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 MIL-HDBK-1013/1A
Plywood on joists may include thicknesses from 14 to 1-1/8 inches (6 to 28
mm). The plywood is supported on joists ranging from 2 by 4 inches (50 by
100 mm) up to 2 by 14 inches (50 by 350 mm) on 12-, 16-, or 24-inch (300-,
400- or 600-mm) centers. The stressed skin plywood panels are typically 1/2-
to 1-inch (13- to 25-mm) plywood supported on joists of 2- by 4-inch to 2- by
14-inch (50- by 100-mm to 50- by 350-mm) on 12-, 16- or 24-inch (300-, 400-
or 600-mm) centers. The ceiling joists are then covered by 3/8-inch (9-mm)
plywood. The wood deck-on-beams option consists of 1-, 1-1/8-, or 1-1/4-inch
(25-, 28-, or 32-mm) plywood or 2- by 6-inch (50- by 150-mm) wood decking
supported on sawn or glue-laminated wood beams on 4- or 8-foot (1,200- or
2,400-mm) centers. Regardless of the degree of security, the choice of wood
construction must be in accordance with the fire protection requirements set
forth in MIL-HDBK-1008.
Table 43
Existing Roof/Floor Wood Construction
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*
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Maximum Penetration Times
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*
Building
(minutes) Achievable
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Low
Medium
High
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* Wood
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(a)
1.6
1.5
* Roofs
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*
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*
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* Wood
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(a)
1.6
1.5
* Floors
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*
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(a) It is not practical for low-level
threats to attack roofs or floors.
b) Penetration times for existing construction.
Penetration times for conventional wood roof and floor construction options
against optimal combinations of hand and power tools are 1.6 minutes against
the medium-level threat and less than 15 minutes against the high-level
threat (see Table 43).
c) Retrofit options for medium-level threats. Very little
test data is available on retrofit options for hardening against medium-level
threats using hand-held and limited battery-powered tools only. Table 40
shows delay times achieved using 9-gauge (3.8-mm) metal fence material, 1/4-
inch (19-mm) to 3/4-inch plywood, 9-pound (4.1-kg) expanded metal, and 3/16-
inch (4.8-mm) steel plate.
d) Retrofit options for high-severity threats. The steel-
ply retrofit options shown in Figures 46 through 48 and Table 38 or the
riveted or welded steel grating shown in Figures 49 and 50 can be affixed to
180
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