Page 235 - Dynamic Loading and Design of Structures

In practice eqn (5.54) is calculated by using a discrete set of sea states and directions.
Extreme value theory can then be applied to determine the characteristics of the maximum in
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a 100 year (with, say, N=5×10 maxima) or any other reference period.
In some cases we would need to know the joint probabilistic characteristics of several
random response variables x. For instance, the strength check of a steel member subjected to
an axial load N=x and a bending moment M=x is ac-complished with a non-linear
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1
interaction formula, for instance, of the type:

(5.55)