Jerry,
I appreciate the difficulty you're facing, and I don't envy that
sort of problem. Before I sought the services of a registered PE to
certify the hanger assembly, I'd spend a little time on the phone with
the good people at the hanger manufacturer, there are two of them
located very close to us and I would imagine they might be able to
provide a listed assembly to accomplish the support of the piping in the
manner your example noted.
Baring that, you have no alternative, Brad's math and guidance
aside, but to use the services of a PE. You can't use non-listed
components unless they're endorsed by a PE (9.1.2, 9.1.1.5.1). I take
that back, you can do anything you like, whether it's approved for
installation by the AHJ is the determinant, and if something happens,
you're still wrong, particularly if what you "design" fails. And it's
relevant, I think to note that while Brad has correctly explained the
formula for calculating the required section modulus for a cantilevered
beam, the information he provided hasn't addressed the means of
fastening it to the structure, and the capacity of that means, which is
half the question.
You're not an engineer, so why take that sort of liability on
yourself? Sure, from what I've seen of your submittals in the past you
could do the math just fine, but ask yourself this - can you defend it
in court? If the answer is "no", then a manufacturer is the first stop,
and a PE is the next.
Hope it works out for you.
*Ken Wagoner, SET
*Parsley Consulting***
*350 West 9th Avenue, Suite 206
*Escondido, CA 92025-5053
*****Phone 760.745.6181*
Visit our website <http://www.parsleyconsulting.com/>
***
On 4/4/2014 5:31 PM, Brad Casterline wrote:
Required Section Modulus for cantilevered will be the force (pounds) times the distance
(inches), divided by the stress (15,000). The force is the weight of the water-filled
pipe plus 250. The distance is 4" in this case. Not hanging at 15' just means the
force will be less, i.e, if you have these unistrut at 7'-6", the weight will be
half that if they were 15'-0, but you still have to add 250 lbs to get the force. Please
post your results so we can all look at them, and be prepared to be criticized for not
hiring a structural engineer. The 4x thing you mentioned will also be cleared up because
with regular trapeze it is half the force times half the distance.
Brad Casterline
On Apr 4, 2014, at 6:56 PM, "Jerry Van Kolken" <[email protected]> wrote:
I have a retrofit project where I structure will not allow us to install
beam clamps. The existing hangers are unistrut clamp to the beams and
extended 4" out to allow rod a ring to be attached. I would like to use a
similar assembly but I don't know how to calculate the loading to determine
the size of the unistrut. I've heard some stuff about 4x the section modulus
based on the trapezes table in NFPA.
I was also wondering if there is a adjust the section modulus if you are not
planning on hanging at 15'-0"?
Jerry Van Kolken
Millennium Fire Protection Corp.
101 Copperwood Way, Suite H
Oceanside, CA 92058
(760) 722-2722 FX 722-2730
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