Internal actions in beams: The couple developed within a beam section by longitudinal compression at the top and tension at the bottom is called what?

Introduction / Context:
When a beam bends, external loads create an external bending moment. Internally, the compressive and tensile resultants form an opposing couple that resists the applied moment. Knowing the correct terminology is vital for analysis and design communication.

Given Data / Assumptions:

• Beam under bending in the elastic range.
• Linear strain distribution and a neutral axis within the cross section.

Concept / Approach:
The external bending moment must be balanced by an internal resisting couple. The internal couple that the section can develop based on its stress distribution and section modulus is called the moment of resistance. The term “bending moment” refers to the external action, not the internal resistance.

Step-by-Step Solution:
External loads → external bending moment on a section.Internal stresses (compression and tension) form a couple.This internal couple is the moment of resistance which equals the applied bending moment at equilibrium.

Verification / Alternative check:
In elastic analysis, M = σ * Z, where σ is the extreme fiber stress and Z is section modulus; this expression is precisely the section’s moment of resistance.

Why Other Options Are Wrong:

• “Bending moment” denotes the external action, not the internal resistance.
• “Flexural stress moment” is non-standard terminology.
• “None of these” is incorrect because a standard term exists.

Common Pitfalls:

• Using external and internal moment terms interchangeably.

Final Answer:
moment of resistance