Chicago's O'Hare International Airport is home to the largest parking structure under one roof, accommodating six 545,000-square-foot levels and 8,800 parking spaces. Built in 1972, the garage recently underwent $46 million of repairs to extend its service life.

The garage's parking decks are 4 1/4-inch-thick concrete waffle slabs with 7x2-foot post-tensioned beams supported by conventionally reinforced columns. The interiors of the bays are supported by 1x2-foot waffle-slab joists, which are post-tensioned in the north-south direction and conventionally reinforced in the east-west direction. Each elevated slab is divided by seven expansion joints that also serve as drainage troughs. Each level is fed by four reinforced-concrete helical ramps, two each for exit and entrance.

Inspections of the parking structure determined the need for the following repairs:

  • Replacement of the expansion joints and drainage troughs
  • Repair of the post-tensioning system
  • Replacement of the helical-ramp overlays
  • Full- and partial-depth repair of the elevated slabs
  • Installation of deck protection (membrane and sealants)