Page 211 - Marine Structural Design

Chapter 9 Buckling and Local Buckling of Tubular Members 187

C Series
C series experiments are carried out by Smith et al. (1979). Specimens C1 and C2 which are
not accompanied by a denting damage are analyzed. The calculated results for Specimen C2
are plotted together with the measured result in Figure 9.23. Smith wrote in his paper that local
buckling took place when the end-shortening strain reached 2.5 times the yield strain E,,,
while it occurred in the analysis when the strain reached 1.4 E,,. However, the behavior up to
the onset of local buckling is well simulated by the proposed method of simplified elasto-
plastic large deflection analysis. On the other hand, in the case of Specimen C1, local buckling
takes place just after the ultimate strength is attained both in the experiment and in the
analysis. However, the calculated ultimate strength is far below the measured one as indicated
in Table 9.4. This may be attributed to some trouble in the experiment, since the measured
ultimate strength is 1.1 times the fully plastic strength.
D Series
This series is also tested by Smith et al. (1979). The analysis is performed on Specimens D1
and D2. Here, the results for Specimen D1 are plotted in Figure 9.24. It may be said that a
good correlation is observed between the calculated and measured results in the ultimate
strength and in the onset of local buckling. However, the behavior occurring just after the local
buckling is somewhat different between the experiment and the analysis. This may be because
the experimental behavior at this stage is a dynamic one, which is a kind of a snap-through
phenomenon as Smith mentioned. As for the load carrying capacity after the dynamic
behavior, the DENT model gives a better estimate than the COS model.
A similar result is observed in Specimen D2. However, in this case, the predicted onset of
local buckling is later than the measured one.
S Series
This series is a part of the experiments carried out by Bouwkamp (1975). The calculated and
measured results for Specimen S3 are shown in Figure 9.25. First, the measured ultimate
strength is far above the elastic Eulerian buckling strength. This must be due to a difficulty in
simulating the simply supported end condition. Consequently, instability took place just after
the ultimate strength was attained, and a dynamic unloading behavior may occur. After this, a
stable equilibrium path was obtained, which coincides well with the calculated results.