Custom Shape Axial Capacity

[jayrod12]

Hey All, (Likely Josh)

I've created a reinforced w-column using RisaSection, it calculated all the properties correctly (from what my quick hand check suggest). We are adding plates to the flanges to keep the shape symmetrical.

I've also successfully imported said section into R3D including all properties (J and Cw included). However, when checking the axial capacity it was in the range of 10x lower than my hand calcs suggest it should be. That is even with unbraced length set to zero.

So I then modelled just a very basic pinned column with a singular load, again unbraced length set to zero, and it returned a capacity 10x lower than expected.

Anyone ever come across this before? I've attached my test run.

In the end, this reinforcing is actually going to be applied to a pre-eng steel frame, however this axial capacity issue is causing the reinforced frame to be weaker than the original in the model. Which the hand calcs don't agree with.

 

[JoshPlumSE]

It's not possible for me to tell for sure. But, I'm going to guess that the issue is related to the thickness that RISASection is passing to RISA-3D for the flange or web.

RISASection is very good at calculating A, I, the plastic section properties and such. But, when it has to figure out what the thickness of a built up flange is, it can be difficult. We recognize this, though and give you (within RISASection) the ability to override these two values. See attached image.

My guess is that we interpreted the flange thickness as significantly too small. This would result in local buckling controlling the capacity of the member.

 

[JoshPlumSE]

Actually, I was wrong. The web is coming out slender, not the flange. So, it's likely the web thickness that needs to be set manually in RISASection.

 

[jayrod12]

Ah yes,

That appears to have solved it.

Thanks,