The American Society of Civil Engineers sets up this guideline. These are often referred to as ASCE 7 – 93 or ASCE 7 – 02. Wind used to be measured over a mile (ASCE 7 – 93) and now it is measured in 3 second gusts (ASCE 7 – 02).
A 70 mph wind takes about 52 seconds to cover a mile (A 60 mph wind takes a minute to cover a mile, a faster wind will take less than a minute to cover the same distance.)
Now let’s take a look at something called impulse. Impulse is roughly defined as force times time. Wind load is kind of an impulse. Technically this is not correct; but, close enough for this discussion. Think of the impulse as the action required to knock- down your building.
Impulse = Force x Time
Lets look at it in the simple numbers. Say “Impulse” was a number such as 50 . Then 50 can be expressed in two different ways:
50 Impulses = 5 force units x 10 time units
OR
50 Impulses = 10 force units x 5 time units
So the same tent can withstand either 5 or 10 Impulses depending on how many time units you allow. Nothing has changed, just the way things are interpreted and written down.
