Is post-tensioned concrete "prestressed concrete"?

Yes. Prestressed concrete is the umbrella category for any concrete member with a deliberately induced internal compressive force applied before service loads act on it. Pretensioning and post-tensioning are its two methods, distinguished by when the tendon is stressed relative to the concrete curing — not by whether the result counts as prestressed.

Why can't cast-in-place slabs be pretensioned instead of post-tensioned?

Pretensioning requires stressing the strand against fixed abutments before the concrete is poured, so the abutments — not the concrete — react the jacking force initially. A cast-in-place slab has no such abutment available before the pour; the concrete itself is what would need to exist to react against, and it doesn't yet. Post-tensioning solves this by casting the concrete first and stressing against the member's own cured concrete afterward.

What is transfer length in pretensioned members?

Transfer length is the distance, measured from the end of a pretensioned member, over which the strand's prestress force fully transfers into the surrounding concrete via bond after the strand is cut and released. It's a critical zone for shear and anchorage checks near member ends, since the strand isn't yet developing its full effective prestress force within that length.

Why does a precast prestressed beam camber upward before any load is applied?

Because the eccentric prestress force sits below the beam's centroid, it creates an upward bending moment on its own, before any gravity load acts. Once the strand is released and that force transfers into the concrete, the beam bows upward slightly (camber) as a direct result — a visible sign that the intended eccentric compression is actually present, and something precasters intentionally account for in bearing and connection details.

What is the practical difference between bonded and unbonded post-tensioning?

Bonded post-tensioning grouts the duct after stressing, bonding the tendon to the concrete along its length and providing a distributed, redundant load path similar to pretensioned strand. Unbonded post-tensioning leaves the tendon permanently coated and sheathed so it never bonds, relying entirely on its end anchorages for the life of the structure — common in flat-plate floor slabs for its lower friction losses and simpler field installation, but more dependent on anchorage integrity if a tendon is ever damaged.

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Concept Explainer · Civil & Structural

Prestressed vs. Post-Tensioned Concrete — Same Principle, Opposite Order of Operations

Post-tensioning isn't a rival to prestressing — it's one of the two ways prestress force actually gets put into concrete. The other is pretensioning, done before the pour instead of after.

In the field, "prestressed concrete" often gets used loosely to mean the precast beams and planks that arrive on a truck already under compression, while "post-tensioned concrete" refers to the cast-in-place slabs and garages stressed on site — as if the two were separate systems. They're not. Both are prestressed concrete: concrete that has a deliberate internal compressive force built into it so that, once service loads are applied, the concrete stays mostly in compression instead of cracking under tension it can barely resist. The only real difference is when that force is applied relative to the concrete curing, and what that timing forces the mechanism to be.