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8.2 CONFORMANCE WITH SMACNA
A. Requires a design professional to develop a Seismic Hazard Level
(SHL) for specific project for use of its manual. The SHL is derived
from a combination of factors such as applicable building codes,
seismic zones, and importance factors into a single system for
determining appropriate bracing or restraint. A building with an SHL
of "A" requires the strongest restraints, whereas, a building with
SHL of "C" requires the least restraints. The design professional is
responsible for specifying the SHL of "C" requires the least
restraints. The design professional is responsible for specifying the
SHL, not the contractor.
B. Bracing in SHL "A" is designed to resist 48% of the weight of the
ducts or pipes. Bracing in SHL "B" is designed to resist 30%, and in
the bracing in SHL "C" is designed to resist 15% of the weight of the
ducts or pipes. In addition to the horizontal seismic force, a
vertical seismic force equal to one-third of the horizontal force is
included in the analysis.
C. Current building codes require most structures and their components
to be designed for a horizontal seismic force that is a given percent
of the supported weight. Each code has its own method for determining
the percent. The formulas are in the form:
Fp = Cs x Wp
Where Wp is the weight of the ducts or pipes, Fp is the seismic
force, and Cs is a seismic coefficient which represents a combination
of factors that varies with the building code. Use more severe of the
Local Code and the Uniform Building Code (UBC) to determine seismic
force, Fp.
D. The percent horizontal seismic factor is:
%F = Fp/Wp x 100
= Cs x 100
If %F is greater than 48, then manual cannot be used, and an
independent analysis and design is required for all bracing
components.
E. Use SHL "A" if $F is between 31-48, use SHL "B" if %F is between 16-
30, and use SHL "C" is %F is 15 or less.
8.3 CONFORMANCE WITH NUSIG
A. NUSIG has developed guidelines as a service to the design
professionals. The guidelines are not intended as a substitute for
design. The design of seismic bracing remains the responsibility of
the design professional who must review the specific project for its
applicability before using or specifying NUSIG guidelines.
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