the roof slab are two-way post-tensioned concrete flat slabs. Installing the interior ramp required demolition of a section of the post-tensioned roof. Complicating the demolition and construction of the new ramp was the requirement that the parking garage remain open throughout the project. To save time and money, the general contractor decided to build a portion of the new ramp before demolishing the roof slab. Using this approach, the contractor also created a platform on which to support shoring and catch falling debris from the demolition phase. In addition, the post-tensioning subcontractor detensioned and restressed the roof-slab tendons in three phases, eliminating the need to shore the entire roof slab.