If concrete floor wearing slabs are specified, they
should be thick enough to hold anchor bolts for
equipment, supports, and interior partitions.
Concrete wearing slabs may be provided in most
applications with a minimum thickness of 100 mm (4
inches). The Air Force is opposed to placing
concrete wearing slabs over shielding steel because
of problems with testing and repair. Placing
concrete over floor shielding requires a waiver from
HQ AFCESA/ENE.
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Floor EM shielding shall be covered by a reinforced cast-in-place concrete
slab [100] [_____] mm [4] [_____] inches thick. Seismic requirements shall
be [in accordance with Sections 13080 SEISMIC PROTECTION FOR MISCELLANEOUS
EQUIPMENT, 15070A SEISMIC PROTECTION FOR MECHANICAL EQUIPMENT, and 10270
ACCESS FLOORING (if needed)].
2.4
EM SHIELDING ENCLOSURE REQUIREMENTS (BOLTED CONSTRUCTION)
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NOTE: For the EM shielding enclosure, choose either
welded or bolted construction. The unused method
should be deleted from the project specification.
Welded construction will usually consist of
continuous 1.897 mm (14 gauge) thick steel plate and
angles to form the enclosure. Thicker material may
be used if it is more cost-effective or required for
structural reasons. Welded construction is used
when a shielded facility requires a long
maintainable service life of high-level protection,
100 dB attenuation, or HEMP protection, 100 dB.
Bolted construction is associated with a lower level
(50 dB) of maintained shielding effectiveness.
Bolted construction will usually consist of modular
panels bolted together with metal strips or
channels. Panels are commonly plywood with steel
sheets laminated to one or both sides. Bolted
construction is used when a shielded facility's
service life is short, 10 years or less, or the
system is required to be demountable for change of
location. This system requires more maintenance
than a welded system and requires access to the
panels. The EM shield layout may restrict
attenuation testing of the enclosure. It is
desirable for large facilities to place the shield
at least 1 meter (3.3 feet) inside the exterior
walls, although cost and construction restrict this
consideration. The floor shielding can be tested by
SELDS test but not by IEEE Std 299 if it is on
grade. The facility layout must be carefully
planned to allow for testing and shield maintenance.
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2.4.1
Panel Construction
Flat steel sheets shall be laminated to each side of a 20 mm 3/4 inch thick
SECTION 13095A
Page 19
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