Modeling a bolt group

[Anonymous]

Hello

Anyway know of a good way to model a bolt group in ARSA ? I have a "lever" of two welded rectangular hollow sections connected to a timber beam and I'm trying to figure out the best way to get reactions for the connecting bolts.

Thank you,

Tanel

[StefanoPasquini6790]

Hi,

My personal suggestion is to model the whole structure in shell elements, simulating the real behaviour of the beams.

Pay attention to the torsion on timber support beam.

Greetings

[Anonymous]

Hey

Good idea, however what would be the best approach to modeling the bolts? Using a 10mm diameter steel bar? Where would you put the support?

Thanks

[StefanoPasquini6790]

Hi,

yes, for bolts I would use a 10 mm diameter steel bar, keeping in mind that the real strength of bolts is much more higher than the simple steel.

Greetings and good luck, post your model image after you make it.

[Anonymous]

I changed the load-bearing structure a little bit: got rid of the timber member and added a vertical UPE80 instead. Robot is able to calculate this nicely - no instabilities. However this is probably not the best way to model a bolt, because currently the effects of the washer on one side and the nut on the other side are not taken into account. There are very large stress concentrations where the bar element meets the shell element. The upper bolt, which has the highest tension should spread it to larger area, because the head of the bolt is much larger than the shank of the bolt. Any ideas how to factor in the effect of the bolt head?

AutoCAD screenshot:

I modeled all the steel elements (UPE80 & RHS - rectangular hollow section) as shell elements with correct thicknesses. The 3 bolts are bar elements with a thickness to 10mm. I also added a rigid link (x-direction only) to simulate the contact between the bottom edge of the RHS and the UPE80.

3D view of connection:

Side view showing the bolts and a rigid link (X-direction only)

Stress concentration near the upper bolt. REASON: bolt head diameter is not taken into account.

[StefanoPasquini6790 · Accepted solution]

Very nice work tanel96,

To solve the issue of the stress peak in the bolts connection you have only to select the option, in the parameter label of the map for panels, to "reduce the peack over the column head" and you will see that the stress will decrease.

Hope I helped you, step by step you will become a great structural modeller....

[Anonymous]

"Reduce the peak..." switch had very little to no effect at all. So the question remains... how to model a bolt connection in Robot that would take into account the nut and washer (they are larger in diameter than the shank of the bolt and therefore distribute axial load onto a larger area). Also bear in mind, that the bolt works both in tension and in shear. In Abaqus for example, there is something called a "contact element" which enables to simulate this effect.

[Artur.Kosakowski]

For such element types you may want to look at other Autodesk programs such as Nastran or Simulation Mechanical instead. 

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