FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

Volume II DETERMINING SITE-SPECIFIC LOADS 8
EXAMPLE 8.3. HYDRODYNAMIC LOAD ON PILES VERSUS BREAKING WAVE LOAD
ON PILES (concluded)
Solution for #2: The load from a breaking wave on a pile is calculated with Equation 8.5 as follows:
where:
H b is the height of the breaking wave or (0.78)d s
F brkp = 1,816 lb/pile
Note: The load from the breaking wave is approximately 3.5 times the lower estimate of the hydrodynamic
load. The upper estimate of the hydrodynamic load exceeds the breaking wave load only because of the very
conservative nature of the upper flood velocity estimate.
8.5.10 Debris Impact Loads
Debris impact loads are imposed on a building by objects carried by moving water. The magnitude of these
loads is very difficult to predict, but some reasonable allowance must be made for them. The loads are
influenced by where the building is located in the potential debris stream, specifically if it is:
Immediately adjacent to or downstream from another building
Downstream from large floatable objects (e.g., exposed or minimally covered storage tanks)
Among closely spaced buildings
A familiar equation for calculating debris loads is given in ASCE 7-10, Commentary. This equation has been
simplified into Equation 8.9 using C Str , the values of which are based on assumptions appropriate for the
typical coastal buildings that are covered in this Manual. The parameters in Equation 8.9 are discussed
below. See Chapter C5 of ASCE 7-10 for a more detailed discussion of the parameters.
Equation 8.9 contains the following uncertainties, each of which must be quantified before the effect of
debris loading can be calculated:
Size, shape, and weight (W) of the waterborne object
Design flood velocity (V)
Velocity of the waterborne object compared to the flood velocity
Duration of the impact ( t) (assumed to be equal to 0. 03 seconds in the case of residential buildings is
incorporated in CStr , which is explained in more detail below)
Portion of the building to be struck
COASTAL CONSTRUCTION MANUAL
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