Torsion in wide flange

[wilberz]

Is the Ix or Iy axis in the moment of inertia or/and the Wx or Wy axis in the section modulus of the wide flange has more to do with torsion resistance? Which, Ix, Iy, Wx, Wy is more related to torsion resistance?

See the animation of the torsion in:

https://en.wikipedia.org/wiki/I-beam

Most wide flange have large Ix, Wx and small Iy, Wy values.. should you get one with higher value of Iy, Wy to get more torsion resistance? Higher Iy, Wy also also happened to be a preference to use as column because of higher biaxial resistance. Is this also true for torsion?

I think this is related to warping constant. In short. Warping constant is more to do with Ix, Iy, Wx, or Wy?

 

[KootK]

Iy/Wy. Wide flange torsional response is largely the story of the flanges flexing laterally in opposite directions.

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.

 

[wilberz]

Iy/Wy. Wide flange torsional response is largely the story of the flanges flexing laterally in opposite directions.

For secondary wide flange that frames into the primary wide flange at one side only.. it sure can introduce torsion.. is it not.. so I guess the preference for larger values of Iy/Wy looked for in steel column design is also good for beam torsion resistance. Do you handle torsion by looking for higher values of Iy/Wy which can become expensive or put plates on the flange sides?

 

[BAretired]

A secondary beam framing into a primary wide flange is not considered to impart torsion unless it is framing in eccentrically. The end of the secondary beam rotates slightly as it deflects and that may impart a slight torsional moment to the primary beam but it is not necessary to consider that in design.

BA

 

[wilberz]

A secondary beam framing into a primary wide flange is not considered to impart torsion unless it is framing in eccentrically. The end of the secondary beam rotates slightly as it deflects and that may impart a slight torsional moment to the primary beam but it is not necessary to consider that in design.

I said framing at one side only. This is the same as framing in eccentricity.. because the primary wide flange would twist to the right slightly if there is only one secondary beam framing at the right side with no beam on the left. This is called eccentrically.. is it not.. what else do you mean by framing in eccentrically then?

 

[BAretired]

If the secondary beam is deemed to be hinged some distance away from the web of the primary beam, it imparts a torsion which must be considered in design. If it connects directly to the web using an end plate or angle such that the secondary beam limits rotation of the primary beam, it need not be considered.

What does your connection look like? Show us a detail.

BA

 

[wilberz]

If the secondary beam is deemed to be hinged some distance away from the web of the primary beam, it imparts a torsion which must be considered in design. If it connects directly to the web using an end plate or angle such that the secondary beam limits rotation of the primary beam, it need not be considered.

What does your connection look like? Show us a detail.

Actually the "secondary beams" are just C-purlins welded 23.5" on top of the primary wide flange which functions as rafter of a gable joined at the middle with center ridge.. and the roofing used will be light sheeting.. but when the wind bears down on the roof sheet such as during hurricane.. the purlin can vibrate and won't this introduce torsion to the primary wide flange?

 

[BAretired]

Don't know. Can't quite picture what it looks like.

BA

 

[hokie66]

wilberz,

You need to distinguish between compatibility torsion and equilibrium or stability torsion. It is common practice to ignore compatibility torsion, but you must design for equilibrium torsion.