maintained. See Paragraph (4) below for acceptable
sway bracing details.
(c) Flexible piping systems. Piping systems
that are not in accordance with the rigidity
Flexible couplings and expansion
requirements of Paragraph 10-3e(4)(b) (i.e., period
joints. Flexible couplings will be provided at the
less than 0.05 second) will be considered to be
bottoms of risers for pipes larger than 3 inches
flexible (i.e., period greater than 0.05 second).
(89mm) in diameter.
Flexible couplings and
Flexible piping systems will be designed for seismic
expansion joints will be braced laterally unless such
forces with consideration given to both the dynamic
lateral bracing will interfere with the action of the
properties of the piping system and the building or
flexible coupling or expansion joint. When pipes
structure in which it is placed. In lieu of a more
enter buildings, flexible couplings will be provided
detailed analysis, the equivalent static lateral force is
given by Equation 10-1, with aP = 2.5. The forces
to allow for relative movement between soil and
will be distributed in proportion to the weight of the
pipes, contents, and attachments. If the weight of
5. Spreaders. Spreaders will be provided
the attachments is greater than 10 percent of the
at appropriate intervals to separate adjacent pipe
weight of the pipe, the attachments will be separately
lines unless the pipe spans and the clear distance
braced, or substantiating calculations will be
between pipes are sufficient to prevent contact
If temperature stresses are appreciable,
between the pipes during an earthquake.
substantiating calculations will be required.
(b) Rigid and rigidly attached pipes will be
1. Separation between pipes. Separation
designed in accordance with Equation 7-1, where WP
will be a minimum of four times the calculated
maximum displacement due to FP, but not less than
is the weight of the pipes, the contents of the pipes,
and the attachments. The forces will be distributed
4 inches (102mm) clear between parallel pipes,
in proportion to the weight of the pipes, contents,
unless spreaders are provided.
and attachments. A piping system is assumed rigid
if the maximum period of vibration is 0.05 second
2. Clearance. Clearance from walls or
(for pipes that are not rigid, see Paragraph (3)
rigid elements will be a minimum of three times the
calculated displacement due to FP, but not less than
Figures 10-5, 10-6, and 10-7, which are
based on water-filled pipes with periods equal to
3 inches (76mm) clear from rigid elements.
0.05 second, are to be used to determine the
allowable span-diameter relationship for structures
3. Alternative method for flexible piping
conforming to Seismic Design Categories C, D, E,
systems. If the provisions in the above paragraphs
and F for standard (40S) pipe; extra strong (80S)
appear to be too severe for an economical design,
pipe; types K, L, and M copper tubing; and 85 red
alternative methods based on rational and substantial
brass or SPS copper pipe.
analysis may be applied to flexible piping systems.