Torsional rigidity of a plate 2

• Jan 18, 2021

• #2

rowingengineer

Structural

Jun 18, 2009

2,463

I would do the same calcs as for a beam. Treating the plates as beams.

 

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• Jan 18, 2021

• #3

jimstructures

Structural

May 6, 2009

389

BAGW,

This connection has the torsional rigidity of a limp spaghetti noodle, well past al dente. You must restrain the flanges from warping to restrain the I section from rotating torsionaly. This joint is even worse since the flanges are not even connected. A rectangular or pipe section would be a lot more effective.

Jim

 

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• Jan 18, 2021

• #4

skeletron

Structural

Jan 30, 2019

845

Jim for the win!

The goal with torsional rigidity is to try and make everything "close-celled" or tubes. Then the warping component basically nosedives out of the equation.

 

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• Jan 19, 2021

• #5

DaveAtkins

Structural

Apr 15, 2002

2,850

For a rectangle, J = b*t^3/3. So there is some torsional rigidity, but not much.

DaveAtkins

 

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• Jan 19, 2021

1
• #6

goutam_freelance

Mechanical

Jan 25, 2003

441

From Theory of elasticity-Timoshenko

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

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• Jan 19, 2021

• #7

WARose

Structural

Mar 17, 2011

5,593

To expand a bit further on Dave's equation, for multiple pieces in a cross section: J= ∑(bt[sup]3[/sup]/3)

where:

b=length of each cross-sectional element
t=thickness of each cross-sectional element

This formula is (of course) a approximation....but I have found it to be sufficient in most cases.

 

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• Jan 19, 2021

• #8

KootK

Structural

Oct 16, 2001

18,043

BAGW said:

I am trying to decipher the requirement in AISC for seismic connection.

Click to expand...

Which particular requirement in AISC 341-16? The bar is higher for some applications than others.

With regard to your torsional stiffness/flexibility here, there are a few considerations:

1) St. Venant Torsion in the plates per Dave and goutam.

2) Warping torsion in the plates.

3) Prying action in bolts and local flexibility of the beam webs of both the supporting and supported beams.

4) St. Venant Torsional in the supporting beam.

5) Warping Torsion in the supporting beam.

In a high seismic application without a diaphragm, I'd expect you to need discrete bracing of both flanges near the splice as well as a torsional robust splice connection. But, again, much depends on what AISC provision we're talking about.

 

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• Jan 21, 2021

• Thread starter
• #9

BAGW

Structural

Jul 15, 2015

388

@ KootK

I am referring to AISC 360-10. Thanks

 

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• Jan 21, 2021

• #10

KootK

Structural

Oct 16, 2001

18,043

BAGW said:

I am referring to AISC 360-10.

Click to expand...

Come now, I know that. I'm asking about the particular provision within AISC 360-10 that you're trying to satisfy.

 

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• Jan 21, 2021

• Thread starter
• #11

BAGW

Structural

Jul 15, 2015

388

Sorry, I was still editing the post. You were very quick to respond lol

I am looking at AISC 360-16 multitier torsional requirement at the beam column connection for braced frame.

Say beam stub will be CJP welded to the column and the stub will be attached to the strut with the connection above. And this connection must have the torsional rigidity per AISC

So was trying to calculate the thickness reqd to meet the rigidity requirement per Appendix 6 torsional bracing requirement

 

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• Jan 21, 2021

• #12

KootK

Structural

Oct 16, 2001

18,043

No sweat. Are you sure that you don't mean this requirement from 341-16 rather than 360-10? If so, the connection demand is not meant to be torsional but, rather, weak axis flexure. And that probably means flange plates.

 

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• Jan 21, 2021

• Thread starter
• #13

BAGW

Structural

Jul 15, 2015

388

Yeah I was talking about this requirement. I correct the typo to AISC 3610-16 above.

So with the web plates, it is nearly impossible to achieve this correct.

Which is used to check the stiffness? Appendix 6 column bracing per AISC 360-10?

 

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• Jan 21, 2021

1
• #14

KootK

Structural

Oct 16, 2001

18,043

BAGW said:

So with the web plates, it is nearly impossible to achieve this correct.

Click to expand...

I would say so. I can think of one possible mechanism, shown below, but it relies on there not being a gap between the beams.

Are flange plates not viable?

Are beam end plates, with shims if necessary, not viable?

Is there nothing else in the vicinity of the column that could brace it torsinally? A beam on the other side of the frame? A perpendicular beam?

BAGW said:

Which is used to check the stiffness? Appendix 6 column bracing per AISC 360-10?

Click to expand...

Appendix six doesn't cover column torsional bracing directly. Instead, they refer you to the article shown below.

 

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• Jan 23, 2021

• Thread starter
• #15

BAGW

Structural

Jul 15, 2015

388

Very informative. Thanks

 

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