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Simply Supported Beam — Concentrated Moment at Position a

Use this free calculator to analyze a simply supported beam with a concentrated (point) moment M applied at distance a from the left support along a span L. It returns support reactions, shear force, bending moment, slope, deflection, and bending stress, and plots the distributions.

Simply supported beam of length L with a concentrated moment M at distance a from the left support; reactions R1 and R2 indicated.
Diagram of a simply supported beam with a concentrated moment M applied at distance a from the left support.

Global units

Choose base units for all inputs and results. Change Force/Length first; other unit groups follow automatically.

Input parameters

Unit: lbf·in
Unit: ft
Unit: ft
Unit: ft
Unit: ksi
Unit for c:
Unit: in⁴
  • Use dot “.” as decimal separator.
  • Constraints: 0 ≤ a ≤ L and 0 ≤ x ≤ L.
  • Sign convention: shear/deflection positive upward; moments positive when compressing top fibers (sagging).

Need I? Try Sectional Properties Calculators.

Results

ParameterValue
Reaction Force R₁ --- lbf
Reaction Force R₂ --- lbf
Shear @ x (Vₓ) --- lbf
Max Shear (Vmax) --- lbf
Moment @ x (Mₓ) --- lbf·in
Max Moment (Mmax) --- lbf·in
Slope @ x (θₓ) --- radian
Max Slope (θmax) --- radian
End Slope Left (θ₁) --- radian
End Slope Right (θ₂) --- radian
Deflection @ x (yₓ) --- inch
Max Deflection (|y|max) --- inch
Bending Stress @ x (σₓ) --- psi
Max Bending Stress (σmax) --- psi

Charts

Moment, shear, slope, and deflection plots update after calculation.

About this load case

For a simply supported beam with a concentrated moment M at position a on span L, the support reactions are R₁ = −M/L and R₂ = +M/L. Using Macaulay brackets ⟨·⟩, the field equations are:

  • V(x) = R₁
  • M(x) = R₁ x + M ⟨x − a⟩⁰
  • θ(x) = θ₁ + R₁ x²/(2 E I) + M ⟨x − a⟩¹ /(E I)
  • y(x) = θ₁ x + R₁ x³/(6 E I) + M ⟨x − a⟩² /(2 E I)

End slopes:

  • θ₁ = −M(2L² − 6aL + 3a²)/(6 E I L)
  • θ₂ = +M(L² − 3a²)/(6 E I L)

Sign convention: shear and deflection are positive upward; bending moments are positive when the top fibers are in compression.

Related calculators

References

  • Young & Budynas — Roark’s Formulas for Stress and Strain, Ch. 8.
  • Oberg et al. — Machinery’s Handbook, 30th ed.
  • Beer & Johnston — Mechanics of Materials, classic SSB solutions.