Hi trungce,

Have you tried checking the other angles of the interaction diagram?

Based on the results you've sent, you may try looking to the interaction diagram at 36 deg.

The capacity curves/surface of reinforced concrete columns subjected to biaxial bending is formed by a series of interaction curves drawn radially from the P axis.

Maybe you are looking on a wrong curve and the governing curve is at 36 deg (for column 1).

Does the diagram take into account the phi factor. It looks like a pure capacity interaction diagram to me.

@ techiestruc

Thank you! I thought we only show the angle recommended by software :D

How did you find the 36 deg result? Assumed that I only use CsiCol without hand calculations. I want to check all load cases in the diagram.

Hi trungce,

I am not familiar with the interface of CsiCol but I assume that it will have same principle used by spColumn.

The interaction diagram for biaxial bending is in 3d wherein 2 orthogonal planes are composed of interaction diagram for X- and Y-axis of the column cross-section.

If there is biaxial bending in the column (which means there is Mx and My moment), then the point of this case is somewhere in between the orthogonal axes and given by Mx-My Angle (deg).

If you want to check the capacity for each case, then you must determine first the location of the point/load case as shown in Mx-My Angle (deg). Once the plane for this Mx-My Angle (deg) is shown, then you will have the corresponding 2d interaction diagram for your case which will then show the N/A angle and other info.

I hope this will answer your query.

@techiestruc

Thank you! :)