OWSJ KL/r

[olivei34]

I am designing some 18" OWSJ, for the KL/r the steel handbook says r is the radius of gyration. I have tried using it for round bar and my web comes out extremely big, but if using the actual radius of the bar the web of these joist come out reasonably sized.

I am wondering which one is the correct one or if both ways are possible. Can anyone help?

Thank You

 

[dgkhan]

no way you should use actuall r. You have to use r= SQRT I/A. there is some short cut like .3d. cnfirm it.
Check if units are compatible.

 

[SteelPE]

Why are you trying to design an OWSJ? Are you trying to back check a design provided by a manufacturer?

 

[olivei34]

Checking the design of a fellow engineer. So then by using this radius of gyration to find lamda, I inserted it into the Cr = 0.9AFy(1+?^(2n))^(-1/n)
to find the compressive resistance of the web member in compression. I think this is the right procedure, Please correct me if I am wrong. If right I will have to chech my math again.

Thank You.

 

[SteelPE]

I assume OWSJ means Open Web Steel Joists…. And that you are from the US.

Maybe I don’t know what the procedure is, but when I have to verify the numbers coming from a manufacturer I refer to my Vulcraft Catalog:

http://www.vulcraft.com/downlds/catalogs/joistcat.pdf

Check page 11 to 15 for the SJI design requirements for K series joists.

Hopefully this will help.

 

[Geometrico]

Careful! As dgkhan states, you must use the radius of gyration, not the radius of the bar! Also, your formula for the "compressive resistance" doesn't seem right. You need to check again more than your math.

 

[BAretired]

The formula Cr = 0.9AFy(1+?^(2n))^(-1/n) is correct for doubly symmetric shapes according to the Canadian code. For hollow sections, n = 1.34.

Perhaps the easiest would be to post your calculation for a typical web member. It is not difficult to check.

BA