Single Equal Leg Angle in Bending 1

[BendingMoment123]

Hi guys

I have an equal angle cantilever as shown in the diagram. It is subjected to a lateral (Vu) and compression force (Pu). I'm using the AISC design code for bending calculations. Will my applied moment (Mu) due to the lateral force be about the major principal axis, minor principal axis or use that moment for both axes? Would I have to resolve that applied moment about each principal axes and how would I do that? Thanks

 

[Guest090822]

In the absence of restraint at top, I would look at the z-axis.

 

[Josha456]

Based on the way its drawn, you will have moment in one of the geometric axes (the ones parallel with the flanges), the minor and major axes are the principal axes and will be at 45° to the geometric ones in an equal angle triangle. You can resolve the principal bending moments with simple trigonometry (cos(45)).

I am not familiar with AISC, but most codes will have you resolve the forces into the principal axes, imagine bending about one geometric axis: the asymmetry will induce bending in the other axis due to the imbalance of stresses and create additional stresses not accounted for, converting to the principal axes will allow for this and you will get accurate stresses. Also in an otherwise unrestrained length, buckling will occur about the minor axis due to moment about the major axis, which will require you to determine the principal moments.

I would also advise caution regarding the possible eccentric moment about both geometric axes due to the compression force, unless AISC allows for this to be ignored (I am not familiar with AISC).

 

[rb1957]

I would do bending about the principal axes. Is Pu on the centroid ?

Your lateral load is in the direction that it "wants" to be. Sure, you could apply it conservatively, to cause bending about the weak axis; and if that's too conservative then apply in the correct direction.

another day in paradise, or is paradise one day closer ?

 

[BendingMoment123]

Thanks for the replies everyone.

@rb1957 Actually part of the axial load will be running through the centroid and the other part will be acting just outside the leg (if you look at the diagram, it's the leg coming out of the screen towards us).

 

[BAretired]

The P-delta effect about the minor principle axis would be critical and would need to be checked.

BA