UFC 4-152-01
28 July 2005
When the ship's energy is resisted through foam-filled or pneumatic fenders, the
resulting force is concentrated in a small area of the ship's hull. In such cases,
the allowable pressure on the ship's hull becomes a critical design issue. Most
fast combatants have a thin hull plating with a low allowable hull pressure. For
more specific information on the ships being berthed, consult NAVSEA. See TR-
6015-OCN, and note that values in Table 7 are based on yielding of the hull
plating and include a 1.5 safety factor. Consequently, when checking for an
accidental condition, the allowable value may be increased by up to 50 percent.
5-4.4.3
Allowable Stresses.
Because ship berthing is a short-term impact type of loading, the following
increases over previously published values are permitted. The fender system
may be designed as a Class B structure.
a. Timber. For operating condition, the allowable stress in flexure
(tension and compression) may be taken as 0.67 X modulus of rupture or
the published allowable values increased by a factor of 2.0, whichever is
less. For the accidental condition, the stress-strain curve may be
assumed to be linear up to 0.9 X modulus of rupture, which should be
taken as the limit.
b. Steel. For operating condition, the allowable stress in flexure (tension
and compression) may be taken as 0.8 X yield stress. For the accidental
condition, full yield stress may be used. However, the sections used
should satisfy compactness requirements or the allowable stress reduced
proportionately. Members should be sufficiently braced for development
of the yield strength.
c. Concrete. Design reinforced and prestressed concrete members not
intended for energy absorption with a load factor of 1.7 over forces
developed due to operating condition; they will be satisfactory for the
accidental condition. Do not allow further prestressed members to
develop tensile stresses in excess of 12 f'c (f'c = 28-day compressive
strength) in the precompressed zone. Prestressed concrete members
specifically designed for energy absorption will have a maximum allowable
working energy (Ewc) equal to 0.67 x the applied load (P) x the deflection
at the point of the applied load. Three criteria must be satisfied to
determine the maximum allowable working energy (Ewc) in the pile section
for a given length:
Maximum concrete compressive strain must be equal to or less
than 0.0021 in/in (00021 mm/mm.)
Maximum stress in the prestressing steel at working energy must
be equal to or less than 210,000 psi (1 447 898.9 kPa.)
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