Damien,
Your definition of "fun" and mine must be drastically different.
It must be an extension of George Bernard Shaw's remarks, to now include
the Irish and the Americans are two peoples separated by a common language.
I see what you're driving at, and there is some considerable merit
there. My own reluctance to endorse that is based on a long career of
working for an FPE who started as a structural and wound up in our
world. Without exception every time I swerved into something like this
his caution meter went into overload.
His thinking, and since he paid my salary I found it expedient to
agree, was that anytime you start moving away from the practice of
following a prescriptive standard for what you're doing in
design/construction there had better be a mountain of data to support
your decision. And, since I couldn't really argue the forces and
equations for structural I didn't really push this sort of thing too much.
It always did strike me as sort of misleading that there was a
"five times" mandate in 9.1.1.2, and nothing else of that nature until a
consideration for pipe stands came into focus.
So the question for me becomes - is the wood block you're
considering a part of the building structure, in which case 9.2.1.3.1
would apply, or is it a hanger per 9.1.1.2, which requires the
registered engineer to sign off on it? The issue is further muddied
when you review the data in 9.1.1.7 for a trapeze. So now perhaps
there's a third designation, is that block a trapeze?
Interesting discussion, and I wish I could say that I have a
definitive answer because I don't.
cheers,
*Ken Wagoner, SET
*Parsley Consulting***
*350 West 9th Avenue, Suite 206
*Escondido, California 92025
*****Phone 760-745-6181*
Visit our website <http://www.parsleyconsulting.com/> ***
On 06/05/2015 2:31 PM, Damien Shannon wrote:
Thank you Steve, Ken & Brad for your replies.
Ken, I have been watching the forum long enough now to know better than to
disagree with Steve :) however, for the benefit of my education and
hopefully to better clarify I would like to 'quiz' the theory.
Couldn't one make the case that you don't have to deal with 9.1.1.2 as
9.1.1.2 is only for hangers that don't fit the prescribed methods for
sizing provided in the remainder of 9.1. The intent being to classify the
hanger purely within 9.1.1.7.
It wouldn't seem that 9.1.1.3 comes into it as we're not talking about
sharing the blocking with other services or such.
If we were to look at it purely within 9.1.1.7 ... As Brad has calculated
and as stated in A.9.1.1.7 "...Table 9.1.1.7 assumes that the load from 15
ft (5m) of water-filled pipe, plus 250lb (114 kg), is located at ....
In the NFPA 13 2013 Handbook exhibit 9.3 shows a photo of a trapeze on page
466 with commentary stating "A trapeze hanger, as shown in Exhibit 9.3 must
be capable of supporting the weight of the water filled piping plus 250lb
(114 kg). Other types of hangers are generally required to be able to
support five times the weight of the water-filled piping plus 250 lb (114
kg). The safety factor of five is used in the traditional listing
requirements for hangers and is also found in the performance-based
criteria of 9.1.1.2 (1), since the trapeze hanger can be considered an
extension of the building structure needed to provide points of hanging for
system piping'.
So the way I have previously understood it was that 2x6 or any trapeze
would only have to meet the 1x WP + 250lb, rather than the 5x WP + 250lb.
Section 9.1.1.7.2 states "Any other sizes or shapes giving equal or greater
section modulus shall be acceptable". The commentary goes on to say "Where
materials other than steel are proposed for use as trapeze members, an
engineering analysis must be completed to determine the material's
compability. Comparable beam strength and appriated fire endurance
characteristics are required.
NFPA 13 does not specifically permit the use of wood trapeze members, and
9.1.5.5 prohibits the use of nails as fastners. However, the building
designer always has the option of allowing a modification of the building
structure to provide a built in trapeze. The manner in which extentions are
made to the building structure must be acceptable to the responsible design
professional."
So, it would seem in JD's situation it is feasible that the original
installer went to the structural engineer to approve the blocking method
for approval, and the the structural engineer would have ok'd the blocking
method based on 1x WP +250lb. Since the structure is of wood construction
it wouldn't be an issues being combustible (no different than a member of
the structure's resistance).
