Building Expansion Joints in Seismic Areas
“We have a project that contains several expansion joints with a 2-in. gap and a 4-in. gap that branch lines will be required to cross multiple times along with the feed main in a few locations. Section 9.3.2.3.1(4) indicates that flexible couplings shall be installed within 24 in. of expansion joints with annex material describing and clarifying the purpose of expansion joints. The architectural and structural documents specifically call out and label these joints as “expansion” and not “seismic,” along with section details indicating rated UL listed joint systems that are to be installed. For expansion joints occurring in regions subject to earthquakes, is there a maximum gap for expansion joints that when exceeded would require the use of a seismic joint assembly rather than the flexible coupling as indicated by 9.3.2.3.1(4)?” We have reviewed NFPA 13, 2013 edition that you indicated as the applicable standard. Our informal interpretation is that there is not a maximum gap size for expansion joints. The standard is explicit that only a flexible coupling is needed within 24 in. of building expansion joints per 9.3.2.3.1(4) regardless of the size of the gap. A seismic separation assembly is required where sprinkler piping, regardless of size, crosses building seismic separation joints at ground level and above per 9.3.3. These two joints are not the same and the standard addresses these separately. Expansion joints are introduced to accommodate building movements caused by shrinkage, creep, or temperature changes. They are often one-way joints, meaning they are usually intended to accommodate movements in the direction perpendicular to the joint. A seismic separation joint will create separate structures. This may be the same building or separation of an adjacent building to accommodate story drift. Although it may appear as a single structure, seismic separation allows these structures to move independently of the adjacent structure. Seismic separation joints have to accommodate movement in both orthogonal directions simultaneously and their spacing is not typically affected by building length or size. To determine if the joint is expansion or seismic separation, structural columns will be typically located on each side of a seismic separation. Structural columns may not be located on each side of an expansion joint. Seismic separation joints typically create a separation between walls, floors, roof, piping, and HVAC ducts that have a functional need to cross the joint. The design of seismic joints is complex and includes proper sizing, adequately sealed from the weather, and it’s safe to walk on. It also provides for adequate movement of other systems crossing the joint while maintaining any fire ratings of the floor, roof and wall systems. ========= 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/20170501/9a46246c/attachment.htm>
