Page 215 - Marine Structural Design

Chapter 9 Buckling and Local Buckling of Tubular Members 191

where k/ko is taken as 0.0,O. 1, 1.0 and 00, where ko = 4EI/1.
The ultimate strength evaluated by the proposed method is slightly lower than the ultimate
strength proposed by the finite element method when the constraint is weak, but it becomes
higher proportionally, as the constraint is increased. However, the proposed method gives a
very accurate ultimate strength.
In the case of K = 00, the axial load still increases after a plastic node is introduced at a
mid-span point where the ultimate strength is attained according to a simplified method. It
begins to decrease after the hlly plastic condition is satisfied at both ends. However, the load
increment after a plastic node has been introduced at a mid-span point is very small.
Therefore, an alternative analysis is performed, in which three plastic nodes are
simultaneously introduced at a mid-span and both ends when the ultimate strength is attained
by a simplified method. The curves for K =Q) in Figures 9.26 and 9.27 are the results of the
latter analysis. Further considerations should be taken when regarding this procedure.

i .a K : SPRING CONSTANT
PIP,
0.a

0.6

0.4

0.2 -. . ISUM

I
0,2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
W/Z
Figure 9.26 Load - lateral Deflection Curves of Simply Supported Tube
with End Constraint Against Rotation

H Series
A series of analyses are performed on H series specimens in order to check the accuracy of
post - local buckling behavior predicted by the present method. The coefficient, n, in Eq.
(9.78) is interchanged between 8 and 16 when using the COS model.
The load vs. lateral deflection relationships and the interaction relationships of internal forces
are plotted in Figures 9.28 and 9.29, respectively. The solid and dashed lines represent the
results obtained from the present method and experiment, respectively, and the chain lines