Torsional Resistance (Blodgett)
Torsional Resistance (Blodgett)
(OP)
I just recently bought "Design of Weldments" and "Design of Welded Structures" by Omer Blodgett and I noticed in his chapters on Torsional Loading he talks about using "Torsional Resistance" rather than polar moment of inertia to calculate torsional stress and deflection. (Chapter 3.6 in "Weldments" or Chapter 2.10 in "Welded Structures")
This is great information but I'm quite surprised as to how much of a discrepancy there is in beams and channels between polar moment of inertia and torsional resistance. If Mr. Blodgett is right (I would imagine he is), then polar moment of inertia J = Ix + Iy is completely irrelevant for beams and channels.
I'm just somewhat shocked that I've never heard of the "Torsional Resistance" method in Blodgett.
I also find it odd that it's presented as an alternate method, when in actual fact when it comes to open members like beams and channels they are totally night and day.
Can anyone shed some light on this?
This is great information but I'm quite surprised as to how much of a discrepancy there is in beams and channels between polar moment of inertia and torsional resistance. If Mr. Blodgett is right (I would imagine he is), then polar moment of inertia J = Ix + Iy is completely irrelevant for beams and channels.
I'm just somewhat shocked that I've never heard of the "Torsional Resistance" method in Blodgett.
I also find it odd that it's presented as an alternate method, when in actual fact when it comes to open members like beams and channels they are totally night and day.
Can anyone shed some light on this?
RE: Torsional Resistance (Blodgett)
So yes, for open sections, the "K" value becomes very important. (The "K" value being equivalent to Blodgett's "R" value.)
I personally haven't used Blodgett's method for torsional member design. I've typically used AISC's Design Guide 9. (Not that there is anything wrong with anything by Blodgett.....I just find DG 9 more straight forward.)
RE: Torsional Resistance (Blodgett)
RE: Torsional Resistance (Blodgett)
RE: Torsional Resistance (Blodgett)
Cheers
Greg Locock
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RE: Torsional Resistance (Blodgett)
RE: Torsional Resistance (Blodgett)