FEMA 453 Design Guidance for Shelters and Safe Rooms

deformed, and transfer them to the underlying beams, trusses,
girders, shear walls, and columns that provide the global structural
resistance. These structural systems must also be able to develop
uplift forces and load reversals that may accompany these extreme
loading conditions. Uplift forces and load reversals are typically
applied contrary to the conventional design loads and, therefore,
details must be developed that account for these contrary patterns
of deformation (see Figure 2-7). Seismic detailing that addresses
ductile behavior despite multiple cycles of load reversals are generally
well suited for all of these extreme loading conditions and
building-specific details must consider each threat condition. Some
construction materials, however, are better suited to developing a
load path that can withstand loads from multiple directions and
events. Cast-in-place reinforced concrete and steel moment frame
construction is more commonly detailed to provide load paths
than in "progressive collapse" designs utilizing panelized or masonry
load-bearing construction. Nevertheless, appropriate details
must be developed for nearly all structural systems.
Structural deSign criteria
Figure 2-
effects of uplift and load
reversals
2-