Page 246 - Marine Structural Design

222 Pari II UZtimate Strength

Local Panel Buckling
Similar to Eq. (10.19) in Section 10.3, the elastic buckling strength of axially compressed
cylindrical panels may be expressed as

(1 1.34)

where L, is distance between adjacent stringer stiffeners. Buckling coefficient k, is a function
of the geometrical parameter M, = L, I& , and may be taken as 4 when M, < 1.73 .
Capanoglu and Baht (2002) proposed to use the following equation for the geometric
parameter k,:
k, = 4a, [1 + 0.038(M, - 2)'] (11.35)

The plasticity correction factor 4 in Section 10.1.6 may then be used to derive inelastic
buckling strength.
Stinger-Stiffened Cylinder Buckling
The elastic stress for column shell combinations may be estimated as:
+Pres

wherep, is Shell Knockdown factor, to be taken as 0.75.
The elastic stress for column:
Z'EI;
Ocd = (11.36)
L2 (A, + s,t)
where Sewis the effective width of shell plating and I, is effective moment of inertia. The
elastic critical stress for unstiffened shell:
t
0.605 E -
=
0, R (1 1.37)
A,
1+--
SeJ
The inelastic buckling stress ccmay be calculated using plasticity correction factor 4 in
Section 10.1.6.
Local Stiffener Tripping
When the torsional stifhess of the stiffeners is low and the shell skin D/t ratio is relatively
high, the stiffeners can experience torsional instability at a stress lower than that required for
local or orthotropic buckling. When the stiffener buckles, it loses a large portion of its
effectiveness in maintaining the initial shape of the shell. This reduction in lateral support will
eventually lead to overall shell failure. Much of the load carried by the stiffener will then be
shifted to the shell skin. Therefore, restrictions on the geometry of the stiffeners are applied in
the design codes to avoid this failure mode. The restrictions on the geometry of the stiffeners
are similar to those used for stiffened plates. Out of straightness of the stiffeners can result in a