[TowerTalk] windload rating of triex LM470e tower to be independently ver...
Al Williams
alwilliams@olywa.net
Tue, 26 Sep 2000 14:39:40 -0700
I seem to be missing something--but this my first tower permit experience.
It wasnt the county that specified the 4000 lb rating. Rather it was the
tower mfr indirectly specifying 4000lb by stating that the foundation design
(I presume that means the mfrs rebar, welding to erection plates, and
amount/strength of the concrete) requires normal soil and then goes on to
state that "normal soil" is 4000lb.
Not being experienced, I would read this as either faulty documentation or
his design is not adequate for "typical" soil i.e. not massive crystalline
bedrock.
BTW, the design calls for only 3 1/2 cu yards of cement for a wind/antenna
of 70mph/24 sq ft whereas the comparable US tower HDX572 calls for 5 cu
yards for 70mph/18 sq ft.
k7puc
I really appreciate the responses.
k7puc
----- Original Message -----
From: "Lonberg, Hank" <Hank.Lonberg@Harrisgrp.com>
To: <K7LXC@aol.com>; <alwilliams@olywa.net>; <towertalk@contesting.com>
Sent: Tuesday, September 26, 2000 1:51 PM
Subject: RE: [TowerTalk] windload rating of triex LM470e tower to be
independently ver...
>
> Steve:
>
> I've already responded to Al directly on this matter but in the case of
the
> "normal soil" thingie, I'll respond to the reflector in general.
>
> When you do not have a soils report done by a soils engineer that
discusses
> the allowable vertical bearing pressure and other parameters for your
> project's specific site then, in the case of UBC jurisdictions, the local
> building people default to Table 18-I-A - Allowable Foundation and
Lateral
> Pressure in the UBC itself. In this table the soils are classified 1 to 5
> with 1 being Massive Crystalline Bedrock with an allowable bearing
pressure
> of 4000 pounds per square foot. Class 5 or worst case soil is clay, or
sandy
> silty clay etc. and has an allowable bearing pressure of 1000 pounds per
> square foot.
>
> I normally use the class 5, worst case, as most hams do not want to pay
the
> $5000 to $10000 for a proper, by engineering standards, soils
investigation
> and report. This approach placates the building officials usually.
>
> Again if you don't have to get a permit then what you do is what you are
> liable for.
>
> Ciao
>
> Hank Lonberg P.E. / KR7X
>
>
> -----Original Message-----
> From: K7LXC@aol.com [SMTP:K7LXC@aol.com]
> Sent: Tuesday, September 26, 2000 12:31 PM
> To: alwilliams@olywa.net; towertalk@contesting.com
> Subject: Re: [TowerTalk] windload rating of triex LM470e
> tower to be independently ver...
>
>
> In a message dated 9/26/00 11:24:52 AM Pacific Daylight Time,
> alwilliams@olywa.net writes:
>
> > Yesterday, after an hours long session with the county engineer
> and his
> > supervisor reviewing the analysis I was informed that I would
> have to have
> > the tower and foundation analysis reviewed and certified by a
> Washington
> > State Professional Engineer. I believe they were uncomfortable
> with the
> > analysis (copy including stamped by a California State
> registered
> > professional engineer) because of the following:
>
> They are uncomfortable because you *have* to have a local state
> PE stamp.
> Every state and/or tower construction permit I've ever run into is
> the same
> way.
>
> It's easy enough for a PE to get reciprocity with other states
> since it's
> just a paperwork deal but most are only licensed in their own state.
> Rohn is
> a tower company that can provide PE stamps for all states because
> there
> business is national and this way they're in control of the
> situation (and
> can get you to pay for it!).
> >
> > 1. The county engineers were informed several times that the
> California
> > engineer would call to discuss the analysis but not call was
> received.
> >
> What's to discuss? The local building department has their book
> of
> building codes and YOU have the responsibility of complying with
> them. Even
> if they actually did talk to someone, they still require locally
> stamped
> plans.
>
> The big problem is that virtually no one that you talk to in the
> building
> department has ever seen or reviewed the plans for a radio tower.
> They look
> at it likes it's a habitable structure (which it isn't obviously)
> and try to
> apply other rules that you can argue don't apply (like a soil test).
> My most
> *memorable* experience with a local building department inspector
> was having
> to take the time to show him that the four things he dinged us with
> either
> were totally wrong to begin with or didn't apply. Many times YOU
> have to help
> THEM to understand what's going on.
>
> > 2. The Foundation Installation stated that "The tower footing
> design
> > shown is based on normal soil criteria...." and "Normal soil is
> defined as
> > cohesive soil with an allowable vertical bearing load capacity of
> 4000
> > pounds per square foot". The analysis contains a table listing
> various
> > soils. The listing for 4000 pounds is defined as massive
> crystalline
> > bedrock !!!!!!!!
>
> This sounds really fishy but I'm not a soils engineer so can't
> give a
> definitive answer. Maybe Hank, KR7X, can weigh in on this one. The
> TIA-222
> Tower Standard calls 4kpsf "normal soil" - and says that "rock" is
> not to be
> considered normal soil".
> >
> > 3. The county engineer asked several times who crossed out 70
> and hand
> > wrote 80 for the wind speed and who crossed out 24 and hand wrote
> 15 for
> the
> > maximum antenna wind area.
> >
> Huh? Another excellent reason for locally stamped drawings. When
> a PE
> stamps plans, they are accepting responsibility for the design and
> it's
> compliance to all germane regs (as well as paying big bucks for
> 'Errors and
> Omissions' insurance). THAT'S what the building department wants to
> see -
> they want SOMEONE ELSE to take responsibility for the design. They
> just
> 'check' the plans.
>
> > 4. The county engineer was also uncomfortable with the
> diagrams and
> > anaylsis of the rebar in the footing but I am not knowledgable to
> describe
> > this concern.
>
> You're talking to the wrong people - these guys don't have a
> clue. Get a
> local PE to stamp your drawings and THEN take them to the building
> department.
>
> DO NOT take your plans to an engineering firm (read $1k or more
> to do
> it). I can give you the name of a PE who can do it for you at a
> significantly
> lower price. He's done more than six sets of plans for me including
> a US
> Tower crank-up with a high windspeed and seismic calcs. Volunteer
> Engineers
> are easily locatable from the ARRL website for just about anywhere
> in the
> country.
>
> Cheers, Steve K7LXC
> Tower Tech
>
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