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 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" if %F is 15 or less.
12.3
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.
B.
NUSIG manuals of designs are pre-calculated from 0.05g through
1.00g in increments of 0.05g.
12.4
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 structural members, and length and sizes of
welds anchored to steel members.
12.5
DRAWINGS
A.
Where SMACNA or NUSIG details are incomplete or not
applicable, show complete seismic restraint requirements and
coordinate with the specifications. Coordinate mechanical
work with architectural and structural work. Special
provisions and details may be required.
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