FEMA 453 Design Guidance for Shelters and Safe Rooms

In order for the glazing to realize its theoretical capacity, it must
be retained by the mullions with an adequately sized bite, by
means of a structural silicone adhesive, or a combination of the
two. Furthermore, in order for the mechanical bite and silicone
adhesive to be effective, the mullion deformations over the length
of the lite must be limited (see Figure 2-13). Unfortunately, the
maximum extent of deformation that the mullion may sustain
prior to dislodging the glass is poorly defined. A conservative limit
of 2 degrees is often assumed for typical protective glazing systems;
however, advanced analytics may justify a significantly greater mullion
deformation limit. Mullions must therefore be able to accept
the reaction forces from the edges of the glazed elements and
remain intact and attached to the building. Analyses of mullion
deformations and anchorage details are required to demonstrate
the safe performance of the glazed fenestration.
Window of protected spaces
may be bullet-resistant
Strengthened mullion system must
be stronger than glass to hold
fractured window in place
Figure 2- Protective façade design
Structural deSign criteria
Strong attachment
to secure mullion
insulated glazing with
laminated inner lite
Window adhered to the
frame with structural silicone
sealant to keep fractured
window in frame
2-2