Prestress Force Calculator

• P₀ = A_ps · f_jack (jacking force)
• P = P₀ · e^{-(kL + μθ)} (friction/wobble model)
• ΔP_seat ≈ E_ps · A_ps · (Δs / L) (seating estimate)
• P_after = P · (1 − loss%/100) (percent-based losses)

1. Select a unit system (SI or US).
2. Choose how you want to define tendon steel: strands, direct area, or bar diameter.
3. Enter jacking stress and tendon length.
4. Enable loss components you want to include, then fill the fields.
5. Press Calculate to see results below the header.
6. Use the download buttons to export a CSV or PDF report.

1) What this prestress force check tells you

This calculator estimates tendon force at key stages: jacking force, force after friction, and effective force after seating, elastic shortening, and long-term losses. It supports rapid design checks, submittal reviews, and field verification when stressing records are available. Use the loss toggles to match your calculation scope and standardize reporting across tendons.

2) Steel area inputs and common tendon data

You may define steel by direct area, strand count, or tendon diameter. Typical values include 12.7 mm strand area of about 98.7 mm² (0.5 in strand about 0.153 in²). For bars, the tool uses A = n·πd²/4 to convert diameter to total area. Confirm strand type, count, and units, because force scales directly with total area.

3) Jacking stress selection and immediate force

Jacking stress is commonly set as a fraction of ultimate strength based on project criteria and equipment limits. Many systems fall near 0.70–0.80 of ultimate for planning, but your specifications control. The calculator converts stress to force using P0 = Aps·fjack, which is useful for checking pump gauges, target elongation expectations, and stressing sequence notes.

4) Friction and alignment sensitivity

The friction step follows P = P0·e^{-(kL + μθ)}. Use k for wobble (minor misalignment along the duct) and μ with θ for curvature. Increases in L, k, or angle change reduce end force, so confirm tendon geometry and duct alignment during installation. When inputs are uncertain, run a small sensitivity sweep to bound expected end forces.

5) Seating, elastic, and long-term losses for reporting

Seating loss is estimated with ΔP ≈ Eps·Aps·(Δs/L). The distribution factor (0–1) approximates how slip affects average force along the tendon. Percent-based elastic and long-term losses provide practical inputs for comparisons; long-term loss typically represents creep, shrinkage, and relaxation in one value. Document assumptions and export the CSV or PDF for project records.

1) Is this a code-compliant design output?

No. It is a quick-check calculator. Confirm final losses, stressing sequence, and limits using your governing code, project specifications, and supplier data.

2) Which force should I compare to capacity checks?

For service checks and long-term performance, use the effective force (Peff). For stressing equipment and temporary checks, use the jacking force (P0) and end force after friction.

3) What should I enter for θ?

Enter the total change in tendon angle in radians along the profile. For multiple curves, add the angle changes. If you only have degrees, convert using radians = degrees·π/180.

4) How do I pick the seating distribution factor?

Use 0.50 for a simple average estimate when details are unknown. Increase it if slip affects a larger portion of the tendon, and reduce it if the slip effect is very localized.

5) What does the wobble coefficient k represent?

k captures unintentional deviations and duct imperfections along the length. It is project-specific and depends on duct type, workmanship, and tolerance. If uncertain, consult vendor guidance.

6) Why are elastic and long-term losses entered as percentages?

Percent inputs allow rapid scenario testing when full time-dependent analysis is not required. They should be refined using detailed calculations when you finalize the design or approve stressing procedures.

7) Can I use US units and still keep the friction model?

Yes. Ensure k uses 1/ft, length uses ft, and stress uses ksi. The exponential friction model is dimensionless, so it remains consistent when inputs are in compatible units.