Brad,
I'm not following your conclusions with the information you've provided.
Remember that the values in Tables 9.3.5.5(a)-(l) are maximum allowable
loads for various types of pipe and spacing of the lateral braces from
each other.
Consider that if you were bracing 4" schedule 10 pipe, and the lateral
braces were spaced greater than 35' apart, but less than 40' apart the
maximum allowable load 769#. It is true that the maximum allowable load
if the lateral braces were spaced closer together, for example greater
than 25' but less than 30', the value from Table 9.3.5.5.2(a) for the
maximum allowable Fpw in the ZOI is no 1,071#.
You're of course welcome to tentatively space your lateral braces at the
maximum spacing of 40' per 9.3.5.5.2.2. The very next paragraph,
9.3.5.5.2.3 mandates that the Fpw cannot exceed the allowable loads in
the tables. As a result of that consideration you may indeed have to
respace the lateral bracing to be closer together in order to have the
resulting ZOI Fpw not exceed the allowable load.
The tables aren't backwards by any means. The values for, say 2½" pipe
are lower than that for 4" piping - _*at the same brace spacing*_ -
because when the strength of materials calculations are completed it's
obvious that the smaller pipe is susceptible to significant damage at
much lower values.
One very valuable illustration for what these tables are addressing is
that they take into consideration the allowable load between the lateral
braces depending on their spacing.
As I am a member of the hanging and bracing committee please see the
disclaimer below.
sincerely,
*Ken Wagoner, SET
*Parsley Consulting***
*350 West 9th Avenue, Suite 206
*Escondido, California 92025
*****Phone 760-745-6181*
Visit the website <http://www.parsleyconsulting.com/> ***
On 11/27/2017 11:16 AM, [email protected] wrote:
Thanks Ken, yes, I understand this.
And I understand the zone of influence and so forth.
But these Max Load Tables threw me when I got into them more- they
seemed 'backwards'. In terms of calcing the loads in the Z.O.I., the
40' spacing will be greater than the 20' spacing. But I read Appendix
E and figured it had to due with pipe deflection, not just total
weight. So If these tables apply I cannot 'tentatively' space lateral
braces at 40'. And I cannot know my calc for 4" main at 40' works and
assume my 2.5" main at 40' works because it is 'less demanding'.
I hope this makes sense.
thanks again,
Brad
*IMPORTANT NOTICE: This correspondence is not a Formal Interpretation
issued pursuant to NFPA Regulations. Any opinion expressed is the
personal opinion of the author and does not necessarily represent the
official position of the NFPA or its Technical Committees. In addition,
this correspondence is neither intended, nor should it be relied upon,
to provide professional consultation or services**
**
**It should be noted that the above is my opinion as a member of the
NFPA Automatic Sprinkler System Hanging and Bracing Committee in
accordance with the NFPA Regulations Governing Committee Projects and
should therefore not be considered, nor relied upon, as the official
position of the NFPA or its Committees*
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