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 > > > > > > > > > > > > --- > > This email has been checked for viruses by Avast antivirus software. > > https://www.avast.com/antivirus > > _______________________________________________ > > Sprinklerforum mailing list > > [email protected] > > > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkl > > er.org > > > > _______________________________________________ > > Sprinklerforum mailing list > > [email protected] > > > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkl > > er.org > > > > > > -- > > *Damien Shannon* > _______________________________________________ > Sprinklerforum mailing list > [email protected] > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org > _______________________________________________ > Sprinklerforum mailing list > [email protected] > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org > -- *Damien Shannon* _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
