28 July 2005
Fender System Behavior.
The fender systems having the most promise for new installations can be
classified into three groups in terms of their behavior:
Flexible Pile Types.
The flexible pile types, or various fender piles discussed earlier, have basically a
linear force-deflection relationship. Cantilevered piles or "monopile" systems
likewise have a basically linear force-deflection relationship.
Buckling Column Types.
The buckling column types behave linearly up to a point where the rubber starts
to buckle and behave nonlinearly from there on. Because the buckling type
fender systems have the highest energy-absorption capacity for a given
deflection and reaction, they are in very wide use in commercial piers and
wharves. Due to the nature of the reaction/deflection/energy-absorption
relationship of these types of fenders, a very high reaction (close to maximum)
occurs during virtually every berthing operation and the berthing structure must
be designed with this fact in mind. This fact also causes the fender to be
relatively rigid when smaller ships use a berth designed for larger ones.
Many buckling-type fenders cause rather high contact pressures against the
ship's hull and consequently require a panel to distribute and thus reduce the
pressure. Size and locate the panel to ensure proper contact with both the
largest and smallest vessels to use the berth. Another characteristic of these
fenders to consider is their lowered performance when impacted by a vessel
approaching at an angle to the berth or with a velocity component in the
longitudinal direction. The reduction in energy-absorption capacity may be as
much as 20 percent when the approach angle is 5 deg. to 10 deg., with additional
reduction when combined with shear strain.
Pneumatic, Foam-Filled and Side-Loaded Rubber Fenders.
The pneumatic, foam-filled, and side-loaded rubber fenders exhibit very similar
behavior with the reaction force building up more than proportional to increasing
deflection. The floating pneumatic and foam-filled fenders have a similar
appearance and similar reaction/deflection relationship. Compared to the
buckling types, these fenders require greater deflection for a given reaction and
energy-absorption capacity. The pneumatic and foam-filled fenders present a
very large surface to the ship's hull and consequently have low hull contact
pressures. This eliminates the need for a panel between the ship and the fender.
With the pneumatic and foam-filled types of fenders, the maximum reactions will
normally occur only a very few times during the life of the facility, permitting the
use of higher stress levels in the supporting structure. However, they require a
rather large, solid face on the supporting structure, which may increase its costs.
The main difference between pneumatic and foam-filled fenders is that the