FEMA 453 Design Guidance for Shelters and Safe Rooms

precast panels, the spacing of the anchorages will determine the
span of the mullions and the force each anchorage is required
to resist. Embedded anchors within the precast panels will be required
to accept these anchorage forces.
Fully grouted and reinforced CMU façades may be designed to
accept the large lateral loads produced by blast events; however,
it is often difficult to detail them to transfer the reaction forces to
the floor slabs. A continuous exterior CMU wall that bears against
the floor slabs may avoid many of the construction and connection
difficulties, but this is not typical construction practice. Brick
or stone veneer does not appreciably increase the strength of the
CMU wall, but the added mass increases its inertial resistance.
2.5 exiSting cOnStructiOn: retrOFitting
cOnSideratiOnS
Although retrofitting existing buildings to include a shelter can
be expensive and disruptive to users, it may be the only available
option. When retrofitting existing space within a building is considered,
data centers, interior conference rooms, stairwells, and
other areas that can be structurally and mechanically isolated provide
the best options. Designers should be aware that an area of a
building currently used for refuge may not necessarily be the best
candidate for retrofitting when the goal is to provide comprehensive
protection.
An existing area that has been retrofitted to serve as a shelter is
unlikely to provide the same degree of protection as a shelter
designed as new construction. When existing space is retrofitted
for shelter use, issues have arisen that have challenged both
designers and shelter operators. For example, glass and unreinforced
masonry façades are particularly vulnerable to blast
loading. Substantial stand-off distances are required for the unprotected
structure and these distances may be significantly reduced
through the use of debris mitigating retrofit systems. Furthermore,
because blast loads diminish with distance and incidence
of blast wave to the loaded surface, the larger threats at larger
Structural deSign criteria
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