Wind to Force

Wind pressure increases with the square of wind speed. This means if wind speed doubles, the pressure quadruples. At 180 mph (Florida Keys design speed), the basic velocity pressure is about 83 psf. The formula is qz = 0.00256 x Kz x Kzt x Kd x Ke x V squared, where V is wind speed in mph. The 0.00256 constant comes from converting units and accounting for air density.

Velocity pressure (q) is the dynamic pressure created by wind striking a surface. It represents the kinetic energy of the moving air converted to pressure. This base pressure is then modified by various factors to determine actual design pressures on different parts of a building. It is the starting point for all wind pressure calculations in ASCE 7.

Pressure depends on kinetic energy, which is proportional to velocity squared. When wind speed doubles, you have twice as much air hitting the surface at twice the speed, resulting in four times the energy transfer. This is why hurricane damage increases dramatically with wind speed. A Category 5 hurricane causes much more than twice the damage of a Category 2 because of this squared relationship.

At 180 mph with standard conditions, the basic velocity pressure (qz) at 33 feet height is approximately 83 psf. This assumes Exposure D, which is typical for the Florida Keys. Actual pressures on building surfaces are then calculated by applying pressure coefficients (GCp or GCpi) to this base value. Wall and roof pressures can be higher or lower depending on their location and orientation.