FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

Volume II DETERMINING SITE-SPECIFIC LOADS 8
EXAMPLE 8.4. FLOOD LOAD EXAMPLE PROBLEM (continued)
Find:
• Local government requires 1.0 ft freeboard; therefore DFE = 14.0 ft NGVD (BFE) + 1.0 ft =
15.0 ft NGVD
• Building to be supported on 8-in. × 8-in. square piles, as shown in Illustration A
• Direction of wave and flow approach during design event is perpendicular to shoreline (see
Illustration A)
• The assumption is no grade beam or slab-on-grade present
1. Primary frontal dune reservoir: determine whether dune will be lost or provide protection
during design event
2. Eroded ground elevation beneath building resulting from storm erosion
3. Design flood depth (d s ) at seaward row of piles
4. Probable range of design event flow velocities
5. Local scour depth (S) around seaward row of piles
6. Total localized scour (S TOT ) around piles
7. Design event breaking wave height (H b ) at seaward row of piles
8. Hydrodynamic (velocity flow) loads (F dyn ) on a pile (not in seaward row)
9. Breaking wave loads (F brk ) on the seaward row of piles
10. Debris impact load (F i ) from a 1,000-lb object acting on one pile
Solution for #1: Whether the dune will be lost or provides protection can be determined as follows:
• The cross-sectional area of the frontal dune reservoir is above the 100-year stillwater elevation
and seaward of the dune crest.
• The area (see Example 8.1, Illustration B) can be approximated as a triangle with the following
area:
Where b is the base dimension and h is the height dimension of the approximate triangle:
A = 44 ft 2 but the area shown is slightly larger than that of the triangular area, so assume
A = 50 ft 2
COASTAL CONSTRUCTION MANUAL
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