My college degree is in Civil Engineering and I did a lot of structures courses. That was many moons ago, but I still recall some of it. The calculations to determine the loading on the cantilevered support are not all that difficult. The maximum loads on the support (shear and bending) will be at the point of connection to the beam that is nearest the cantilevered load. Once those are determined and an allowable deflection chosen, then a section modulus can be selected to provide that result. You can then compare that to the various products available for the support (i.e Unistrut). This is something a structural engineer with a contemporary computer program can do very easily. Unless you have a good understanding, leave it to the pros. Isn't that what we tell laymen that try to mess with sprinklers?
Todd G Williams, PE Fire Protection Design/Consulting Stonington, CT www.fpdc.com 860-535-2080 (ofc) > On Apr 4, 2014, at 9:39 PM, Brad Casterline <[email protected]> wrote: > > Good words and thoughts Ken. I liken this situation to every sprinkler design > aspect I do; I do the 'leg work' and present it to a P. E., for > verification. I feel like an X-ray technician in this regard-- I know how to > run the machine, but I would not feel comfortable making any final diagnosis > or plan of action with-out giving it to the Doctor first:) > >> On Apr 4, 2014, at 8:21 PM, Parsley Consulting <[email protected]> >> wrote: >> >> 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 >>>> >>>> >>>> >>>> _______________________________________________ >>>> 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 > _______________________________________________ > 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
