Risa3d Plate Analysis

[KingKongdoor]

Can you use Risa3d plate tools to accurately model stresses in a member, such as a column and base plate interaction? I have modeled a column section and base plate using plates. The stresses calculated look reasonable. Just wondering how accurate risa is being used in this manner and if anyone has had experience analyzing something like this with risa plates? Its kind of more for fun than work but if it can provide something to compare other results with it could possibly be beneficial for work. For example, checking stresses of weird complex built up members observed in the field.

Thanks,

 

[JoshPlumSE]

Yes, the RISA plate element should be accurate for the type of analysis you're talking about. There is one important caveat though. Don't expect the analysis to predict buckling of webs or stiffeners. You'll get accurate forces, stresses and deflections and such. But, you won't see geometric non-linearity in the results (i.e. buckling).

 

[KingKongdoor]

Yeah, i figured it wouldn't be able check buckling cases.

 

[KootK]

I'd say that RISA would be as accurate as anything else FEM. To some extent, localized fabricated element stresses tend to be heavily influenced by residual weld stresses which would not be accounted for. The story of the column and base plate interaction, in particular, would be heavily impacted by how you're modelling the concrete/grout. RISA actually has a nifty too just for that: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KingKongdoor]

The column base plate connection I modeled was part of industrial equipment and did not have grout concrete interaction. For a case with concrete grout interaction I would probably just assume the plate is only supported at the bolt locations. This would be conservative I think. I could maybe add roller supports on the perimeter of the plate only at the compression side of the connection if its a moment connection. Haven't looked in to doing anything like this yet but I should be able to model it and check with hand calcs and a base plate program if necessary.

 

[kiskertlugas]

I'd be carefeul designing a base plate connection according to a FEM model.

Connections heavily depend on more complex material behaviours, and often backed by serious testing and experiments.

That's why those formulas are implemented in the codes. I'd rely on the codified methods.

 

[dik]

Unless considerable uplift, I would consider the load essentially in the areas of the columns, not the bolts. Else, the normal formulae for design of plates works well with the added conservative factor exhibited by thick plates, where the effect of in plane stresses are normally not considered. Avoid using gussets to extend the column... it's normally less expensive to use a thicker base plate.

Dik

 

[KingKongdoor]

If the connection in question fits a formula provided in codes I would of course use that over any results from a FEM. I was just curious how accurate a FEM was at calculating stresses for odd/weird connections discovered in the field. I have had a few jobs recently which involved determining possible ways to fix structural issues in industrial applications. Majority of issues were caused by existing framing and connections not being designed by an engineer. Just some guy welding stuff together and throwing lots of steel around. Completely replacing a structural system for existing equipment in a plant is typically not an option do the cost of down time.