Calculate J and Cw for W Section 6

[dik]

Does anyone have formulas for calculating J and Cw, Torsional Constant and Warping Constant given b, h, t, and w? Also if someone has formulae for J and Cw for a W section with plates welded across the toe of the flanges? Thanks in advance.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[canwesteng]

I think torsionally it will behave like a closed section, as the J portion is going to be much stiffer than the Cw portion, and the web contributes next to nothing for the J portion. Would be interesting to see what FEA turns out.

 

[Agent666]

I think torsionally it will behave like a closed section, as the J portion is going to be much stiffer than the Cw portion, and the web contributes next to nothing for the J portion. Would be interesting to see what FEA turns out.

For the section I posted above:-

Ratio of "with web + PL outstands" vs "no web + PL outstands" properties

J ratio = 1.0031045738329498
I_w ratio = 1.022760776472564

So virtually no difference .....myth confirmed

central web and plate outstands shouldn't contribute significantly to J

Without plate outstands

Ratio of "with web + PL outstands" vs "no web & no PL outstands" properties

J ratio = 1.2202309914823597
I_w ratio = 1.287435089797051

So significant difference..... myth busted
EDIT - SEE UPDATE A FEW POST DOWN...

Iw is usually taken as zero for closed sections

Correct, but not because it is actually zero. I believe it's more about the fact that the influence of warping is simply much smaller as to be negligible for closed sections.

 

[Settingsun]

Thanks, Agent. What are the values for the last case?

I'd have thought the contribution of outstands would be in proportion to the increase in section area at most, but it looks more than that. I wonder if there is real increase in accuracy considering pg 38 of El Darwish.

 

[dik]

Agent666, thanks for the extraordinary effort I was certain that the approximation using the HSS 6x6 was safe with the internal 'web' just being a little frosting. I'm really impressed with the github FEM... can you post a direct link to the program, and I'll download a copy and look into it... I'm not a big fan of FEM... used it 50 years back when I wrote my own 3D program and used it on gas bearings for turbines as well as failure of amalgam material in human teeth. Ran into a dentist, in the student union building, with a failure problem with failure at the junction of steel pins and amalgam. Found out the amalgam was like concrete... high compressive strength and low tensile strength... and I casually asked him if the problem could be a tensile fatigue failure of the amalgam... kept me busy for the next six months...

Maybe time to take another look at FEM. I found it a little unwieldly and often produced answers that were non intuitive unless you understood what you were doing. I figured the approx would be within 5% and on the safe side...

This and my earlier posting about plating columns are related to a current project with a W6 going up 18' and the client wanting to mount a 1T with 12' boom jib crane on it. Thanks so much for the effort.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[r13]

On the first case, I wonder what is the result if the web is placed horizontally connecting the long side plates.

 

[Settingsun]

Agent's last section is narrower than the others.

 

[Agent666]

Yeah you're right. Will review and post update.

 

[Agent666]

Rookie error fixed:-

new ratio as follows

Ratio of "with web + PL outstands" vs "no web & no PL outstands" properties

J ratio = 1.0036873338868806
I_w ratio = 1.1199319857735646

So again not much difference in J, but 10% difference in warping constant (but for design would be equal to zero so perhaps irrelevant).

So moral of the story, boiling it down to a single closed RHS is probably conservative by a small margin.



Dik, posted link earlier to it. But here it is again, just follow the install instructions.

 

[Settingsun]

Good stuff, Agent. I was almost ready to disavow FEA for section properties - couldn't reconcile such a big increase.

 

[dik]

I caught it earlier, but couldn't fine an *.exe file unless it has to be compiled... have to dust off my C++ compiler... haven't used it in a decade or two... You have been an incredible help... just confirming pretty much what I thought... even though you think your right... it's nice to know for sure... as far as the 10% difference in warping constant, it should be to the good real vs. pretend... and nothing to do with the price of wine in California...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[engineering_patrol]

This tool might be what you are looking for.

 

[dik]

thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[DrZoidberWoop]

I've spent the better part of 4 hours trying to get that FEA program up and running. I guess I'm not good enough at Python/computers to make it happen. Bummer. Wish there was a basic tutorial for us dummies.

 

[Agent666]

What version of python (I've yet to get it to work with 3.9, some issue with something numpy related)? You installed pip first right to be able to install?

Installed meshPy from its repository? I vaguely seem to remember the wheel linked to in install instructions only supported up to version 3.6 last time I checked. To get it working with 3.7 and 3.8 I had to install it direct from the source repository.

 

[Agent666]

You also have to have python on your PATH environment variables, that seems to cause a few hickups for new users. Search Google and you'll find some guides.

 

[dik]

3.9 was the one I just downloaded and installed... will back up a bit... thanks

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[DrZoidberWoop]

I cheated. Handed it over to the IT guy at work. He had it working in about 10 mins. Gonna ask him to document each step so a potato-brain like me can get it up and running. I wish I had learned more than Excel and VB net over the years. So much power in that damn computer box.

 

[rb1957]

don't be so hard on yourself ... even you "potato-brain" mixed your problem (sure, by asking someone to help you).

another day in paradise, or is paradise one day closer ?