Engineering & Analysis Methods > Local Buckling & Local Postbuckling

boundary conditions for local buckling of stiffened panel component

**ohba**:

For the analysis related to local buckling of stiffened panel skin (clear spane between stringers) :

a) what boundary conditions are assumed ? Is it simply supported, clamped or is the rotational restrain provided by the stringer taken in to account (if yes, how is taken in to account) ?

b) what is the width considered for local buckling ? is it just the width measured between the edge of the stiffener flange (which can be found in the variable tab) or is there a correction applied on that value ?

Thank you

**Phil**:

For a stiffened panel with a flange (such as a T or and I), HyperSizer does local buckling analysis of the "Spacing Span" object, which includes both the Open Span between the flanges, and the flange/facesheet bonded region.

In the current software, HyperSizer creates an ABD matrix which is equivalent to the spacing span region. This ABD matrix includes the effects of the eccentricity between the bonded region and the open span, and therefore includes non-zero B terms. HyperSizer then does a buckling analysis of this region assuming a rectangular plate with the equivalent ABD terms.

The boundary conditions on this buckling analysis are Simple on all edges, therefore the rotational restraint of the stiffener is not included in this analysis.

Because the buckling analysis includes both the open span and the bonded retion, the width for this local buckling analysis is equal to the stiffener spacing, or the distance from the middle of one web to the center of the next.

**Phil**:

One additional comment I would like to make is that local post buckling of this region is a capability that we will be working in the next few months (we are presenting a local post buckling paper at this years AIAA SDM conference in Palm Springs) and as part of that effort, we will be working to improve the accuracy of the local buckling analysis which will most likely be focused on more accurately taking the eccentricity and the rotational constraint of the stiffener into account.

**ohba**:

Thanks for the reply Phil,

For the hat type stringers, how is the width defined for the local buckling analysis of the "closed span" and "open span" object ? Is the width measured from the mid point of the bonded flange ?

**Phil**:

For hats, the closed span buckling is from mid-point of the point where the one of the two WEBs intersects the upper flange to the other flange. That is, it is the distance between the webs.

I would not recommend using the Open span object for local buckling. I would recommend using the Spacing span, just as with the uniaxial concepts (I or T). That distance is from the top of the left web of one stringer to the top of the right web of the next stringer. I'll try to post a couple of snapshots.

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