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Re: [TowerTalk] HDBX-48 figures for 90 mph zone

To: Mike Cizek <>,
Subject: Re: [TowerTalk] HDBX-48 figures for 90 mph zone
From: "henry.lonberg" <>
Date: Wed, 7 Dec 2011 18:53:25 +0000 (UTC)
List-post: <">>

Mike etal: 

All this talk got me curious about the loading capacity of the 48' HDBX. 

When I was engineering the tower installation for K9CT's new station, he 
requested using 64' BX towers for the 80m 4-Square antenna system. 

The design criteria was TIA 222-G and 90mph design wind velocity. 

Given the following criteria: 

TIA 222-G criteria, 90mph design wind velocity, exposure "C", 222-G for 
category I structures does not require ice or seismic load consideration. 

I threw 10 sf of antenna at 51' (3' above top- Rohn criteria). 

The results show that the system was at about 80% utilization with this load 
configuration. However the 10' max boom caution from Rohn still is applicable. 

This tower system uses aluminum rivets at the diagonal to leg conntections and 
grade 5 bolts at the leg splices. The aluminum rivets are the reason for the 
10' maximum boom length. This keeps the potential torsion loading down. This 
torsional loading coupled with the lateral shear is what stresses the diagonal 
connections where the aluminum rivets are located. 

Sorry about the delay but paying clients come first! 


Lonberg Design Group, Ltd. 

H. Lonberg, P.E.,S.E. / KR7X 


----- Original Message -----

From: "Mike Cizek" <> 
To: "Gene Fuller" <>, "Jim Thomson" <>, 
Sent: Wednesday, December 7, 2011 8:22:21 AM 
Subject: Re: [TowerTalk] HDBX-48 figures for 90 mph zone 

Bottom line.....the manufacturer wants $1400 (one thousand four hundred 
dollars) to provide the drawings.  I have already told the guy we need to 
look at other options; all of which were more expensive, until we figured in 
the cost of getting proper drawings from Shelby.   

Thanks to everyone for the replies; we can close this thread and move on to 
something useful and more fun now :-) 


Mike W3MC 

-----Original Message----- 
[] On Behalf Of Gene Fuller 
Sent: Wednesday, 07 December, 2011 10:56 
To: Jim Thomson; 
Subject: Re: [TowerTalk] HDBX-48 figures for 90 mph zone 

Bottom line, if the manufacturer can't, or won't, give you 90 mph data or at 
least the projected tower area and, taking into account the materials used, 
the maximum allowable restraining moment, then they probably know nothing 
about things like section modulus and moment of inertia and never did the 
calculations themselves, in which case I would have second thoughts about 
buying their tower. 
Gene / W2LU 

----- Original Message ----- 
From: "Jim Thomson" <> 
To: <> 
Sent: Wednesday, December 07, 2011 7:24 AM 
Subject: [TowerTalk] HDBX-48 figures for 90 mph zone 

> Date: Wed, 07 Dec 2011 00:19:21 -0500 
> From: K8RI <> 
> Subject: Re: [TowerTalk] Fwd:  HDBX-48 figures for 90 mph zone 
> To: 
> Message-ID: <> 
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed 
> On 12/6/2011 11:13 PM, wrote: 
>> In a message dated 12/6/2011 4:43:51 P.M. Eastern Standard Time, 
>> writes: 
>> As I  recall wind pressure "on a flat surface" at 70 mph is 20.6 lbs/sq 
>> ft., 
>> so  if the  tower is rated for 
>> 18 sq ft at 70 mph, would it be too much of  a stretch to say to the 
>> zoning 
>> board that since wind pressure at 90 mph is  34 lbs/sq ft, by simple 
>> math, 
>> the tower should be good for 10.9 sq ft at  90 mph ? 
>> Gene / W2LU 
> Regardless of wind area isn't there a boom length limitation on both the 
> BX and HDBX series? 
> 73 
> Roger (K8RI) 
> ##  yes, I think they reduced it to just 10' years ago..and sales 
> plummeted. 
> Just fudge the ant wind load a bit, and perhaps 'take out' one section on 
> paper. 
> Then when u install it, add the extra section back in.   IF you ever did 
> hit it with 
> a 90 mph wind, and a big ant, ur gonna be in for an eye opener.   That 
> thing about 
> 70 mph = 20.6 sq feet.  That's from 1976. 222- REV-D.   It's now REV G ! 
> A Trylon T-500, 72' good for 22 sq feet @ 70mph....but only 6 sq 
> feet 
> at 100 mph.  The tower itself will eat up all the windload.   Toss in any 
> ice,and 
> you can kiss it goodbye.   I wonder if the factory will even give you a 
> windload 
> rating for 90 mph ? 
> Jim  VE7RF 
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