How do posttensioned concrete floors reduce sagging and cracking?

Posttensioned concrete floors reduce sagging and cracking by utilizing the principles of prestressed concrete to counteract the tensile forces that typically cause concrete to fail.12

In this process, steel cables are placed within ducts cast into the concrete. Once the concrete has hardened and gained sufficient strength, these cables are stretched using hydraulic jacks and anchored at the exterior of the member. This action serves two primary purposes:23

• Compression: By applying a measured stretching force to the steel, the process transmits a compressive force to the concrete. This compression neutralizes the stretching (tensile) forces that would otherwise cause the concrete to rupture under load.12
• Upward Arching: The tensioning process effectively bends the floor into a slight upward arch. This pre-emptive shaping reduces deflection—or sagging—and cracking when the actual service load is applied to the structure.3

By managing these internal stresses, posttensioning allows for the construction of shallower, lighter, and more elegant floor systems that can span greater distances than ordinary reinforced concrete.123