of "C" requires the least restraints. The design professional is
responsible for specifying the SHL not the building contractor.
2.15.2.2 Bracing in SHL "A" is designed to resist 48 percent of the
weight of the ducts or pipes. Bracing in SHL "B" is designed to resist
30 percent, and in the bracing in SHL "C" is designed to resist 15
percent 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.
2.15.2.3 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
Wp is the weight of the ducts or pipes
Fp is the seismic force
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
2.15.2.4 The percent horizontal seismic factor is:
F (Percent) = (Fp/Wp) x 100
= Cs x 100
If F (Percent) is greater than 48, then manual cannot be used, and an
independent analysis and design is required for all bracing components.
2.15.2.5 Use SHL "A" if F (Percent) is between 31-48, use SHL "B" if F
(percent) is between 16-30, and use SHL "C" if F (percent) is 15 or
less.
2.15.3 CONFORMANCE WITH NUSIG
2.15.3.1 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.
2.15.3.2 NUSIG manuals of designs are pre-calculated from 0.05g through
1.00g in increments of 0.05g. Coordinate with Construction Standard,
CD-54.
2.15.4 CALCULATIONS
Unless otherwise shown by SMACNA or NUSIG, provide detailed structural
calculations for VA's review on design of hangers, supports, anchor
bolts, and connections. Show sizes, spacing, and length for securing to
HVAC DESIGN MANUAL
2-60
HVAC SYSTEMS AND EQUIPMENT
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