FEMA 453 Design Guidance for Shelters and Safe Rooms

uilding. Locating the shelter in the basement, for slab on grade
buildings, provides the maximum number of floors between occupants
and possible roof debris. Debris catch systems may be
installed beneath roof rafters of single-story buildings; however,
the effectiveness of the debris catch system will be limited if the
zone of roof damage is extensive.
Metal stud blast walls built within the existing building may be
used to supplement the enclosure; however, in order for these
walls to develop their resistance to lateral loads, they must be anchored
to an existing structure. Windows enclosing the selected
shelter must either be laminated or treated with an anti-shatter
film. Either the laminated glass or the anti-shatter film should
be anchored to the surrounding wall with a system that can develop,
but not overwhelm the capacity of the wall. A conservative
estimate of the ultimate capacity of an existing wall may be determined,
in the absence of actual design information, by scaling the
code specified wind pressures with the appropriate factor of safety.
2.6.6 rm1 and rm2 reinforced masonry
Walls with Flexible diaphragms or Stiff
diaphragms and unreinforced masonry
(urm) load-bearing Walls
These buildings have bearing walls that consist of reinforced brick
or concrete block masonry. Wood floor and roof framing consists
of wood joists, glulam beams, and wood posts or small steel
columns. Steel floor and roof framing consists of steel beams or
open web joists, steel girders, and steel columns. Lateral forces are
resisted by the reinforced brick or concrete block masonry shear
walls. Diaphragms consist of straight or diagonal wood sheathing,
plywood, or untopped metal deck, and are flexible relative to the
walls (see Figure 2-35). Foundations consist of brick or concrete
spread footings.
Structural deSign criteria
2-