FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

Volume II DETERMINING SITE-SPECIFIC LOADS 8
COASTAL CONSTRUCTION MANUAL
Figure 8-11.
Water depth versus
wave height, and water
depth versus breaking
wave force against, a
vertical wall
on the order of hundreds of pounds/ square foot were generated by waves that were only 12 to 18 inches
high. See Appendix H for the results of the tests.
8.5.8.3 Wave Slam
The action of wave crests striking the elevated portion of a structure is known as “wave slam.” Wave slam
introduces lateral and vertical loads on the lower portions of the elevated structure (Figure 8-12). Wave slam
force, which can be large, typically results in damaged floor systems (see Figure 3-26 in Chapter 3). This is
one reason freeboard should be included in the design of coastal residential buildings. Lateral wave slam can
be calculated using Equation 8.7, but vertical wave slam calculations are beyond the scope of this Manual.
Equation 8.7 is similar to Equation 8.8 (hydrodynamic load) with the wave crest velocity set at the wave
celerity (upper-bound flow velocity, given by Equation 8.2b) and a wave slam coefficient instead of a drag
coefficient. The wave slam coefficient used in Equation 8.7 is an effective slam coefficient, estimated using
information contained in Bea et al. (1999) and McConnell et al. (2004).
Wave slam should not be computed for buildings that are elevated on solid foundation walls (the waveload-on-wall
calculation using Equation 8.6 includes wave slam) but should be computed for buildings that
are elevated on piles or columns (wave loads on the piles or columns, and wave slam against the elevated
building, can be computed separately and summed).
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