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Wind Load Calculator

Calculate wind loads on buildings per ASCE 7-16 / BS EN 1991-1-4. Computes velocity pressure, design wind pressure, base shear, and overturning moment.

Structural Loads Structural engineers, architects, building designers Commercial Intent: HIGH

Engineering Formulas

Velocity Pressure

qz = 0.613 × Kz × Kzt × Kd × V²  (SI, V in m/s)
qz = 0.00256 × Kz × Kzt × Kd × V²  (IP, V in mph)

qz: Velocity pressure at height z

Kz: Exposure coefficient

Kzt: Topographic factor

Kd: Directionality factor

V: Basic wind speed

Exposure Coefficient Kz

Kz = 2.01 × (z / zg)^(2/α)
where α and zg depend on exposure category

z: Height above ground (m)

zg: Gradient height (365.8m B, 274.3m C, 213.4m D)

α: Exponent (7.0 B, 9.5 C, 11.5 D)

Design Wind Pressure

p = qz × G × Cp – qi × GCpi
qi = qz at roof height (internal)

G: Gust effect factor

Cp: External pressure coefficient

GCpi: Internal pressure coefficient

Total Wind Force

F = p × A
Vbase = F
MOT = F × h/2

F: Total wind force (kN)

A: Projected area (width × height)

M_OT: Overturning moment (kNm)

Worked Example

Mid-Rise Building in Open Terrain (ASCE 7-16)

windSpeed: 40unitSystem: SIexposureCategory: CbuildingHeight: 30buildingWidth: 20buildingLength: 40importanceFactor: 1.0topographicFactor: 1directionalityFactor: 0.85gustEffectFactor: 0.85internalPressureCoeff: 0.18pressureCoefficient: 0.8

Kz at roof (30m)

Kz = 2.01 × (30/274.3)^(2/9.5) = 1.18

Velocity Pressure

qz = 0.613 × 1.18 × 1.0 × 0.85 × 40² = 984 Pa

Design Pressure

p = 984 × 0.85 × 0.8 – 984 × 0.18 = 669 – 177 = 492 Pa

Total Force

F = 492 × (20 × 30) = 295,200 N = 295 kN

Base Shear

V = 295 kN

Overturning Moment

M = 295 × 30/2 = 4,425 kNm

Result: Velocity pressure qz = 984 Pa, Design pressure p = 492 Pa, Base shear V = 295 kN, Overturning moment = 4,425 kNm

Engineering Notes

ASCE 7-16 uses ultimate wind speeds (3-second gust at 10m in open terrain).

Always check both positive and negative internal pressure coefficients.

For MWFRS, the wind load is typically applied as a uniform pressure over the projected area.

Component and cladding (C&C) loads are higher than MWFRS loads — use separate analysis.

Wind loads are typically combined with dead load and live load per load combinations.

Assumptions

• Wind direction is normal to the face analyzed

• Building is regular-shaped (no complex geometry)

• Simplified method per ASCE 7-16 Chapter 27

• No dynamic response analysis (gust effect factor approach)

• Internal pressure acts uniformly within the building

Common Mistakes

✕ Using gust speed instead of 3-second gust wind speed

✕ Forgetting to check both positive and negative internal pressure cases

✕ Using the wrong exposure coefficient Kz formula for the selected code

✕ Not verifying that the building qualifies as rigid vs flexible

✕ Applying wind loads only in one direction (wind can come from any direction)

Frequently Asked Questions

What is velocity pressure in wind load calculations?

Velocity pressure (qz) is the pressure exerted by wind at a given height, accounting for exposure, topography, and directionality. It is the starting point for determining design wind pressures on building surfaces.

How do I choose the exposure category?

Exposure B: urban/suburban areas with many obstructions. Exposure C: open terrain with scattered obstructions (most common). Exposure D: flat, unobstructed areas adjacent to large water bodies.

What is the difference between rigid and flexible structures?

Rigid structures (G=0.85) have a natural frequency > 1 Hz — most low/mid-rise buildings. Flexible structures (G=0.925) have natural frequency ≤ 1 Hz — tall/slender buildings where wind gusts cause dynamic response.

When should I use internal pressure coefficient?

For enclosed buildings, GCpi = ±0.18. For partially enclosed buildings with openings, GCpi = ±0.55. Internal pressure can add to or subtract from external pressure, so both sign cases should be checked.

What are typical external pressure coefficients?

Windward wall: +0.8. Leeward wall: -0.3 to -0.5 depending on building proportions. Side walls: -0.7. Roof: -0.7 to -1.3 depending on slope and location.

Does this calculator handle parapets and roof overhangs?

This calculator provides simplified wind loads for main wind force resisting systems. Parapets, roof overhangs, and components/cladding require additional pressure coefficients per ASCE 7 Chapter 30.