Torsional moment vs bending moment

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SUMMARY

The discussion centers on the definitions of torsional and bending moments in structural analysis, specifically in relation to a beam's axes. The participant clarifies that for the red circled beam, the moment about the x-axis is a torsional moment, while moments about the y and z axes are bending moments. Conversely, for the blue circled beam, the moment about the z-axis is considered torsional, with x and y axes moments being bending. The use of Staadpro is mentioned, indicating that it employs both global and local coordinate systems, where local definitions of moments are crucial for accurate analysis.

PREREQUISITES
  • Understanding of structural analysis concepts
  • Familiarity with Staadpro software
  • Knowledge of global and local coordinate systems in engineering
  • Basic principles of torsional and bending moments
NEXT STEPS
  • Research the definitions and applications of torsional and bending moments in structural engineering
  • Explore the functionalities of Staadpro for analyzing structural frames
  • Study the differences between global and local coordinate systems in engineering analysis
  • Learn about the implications of moment definitions on structural design and safety
USEFUL FOR

Structural engineers, civil engineering students, and professionals involved in the analysis and design of structural frameworks will benefit from this discussion.

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

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