Pile Design and Construction Practice, Fifth edition

The bending moment Mon the pile is equal to H(ezf) therefore

(8.4)

If required the more-rigorous methods described in Sections 6.3.3 and 6.3.4 can be used to
calculate the deflection of the pile head and hence the work done in bringing the ship to rest.
The bending moment which can be applied to a pile is limited by the allowable working
stress on the extreme fibres of the material forming the pile for normal berthing impacts, or
by the yield stress with abnormal berthing velocities. Thus if the allowable resistance
moment Mais used in equation 8.4 the capacity of the pile to absorb kinetic energy can be
calculated and compared to the kinetic energy of the moving ship which must be brought to
rest. If the capacity of the pile is inadequate the blow from the ship must be absorbed by
more than a single pile. In practice, vertical piles are grouped together and linked at the head
and at some intermediate point (Figure 8.1a) to form a single berthing dolphin, or are spaced
in rows or ‘bents’in the berthing head of a jetty structure. In the latter case the kinetic energy
of the ship may be absorbed by a large number of piles. In the case of a pile fixed against
rotation by the deck slab of a structure (Figure 8.3b) it was shown in equation 6.21 that

(8.5)

The bending moment caused by a load at the fixed head of a pile is equal to , and
thus the work done is the same as shown in equation 8.4.
BS6349 points out that in the case of a piled wharf erected parallel to a sloping shore line,
the piles supporting the rear of the deck, being more deeply embedded than those at the front
will resist a much higher proportion of the horizontal forces imposed on the fendering. It
may be necessary to consider sleeving the rearward piles to equalize the flexural resistance.

1

2 H(ezf)

distance y moved point A

H(ezf)^3

12 EI

work done

M^2 (ezf)

6 EI

Piling for marine structures 401

Figure 8.3Lateral movement of fender piles due to impact force from berthing ship (a) Single
free-headed pile (b) Group of fixed-headed piles.

A H A H

e e

y y

zf zf

Point of fixity

(a) (b)