Flexural Strength of WT section along it's minor Axis as per AISC 360 2

[ALPHA756]

Hello there,

I need to know how I should evaluate the strength of WT section along its weak axis. AISC 360 doesn't talk specifically about it.

Just to clarify you little bit about the problem, I am currently trying to design the WT vertical bracing member, and typical connection will be bolted connection with the flange of WT section.

So, the member is subjected to two kinds of factored moment,
1) Due to connection eccentricity (which will be act along the strong axis of WT section)
2) Self weight of the member itself (acted along the weak axis of the WT section)

Based on section F9, of chapter F, AISC 360 I am able to obtain the strength of WT section along its strong axis, but don't know how to evaluate its strength along it's minor axis.

If the above problem is consisting of WT horizontal bracing, it will be much simple. I can easily use the reference technical paper "Tables for Eccentrically Loaded WT Shapes in Compression" to evaluate the strength of WT section.

 

[phamENG]

I would conservatively approach it as a plate, ignoring the stem. The stem is at the neutral axis and has virtually no impact on the flexural strength. So in terms of pure flexure, the flange might as well just be a single plate. Stability gets a bit more complicated, but if it works as a plate for that, too, then I wouldn't worry about it.

 

[Lomarandil]

If the WT is connected through the flange (as you say), I would design the WT in weak axis as though the web didn't exist (e.g. as a plate)

edit: zing! sniped.

 

[phamENG]

edit: zing! sniped.

Got 'im!

 

[BridgeSmith]

My AISC steel manual has weak axis (Y-Y) section properties for WT sections. I wouldn't expect them to be significantly different from the 'flange as a plate' assumption, but why not just use the table value?

 

[ProgrammingPE]

If you compare the weak axis section properties of a WT to the properties of just its flange, Sy is at most only 2% greater when considering the entire WT.

For a WT18x462.5 (shape with largest difference in Sy):

Sy = 266 in³
Sy,flange = 1/6*tf*bf² = 1/6*(4.53 in)*(18.6 in)² = 262 in³​

The WT is also most likely going to be controlled by Lateral-Torsional Buckling. The Specification for Structural Steel Buildings, AISC 360, has a section that addresses this specifically for plates (Section F11.2), but you'd be on your own for figuring out how to do this for WT's in the weak axis direction (Section F12.2).

Structural Engineering Software:

http://www.structuralcentral.com

Structural Engineering Videos:

http://www.youtube.com/structuralcentral

 

[ALPHA756]

Thanks everyone for the input.

I conclude that I can assume the WT section as a plate (that is its flange element) by ignoring the contribution from the stem along its weak axis bending. And I can conservatively use section F11 of AISC 360.

 

[ALPHA756]

In addition to the above comment please go through commentary F9 of AISC 360-16, and read the paragraph near equation C-F9-3. That might be helpful as well.