Structural Engineering · Engineering Glossary
Post-tensioned (PT) concrete is a form of prestressed concrete in which high-strength steel tendons are tensioned after the concrete has cured, placing the concrete in compression and dramatically improving its ability to span long distances and resist cracking. PT slabs and beams are common in parking structures, high-rise floors, and slabs-on-grade in expansive soil areas.
In unbonded post-tensioned construction (the most common in buildings), monostrand tendons — a single 0.5-inch diameter strand coated with grease and wrapped in plastic sheathing — run through the concrete slab or beam and are anchored at the slab edges. After curing, a hydraulic jack pulls each strand to a design stress (typically 175–180 ksi) and it is locked off at the anchorage. The prestress force keeps the concrete in compression, effectively eliminating tensile cracking and allowing longer spans with shallower sections. Post-tensioned slabs-on-grade are used in expansive soil areas because the prestress can resist the uplift forces from soil expansion better than conventional reinforced slabs. PT design requires specialized detailing knowledge and experienced engineers.
Apex Grid Engineering maintains this glossary as a resource for architects, contractors, developers, and property owners who encounter unfamiliar engineering terminology on their projects.
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