ever, be noted that Kapitan Nikolayev is fitted with
under normal handling conditions. Unfortunately,
stainless steel compound plate in the ice belt area,
there are so many classifications by the different
which may be effective in reducing the chances of
societies that it is difficult to establish equivalency
getting stuck in ice.
among them (Santos-Pedro 1994, Toomey 1994). A
limited equivalency among the ice classifications
of the various societies is given in the Appendix A
of a companion report by Mulherin (1994). At pre-
STRUCTURAL DESIGN OF
sent, an effort is underway to standardize ice
POLAR SHIPS
classes as international navigation through Arctic
Structural design involves the selection of ma-
routes, such as the Northern Sea Route and the
terial and sizes of plates and frames for maintain-
Northwest Passage, becomes more attractive for
ing the structural integrity of a polar ship under
shipping products between the North Atlantic and
loads from waves and ice during its normal op-
the North Pacific (Santos-Pedro 1994). While com-
eration (Dick et al. 1987). As a result of research
paring the ice-strengthening requirements accord-
and experience, much has been learned about the
ing to the Russian Register Rules and Canadian
nature of ice loads and the mechanics of ice fail-
Arctic Shipping Pollution Prevention Regulations
ure. Full-scale measurements of ice loads on many
(CASPPR), Karavanov and Glebko (1994) have
ships have yielded an empirical description of ice
presented an extensive comparison of the ice loads,
forces and pressures that is used in design. The
section modulus and shear area of frames, and
magnitude of ice loads, the existence of significant
thickness of shell plating. The new CASPPR (1989)
damage and the emergence of affordable nonlin-
regulations call for smaller scantlings and thinner
ear finite element analysis packages have together
shell plates than those required by Russian Rules
led to the wide use and acceptance of plastic de-
because CASPPR allows a certain amount of plas-
sign (plastic design allows some deformation of
tic deformation of the structure under extreme ice
the structure under extreme ice loads).
loads.
Classification of
Ice loads and pressures
Compression of ice at low strain rates results in
polar ships
All commercial vessels, including most ice-
creep deformation with or without micro-crack-
breakers, but excluding government-owned ves-
ing. The constitutive relations between stress and
sels, are classified according to the rules developed
strain for creep deformation at low strain rates are
well known. At higher strain rates (>103 s1), the
by six classification societies: Lloyds Register (LR),
ice fails in a brittle manner, resulting in instabili-
Det norske Veritas (DnV), American Bureau of
ties caused by macro-cracking. The failure mecha-
Shipping (ABS), Bureau Veritas (BV), Germanis-
nism for brittle failure has not been fully under-
cher Lloyd (GL), and Russian Register of Shipping
stood. Failure loads or pressures also depend on
(RS). Besides the rules of the classification societ-
the state of stress, e.g., uniaxial vs. multiaxial. At
ies, there are three national sets of rules to control
present, the dependence of compressive failure of
navigation in ice-covered waters: FinnishSwed-
ice under multiaxial loading at different strain rates
ish, Russian and Canadian. The classification of a
is being studied by researchers all over the world
vessel is used for insurance and to comply with
(e.g., Frederking 1977, Richter-Menge et al. 1986,
the international regulations, such as the Safety of
Smith and Schulson 1994, etc.).
Life at Sea (SOLAS) and prevention of pollution.
There have been attempts made to relate the
Government-owned vessels are also surveyed for
forces exerted on a ship or a structure by crushing
compliance with recognized national and interna-
of ice to the uniaxial compressive strength of ice,
tional standards.
but these attempts to obtain empirical relationships
The classification societies are responsible for
through the use of many coefficients have not been
approving the design and supervising the con-
fruitful. Although much has been known about the
struction of individual vessels to ensure confor-
forces from flexural failure and compressive fail-
mity with the standards set by international con-
ure of ice at low strain rates, the understanding of
ventions and by the classification of that vessel.
brittle failure is still incomplete at high rates of
The vessels are subjected to annual and special
loading and in a multiaxial state of stress. Results
surveys throughout their lives (Toomey 1994).
of small-scale indentation experiments on fresh-
The ice classification of a vessel depends on its
water ice indicate that brittle failure is activated at
capability to resist damage while navigating in ice
12
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