3 Corrugated Bulkhead

3.1 General

3.1.1 Three buckling failure modes are to be assessed on corrugated bulkheads:

Corrugation overall column buckling.
Corrugation flange panel buckling.
Corrugation web panel buckling.

3.2 Reference stress

3.2.1 Each corrugation flange and web panel is to be assessed.

3.2.2 The membrane stresses at element centroid are to be used.

3.2.3 The maximum normal stress parallel to the corrugation, σ_x, is the maximum of the 2 following stresses:

The normal stress parallel to the corrugation taken at b/2 from the corrugation ends,
The normal stress parallel to the corrugation within the mid span of the corrugation.

When the corrugation end is fitted with a shedder plate, the normal stress parallel to the corrugation at end is to be taken at b/2 from the intersection of the shedder plate with the point at mid breadth of the flange or of the web, as the case may be.

The maximum shear stress is the shear stress which is maximum at the corrugation flange or web at the point b/2 from ends as defined above for the normal stress parallel to the corrugation.

The in plane stresses, σ_x and σ_y, and shear stress, τ, are to be taken as the element stresses averaged over the width of the considered member (flange or web) at the considered location.

When the stress value at b/2 from ends cannot be obtained directly from FE element, the stress at this location is to be obtained by interpolation. This interpolation is to be made on elements extending over a distance equal to 3b to a point located at b/2 from the end of the corrugation or from the intersection of the shedder plate if fitted, measured at the mid breadth of the flange or of the web. The interpolation of the in plane stresses, σ_x and σ_y, are to be made in accordance with Ch 8, App 1, [2.1].

The shear stress at b/2 is obtained by linear interpolation between the elements most close to 'b/2' location.

For the application of this requirement, b is defined as follows:

b : Width of the considered member of the corrugation, i.e. flange or web.

3.2.4 Where more than one plate thicknesses are used for flange panel, maximum stress is to be obtained for each thickness range and to be checked with the buckling criteria for each thickness.

3.3 Overall column buckling

3.3.1 The overall buckling failure mode of corrugated bulkheads subjected to axial compression is to be checked for column buckling (e.g. horizontally corrugated bulkheads and vertically corrugated bulkheads subjected to local vertical forces).

Table 2 : Application of overall column buckling for corrugated bulkhead

Bulkhead orientation	Corrugation Orientation
	Horizontal	Vertical
Longitudinal bulkhead	Required	Required, when subjected to local vertical forces (e.g. crane loads)
Transverse bulkhead	Required

3.3.2 Each corrugation unit within the extension of half flange, web and half flange (i.e. single corrugation as shown in grey in Figure 10) is to satisfy the following criterion:

η_Overall ≤ η_all

where:

η_Overall : Maximum overall column utilisation factor, as defined in Ch 8, Sec 5, [3.1.1] and Ch 8, Sec 5, [3.1.2], considered as a pillar with a unsupported length taken as the length of the corrugation.

Figure 10 : Single Corrugation

3.3.3 End constraint factor, f_end corresponding to pinned ends is to be applied except for fixed end support to be used in way of stool with width exceeding 2 times the depth of the corrugation.

3.4 Local buckling

3.4.1 The compressive buckling strength of a unit flange and a unit web of corrugation bulkheads is to satisfy the following criterion:

η_Corr ≤ η_all

where:

η_Corr : Maximum unit flange or unit web utilisation factor, as defined in Ch 8, Sec 5, [3.2.1].

Two stress combinations are to be considered for the application of the above criterion:

The maximum normal stress parallel to the corrugation, σ_x, combined with the stress perpendicular to the corrugation, σ_y, and with the shear stress, τ, at the location where the maximum normal stress parallel to the corrugation occurs.
The maximum shear stress, τ, combined with the normal stress parallel to the corrugation, σ_x, and with the stress perpendicular to the corrugation, σ_y, at the location where the maximum shear stress occurs.

The buckling assessment is to be performed for an aspect ratio α equal to 2, and for the thicknesses of the member where the maximum compressive/shear stress occurs (see [3.2.4]).