Wow, what a great post! Sent from my iPad
> On Oct 22, 2013, at 3:38 PM, "Steve Leyton" <[email protected]> > wrote: > > Mark you ignorant slut: > > I have been out of my office all day, so this is the first opportunity > I've had to sit thoughtfully at a keyboard. I sincerely apologize that > yesterday's responses didn't meet your standard of care. Nonetheless, > I'm glad you feel sated or satiated or salivated or however it is that > you feel. Feelings are good. However (and Ken, please feel free to > join if you feel compelled) I am not sure that Tom's answer is complete, > and as such I respectfully demur on a couple of points. > > The concept at work is the different "harmonics" of movement in the > building and the relativity of anchorage. If mains are braced, lines > restrained and ceilings also rigidly braced to the SAME structural > assembly above, then the likelihood of them moving harmoniously in an > earthquake is high, which reduces and can even eliminate the counter > directional movements such as caused by branch line whiplash. But > rigidly bracing a ceiling is very expensive and very rarely undertaken, > so in nearly every new building where ceilings are simply laterally > braced and furnished with compression struts, the overhead piping is > going to be moving with the roof or floor above, while the ceiling is > expected to move differentially and/or float between structural > assemblies all potentially moving differentially from one another. > > The ASCE prescriptives are based on the concept of building flexibility > into the interface between overhead piping and ceiling, that interface > being ... arm-overs and drops. ASCE 7 requires at non-rigidly braced > ceilings that either the oversized annular space, or a swing joint or a > flexible hose connection be provided. So laterally restraining such > piping is counter-intuitive. And, as far as "lines in the sand" or the > issue of super long arm-overs, I am not sure that we're done. > > Sprinklers have lagged behind other disciplinary designs for the past 20 > years for seismic protection. Since harmonizing 13 with ASCE 7, we've > joined the 21st Century for sure but as the 2010 and 2013 editions are > adopted, and as more states and AHJ's begin to implement requirements > for seismic protection of building systems, these practices are going to > come as something of a shock for sprinkler contractors and designers. I > never thought we'd have to be structural engineers, but there are > elements of SE in what we're doing here in CA right now for certain > agencies. If you look at Ken's slides from the convention (link was > posted yesterday), you'll see at the end an exercise for calculating > what is called "deflection" of an exemplar riser nipple. It's not > called that in the slides, but that's the force being applied. There > are forces - deflection and compression - and there is displacement. > ASCE 7 requires that building systems be proven adequately protected > from force and displacement and there are formulas for calculating this > stuff. The ASCE 7 method (simplified but not short-cut in NFPA 13) for > calculating braces is based on worst-case scenarios; if you were to do > site specific calculations it's even more complicated as you have to > multiply by factors for different kinds of structure, even different > weights of concrete in some cases, and differing seismic force factors > from site to site. So Ken's exercise is a taste of what may be to > come, as it's sound engineering principal to also take deflection into > account for hangers and braces (that's what the references to net > vertical reaction forces allude to in the standard now). ASCE 7 has a > formula for calculating the longest allowable distance of hangers, based > on piping weight and the seismic force, and it takes the potential > deflection and displacement of the piping into account in that formula. > > > I guess the point is that is a systematic, rather than a specifically > elemental approach. The flexibility of drops, combined with the > rigidity of mains and lines, is what makes it work. The establishment > of adequate resistance to force in the piping and hangers and sway brace > arms are all important factors in assessing the overall design. > > I hope that answers your question(s) ... > > > My opinion only but I'm not on the committee so the disclaimer is just > to make me sound important, > > Steve Leyton > > > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of > Mark A. Sornsin, P.E. > Sent: Tuesday, October 22, 2013 9:40 AM > To: [email protected] > Subject: RE: NFPA 13 '10 9.3.6 BL Restraint > > Tom, > > Thank-you for your thoughtful and insightful reply. It addressed our > question and, therefore, should be a model for all of the Forum - > especially Steve and Ken. > > Bottom line is, yes, there are 8 ft. arm-overs that would not require > restraint to meet seismic requirements; and there are 8 ft. branch lines > feeding two sprinklers that would require restraint. It seems to be a > bit of a cross-over in the rules, but ultimately doesn't happen much and > thus isn't considered to be a real problem. > > I can't speak for Chris (despite having done so before), but I feel > satiated. > > Mark A. Sornsin, P.E. | Karges-Faulconbridge, Inc. | Fire Protection > Engineer | Fargo, ND | direct: 701.552.9905 | mobile: 701.371.5759 | > http://www.kfiengineers.com > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Tom > Wellen > Sent: Tuesday, October 22, 2013 10:00 AM > To: [email protected] > Subject: Re: NFPA 13 '10 9.3.6 BL Restraint > > Mark and Chris, > > > I'll take a stab at this. The west coast is still grinding the coffee > beans. > > The length of an armorer is not expected to be very long. The adjacent > branch lines cannot exceed 20 feet apart for extended coverage > sprinklers and 15 ft for standard spray sprinklers. If the armorer is > over 10 ft long coming off a cross main or branch line, it should be > considered to be piped from the adjacent branch line. The main > objective is to use less pipe, correct? Why waste pipe length? > > So, if that is the case, the committee is not worried about a line with > a single sprinkler and provided the definition of an armover. A line > with two or more sprinklers is defined as a branch line where they can > be of considerable length. The longer the line, the more it will have a > whipping action. Thus, Table 9.6.3.4(a) specifies the spacing needed for > restraints based on the Cp in that area and the pipe size ranging from > 26 ft to 53 ft. An armorer shouldn't whip around so much due to its > short length so restraint is not required. Can there be instances where > there are long armorers? Sure, especially if there is a drop from a 40 > ft ceiling to a ceiling at an 8 ft level. 9.3.6.7 Drops and armorers > shall not require restraint. What a mess that would be to restrain a > drop located 32 ft from the ceiling. Steve commented that ceiling grids > should be rigidly braced. If not, then the oversized hole for the > sprinkler is necessary in the ceiling to keep the ceiling from bre > aking the fusible element. Will fusible elements still still break > during an earthquake from the ceiling? Probably. The cost benefit of > providing restraints on every drop does not warrant them to be > installed. > > NFPA 13 is full "lines in the sand" that we don't know the true history > behind them but it seems mostly just to give a warm fuzzy (i.e. 4 ft > obstruction rule, area limitations of 52,000 sf, etc....) and armorers > and branch lines is just one of them. It doesn't fit all applications, > but the baseline requirement is established. > > > Tom Wellen > AFSA > _______________________________________________ > 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
