Irregular Column N.A 1

Neither!

The NA rotates clockwise, see below:



You can download the section properties spreadsheet from:
For design, I'd suggest rotating the shape so the Neutral Axis is horizontal, then use a program for irregular cross section design.

Doug Jenkins
Interactive Design Services

SpColumn is a good program that you can use for irregular shapes. With that said the neutral axis is dependent on the direction of the applied load (i.e. one column can have multiple neutral axes if it has load applied in multiple directions). If you know the applied load’s direction it should be simple mechanics of materials problem to determine the location.

OK,ignore my previous post.

If you apply a moment about the YY axis in your diagram, the resulting stresses must have zero moment about the perpendicular ZZ axis. The only way you will get that is if the neutral axis is parallel to lines AB and DC.

Doug Jenkins
Interactive Design Services

Thanks IDS

That makes sense.

Your neutral axis will be skewed somewhat and this will introduce biaxial bending (may not be significant) The Mx and My compoments will not likely align with the neutral axis... gets really confusing.

Dik

My biaxial moment spreadsheet will work for this problem, but it needed a bit of adjustment to deal with the case of zero transverse moment.

You can enter applied moments and click the "Adjust NA Angle" button to find the Neutral Axis angle and location. For zero transverse moment the angle is found to be exactly parallel to the top and bottom faces:



Or you can enter a neutral axis angle (for instance zero), then use Excel Goal-seek to adjust the MY value so that the Angle error is zero:




Link for spreadsheet download




Doug Jenkins
Interactive Design Services

IDS,

Thank you so much.