Monorail Weak Axis Bending

[JrStructuralEng]

This might sound like a silly question, but the reference manual i'm reading confused me.

When considering side thrust and weak axis bending on a monorail I understand that you consider only one flange to contribute to weak axis bending strength.

However, in this design example i am reading, the beam is unsupported along its entire length and it appears when they check combined bending (i.e. Mfx/Mrx + Mfy/Mry =< 1.0) they assume the compression flange is braced. Shouldn't the flange be considered unbraced (i.e calculated Mu and determine the reduced value of Mry?

 

[JrStructuralEng]

that first post should read

"you consider only THE flange"

 

[Stillerz]

what example are you reading?

 

[JrStructuralEng]

Crane Supporting Steel Structures - Design Guide 2nd Edition - R.A. MacCrimmon

 

[ishvaaag]

If they are welded as usual the built-up section must be checked for the effect of the proper set of combinations of independent loading sets.

 

[jike]

Have you included bottom flange bending due to the wheels riding on the lower flange? Then use Mohr's circle to combine stresses from this primary and secondary bending.

A monorail beam should be designed as laterally unsupported between supports unless there are other intermendiate lateral braces present.

Recognize that the hanging load from the bottom of the beam is a "righting" load that will have a tendency to pull the beam back vertical unlike a load on the top flange which will have a tendency to push the beam over.