FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

Volume II DESIGNING THE FOUNDATION 10
COASTAL CONSTRUCTION MANUAL
Figure 10‑14.
Section view of a
foundation constructed
with reinforced concrete
beams and columns to
create portal frames
SOURCE: ADAPTED FROM
FEMA P-550, SECOND
EDITION, CASE H
The grade beams that are shown in Figures 10-13 and 10-14 should not be used as structural support for a
concrete slab that is below an elevated building in Zone V. Although a concrete slab may serve as the floor of
a ground-level enclosure (usable only for parking, storage, or building access), the slab must be independent
of the building foundation. If a grade beam is used to support the slab, the slab becomes the lowest floor
of the building, the beam becomes the lowest horizontal structural member supporting the lowest floor,
and the bottom of the beam becomes the reference elevation for flood insurance purposes. For buildings in
Zone V, the NFIP, IBC and IRC require that the lowest floor elevated to or above the BFE be supported by
the bottom of the lowest horizontal structural member. Keeping the slab from being considered the lowest
floor requires keeping the slab and grade beams separate, which means the slab and grade beams cannot be
monolithic or connected by reinforcing steel or other means.
Like the driven, treated pile foundation discussed in Section 10.6.1, the foundation designs discussed in this
section are based on presumptive piling capacities that should be verified prior to construction. Also, design
professionals who develop foundations designs for specific buildings and have site information on subsurface
conditions can augment the FEMA P-550 design to provide more efficient designs that reduce construction costs.
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