DS 2-8 Earthquake Protection for Water-Based Fire ... - FM Global

2-8 Earthquake Protection
Page 10 FM Global Property Loss Prevention Data Sheets
2. For crossmains, the zone of influence includes the tributary length of crossmain being braced plus
the length of all branch lines attached to that section of crossmain that are not distributed to branch
line longitudinal sway bracing.
3. For branch lines that require sway bracing, the zone of influence typically includes the length of
the branch line to the left and right of the sway brace that is tributary to that sway brace. The tributary
length of pipe between the first lateral sway bracing location and the crossmain connection may either
be based on an equal distribution to the crossmain longitudinal bracing and the first lateral sway
bracing location (see Section 2.2.1.2.3[C][2]), or may be totally distributed to the first lateral sway
bracing location.
C. Longitudinal two-way sway bracing:
1. For feedmains, the zone of influence includes the length of the feedmain to the left and right of the
sway brace that is tributary to that brace.
2. For crossmains, the zone of influence includes the tributary length of crossmain being braced; do
not include loads from branch lines, except when a portion of branch line lateral sway bracing is being
included as described in Section 2.2.1.2.3(B)(3).
3. For branch lines that require sway bracing, the zone of influence typically includes the length of
the branch line to the left and right of the sway brace that is tributary to that sway brace. The tributary
length for the piping between the crossmain and the first sway bracing location should be based on
an equal distribution between that bracing location and the crossmain lateral sway bracing as described
in Section 2.2.1.2.3(B)(2).
D. For sway bracing at horizontal changes in direction that is located within 2 ft (0.6 m) of the end of a
feedmain or crossmain connection to a perpendicular main of the same or smaller diameter, and which will
be used as a lateral sway brace for one pipe and a longitudinal sway brace for the perpendicular pipe,
the zone of influence includes the total tributary lateral and longitudinal weights of mains and branch lines
as described above.
2.2.1.3 Configuration and Design of Sway Bracing
2.2.1.3.1 Provide sway bracing to resist horizontal seismic loads. Sway brace(s) at each location should be
capable of resisting the horizontal design load (H) as determined per Section 2.2.1.2. In addition, provide
additional members to resist any net vertical force component that occurs as a result of sway brace placement
(see Section 2.2.1.3.5[D]).
2.2.1.3.2 A properly sized and attached U-bolt that fastens the pipe directly to, and holds the pipe tightly
against, a structural supporting member may be used as a lateral sway brace when located on horizontal
piping, or as a four-way sway brace when located on vertical piping. Consideration of a vertical resultant force
is unnecessary for this configuration.
2.2.1.3.3 Do not use U-hangers, including wraparound types, as lateral sway bracing for feedmains and
crossmains.
2.2.1.3.4 Wraparound U-hangers may be used as lateral sway bracing for branch lines that need sway bracing
if they meet the following criteria:
• They have both legs bent out at least 30 degrees from the vertical,
• They are the proper diameter and length per Tables 2 through 7 for the seismic loads involved,
• They are properly attached to the building structure per Section 2.2.1.3.6, and
• There is no more than 1 ⁄ 2 in. (13 mm) of space between the top of the branch line piping and the
wraparound portion of the U-hanger.
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