Cross Section Optimiser Deflection Query

Hey there,

I’m currently working on a truss for a project, where I am getting this warning saying that the truss fails in deflection, but “0 cross sections reached the maximum cross section size”. Basically the max section size used was a 254x254x167 UC, but my pool of member sizes that it could choose from had much larger UC section available for selection, so why did it not just keep sizing up until it passes in the deflection criteria. There is room for larger sections within the depth of the truss, so I am not sure why. Has anyone came across this warning before?

Thanks in advance.

01. Optimised Model 1.gh (102.6 KB)

Hi Jack,

it seems like there might be a small bug in the optimisation component.

However a workaround is to set SLS as LCasesUtil and MaxUtil as 0.2

Hi Matthew,

Thank you for your response.

By setting the SLS to LCasesUtil, from my understanding would mean, the structure would only consider the SLS load case for both ULS and SLS analysis, which of course is not what we are looking to achieve here.

I think the way I had it set up was correct, as by default it will optimise for both ULS and SLS in terms of axial force analysis etc, and by attaching the SLS to the LCasesDisp it only optimises for displacement for the SLS which i what we would like it to do.

Either its a bug, or maybe the truss simply does not work at an 80m span at 2.5m depth (span to depth ratio of roughly 30) for even the largest members available in the group in terms of deflection criteria. Hence, the optimiser then will ignore this criteria and will optimise for stress only.
I would like to hear your thoughts on this take, as I put the same model into robot with the largest readily available UC sections, and got deflection values over the SLS span/360 limit that we are looking to go with, and they were also outside the limit - but they were also quite heavy too so maybe smaller sections could work. But right now I am assuming this geometry is simply just not possible with the standard UC member sections available in industry.

Kind Regards,

Jack.

Hi @Jack_Lawless,
thanks for you definition!
Yes this seems to be a bug in Karamba3D. I will try to fix it a.s.a.p. and keep you updated.
– Clemens

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