Torsional constant for I beam with base plate
Torsional constant for I beam with base plate
(OP)
Hi,
How to estimate torsional constant for a I section with a base plate at the bottom flange?
Can I simply add the torsional constant of the plate tb^3/3 to the torsional constant of the I section?
Or DO I need to consider the thickness of bottom flange = thickness of bottom flange of I section + Thickness of base plate and then recalculate the torsional constant of I section? - Since It is assumed that the plate and the I section acts together.
Any comments on the above is highly appreciated.
Thanks
Mukund
How to estimate torsional constant for a I section with a base plate at the bottom flange?
Can I simply add the torsional constant of the plate tb^3/3 to the torsional constant of the I section?
Or DO I need to consider the thickness of bottom flange = thickness of bottom flange of I section + Thickness of base plate and then recalculate the torsional constant of I section? - Since It is assumed that the plate and the I section acts together.
Any comments on the above is highly appreciated.
Thanks
Mukund






RE: Torsional constant for I beam with base plate
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.
RE: Torsional constant for I beam with base plate
Certainly for a riveted or bolted connection, I would be surprised to find the elements truly "acting together" for torsion.
Also, some codes (AASHTO) specifically want J to be computed as the sum of elements -- presumably because of the proportions of typical bridge cross-sections.
RE: Torsional constant for I beam with base plate
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.
RE: Torsional constant for I beam with base plate
The estimated "J" calculated by considering as an single elements is approx. 2.5 times greater than the value of "J" calculated as individual elements.
I don't want to be too conservative. So, would it be reasonable to consider them as single element if I have sufficient weld resistance?
Thanks again.
Mugundan.
RE: Torsional constant for I beam with base plate
If the bottom flange and plate are very thick, and the weld demand is low other than torsion (I'm imagining 1" flange and plate thicknesses, but you would prefer to use a single pass weld), I'd consider using the greater value of the individual elements or a representative single element with a total thickness =2*weld throat.
RE: Torsional constant for I beam with base plate
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.
RE: Torsional constant for I beam with base plate
Please find calculations in the attachmentLink. Although the difference in buckling resistance is small, there is a considerable difference in the effects because of the value of "Torsional constant". Since the Effects are high, the section fails if I treat it as individual plates and this was the reason I posted this question.
Thanks
Mugundan.