Appendix B to Part 154 - Stress Analyses Definitions
46:5.0.1.3.15.5.101.40.14 : Appendix B
Appendix B to Part 154 - Stress Analyses Definitions
The following are the standard definitions of stresses for the
analysis of an independent tank type B:
Normal stress means the component of stress normal to the
plane of reference.
Membrane stress means the component of normal stress that
is uniformly distributed and equal to the average value of the
stress across the thickness of the section under consideration.
Bending stress means the variable stress across the
thickness of the section under consideration, after the subtraction
of the membrane stress.
Shear stress means the component of the stress acting in
the plane of reference.
Primary stress means the stress produced by the imposed
loading that is necessary to balance the external forces and
moments. (The basic characteristic of a primary stress is that it
is not self-limiting. Primary stresses that considerably exceed the
yield strength result in failure or at least in gross
deformations.)
Primary general membrane stress means the primary
membrane stress that is so distributed in the structure that no
redistribution of load occurs as a result of yielding.
Primary local membrane stress means the resulting stress
from both a membrane stress, caused by pressure or other mechanical
loading, and a primary or a discontinuity effect that produces
excessive distortion in the transfer of loads to other portions of
the structure. (The resulting stress is a primary local membrane
stress although it has some characteristics of a secondary stress.)
A stress region is local if:
where: S1 = distance in the
meridional direction over which the equivalent stress exceeds 1.1
f. S2 = distance in the meridional direction to another region
where the limits for primary general membrane stress are exceeded.
R = mean radius of the vessel. t = wall thickness of the vessel at
the location where the primary general membrane stress limit is
exceeded. f = allowable primary general membrane stress.
Secondary stress means a normal stress or shear stress
caused by constraints of adjacent parts or by self-constraint of a
structure. The basic characteristic of a secondary stress is that
it is self-limiting. Local yielding and minor distortions can
satisfy the conditions that cause the stress to occur.