[TowerTalk] Wind Load Spec Differences Between Tower and Antenna

[Steve Dyer W1SRD]

I tried to get an answer from SteppIR to no avail so I thought I would 
reach out to the TT community. Searched TT archives and googled for 
answers. I've read K7NV's and W6NL's writeup as well about this subject.

Would like to be confident my LM-470 can handle a DB36 (17.5 sq ft using 
100 MPH EIA-222-C) .
I believe the 4 El SteppIR (9.7 sq ft) is fine on the WT51

Usual caveats about crank it down in the wind already noted. Also, the 
Tashjian specs are for a *new* tower. I don't know the vintage or 
history of the LM-470 I have. It came with the property.

Thanks es 73,
Steve
W1SRD

Here is my original email to SteppIR:

I am sure I am not the first to ask to understand the difference between 
wind load ratings.

SteppIR calculates wind load using EIA-222-C at 100 mph (wind zone B)  
which is equivalent to 120 mph for a 3 second average used by 
EIA-222-G.  See Leeson, W6NL ( 
http://www.kkn.net/dayton2007/w6nl_ant.pdf )!

Tashjian uses TIA-222-G 85 mph 3 sec average which maps to a 70 mph 
fastest mile (222-A wind zone A).

This leads me to to the questions:

1. Is a tower rated at 13 sq ft/85 mph using 222-G is OK for the 4 El? 
Tower is a WT-51.
2. Is a tower rated at 18 sq ft/85 mph using 222-G is OK for the DB36? 
Tower is a LM-470D.

I understand you cannot commit to the safety of the tower, but I need to 
reconcile and understand the differences between the two measurement 
systems before I go forward.