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Post-Tensioned Anchor Seating Loss Calculator

Estimate the prestress force lost to anchor seating (wedge draw-in) in a short post-tensioned tendon.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
49.21 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Stress loss from anchor seating

83.19 MPa

Check your inputs

This simplified short-tendon method assumes the seating loss propagates the full tendon length — a licensed PT designer must verify this assumption and account for friction losses along the tendon for a final design.

Stress loss (imperial)
12065 psi
Force loss per strand
8.21 kN
Force loss per strand (imperial)
1845.77 lbs

Running these inputs gives 83.2 MPa as the stress loss from anchor seating. Expect some drift against the real job; the calculation is solid but conditions on site are not. Currently reading for United States under IRC 2024 — pick a different market above and the figures re-cast accordingly.

Add the equipment this sizes

This result is a specification — 83.185 MPa — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Post-Tensioning Institute (PTI) simplified short-tendon seating loss method: stress loss = (anchor set / tendon length) x strand modulus of elasticity — valid when the seating-loss effect propagates the full tendon length, the common case for short-to-medium span slab tendons
  • Standard 7-wire strand elastic modulus: 28,500,000 psi; typical anchor set (wedge draw-in) is commonly 1/4 to 3/8 in depending on the anchorage system

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Frequently asked questions

What is 'anchor set' or 'wedge draw-in'?
When the stressing jack releases a tendon, the wedges grip the strand and settle slightly into the anchor casting before fully locking — that small settlement distance is the anchor set, and it releases a small amount of the applied prestress force.
Is this loss significant?
For short tendons it can be a meaningful fraction of the total prestress force, since the same fixed seating distance is spread over a shorter length — which is exactly why this calculator's ratio uses tendon length in the denominator.
Does this replace a full PT design?
No — a complete post-tensioning design also accounts for friction losses along the tendon profile, elastic shortening, creep, shrinkage, and relaxation losses, and must be performed by a licensed PT designer.