Quantcast Retrofit Construction Design

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MIL-HDBK-1013/1A
5)  Miscellaneous Openings.  Structure openings, such as skylights,
roof-hatches, scuttles, elevator shafts, ash dumps, rubbish chutes, fire
escapes, and roof access ladders, offer access to intruders and should be
considered in hardening plans.  One should try to eliminate openings that are
not absolutely necessary.  The approach to upgrading those that remain will
be dictated by the structural elements involved, that is, by appropriate
design of walls, roofs, doors, and locking mechanisms.
5.6
Retrofit Construction Design
5.6.1
Introduction.  This section provides design options for retrofiting
an existing building against forced entry attack.  Paragraph 5.6.2 addresses
the very high-severity threat involving explosives in combination with hand,
power, or thermal tools.  This is followed by options to protect against
low-, medium-, and high-severity threats involving hand, power, and thermal
tools only.  Paragraph 5.6.3 provides options for walls, par. 5.6.4 for roofs
and floors, par. 5.6.5 for doors, par. 5.6.6 for windows, and par. 5.6.7 for
utility openings.  The objective of the design is to supplement the
penetration time offered by the existing building construction with retrofit
options that achieve the required penetration delay times against the design
threat severity for the building established in Section 2.  The design must
also assure a balanced design between all building components.  This means
approximately equal penetration delays for each with no vulnerable weak
links.  The following pages provide forced-entry delay times one can expect
from the existing construction followed by the penetration-time enhancement
afforded by various retrofit design options.
5.6.2
Considerations Related to the Very High-Severity Threat.  The use
of explosives in bulk or flyer plate form can be especially effective in
quickly producing holes large enough for an intruder to enter. Only buildings
made of reinforced concrete 12 inches (305 mm) or more in thickness can
provide penetration delay times greater than 1 minute (see Table 19).  In
general, there are no retrofit options that can protect existing construction
from an explosive penetration attack.  The only choice is to locate the
critical area being protected internally and low in the building, well away
from exterior walls, roofs, etc.  The exterior of the building will serve as
a sacrificial barrier forcing the intruder to penetrate multiple barriers.
5.6.3
Wall Retrofit Construction for Low- Through High-Level Threats
5.6.3.1
Summary.  Table 37 summarizes the maximum penetration delay times
achieved by existing wall construction in use today.  Only in the case of
reinforced concrete with thicknesses of at least 12 inches (305 mm) do
barrier penetration times exceed 30 minutes for high-level threats.
Reinforced concrete less than 12 inches (305 mm), offers single barrier
penetration times under 30 minutes.  Conventionally constructed masonry and
stud/girt walls provide penetration times up to 18 minutes and 1.5 minutes,
respectively.  The following pages contain information to estimate the
penetration times offered
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