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[TowerTalk] Guywire anchors/concrete

 To: [TowerTalk] Guywire anchors/concrete wa4dou@excite.com (wa4dou@excite.com) Sat, 17 Jul 1999 19:58:21 PDT
 ```Hi Gang, Thank you for your comments. I do realize that the concrete in the ground is nothing more than a "dead man". In addition to the weight of the concrete alone, the resistance of the soil between it and the tower and the soil above it and towards the tower represents a very formidable barrier to the movement of the concrete "dead man" in the event that the tower guy could overcome the weight of the concrete alone. Therefore there is a composite strength of the two that is expressed by Rohn as "reaction" in ft. lbs.,both horizontally and vertically( or lateral and uplift capacity).(This assumes that we are dealing with "normal" soil which is defined by Rohn as soil of a cohesive nature with a horizontal bearing capacity of 400 lbs. per square ft. per lineal ft. of depth.)This "reaction" in foot pounds varies from 710 #(H)-780#(V)for a 70 mph, 40 ft. high, 25G tower with 18.4 sq. ft. of windloading on top(and 1 guy wire) to 4460#(H)- 3310#(V)for a 25G tower in 90 mph wind with a 160 ft. high, 25G tower (with 5 guy wires). My contention is that if Block 4A is suitable for both extremes then it must be "extreme" overkill for the 40 footer and just "adaquate" for the much taller ,5 guy tower in 20 mph stronger wind. Being neither a "structural" engineer nor an old and experienced tower builder, i was soliciting comment on whether others had focused on this before and what their opinions might be like. Its been my experience that one does not know a subject well until one knows it backwards and forwards, inside and out. I'm attempting to learn every possible thing i can about this subject in a very short time period. I'm really glad i stumbled across this reflector a few days ago and i'm studying the "archive." Now that i've become conscious of towers coupled with a personal interest and involvement, i am seeing a lot of housebracketed towers with 1 bracket 10-20 ft. high and as many as 4 and 5 sections above the bracket with antennas on top that would be marginal if the tower only had 2 or 3 sections above the bracket(according to Rohn).These things are 10-15-20-25-30 yrs. old and continue to stand year after year and defy the specs. Truly Rohn must over engineer these things generally speaking for those who will not adhere to "good practices." It is not my intention to encourage anyone to ignore the specs and standards that Rohn promulgates. Only to understand where and when i can make intelligent choices or departures from specs. My objection to Block 4A was based on having to hand dig the guy anchor holes. I was told by several that a "terramite" or backhoe could not be expected to dig square holes, 3 X 3 X 4'. I don't want the dirt in the vertical walls to be disturbed so i elected to dig them manually. Its a lot of work! Someone gave me the idea to use an augar to drill the dirt. I'm going to seriously investigate that option. Thanks guys! Hope better understanding for all of us results from all these 2 finger typed words.:o) 73 Roy Lincoln WA4DOU On Sat, 17 Jul 1999 18:55:12 +0100, Pete Smith wrote: > At 01:42 PM 7/17/99 EDT, K7LXC@aol.com wrote: > > > >In a message dated 99-07-17 11:16:07 EDT, wa4dou@excite.com writes: > > > >> Anyway, how many of you have, in building or planning low towers, noted > >> that Rohn specifies Block no. 4A(Concrete Anchor Data)for all 25G tower > >> installations up thru 110 mph, > >> and to 100 ft. with 45G in 110 mph wind before they upgrade to 4B. > >> I realize that i've heard it said repeatedly over the years that Rohn is > >> very conservative in their rateings.I also realize that it can be very > >> dangerous to "second guess" Rohn, or to depart from their specs.without a > >> lot of knowledge. > >> It is easy to look at a 50 or 60 ft 25G tower with 110 mph specs and > draw > >> a conclusion that Block 3D or 3E would be totally adaquate for anchoring > >> purposes. My anchors are GAC25's which are only 5-1/2 feet long as opposed > >> to GAC30's which are 7 ft. long. Since i am digging these holes > >> with post hole diggers and a shovel, i don't relish digging the last 1 > foot > >> of depth between 3 and 4 ft. or even to 3-1/2 feet deep. I'd even make a > >> concession and pour the concrete 1-1/2 feet deep which is 50 % deeper than > >> called for in Block 3D and more than 3E, knowing full well that there > would > >> be less "earth cover". > >> Am i barking up the wrong tree here? > > > > The LXC Prime Directive is to "DO what the manufacturer says". Let me > >put it like this - how well are you going to sleep when that big windstorm > >comes barreling through knowing that your hole wasn't as deep as the > >manufacturer recommended? > > The weight of the concrete is far from the whole story for a buried guy > anchor -- the weight of the earth above the anchor is the rest of it. > The problem with burying a guy anchor more shallowly is that it will have > just that much less ability to resist the pull of the guy wire. > > 73, Pete Smith N4ZR > n4zr@contesting.com > > Sometimes a tower is just a tower _______________________________________________________ Get your free, private email at http://mail.excite.com/ -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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