Moment of Resistance
The bending moment a section can safely resist at its design limit state
The moment of resistance (MR) is the maximum bending moment a structural cross-section can carry, computed from the internal stress couple of the section's materials at the design limit state. For an RCC beam by limit-state design (IS 456 Cl. 38 and Annex G), it is the couple between the compression in the concrete stress block (0.36 fck b xu) and the tension in the steel (0.87 fy Ast), with the lever arm between them; design requires MR ≥ the factored applied moment Mu.
The balanced (limiting) moment of resistance corresponds to the maximum neutral-axis depth (xu,max) at which concrete crushing and steel yielding are simultaneous — below it the section is under-reinforced and ductile (the desirable design), above it over-reinforced and brittle (avoided). For structural steel (IS 800), the moment capacity is the plastic/elastic section modulus times the design strength, reduced for member buckling. MR is the single most-used quantity in flexural member design — sizing depth, steel area and grade all flow from making MR meet Mu with the right (ductile) failure mode.
- Flexural design of RCC beams + slabs (IS 456)
- Steel beam moment-capacity design (IS 800)
- Sizing section depth + reinforcement area
- Ensuring ductile (under-reinforced) behaviour
- Capacity assessment + retrofit of existing members