Is there a maximum all-thread rod length called out in NFPA 13?
This application isn't for seismic, but a general hanger for pipes 2-inch and under in diameter. Thanks. Sent in anonymously for discussion. Discuss This | Submit Your Question | Subscribe
2 Comments
CJ Bonczyk
1/27/2021 11:28:22 am
To my knowledge NFPA does not provide a limitation on the total hanger rod length connected to a horizontally loaded pipe. Hangers are intended to only be loaded axially (along the rod). Additional hangers or restraints could be required due to additional lateral loads on the pipe depending on the pitch of the pipe. Handbook Section 17.2.1.6 states that the rods must not be formed or bent and the rod must be axially loaded to the structure. Axial loading is the stresses via both tension and compression vertically in both directions on the element (or rod in this case). Thus, NFPA only requires that the hanger assembly and its components be designed to carry those axial loads based on the point load weights/structural attachment/and any seismic requirements. Any transverse (non-axial) loading on the pipe is addressed in NFPA 13 17.2.1.3. The big issue I see with multiple rod lengths connected via rod couplings is dependent on (1) any system water hammer in change of direction due to velocities in the pipe and (2) the system type. A dry or deluge system with a large amount of water pressure could cause the pipe to sway significantly when tripped if not secured adequately. Also it is important to ensure the shear and tension strengths of the structural fasteners are not beyond their limitations causing a failure. This would have to be evaluated by a structural PE. Sometimes its best to shorten the hanger support distances, add retaining straps, add additional lateral supports, etc. or have a structural PE sign off on the hanger design just to be safe.
Reply
Onur Adiguzel
1/31/2021 02:28:33 pm
Practically, rod stifferner required for all tread rod over 1.8 meter in lenght.
Reply
Leave a Reply. |
Free SignupSubscribe and learn something new each day:
CommunityThank You to Our Top
January '21 Contributors!
Your PostThe ToolkitSprinkler Designer or Engineer?
Get all of our tools, including the Sprinkler Database, Friction Loss Calculator, Fire Pump Analyzer and more: Filters
All
Archives
February 2021
Daily
Daily discussions are open-ended fire protection, fire alarm, and life safety questions submitted anonymously for the benefit of sharing expertise and learning from other perspectives. Anyone can submit a question here:
Exam Prep2020 PE Prep Guide
(Available Now!) PE Prep Series
(Available Now!) 2020 PE Prep Series
Current Leaderboard (Click to enlarge) PE Problems
Visit July-October for daily Fire Protection PE Exam sample questions.
Solutions are posted the day after posting. Comment with your solutions, questions or clarifications. Please note that questions posted are unofficial and in accordance with NCEES rules are intended to be similar to actual exam questions, not actual exam questions themselves. |