Post-tensioned (PT) concrete is concrete reinforced with high-strength steel tendons that are stressed after the concrete has hardened, putting the concrete into compression so it can span farther and crack less.
In U.S. parking structures, the common system is unbonded monostrand tendons: each strand is greased and sheathed, draped through the slab or beam, anchored at each end, and stressed with a hydraulic jack once the concrete reaches strength. PT lets cast-in-place garages achieve long spans with thin slabs and beams, and the compression helps keep decks crack-free and watertight.
The stretched tendons squeeze the concrete and, because they are draped high over supports and low at midspan, push up against the loads the floor will carry. That lets floors span long distances with thin slabs and fewer cracks. Cast-in-place PT is one of the most common framing systems for U.S. parking structures, alongside precast.
Why garages use it
- Long, column-free spans that suit the parking module. See clear-span construction.
- Monolithic floors with few joints, so fewer places for water to get in.
- Freedom to shape ramps, curves and odd sites.
Durability
- Encapsulation. Modern parking-grade systems fully encapsulate the strand and anchorages to keep water and chlorides out. Older garages with unencapsulated systems are more vulnerable.
- Anchorages. Pockets at slab edges must be filled and protected; corrosion often starts there.
- Restraint cracking. PT decks shorten over time; stiff walls and cores in the wrong places restrain that movement and cause cracks.
Working with PT
- Tendons carry enormous force. Locate them by scanning before coring, cutting or drilling, and never cut one without an engineered plan.
- Corroded tendons can fail suddenly; condition surveys should look for signs such as rust staining, cracking along tendon paths and anchorage distress.
The Parkonomics view
Post-tensioning is the backbone of the cast-in-place parking garage. Its long-term value depends on keeping water out of the tendons, so encapsulation, sealers and anchorage protection deserve as much attention as the stressing. Budget for the membrane, the drains and the condition survey up front; they are what keep a fifty-year structure from becoming a thirty-year one.
Related terms: Precast Pretensioned Concrete, Chloride-Ion Contamination, Clear-Span Construction, Spalled, Structural Systems of Parking
Further reading: The Evolution of U.S. Parking Structures in 2026