Loads from Branch Lines
“For apartment building projects, we typically run a main in a corridor and then have branch lines that tie into the heads of the units. When calculating the lateral brace loads, it is obvious that we must include the loads of the branch lines that run perpendicular to the main. Do we also need to include the load of the pipes that run off the branch line that are parallel to the main?” We have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is the weight of all pipe connected to the branch line within the zone of influence need to be included. The zone of influence includes the weights of branch lines, armovers, drops, return bends, and sprigs. The direction of the pipe, whether parallel or perpendicular to the main, does not matter. Section 9.3.5.9.6 states, “The zone of influence for lateral braces shall include all branch lines and mains tributary to the brace, except branch lines that are provided with longitudinal bracing or as prohibited by 9.3.5.9.6.1.” The annex for this indicates that the zones of influence do not have to be symmetrically based on brace spacing. It is the intent of NFPA 13 that the chosen zone of influence be the worst-case load scenario. In addition, the annex material at the end of A.9.3.5.9 indicates that the factor of 1.15 is intended to approximate the additional weight of all valves, fittings, and other devices attached to the system. There is no mention of drops, armovers and sprigs so consider the definition of a branch line. The definition of a branch line is the pipes supplying sprinklers, either directly or through sprigs, drops, return bends, or armovers. Thus, the weight of the water-filled pipe for determining horizontal loads within the zone of influence should include armovers, drops, return bends, and sprigs. This may be clarified in the 2019 edition of NFPA 13 but this has yet to be processed through the standards-making process. ========= Technical Update is prepared by the Technical Services Dept. of the AFSA: Roland Huggins, a PE registered in fire protection engineering, Vice President of Engineering and Technical Services; and Tom Wellen, a PE registered in fire protection engineering and Tom Noble E.T., a Technical Programs Specialist. This is provided with the understanding that the AFSA assumes no liability for this opinion or actions taken on it and they are not to be considered the official position of the NFPA or its technical committees. Copyright 2017, American Fire Sprinkler Association. All Rights Reserved. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.firesprinkler.org/private.cgi/sprinklernotes-firesprinkler.org/attachments/20170320/aeeabd70/attachment.htm>
