Calculator Inputs
Example Data Table
| Span (m) | Weight (N/m) | Horizontal Tension (N) | Left Support (m) | Right Support (m) | Sag (m) |
|---|---|---|---|---|---|
| 80 | 1.5 | 2800 | 10 | 10 | 0.4286 |
| 120 | 1.8 | 3500 | 12 | 12 | 0.7714 |
| 150 | 2.4 | 4200 | 14 | 13 | 1.6071 |
Formula Used
The calculator uses the common parabolic sag model for practical span analysis.
Sag: d = (w × L²) / (8 × H)
Where: d is sag, w is cable weight per unit length, L is span, and H is horizontal tension.
Support reaction: V = (w × L) / 2
Maximum tension: T = √(H² + V²)
Thermal extension: ΔLt = L × α × ΔT
Elastic extension: ΔLe = (H × L) / (A × E)
For comparison, a catenary sag estimate is also shown. It helps advanced users judge approximation error on longer spans or lower tension cases.
How to Use This Calculator
- Enter the horizontal span length in meters.
- Enter cable weight per meter in newtons.
- Enter the expected horizontal tension value.
- Provide left and right support heights.
- Add temperature change, area, and modulus if needed.
- Enter cable strength and safety factor.
- Select the suitable calculation mode.
- Press Calculate to view results above the form.
- Download the output as CSV or save it as PDF.
About Cable Tension Sag Calculation
Why Sag Matters
Cable sag affects clearance, safety, and support loading. Engineers study it before installation. A low sag may increase tension sharply. A high sag may reduce ground clearance. This tool helps balance those competing limits.
Core Inputs for Better Results
The main inputs are span length, distributed cable weight, and horizontal tension. Support heights also matter. Uneven supports change the lowest point location. Temperature change can lengthen the cable. Material stiffness and area influence elastic stretch.
Physics Behind the Model
Many field checks use the parabolic sag equation. It is simple and fast. It works well for moderate sag conditions. The calculator also reports a catenary comparison. That helps users see whether the simplified model remains acceptable.
Tension and Support Load
Tension is not only horizontal. The cable also carries vertical load from its own weight. The end support force combines both parts. This combined force matters during support selection, anchor design, and maintenance planning.
Uneven Supports and Clearance
Real spans are not always level. One support may sit higher. In those cases, the lowest point can move away from midspan. Clearance checks become more important near roads, rail lines, water crossings, and equipment zones.
Temperature and Stretch Effects
Warm conditions usually increase cable length. That can increase sag. Elastic stretch also changes the loaded length. These effects may appear small on short spans. They become more meaningful on long spans or highly stressed cables.
Design Screening Use
This calculator is useful for early design screening, classroom analysis, and maintenance checks. It helps compare scenarios quickly. It does not replace detailed code-based design. It does provide fast estimates for better engineering judgment.
Practical Review Tips
Review sag, maximum tension, allowable tension, utilization, and clearance together. One good number alone is not enough. Safe cable performance depends on the full picture. Use multiple cases to test changing weather, loading, and support geometry.
FAQs
1. What does this calculator estimate?
It estimates cable sag, support reaction, maximum working tension, loaded cable length, thermal extension, elastic extension, and approximate clearance for a span.
2. When should I use the parabolic model?
Use it for practical engineering estimates where sag is modest relative to span length. It is common for preliminary checks and routine field calculations.
3. Why is catenary sag also shown?
The catenary result gives a comparison point. It helps you judge whether the simpler parabolic approximation is still close enough for your case.
4. What units should I enter?
Use meters for lengths, newtons per meter for cable weight, newtons for force, pascals for elastic modulus, and square meters for area.
5. How do uneven supports affect the result?
Uneven supports can shift the lowest point away from midspan. That can change local clearance and influence where the cable appears to dip most.
6. Why does temperature matter?
Temperature change can alter cable length through thermal expansion. A longer cable may produce greater sag under the same span and tension conditions.
7. What is allowable tension?
Allowable tension is the cable breaking strength divided by the selected safety factor. It offers a simple screening limit for safer operation.
8. Is this tool suitable for final design approval?
It is best for estimation and screening. Final approval should also consider codes, wind, ice, dynamic loading, fittings, and full structural review.