[TowerTalk] field-day mast anchoring question

Gary K9GS garyk9gs at wi.rr.com
Sun Jan 24 00:41:31 EST 2016


I my town they are doing some road construction around the main 
intersection.  They have some temporary telephone poles in place and use 
large concrete blocks with a loop on the top to guy the telephone 
poles.  I'd estimate the block to be about 3 X 3 feet X 4 feet long.

The loop is ~3/4"-1" steel cable.

The telephone poles are used to hold up traffic signals that span the 
intersection so there is quite a bit of weight up there and also a lot 
of wind load.





On 1/22/2016 11:06 AM, jimlux wrote:
> On 1/22/16 7:31 AM, dw wrote:
>>
>> For those familiar with the AB-621 military launcher mast units.
>> Lets say there was an interest in using this on a field day event, where
>> there is a concern that the ground is too soft to safely establish
>> anchors.
>> Is there a possibility of using concrete wall-barrier blocks bolted
>> together, as dead-weights to safely hold the anchors?
>
> Sure..
>
> The catering/party equipment rental places do this all the time, as do 
> riggers for theatrical/music performances.  They have big concrete 
> blocks with a big loop sticking out of the top (rebar or a piece of 
> pipe bent in a U) that they connect their guys to. We've got a 90 
> foot-ish structure in a parking lot at JPL with a bunch of 5000 lb 
> blocks like this holding it in place.
>
> I've also seen portable anchors that you fill with water.  You're 
> basically relying on bulk mass to hold things in place.   IN some 
> places, dragging a hose to fill a kiddie pool or trash cans or trash 
> bags is easier than dragging concrete blocks around.
>
> You could also look into what are called FIBC (Flexible Intermediate 
> Bulk Carriers) which are those big fabric bags full of just about 
> everything you see on the back of a semi flatbed truck.  They hold 
> about a cubic yard, they cost about a dollar (empty), and you might be 
> able to rent/borrow/buy things like a yard of gravel or dirt in a 
> FIBC.  If you have something that can move a couple of tons around.
> They're pretty nice because they have a strong fabric strap handle 
> (how you pick it up with a crane, forklift, etc.) that you can hook 
> your guy to.  And, depending on what it's filled with, it will spread 
> out and conform to the ground surface.
>
> I've not tried it, but I'll bet you could get one of these things, 
> line it with polyethylene sheet, and fill it with a ton of water 
> pretty easily. They're really strong, really cheap, and store very 
> compact when empty.  (actually, just looking up prices, I see that 
> they actually make liners for these things so they can hold liquids).  
> Looks like they're about $15-20 each on amazon when you buy just one, 
> brand new.
>
>
>
>
>
> You need to calculate what sort of loads you're going to see, and make 
> sure you have enough mass to hold it.  You can probably figure 
> something like a friction coefficient of 0.3 or something for the 
> sliding motion/horizontal component.
>
> https://www.nzta.govt.nz/assets/resources/surface-friction-conference-2005/8/docs/frictional-characteristics-roadside-grass-types.pdf 
>
>
> has a handy table of sliding friction of a concrete filled tyre (in 
> NZ) across grass and dirt.  (It's all about locked wheel skids and 
> distances).  As you might imagine, grass is slippery when wet.
>
>
>
>> For example, I think I can come up with a number of 60lbs cement
>> wall-barrier slabs that can be bolted together for each anchor point.
>> If this would be a viable option, how much weight on the anchor blocks
>> would guarantee a safe installation?
>> The intent is to put up a 40 meter 2 element yagi, without a rotor, at a
>> height of 50 feet.
>>
>> Thanks in advance.
>> N1BBR
>>
>
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> -- 
> 73,
>
> Gary K9GS
>
> Greater Milwaukee DX Association: http://www.gmdxa.org
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