Torsional moment vs bending moment

[kitzlongg]

Homework Statement

Anyone here familiar with StaadPro? In the software, Moment about x axis was defined as torsional moment.. While moment about z and y axes are bending moment... Why is it ?

Relevant Equations

Not applicable

The direction of x, y and a axes were shown in the highlighted part..

I think it is wrong. For red circled beam, i kinda agree that Moment about x-axis was defined as torsional moment.. While moment about z and y axes are bending moment...

But for blue circled beam, I think that Moment about z axis was defined as torsional moment.. While moment about x and y axes are bending moment...

Please correct me if I am wrong.

 

[PhanthomJay]

I have not used Staadpro, but I suspect that it uses both a global coordinate system (highlighted by you) and a local coordinate system for individual members of the frame, in which system the local x-axis is always along the axial length of the member. Thus , Mx moments are always torsional, regardless of the members location specified in the global coordinate system.

 

[Dr.D]

In structural analysis, the terms "bending" and "torsional" usually refer to transverse and axial moments respectively. These are essentially local definitions.