FEMA 453 Design Guidance for Shelters and Safe Rooms

steel and precast concrete systems must also be designed and
detailed to accommodate uplift forces and rebound resulting
from blast loads. The use of headed studs is recommended
for affixing concrete fill over steel deck to beams for uplift
resistance.
m Redundancy. Multiple alternative load paths in the verticalload-carrying
system allow gravity loads to redistribute in the
event of failure of structural elements.
m Ties. An integrated system of ties in perpendicular directions
along the principal lines of structural framing can serve to
redistribute loads during catastrophic events.
m Ductility. Structural members and their connections may
have to maintain their strength while undergoing large
deformations in response to blast loading. The ability of
a member to develop inelastic deformations allows it to
dissipate considerable amounts of blast energy. The ratio of
a member’s maximum inelastic deformation to a member’s
elastic limit is a measure of its ductility. Special detailing
is required to enable buildings to develop large inelastic
deformations (see Figure 2-6).
Historically, cast-in-place reinforced concrete was the preferred
material for explosion-mitigating construction. This is the material
used for military bunkers, and the military has performed
extensive research and testing of its performance. Among its benefits,
reinforced concrete has significant mass, which improves
its inertial resistance; it can be readily proportioned for ductile
behavior and may be detailed to achieve continuity between
members. Finally, concrete columns are less susceptible to global
buckling in the event of the loss of a floor system. However, steel
may be similarly detailed to take advantage of its inherent ductility
and connections may be designed to provide continuity between
members. Similarly, panelized precast concrete systems can be detailed
to permit significant deformations in response to explosive
loading, as demonstrated by the performance of Khobar Towers.
2- 0 Structural deSign criteria