Buckling of transverse bulkheads - part 2

General

  

This presentation about buckling of longitudinally reinforced transverse bulkheads the is a continuation of the presentation “Buckling of transverse bulkheads (part 1) - 

Buckling of vertically reinforced transverse bulkheads”

Buckling of plate pannel

The buckling of plate panels loaded with linear loads one edge or two edges is well documented by various structural codes including the ship’s classification rules.

The assessment of buckling of the plate partially loaded on edge(s) is practically not documented by codes. Obviously, the study of this phenomenon could be done using finite element models but this approach is not necessary very practical.

This is a limitation for the presentation below.

Disclaimer

This text represents only the author personal opinion about the engineering topics presented. This personal opinion is not comprehensive and definitive and it is rather an invitation for discussions, comments and feedback and shall be considered accordingly.

The author can’ take any responsibility for any type of use of this text. 

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Buckling of longitudinally reinforced transverse bulkheads

Additional Information

  

The Figure 3.5 of 1995 edition of DNV CN 30.1 provides guidance regarding the analysis of buckling of longitudinally reinforced bulkheads. 

The stress sy= F/tw/li shall be applied along the entire length of the long edge of the first panel below deck. 

An alternative approach, less conservative, is based on the fact that the load is spread into the plate and at distance z below deck the stress is: sy= F/tw/(li +2*z). The stress decreases at a great rate if the distance from the deck increases.  

Could be used other stress?  

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Visit “Buckling of transverse bulkheads (part 1) - Buckling of vertically reinforced transverse bulkheads”

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The stress at the middle of panel

The table below is an example of stresses calculated for the application of 10 t on a plate panel with t=10.0 mm and s= 600 mm.  

  

Considering that the buckling deformation is maxim at the middle of the plate it could be suggested that the stress at z=s/2, sy= F/tw/(li +s), should be used.  Nevertheless, it can be noted that the stresses at the middle of the panel are less sensible to the value li. 


With every distance s below deck, the li increases with 2s therefore after two longitudinal spaces below deck the load is spread over (li +4*s). The space between transverse girder is in general in the range of 3a to 4a (a is the frame spacing) where, in general a is about equal s. 

This leads to the conclusion that the first two rows of panels below deck are the most critical for buckling.


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Brackets below main deck

In many case, the brackets are arranged on the first plate panel below main deck between the vertical girders. In this case the buckling capacity of the 1st panel below deck is considerable improved.

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The force is located on top of the vertical girder

If the force is located on top of the vertical girder, the assessment of buckling strength could be done in accordance with the formula used for vertical stiffeners. 

It is not clear if plate strip to be considered could be 40*t.

Considering that, in case the plate panels buckle, the triangular areas figured nearby the short edges won’t lose the stability, it would make sense replacing the 40*t used for vertically stiffened bulkhead with 2*s/2= s.