Calculator Inputs
Example Data Table
The table shows typical sample values. Use project-approved values for final stressing work.
| Case | Strands | Length | Area Each | Force Each | Modulus | Elastic Elongation |
|---|---|---|---|---|---|---|
| Short beam | 1 | 15 m | 140 mm² | 193.5 kN | 195 GPa | 106.32 mm |
| Long tendon | 12 | 30 m | 140 mm² | 193.5 kN | 195 GPa | 212.64 mm |
| Bundle with seating | 19 | 38 m | 150 mm² | 205 kN | 195 GPa | 266.15 mm |
Formula Used
Basic elastic elongation:
ΔL = P × L / (A × E)
Friction and wobble exponent:
X = μθ + kL
Average force factor:
Favg factor = (1 - e^-X) / X
Adjusted elongation:
ΔL = Pavg × L / (A × E)
Jack stroke target:
Jack target = elastic elongation + anchorage set + dead end slip
Measured variance:
Variance % = (Measured - Theoretical) / Theoretical × 100
The calculation assumes linear elastic behavior. Final acceptance should follow the project specification, approved shop drawings, and field inspection requirements.
How to Use This Calculator
- Enter the number of strands in the tendon or bundle.
- Add tendon length using your preferred unit.
- Enter strand area and elastic modulus from certified material data.
- Add jacking force as either force per strand or total bundle force.
- Enter friction, angular change, and wobble values when needed.
- Add anchorage set and dead end slip allowances.
- Enter measured elongation after field stressing, if available.
- Press the calculate button and review the result above the form.
- Use CSV or PDF buttons to save the calculation output.
Prestressing Strand Elongation Guide
Why Elongation Matters
Prestressing strand elongation is a key field check. It confirms that the strand has stretched as expected under the applied jacking force. A correct reading helps the crew compare force, length, area, and modulus in one clear review. It also helps spot wrong gauge readings, strand seating issues, or unexpected friction.
Core Calculation Idea
The main formula is simple. Elongation equals force multiplied by length, divided by area and elastic modulus. The calculator applies this rule after converting all inputs into consistent units. It can also adjust the force for friction and wobble. This is useful for curved tendons, long tendons, and ducted post-tensioning systems.
Field Adjustments
Anchorage set and dead end slip can change the jack reading. The elastic stretch shows the theoretical tendon extension. The jack stroke target adds seating allowance. The locked elongation estimate subtracts seating allowance. These values help users understand the difference between pulling movement and final locked-in extension.
Stress and Safety Review
The calculator also estimates jacking stress. It compares that stress with a selected percentage of ultimate strand strength. This does not replace an engineer’s approval. It is a screening check. If the stress percentage is high, the result warns the user. Project limits should always control the final decision.
Measured Elongation Check
Measured elongation can be entered after stressing. The calculator compares it with the theoretical elongation. A variance outside the selected tolerance should be reviewed. Common causes include incorrect strand length, wrong area, friction, seating loss, gauge error, or recording mistakes.
Best Practice
Use certified strand properties. Use calibrated jacks and gauges. Confirm units before stressing. Record actual readings carefully. For final acceptance, follow the drawings, stressing sequence, inspection plan, and governing code.
FAQs
1. What does strand elongation mean?
It is the elastic stretch of a prestressing strand under jacking force. It helps confirm that the applied force and field movement match the expected design behavior.
2. Which formula is used?
The calculator uses ΔL = PL / AE. P is force, L is tendon length, A is steel area, and E is elastic modulus.
3. Can I calculate multiple strands?
Yes. Enter the strand quantity and choose whether the jacking force is per strand or for the total bundle. The calculator adjusts total area and force.
4. What is anchorage set?
Anchorage set is movement caused when wedges or anchors seat after stressing. It can reduce locked-in elongation and may require allowance in jack movement.
5. What does friction coefficient do?
Friction reduces effective force along a tendon. This calculator uses μθ plus wobble kL to estimate average force for elongation calculation.
6. Why enter measured elongation?
Measured elongation lets you compare field readings with theoretical elongation. A large difference may show friction, seating, gauge, or input problems.
7. Is this calculator enough for final approval?
No. It is a checking aid. Final approval should follow project drawings, engineer instructions, calibrated equipment records, and applicable construction standards.
8. Can I export the result?
Yes. After calculation, use the CSV or PDF buttons. They save key inputs, elongation values, stress checks, and result notes.