A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Level Two (Advanced FAQs)
Part II: Design of Marine Structures
1. In fender design, when calculating the berthing energy absorbed
by fenders, should engineers take into account energy absorbed by
piers? (FD1)
The design of a fender system is based on the principle of conservation of
energy. The amount of energy brought about by berthing vessels into the
system must be determined, and then the fender system is devised to
absorb the energy within the force and stress limitations of the ship's hull,
the fender, and the pier.
Firstly, the energy released by the largest/heaviest vessel allowed to use
on the pier is determined to be delivered to the pier by first impact. Then,
the energy that can be absorbed by the pier would be calculated. For pier
structures that are linearly elastic, the energy is one-half the maximum
static load times the amount of deflection. However, in case the structure is
extremely rigid, it can be assumed to absorb no energy.
The energy to be absorbed by fender system should be the total energy of
berthing vessels deducting the energy absorption by pier structures. Finally,
a fender system capable of absorbing the amount of energy without
exceeding the maximum allowable force in the pier should be chosen from
fender product catalogue.
2. Why do vessel operators choose to contact the fender system at its
bow instead of mid-ship location during berthing operation?
When calculating berthing energy of vessels, there is a factor called
“eccentricity factor” which accounts for different berthing energy when the
vessel contact the fender system at different locations of the vessel.
For instance, for mid-point berthing the eccentricity factor is unity which
means there is no loss of berthing energy. For third-point berthing and
quarter-point berthing, the eccentricity factor is 0.7 and 0.5 respectively. In
fact, engineers always attempt to reduce the amount of berthing energy to
be absorbed by fender system and pier structures. As such, it is
recommended for vessels to contact fender system at its bow or stern
because the reaction force would produce a rotational moment to the
vessel which dissipates part of vessel’s energy.
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