Wind Load Velocity Pressure Calculator

In imperial units (V in mph), velocity wind pressure is qz = 0.00256 × Kz × Kzt × Kd × Ke × V² (in psf). In SI metric units (V in m/s), qz = 0.613 × Kz × Kzt × Kd × V² (in Pa).

Directionality factor Kd accounts for reduced probability of maximum wind speed aligning with critical building axes. ASCE 7 Table 26.6-1 assigns Kd = 0.85 for main wind force resisting systems (MWFRS) and component/cladding.

Kz evaluates ground surface roughness and height above ground z. Exposure Category B (urban/suburban) produces lower Kz than Exposure C (open terrain) or Exposure D (flat coastal).

Topographic factor Kzt accounts for wind speed-up over isolated hills, ridges, or escarpments. For flat terrain, Kzt = 1.0.

Design wind pressure for rigid enclosed buildings is p = qz * (G * Cp - GCpi), where G is gust-effect factor (0.85 default), Cp is external pressure coefficient, and GCpi is internal pressure coefficient.

The calculator implements the standard ASCE 7 Directional Procedure for regular-shaped rigid buildings. Flexible tall structures (frequency < 1 Hz) or complex shapes require wind tunnel testing.

Saudi Building Code SBC 301 directly adopts ASCE 7-16 Chapter 26-30 wind load Analytical Procedures, utilizing local 3-second gust basic wind speed maps for Saudi regions.

ASCE 7 Risk Category II ultimate wind speeds range from 100-115 mph in interior US regions to 140-180+ mph along hurricane-prone Atlantic and Gulf coasts.

Basic wind speed V is the 3-second gust wind speed at 33 feet (10m) above ground for Exposure Category C, measured in mph or m/s.

Risk Category I covers temporary structures, Category II covers standard buildings, Category III covers high-occupancy structures, and Category IV covers essential facilities like hospitals with higher importance factors.

Exposure B applies to urban and suburban wooded areas; Exposure C applies to open terrain with scattered obstructions; Exposure D applies to flat, unobstructed coastal water surfaces.

Velocity pressure is computed using qz = 0.00256 × Kz × Kzt × Kd × Ke × V², where Kz is velocity pressure coefficient and V is wind speed.

ASCE 7 specifies GCpi = ±0.18 for enclosed buildings and ±0.55 for partially enclosed structures due to internal pressurization risks.

Roof corners and ridge edges create flow separation and vortex shedding, causing severe local suction pressures (high negative GCp values).

IBC Section 1609 requires that design wind pressure for main wind force resisting systems (MWFRS) not be less than 16 lbs per square foot (0.77 kPa).

As wind flows up a ridge or hill, streamlines compress, accelerating wind velocity (up to 2x) at the crest.

Wind blowing over a flat roof creates aerodynamic lift (Bernoulli effect), creating strong upward suction forces that require continuous structural tie-downs.

C&C wind loads calculate localized peak pressures on individual elements like wall sheathing, windows, and roof tiles, whereas MWFRS calculates global structural frame loads.