01-06
determining appropriate bracings or restraints.
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
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.
6.3 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.
6.4 CALCULATIONS
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