# I don't understand how this works..

• Nov 2nd 2009, 04:20 PM
WTF
I don't understand how this works..
Can someone help me understand the following?
I can do it all, but I don't understand how M(z,cat) equals 0.79?

The Site Wind Speed, Vz, is all the five wind factors multiplied together
Vz = V * Mls* M(z,cat) * Mt * Mr (m/s)

The information for M(z,cat) is :

Terrain
Category 3

Building Height (m) 7.5

(z,cat) 0.79

The numbers pertaining to the above are taken from a table, I will recreate here :

Multiplier, M
(z,cat)

Height, z Terrain Category 3
(m)

≤3 0.75
5 0.75
10 0.83
15 0.89

I really don't get the relationship between 0.75, Category 3 and 0.79 are,
I don't understand what I need to do to have the answer equal 0.79?!

Thanks,

WTF
• Nov 3rd 2009, 07:05 AM
Wilmer
Quote:

Originally Posted by WTF
Terrain
Category 3
Building Height (m) 7.5
(z,cat) 0.79
The numbers pertaining to the above are taken from a table, I will recreate here :
Multiplier, M
(z,cat)
Height, z Terrain Category 3
(m)
≤3 0.75
5 0.75
10 0.83
15 0.89

Looks like a simple "proportion is used:
you have 5 : .75 and 10 : .83
so (being halfway between 5 and 10) 7.5 is simply (.75 + .83)/2 = .79