×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Do Stiffeners resist torsion in W-Shape?

Do Stiffeners resist torsion in W-Shape?

Do Stiffeners resist torsion in W-Shape?

(OP)
Is adding transverse stiffeners to a wide flange beam a viable option to resiste torsion?  We have had this discussion in every company I worked for, whether adding stiffeners at so often along the length of the member will increase the torsional properties of the beam.  If this is the case, can you point me to a reference on how to size and space the stiffeners.  I have already looked at Design Guide 9.

RE: Do Stiffeners resist torsion in W-Shape?

Stiffeners cannot resist significant torsion.  The beam must either be designed for the torsion, or diagonal braces from the bottom flange up to the deck must be added.

If there is a deck welded to the top flange of the beam, a small amount of torsion could be taken out of the beam by the deck--in this case, the stiffeners will help.

DaveAtkins

RE: Do Stiffeners resist torsion in W-Shape?

Stiffners do nothing for torsion as DaveAtkins states.  Adding side plates to WF beams to create a tube-type section will add significantly to torsional strength and stiffness.  But vertical web stiffners don't help.

RE: Do Stiffeners resist torsion in W-Shape?

In certain circumstances, adding stiffeners can be used to brace the compression flange of a plate girder.  This is covered in the SSRC Guide to Stability Design Criteria for Metal Structures",  under "Plate Girder With Elastically Braced Compression Flange."  This is not the same as adding torsional stiffness to a beam, but it's close.  

RE: Do Stiffeners resist torsion in W-Shape?

Bracing the compression flange with stiffeners is not torsional bracing.  Compression flange bracing is required in many situations but these stiffeners do not satisfy torsion stiffness requirements.  Good Luck.

RE: Do Stiffeners resist torsion in W-Shape?

The only thing the stiffeners might do is help reduce the warping of the wide flange section, but I know of no way to quantify this, and there is certainly nothing in any code that I know of.  Aside from that, I agree with the above that the stiffeners described do not appreciably help torsion resistance.

RE: Do Stiffeners resist torsion in W-Shape?

What jmiec may be suggesting is using the stiffners as a sort of cantilever arm that extends out to the compression flange.  This works as long as there is a sort of moment connection between the end of the stiffner and some outside bracing element.

An example:  You have a sky walk that is comprised of two 36" deep wide flanges spaced, say, 8 feet apart.  The deck of the skywalk is a steel channel, metal deck, concrete slab assembly with the channels spanning from bottom chord of WF to bottom chord....i.e. the deck is set down low and the WF beam compression flanges are about 3 feet above the deck....with no lateral bracing.

You can use vertical web stiffners, rigidly attached to the cross channels such that you have an effective, rigid, "U" shape comprised of vertical stiffner, horizontal channel, and then vertical stiffner.

Thus, the stiffners can laterally resist the lateral buckling of the top flanges because of their rigid connection to the deck channels.

RE: Do Stiffeners resist torsion in W-Shape?

If you treat the torsionally loaded wide-flange as two parallel rectangular sections (the flanges), each loaded laterally (torsion/h), and then analyze each rectangle as a member in flexure, you can use the stiffeners for "lateral" bracing.  In this way, the stiffeners do help with torsional resistance, though indirectly.

RE: Do Stiffeners resist torsion in W-Shape?

I believe this compression flange bracing concept was used extensively in railway bridges.  Some engineers may think of this as adding torsional stiffness to an I beam.  I brought it up to answer twinnell's original question.

RE: Do Stiffeners resist torsion in W-Shape?

Adding stiffeners like that helps with lateral-torsional buckling, not resistance to an externally applied twisting moment.  They aren't the same thing.

RE: Do Stiffeners resist torsion in W-Shape?

It may decrease the warping but I don't think stiffeners are an economical option to take out torsion, and you are not even taking it out.  And I have no idea how to figure out how much of a decrease there may be.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources