FEMA 453 Design Guidance for Shelters and Safe Rooms

Figure 2-9
Blast damaged façade
2.3.3 Building envelope
Façade components that must transfer the collected loads to the
structural system must be designed and detailed to absorb significant
amounts of energy associated with the extreme loading
through controlled deformation. The duration of the extreme
loading significantly influences the criteria governing the design
of the building envelope systems. Significant inelastic deformations
may be permitted for extraordinary events that impart the
extreme loading over very short periods of time (e.g., explosive
detonations). The building envelope system need only be
designed to resist the direct shock wave, rebound, and any reflections
off of neighboring buildings, all of which will occur within a
matter of milliseconds (see Figure 2-9).
Resistance to blast is often compared to
resistance to natural hazards with the
expectation that the protection against
one will provide protection against the
other. Therefore, as a first step, one
should consider any inherent resistance
derived from a building’s design to resist
environmental loading. Extreme wind
loading resulting from tornadoes may
similarly be of short enough duration to
permit a large deformation of the façade
in response to the peak loading. Certainly,
the debris impact criteria will be
similar to that for blast loading. However,
hurricane winds may persist for extended
periods of time and the performance criteria
for façade components in response
to these sustained pressures permit
smaller deformations and less damage to
the system. Breach of the façade components
would permit pressures to fill the
building and loads to be applied to nonstructural components.
Anchorages and connections must be capable of holding the
2- Structural deSign criteria