Inputs
Formula used
- q = basic wind pressure.
- Metric: q = 0.5 · ρ · V² (Pa).
- Imperial: q = 0.00256 · V² (psf), with V in mph.
- qz = q · Kz · Kzt (height/topography adjusted pressure).
- Projected area option: A = L · D · solidity · sin(θ).
- Design wind force: F = qz · G · Cf · A · Kd · I · SF.
- Uniform line load: w = F / L.
- Overturning moment: M = F · e (lever arm e).
How to use this calculator
- Select units and enter the governing gust wind speed for erection.
- Choose exposure category or enter the project-specific Kz.
- Set Kzt, G, Kd, and I from your criteria.
- Define girder geometry and either compute or directly enter projected area.
- Pick a shape coefficient Cf appropriate to the girder form.
- Press Calculate to view forces, line loads, and overturning moment above.
- Use Download CSV/PDF for submittals and field packages.
Example data table
| Case | Units | V | Exposure | L | D | θ | Solidity | Cf | G | Kd | I |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Typical steel box girder | Metric | 30 m/s | C | 30 m | 2.0 m | 90° | 1.0 | 1.4 | 0.85 | 0.85 | 1.0 |
| Truss girder, partially shielded | Imperial | 70 mph | B | 120 ft | 8 ft | 70° | 0.35 | 2.0 | 0.90 | 0.85 | 1.0 |
| Coastal open terrain | Metric | 35 m/s | D | 40 m | 2.5 m | 90° | 1.0 | 1.2 | 0.85 | 0.85 | 1.0 |
Professional field note: wind load on girders during erection
1) Why erection-stage wind matters
During erection, a girder may be partially supported, temporarily braced, or connected with fewer restraints than the final condition. Wind can introduce lateral forces, torsion, and overturning moments that govern crane picks, temporary bearings, and stability checks. Temporary conditions often control because stiffness, continuity, and diaphragm action are not yet developed.
2) Selecting an appropriate wind speed
Use the governing gust wind speed specified for construction or temporary works by your project documents, authority, or site wind policy. If you have multiple erection stages, consider the most vulnerable stage. Higher elevations can experience higher speeds; if your method provides a height adjustment, apply it through the exposure factor and topographic factor.
3) Terrain exposure and height effects
Exposure conditions influence the wind profile and resulting pressure. Open terrain typically produces higher wind actions than urban shielding. This calculator provides common exposure presets and allows custom Kz when a code-derived value is available. Use Kzt to account for hills, escarpments, or local speed-up zones.
4) Converting wind speed into pressure
Wind pressure scales with the square of speed, so modest increases in speed can produce large force increases. The metric form uses q = 0.5·ρ·V², while the imperial form uses q = 0.00256·V² (psf) for wind speed in mph. Height-adjusted pressure is computed as qz = q·Kz·Kzt.
5) Projected area and wind angle
The effective projected area should represent the face presented to wind. For a solid web or box girder, a practical estimate is A = L·D multiplied by solidity and by sin(θ), where θ is the angle between wind direction and girder axis. For truss girders or complex shapes, enter a direct projected area.
6) Shape coefficient and dynamic amplification
The force coefficient Cf captures how the girder shape attracts wind. Boxier or rougher faces can increase Cf, while truss-like members often require higher coefficients due to flow interaction. The gust factor G provides a practical allowance for gustiness and dynamic response; many temporary checks use values near 0.85–1.00 depending on method.
7) Interpreting force, line load, and moment
The calculator reports total wind force F, uniform line load w = F/L, and overturning moment M = F·e about a selected lever arm. Use these outputs to screen lateral bracing demand, temporary bearing reactions, crane side loading, and stability of falsework. Apply your code’s load combinations and partial factors.
8) Practical controls to reduce risk
Mitigation can be operational and structural: restrict lifts above trigger wind speeds, improve temporary bracing, reduce exposed area by staging, and increase restraint at bearings or pick points. Document the assumed wind direction, erection geometry, and coefficients. If results flag high risk, reassess the erection sequence, temporary works design, and field hold points.
FAQs
1) What wind speed should I enter?
Use the project’s construction gust wind speed or lift restriction threshold. If none is specified, consult the governing standard and your temporary works engineer before selecting a value.
2) When should I use direct projected area?
Use direct area when the girder has openings, irregular geometry, appurtenances, or staged segments where L×D overestimates or underestimates the exposed face.
3) What does the wind angle do?
Angle adjusts the effective area using sin(θ). Parallel wind produces near-zero lateral area, while perpendicular wind produces the maximum projected area and typically the highest force.
4) Is the risk flag a pass/fail check?
No. It is a quick screening indicator based on line load magnitude. Always perform the required stability and strength checks using your project criteria and temporary load combinations.
5) How do I choose the force coefficient Cf?
Select Cf based on girder shape and guidance from your standard or wind provisions. Box or plate-like faces often use lower values than truss-like assemblies.
6) Why is a safety factor included?
Temporary works often require additional conservatism to cover uncertainties in staging, shielding, gustiness, and field tolerances. Enter the factor mandated by your method statement or engineer.
7) Can I use this for final design wind on bridges?
This tool is intended for erection-stage estimates. For final design, follow the governing bridge wind provisions, consider multiple load cases, aerodynamic effects, and code-specific pressure distributions.