FEMA 453 Design Guidance for Shelters and Safe Rooms

spacing of 16 inches that extends into the slab and the wall the
greater of the development length of the bar or 30 inches. Vertical
ties are required from floor to floor at columns, piers, and walls.
The ties should be equivalent to a #4 bar at a maximum spacing
of 16 inches coinciding with the horizontal ties. The ties should
be continuous through the floor and extend into the wall above
and below the floor the greater of the development length of the
bar or 30 inches. Partition walls surrounding critical systems or isolating
areas of internal threat, such as lobbies, loading docks, and
mailrooms, require fully grouted reinforced masonry construction.
It is particularly difficult to extend the reinforcement to the
full height of the partition wall and develop the reaction forces.
Reinforced bond beams are required as for load-bearing walls.
Flat roof systems are exposed to the incident blast pressures that
diffuse over the top of the building, causing complex patterns
of shadowing and focusing on the surface. Subsequent negative
phase effects may subject the pre-weakened roof systems to low
intensity, but long duration suction pressures; therefore, lightweight
roof systems may be susceptible to uplift effects. Two-way
beam slab systems are preferred for reinforced concrete construction
and metal deck with reinforced concrete fill is preferred for
steel frame construction. Both of these roof systems provide the
required mass, strength, and continuity to resist all phases of blast
loading. The performance of conventional precast concrete plank
systems depends to a great extent on the connection details, and
these connections need to be detailed to provide continuity. Flat
slab and flat plate construction requires continuous bottom reinforcement
in both directions to improve the integrity and special
details at the columns to prevent a punching shear failure. Posttensioned
slab systems are particularly problematic because the
cable profile is typically designed to resist the predominant patterns
of gravity load and the system is inherently weak in response
to load reversals.
Structural deSign criteria
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