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

2-8 Earthquake Protection
Page 20 FM Global Property Loss Prevention Data Sheets
2.2.1.3.5 For sway bracing that consists of individual diagonal element(s) or diagonal plus vertical elements,
configure and size these elements per the following guidelines. Braces can be steel pipe, steel angle, steel
rods, or steel flats. Figs. 3 and 4 show bracing options for lateral sway bracing. Figs. 5 and 6 show bracing
options for longitudinal sway bracing.
A. Position diagonal element(s) at an angle of at least 30 degrees from the vertical.
B. For braces used to resist both tension and compression, choose the shape, size, and length of the
braces so the slenderness ratio, l/r (length/least radius of gyration), does not exceed 200, in order to
provide adequate resistance to buckling. Base the slenderness ratio on the actual length of the brace
between attachment points to the structure and the pipe being braced.
C. For braces used in tension only, choose the shape, size, and length of the braces to result in a
slenderness ratio, l/r (length/least radius of gyration), that does not exceed 300. Base the slenderness
ratio on the actual length of the brace between attachment points to the structure and the pipe being
braced.
D. Select each brace so the maximum length between attachment points to the structure and the pipe
being braced does not exceed the length calculated based on the slenderness ratio, l/r, limitations in
Sections 2.2.1.3.5(B) and 2.2.1.3.5(C); and so the brace can resist the percentage of the total horizontal
design load, H, that is assigned to it. These values may be calculated or taken from Tables 2 through
7. These tables indicate maximum allowable lengths for different brace shapes and sizes and maximum
horizontal design load (either H or a fraction of H not less than H/2, depending on sway bracing
configuration) for each brace for three different ranges of angles for the brace as measured from the
vertical. Maximum horizontal design loads are included for l/r = 100, for l/r = 200, and for l/r = 300 (tension
only). The following guidelines apply:
1. For Figs. 3 or 5 using one vertical and one diagonal brace:
a) The angle from the vertical for Brace A must be at least 30 degrees.
b) Size and arrange Brace A to carry in both tension and compression (l/r = 200 or less) the full horizontal
design load H, determined in Section 2.2.1.2.
c) Calculate the net vertical uplift force derived from the horizontal design load H, as:
V F = (H/tan Θ) - 1/2 W P
Where
V F = Net vertical uplift force.
H = Horizontal design load from Section 2.2.1.2.
Θ = Angle of Brace A from vertical.
W P = Weight of the water-filled pipe within the zone of influence.
If V F is less than or equal to 0 (zero), Brace B is not needed.
d) Brace B, when needed, can either be of the same shape and size as Brace A, and connected to
the pipe at the same point as Brace A, without any further calculation, or can be selected on the basis
of the actual calculated net vertical uplift force. Although less desirable, Brace B may be a hanger that
is located no more than 6 in. (150 mm) from the point of attachment on the pipe for Brace A and meets
the following criteria:
• The hanger has been determined to be able to resist the net vertical resultant load uplift force
V F (this may necessitate the use of a rod stiffener or other means, but in any case the l/r should
not exceed 200),
• The hanger is capable of transferring vertical upward loads and is fastened to the structure
by a positive means of mechanical attachment, such as through bolts, lag screws, or concrete
anchors that are properly sized for the load, and
• The hanger attachment to the fire protection system piping is snug and concentric, with no
more than 1 ⁄ 2 in. (13 mm) between the top of the piping and the hanger so that excessive
movement cannot occur.
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