Why a building in Denver sees less wind pressure than one in Miami - even in the same storm! The Ke factor explained.
Since you're building at sea level, you get the simplest calculation:
No reduction for elevation - but also no extra calculations needed. The 0.00256 constant in the velocity pressure formula already assumes sea-level air density.
Think about swimming in a pool vs. walking on land. Water is denser - more molecules packed together - so it pushes harder against your body. Air works the same way!
At sea level, you have the entire atmosphere stacked above you, compressing the air. In Denver, there's less atmosphere above, so the air is thinner and lighter.
A 100 mph wind in Miami has more "oomph" than a 100 mph wind in Denver. Why? More air molecules hitting your building every second. The kinetic energy formula (1/2 x rho x V2) shows that pressure depends on both velocity AND density (rho).
ASCE 7-22 keeps things simple: for any site below 6,000 feet, you can use Ke = 1.0. That covers almost all construction in the eastern U.S. and most of the west.
Only when you're building ski lodges, mountain observatories, or in cities like Albuquerque (5,312 ft) or higher does Ke drop below 1.0.
Even though Broward County always uses Ke = 1.0, understanding WHY helps you:
Ke is a factor that adjusts wind pressure for the air density at the building site's elevation above sea level. Air is denser at sea level and thinner at high altitudes. Denser air creates higher wind pressure for the same wind speed. For most locations below 6,000 feet, Ke = 1.0 is permitted.
Broward County is at sea level, so Ke = 1.0. This is the baseline value representing standard air density. There's no reduction for elevation since Florida's coastal areas are at the lowest possible elevation. The full wind pressure applies.
Higher elevations have thinner (less dense) air. Since wind pressure depends on air density, the same wind speed creates less pressure at altitude. A building at 6,000 feet sees about 80% of the wind pressure as an identical building at sea level. Denver (5,280 ft) uses Ke approximately 0.86.
ASCE 7-22 permits Ke = 1.0 for sites at or below 6,000 feet elevation. Since this covers most U.S. construction, including all of Florida, you can typically use Ke = 1.0. Only mountain locations above 6,000 feet benefit from reduced Ke values.
Ke is part of the velocity pressure formula: qz = 0.00256 x Kz x Kzt x Kd x Ke x V squared. It directly multiplies the velocity pressure. At sea level (Ke = 1.0), it has no effect. At high elevations (Ke less than 1.0), it reduces wind loads proportionally.
Our calculator automatically applies the correct Ke factor based on your project location. Broward County? Ke = 1.0. Denver? We've got you covered.
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