Structure support stress

Discussion in 'Metal Boat Building' started by Lucya, May 18, 2019.

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LucyaJunior Member

Hi all.
Is there any "approximately correct" way to calculate whether the supporting structure could withstand the force of 100 kN without using 3D model and simulation (Solidworks or Inventor etc)?

The 1st image is transversal section.
The 2nd image is sideview to see how long is the base structure and "eye-ring" position regarding it.

The "eye-ring" can handle the F=100kN, as well as welding.
The structure is questionable.

Any directions I would appreciate...
Thank you.

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Lucya,

Firstly, is there anything that joins these 2 bars of the U shape together? And/or, the means of applying the load, does it do that, connect the two?
Or...is it a straight pull from one bar only?

Then the distance from the point of the applied load to the base of the U shaped bar:

And then you'll need to know the size and material properties of the bar.
And then how it is connected to the base plate:

And then, is this structure important in this arrangement?

And is it connected to anything?

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LucyaJunior Member

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Well, it is a simple force x lever = moment.

So, you can calculate the section modulus of this bar = bending stress.
But you also need to check the shear stress and the deflection. Which you can do as you have the section properties.

You can now determine the 2nd moment of inertia of this weld and whether it can transmit/absorb the load that is applied to it., as you have the section properties, and the weld size.

Once you have doen the above, you need to understand, where does this load now go...firstly into the plate it is welded to.
And then...???....that's for you to decide and determine how/where you want this load to be shirked into the arrangement to be safe.
Is it between frames or lined up with a frame, for example. All important questions you need to ask yourself and satisfy.

That's it....simple. No fancy 3D software needed, just a basic understanding of structures.

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LucyaJunior Member

The load goes to the deck plate, shell side plate and the L profile between transversal L profiles (frames 800mm apart).
Deck is 10mm, shell is 8mm and L profile is 100x50x8. The L profile is welded 350mm from shell side.

Could you please give me the calculus with "x-es" instead of actual results (additional infos you have asked) so I can see how it has to be calculated since this is not simpy at all for me, its opposite.
Thank you.

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DejaySenior Newbie

Specifically not what you asked for but Fusion 360 has a FEA simulation module and is free for amateurs and startups. But you probably need / are better off understanding the basic calculations first. And if you do it by hand like ad hoc says I think you are basically splitting those shapes into finite elements that have formulas. Still have to learn this stuff myself!

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This suggests to me that you are unable to follow the basic steps noted above and calculate what is required.
This is very basic stuff for any student of Naval Arch or Structural/Engineering usually 1st year stuff....thus i would ask your superior to do this for you. Since if you unable to even calculate the shear stress, which is a 30 second calculation, the rest is totally beyond you.

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LucyaJunior Member

The moment should be F x L giving 100 kN x 250 mm = 25000 Nm
Bending stress on the rod bar should be 286224 PSI with the deflection of 8.1 mm.
Shear stress = 5.1 MPa
2nd moment of inertia of the weld with a=3,5mm = 210470 mm4

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