Thanks again for any insights to flaws in my thought process.
And, section 9.1.1.3 does seem like it would have been fun committee
meetings Ken :)
Damien Shannon
On 5 June 2015 at 20:47, Brad Casterline <[email protected]> wrote:
https://www.dropbox.com/s/3qiwk9xwo6e65qa/trap.xls?dl=0
Here is a spread sheet I made ~25 years ago for calculating required
section
modulus-- right now it shows hanging 4" S10 centered in a 48" span and I
figured 1x the weight of 15' of pipe +250 lb, and the required section
modulus is .34.
Brad
-----Original Message-----
From: Sprinklerforum [mailto:
[email protected]]
On Behalf Of Steve Leyton
Sent: Friday, June 05, 2015 1:50 PM
To: [email protected]
Subject: RE: suspending from wood members attached to structural
I'd say that 13/2013, 9.1.1.2 (2) leaves that open to interp or argument.
It says that points of support have to be adequate to support the system
but
doesn't tie that directly to the 5x mandate. So corner cutters can try to
say that blocking is part of structure or not part of the hanger. I would
argue that it's DEFINELY not part of structure unless it has been
engineered
as such, which would entail something more than 4x 10d nails as pipe
fitters
often use. If I furnish the load values to the SEOR, and he/she designs
an
attachment that in their professional estimation is adequately attached to
the structure to bear a certain load, then the attachment is load-valued at
whatever they say it is. But if you look to that blocking as a part of the
sprinkler hanger assembly (and in my opinion that's what it is if it's not
an engineered part of the structure, like a trapeze) then a conservative
reading of that section would find that it has to meet the 5x rule. Keep
in
mind that the table that shows different pipe and angle section modulii is
based on 5x WP + 250# and 2x lumber is conspicuously absent from that
table.
Also keep in mind that most truss manufacturers now publish sprinkler
hanger
and bracing installation guides that are chock full of engineered
solutions,
all of which are in compliance with best structural engineering practices
and NFPA 13.
Steve
-----Original Message-----
From: Sprinklerforum [mailto:
[email protected]]
On Behalf Of Damien Shannon
Sent: Friday, June 05, 2015 9:55 AM
To: [email protected]
Subject: Re: suspending from wood members attached to structural
Wouldn't the blocking only have to meet the 1x WP + 250# as wouldn't it be
considered an extension of the building structure/a trapeze?
Damien Shannon.
On 5 June 2015 at 17:27, Steve Leyton <[email protected]> wrote:
2x4 and 2x6 blocks have been casually used for years but we've learned
in the past 10 or so that they are NOT adequate by conventional
engineering standards and the 5x WP + 250# equation. For example,
TrusJoist has block details showing 4x4 members for piping up to 3 or
4" but that's only for certain truss series and spacing that will
support the loads of larger pipe. You'll see a lot of details and
listing limitations for certain application of fasteners that are
limited to 2" pipe, which goes to the ability of the member to handle
the load, not necessarily the capacity of the blocking it's attached to
when blocking is used.
I think the best answer to your question as asked is: Yes - for
engineered products such as joists and trusses, consult the
manufacturer's installation and reference materials and/or consult
with the structural engineer of record.
Steve L.
-----Original Message-----
From: Sprinklerforum on behalf of JD Gamble
Sent: Fri 6/5/2015 9:12 AM
To: [email protected]
Subject: suspending from wood members attached to structural
What are the general guidelines for attaching to wood members attached
to structural wood trusses.
Example: Suspending 1 ΒΌ" steel sch 40 pipe using a 3/8 Sammy , ATR,
and a adjustable swivel hanger from a 2x4 nailed between two wood
trusses? (I don't see where this is an acceptable method of
installation, but don't want to miss the forest for the trees either)
Surveying some existing work and trying to make a fair assessment of
additional hanger changes.
Thanks,
Life Safety Solutions of Sheridan
JD Gamble
[email protected] <mailto:[email protected]>
(307) 763-3361
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