Bridge and Stay Inputs
Enter permanent loads for one deck span. The form divides deck weight between the selected cable planes.
Example Data Table
These sample values match the default calculator inputs and show the purpose of each field.
| Input | Example | Purpose |
|---|---|---|
| Supported deck span | 120 m | Defines the loaded deck length. |
| Deck width | 18 m | Calculates slab volume per deck meter. |
| Average slab thickness | 0.25 m | Calculates slab self-weight. |
| Cable planes | 2 | Splits the deck line load between planes. |
| Stays per plane | 6 | Creates the tributary load distribution. |
| Common stay angle | 32 degrees | Resolves vertical demand into tension and horizontal force. |
Formula Used
Deck dead line load
Load assigned to one cable plane
Idealized harp-stay force
The model assumes straight, parallel stays. It treats cable self-weight as half delivered to each cable end.
How to Use This Calculator
- Enter the deck span carried by the analyzed stay group.
- Enter deck geometry and the project concrete unit weight.
- Add line loads for permanent girders, surfacing, barriers, and services.
- Select one or two cable planes that share the deck load.
- Set the stay count, first anchor distance, and equal spacing.
- Enter the common harp angle and usable tower height.
- Add an estimated cable unit weight and submit the form.
- Review the summary, stay table, and tower-height warning.
- Export the preliminary schedule, then verify it through bridge analysis.
Dead Load Planning for Harp Stays
Load Path Basics
A cable-stayed harp bridge carries deck weight through several near-parallel stays. Each stay supports a defined tributary length of deck. The deck load becomes a vertical cable reaction. Cable inclination then converts that reaction into tension and horizontal tower force.
Permanent Deck Weight
This calculator begins with permanent deck loads. Concrete slab weight comes from width, thickness, and unit weight. Extra line loads can cover girders, surfacing, barriers, utilities, and fixed equipment. An allowance can represent known permanent additions. The combined line load is divided between the selected cable planes.
Tributary Distribution
Stay positions control tributary lengths. The first stay uses the area between the tower and the midpoint toward the second stay. Middle stays use midpoint boundaries on both sides. The final stay receives the remaining deck length. This method gives each stay a logical share of the loaded deck.
Force Resolution
For each stay, the calculator adds half of the cable self-weight at the deck end. The vertical demand is then divided by the sine of the common harp angle. This produces an idealized cable tension. Dividing vertical demand by the tangent of the angle estimates the horizontal force transferred toward the tower.
Geometry Review
The connection elevation is calculated from deck distance multiplied by the tangent of the stay angle. Compare this elevation with usable tower height. A warning appears when a modeled connection rises above that height. This is a geometry check only. It does not establish a workable anchorage detail.
Use measured or scheduled distances, not rounded drawing dimensions. Always keep units consistent throughout the calculation. Loads are entered in kilonewtons per meter. Geometry is entered in meters and degrees. The summary reports kilonewtons and cable lengths in meters. Save input records carefully with each concept revision.
Design Limits
Use the output for early load studies, option comparisons, and checking input consistency. It is not a final bridge design. Real stays sag under self-weight. Their force depends on stiffness, pretension, construction sequence, temperature, wind, live load, seismic actions, and code combinations. Deck bending and tower flexibility also redistribute reactions.
Next Checks
Review the assumed load path before accepting the totals. Confirm whether one or two cable planes share deck weight. Confirm the loaded span and actual anchor spacing. Include every permanent attachment. Then pass the model to a qualified bridge engineer for nonlinear analysis, detailing, and code checks.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates permanent deck load, load shared by each cable plane, stay tension, horizontal tower force, cable self-weight, and idealized connection elevations for a harp arrangement.
2. Does the model include cable self-weight?
Yes. It calculates straight cable length, multiplies it by cable unit weight, and assigns half of that weight to the deck-end vertical demand of each stay.
3. Why must I select the number of cable planes?
The calculator splits the total deck line load equally between one or two cable planes. Use a project-specific distribution when the bridge is not symmetric.
4. What is a tributary length?
It is the deck length assigned to a stay. The calculator uses midpoint boundaries between adjacent deck anchors and the supported span ends.
5. Does the tower-height check prove the geometry works?
No. It only checks whether the idealized connection elevation fits below the entered usable height. Anchorage zones, clearances, and tower shape need separate review.
6. Can I use this for a fan arrangement?
No. The force model assumes a common stay angle. Fan systems use changing angles and different connection geometry, so they need a separate analysis model.
7. Are live loads included?
No. The form covers permanent loads only. Add live load, wind, temperature, seismic actions, construction stages, and required combinations in the final structural analysis.
8. Why does a shallow stay angle increase horizontal force?
A shallow cable needs more tension to produce the same vertical support. Its horizontal component therefore rises quickly as the angle decreases.
9. Should I enter code load factors?
Enter an allowance for known extra permanent items only. Apply governing code factors and load combinations in the engineer’s design model, not as a substitute here.
10. Does the result include deck bending or tower flexibility?
No. The model treats the tributary deck load as directly supported by stays. It does not calculate stiffness-based redistribution, bending moments, or deflection.
11. Can I use the results for construction?
Always confirm final values with the responsible bridge engineer.