At 07:42 AM 7/9/2005, isp@bnjcomp.com wrote:
>Of couse like everyone else here on this list that puts up thier own tower
>I am trying to save money. But also trying to stay safe. The property I
>am putting this on was originally part of a piece of land that was hopeful
>that the city would get a large business to be on. So for that reason
>they did core samples of the property. So I am going to try to acquire a
>copy of the results of those core samples to see what they say. So my
>question is I don't see in Rohn's book a spot for "if XXX sandy conditions
>then modify piers by doing this or that" or "if XXX compactness with clay
>then modify piers by doing this or that".
In general, the mfr won't provide this level of detail. If you're going to
modify the "standard" installation, especially for a tower costing tens of
thousands of dollars, they're going to expect that you have an engineer who
can do the calculations for your local situation. You have to take into
account not only the bearing strength of the soil, the details of the
excavation/compaction method, and local regulatory stuff. Rohn can't be
expected to know all the idiosyncracies of every building department and
soil type.
On the other hand, a local engineer can probably crank this sort of thing
out, along with all the other structural calculations in 10-20 hours at a
$100/hr or so, and an engineer's report would probably be required by the
building department anyway. That's probably <10% of the cost of the
overall job, considering the new cost of the tower, the excavation, the
permitting, etc., especially if you treat it like a business, and you
actully figure in the cost of labor for digging the holes, etc.
> Once I get that where do I look for those modifications. Also I tried
> when I bought this tower to get engineering drawings from ROHN but after
> MANY calls was unsuccessful. Does anyone have any new experience with
> new radian / rohn and think my ability to get those drawings would be
> better? Better question is it seems all the information is in the
> Rohn Catalog and I am wondering what I will get off of those drawings
> that is not in the catalog (since the drawings will probable be for the
> original owners Soil conditions).?
You're talking about engineering drawings prepared for a specific
installation? I'm not surprised that you couldn't get a copy. In some
cases, the drawings remain the property of the engineer/architect who
prepared them. In others, they are owned by the person who paid for the
analysis.
In any case, the drawings may not be of much use to you in a practical
sense. As you say, they would be for a different installation, so you
couldn't use them for your installation. They might be interesting to look
at in an "understanding how the engineering analysis is done" sense, but
you certainly couldn't just plug in your numbers and hope to trust the
results. A lot of times, there's a goodly element of professional
judgement in the analysis and drawings, and most engineers don't put ALL
the gotchas into the analysis. Example: Engineers in San Diego probably
don't even bother doing the ice loading calculations, or even mentioning
that they didn't do them. The local building department isn't looking for
them, the odds of icing occurring are so small that the engineer can be
comfortable (in a professional responsibility sense) not mentioning them, etc.
I am certainly leery of people who ask me for copies of drawings I've done,
and want to know a WHOLE lot about why they want them. The last thing I'd
want is someone to photocopy some drawings I've done (without my knowing
and approving), submit them for their permit, have the counter person not
worry about it not having an original wetstamp, have a disaster, and find
out about it when the legal summons shows up in my mailbox. I'd prevail in
the long run, but it would be expensive and time consuming.
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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