Spreader Bar Design - Stress Analysis

[Anonymous]

HI.. everyone.

I am new to Inventor and I am learning it slowly.

Recently I modeled a spreader bar. (Pic attached)

After modeling the parts, I assembled the spreader bar as per my AutoCAD dimensions.

I would like to do a stress analysis and find out how much the spreader bar can lift and its safety factor.

I provided bearing load on both bottom pad eyes equal to half the total weight to be lifted.

I am struggling how to constrain the model to do the analysis.

Kindly help me regarding this.

[TheCADWhisperer]

Attach your assembly here.

[Anonymous]

Attaching my assembly..

Thanks for the reply.

[TheCADWhisperer]

The angle for your lift cables, ropes or chains is important.

[Anonymous]

The angle is 60 deg.

But do we need to model the slings? Or is this angle for providing top lug force direction?

[jmenier]

Stress analysis is one thing, but if you are in the US there is a mandating code that you need to design spreader bars to. The code is by ASME and called BTH-1-2014 Below The Hook lifting devices. There are some rigorous calculations involved and if you are not an engineer, I would find one to do the design. Let me know if you have questions regarding this, as I do design these types of things regularly. Also if you look hard enough online you can find older codes that have the same method of calculation in them, the last version was 2011.

[johnsonshiue]

Hi! I could be wrong but I think you may need to add Fixed constraint or Frictionless constraint at where you apply the bearing load. The system as is may be unstable.

Many thanks!

[Anonymous]

Thanks for the valuable reply.

I am a Mechanical Engineer Graduate.

But again this is for the Manual Calculation. I am trying to do this through Inventor so that it save my lot of time.

[Anonymous]

Thanks for the response. Let me try.

I think i need to provide frictionless constraints to the top pad eyes and load to the bottom one.

Seriously in this whole world, nobody has designed spreader bar in Inventor...!!!!!!!!!!!!!

Sorry to say this... I couldn't find any over the internet.

[jmenier]

I get your frustration, but if you use that spreader bar and only have a stress analysis that you may or may not have done correctly without any backup calculations, and it fails... well that doesn't look very good for your career. Please don't be lazy with something like this and only rely on a computer simulation, buy the code book and do the calculation. What I did to expedite these calculations was to make an excel spreadsheet where I can easily change values for different configurations and can create a spreader design in a matter of minutes. 

[johnsonshiue]

Hi! Like I mentioned earlier, there is not enough constraint to make the system stably solvable. Instead of using the Fixed Edge constraint, I fixed the two contact faces of the tubes in the middle. I am able to get a sensible result. Could you try it?

Many thanks!

[Anonymous]

Is there an alternate solution for contraining? What if its being lifted by four chain legs and the geometry of the lifting / spreader bars aren't so simple. There should be a way or provision replicate chain elements connected to common lifting Point.

Right now I'm modelling something to replicate the chains and contraining them instead. However, I'm not fully satisfied.

[johnsonshiue]

Hi Lenin,

I don't think modeling chain will get you better result. Although the geometry is realistic, it is too realistic for FEA to solve. One of the rules to run FEA is to replace geometry you don't have control over with simplified geometry or constraints or loads.

In your case, I don't think you are designing the chain. Nor will you make the chain yourself. You just need to know the forces applied to the chain and the allowable deformation. There is no need to solve FEA on the chain.

Many thanks!