Structural Engineering
Beam Deflection & Stress
Calculate maximum deflection, bending stress and reaction forces for common beam loading configurations.
Units:
Maximum deflection L/300 is a common serviceability limit for machine frames. Structural beams: L/250. Precision equipment: L/500–L/1000. Check both strength (stress < allowable) AND stiffness (deflection < limit) — they often give different required sizes.
Simply supported, central load: δ_max = F×L³/(48×E×I) | σ_max = M_max × c / I
Input
Loading configuration iSelect the beam support and loading configuration.
Applied load F (or total w×L for UDL) iPoint load in kN, or total distributed load (w × L) in kN for UDL cases.
kN
Beam span L iClear span length of the beam in metres.
m
Elastic modulus E iYoung's modulus of the material. Steel: 210 GPa, Aluminium: 70 GPa, Cast iron: 100–170 GPa.
GPa
Second moment of area I iSecond moment of area of the cross-section in cm⁴. HEA 100: 349, IPE 120: 318, RHS 100×60×4: 171 cm⁴.
cm⁴
Distance to neutral axis c iDistance from neutral axis to extreme fibre in mm. For symmetric sections: c = h/2.
mm
Result
Maximum deflection δ_max [mm]
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Deflection ratio L/δ
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Maximum bending moment M_max [kN·m]
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Maximum bending stress σ_max [MPa]
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Deflection assessment
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