Well, first off, I wasn't in any way suggesting that he should do
anything different than UST recommended. In fact, I'm not sure how
anyone would get zoning inspection approval if they didn't follow the
drawing pretty much to the letter. I was trying to be facetious about
the "on purpose to limit their liability" bit, but I guess I didn't put
enough tongue into my cheek.
I do find it odd, though, that two very similar towers (both
freestanding heavy duty 70 footers) would have such different rebar
specs. I have a friend who for several years designed concrete bridge
structures here in Arizona, and he told me that within reasonable
boundaries you get similar large scale tensile strengths with several
smaller gauge rebar versus a few larger gauge rebar, but at a more
localized level the several smaller rebar are better for holding
everything togteher (which intuitively makes sense). It's pretty much
up to the engineer whether he chooses to go with lots of small rebar
versus a few large rebar, and my point was simply that I would have
thought that a company like UST would have opted for the more user
friendly approach.
I suppose it is possible that a few sticks of #9 rebar might be stronger
in shear than several sticks of #5 rebar, but I'm having a hard time
picturing how that would apply to a tower foundation. Maybe California
has some sort of general requirement that emphasizes shear strength.
Lastly, I'm pretty sure that a rebar cage is stronger with formed
corners than with tied corners, and some drawings insist on it. It
seems to me that rather few people (or companies) are going to have
equipment capable of forming #9 rebar, so I'm puzzled even more why UST
would have gone with that.
But to be clear, I was not trying to encourage anyone to roll their own
regarding tower foundations, and a quick archive search will show that
I've been pretty vocal on just the opposite. I apologize if I gave
anyone the wrong impression.
73,
Dave AB7E
On 5/24/2010 11:54 AM, K7LXC@aol.com wrote:
>
> In a message dated 5/24/2010 10:29:23 A.M. Pacific Daylight Time,
> towertalk-request@contesting.com writes:
>
>
>> When I see specs like that it always makes me think that the
>>
> manufacturer does it on purpose to limit their liability,
>
> Ya think?!? They also do it to comply with various tower standards and
> building regulations.
>
>
>
>> knowing that almost nobody is going to actually going to follow the
>>
> print.
>
> Jeez, Dave - I know you've been on TT for some time and I can't
> believe you made that statement. You're SUPPOSED to do what the manufacturer
> says. They have real live engineers that come up with those specs. AMATEUR
> back-of-the-envelope calculations ain't gonna cut it.
>
> Cheers,
> Steve K7LXC
> TOWER TECH -
> Professional tower services for hams
>
>
>
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