Meaning
Precompressed horizontal concrete construction incorporates high-strength steel strands tensioned against hardened cast material to resist applied flexural stresses and control cracking. Project teams select a post tensioned slab to minimize overall structural depth, reduce deadweight and extend column-free interior spans. The designation stops applying to pre-tensioned elements where tendons receive prestress forces prior to concrete placement.
Tendon Placement
High-tensile steel strands enclosed in plastic or galvanized metal ducts are draped according to calculated parabolic profiles before concrete casting. Once the slab attains specified compressive strength, hydraulic jacks stress the tendons to impart internal axial compression and upward balancing forces across the post tensioned slab. Grouting procedures seal bonded ducts to lock in stress distributions and protect steel surfaces from chemical corrosion.
Deflection Verification
On-site elongation records compare measured strand extension against theoretical calculations during active tensioning operations. Lift-off audits confirm that the post tensioned slab carries the intended prestress balance before contractors place heavy construction equipment on top. Unbalanced tension sequences risk edge punching shear failures or excessive upward camber at mid-span.
Capacity Limit
Punching shear resistance around support columns limits the maximum span-to-depth ratios achievable in thin plate designs. Secondary cracking from unrestrained thermal contraction can compromise structural action if pour strip closure sequences proceed out of order. Ultimate capacity calculations depend on unbonded tendon ductility remaining intact throughout maximum design load occurrences.
