Weld analysis of fixed plate

[Sjqlund]

Dear fellow engineers

Take a look at this picture:

http://i.imgur.com/vObP2HB.png

Description: We have an open 'box' and we weld a plate to the inside of the box, using fillet welds on all edges on both sides. Plate is light blue, and the dashed lines is the plate if the sides of the box was transparent. The black color is fillet welds.

Question: How would you analyse such a situation?

My own thoughts: The shear stress in the weld can easily be calculated. However it is the edge moment that gives me trouble. The edge moment gives bending stresses in the weld. My first guess would be to try to find the edge moment in a book like "Roark's formulas for stress and strain". In such tabular books, i can though only find edge stresses of a fixed plate, which i'm not sure how to use, or is relevant at all.

Any ideas?

Best regards, Jones

 

[SnTMan]

Sjqlund, weld groups are generally analysed per such as this:

http://www.roymech.co.uk/Useful_Tables/Form/Weld_strength.html

Pay attention to "Table properties of a range of fillet weld groups with welds treated as lines"

Now to get the loads: Roarke Table 26 shows bending stress for flate plates under various edge conditions and loadings. Now you have your (max) bending moment. Alternatively you could get it from beam theory on a unit width basis.

The afore-mentioned link doubtless shows how to combine the direct shear and bending stresses.

This is a simple and widely used method. There are no doubt others.

Regards,

Mike

 

[Sjqlund]

Hi Mike, thanks for helping out

roymech seems like a great ressource.

About the loads. Let me just draw another figure - the plate seem from the side.

http://imgur.com/vKp6BBv

Say i find the max edge bending stress from the Roark table you pointed out. How can i then justify that this stress (corresponding to the top figure) will actually be the bending stress in the weld (bottom figure) ? My point is that the boundary condition is essentially different.

I dont know if my question was very clear; if not please let me know.

The other approach you mention i think i understand. I'd find the moment as 1/8 PL, then find the moment of inertia of the welds and calculate the bending stress. I am though worried that this approach (even if i understand it correctly) is too simplified. Did i describe it the way you meant?

 

[SnTMan]

Maybe get the moment from Sigma = 6*M / t^2?

 

[Sjqlund]

Where is that expression from?

Wouldnt you need to integrate stress over thickness?

 

[Sjqlund]

Ah, i'm being stupid. I see it now. Thank u

 

[Sjqlund]

Ah, i'm being stupid. I see it now. Thank u

 

[SnTMan]

Sjqlund, you're welcome, of course. I'm sure there are other ways, but for my type of work this would normally be good enough and fast enough

Regards,

Mike