Statics and strength

Beam Deflection Calculator for Four Load Cases

Calculate reactions, shear, bending moment, stress, and maximum deflection for four basic load cases.

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Beam model

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Results

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Set the inputs and run the calculation.

Inputs and method

Beam deflection using Euler-Bernoulli theory

Calculate reactions, moment, stress and deflection for basic beam load cases.

Inputs

Length, load and position, Young's modulus E, second moment I and section modulus W describe beam and load.

E describes material stiffness, I section distribution and L load leverage. Deflection therefore grows strongly with L and falls strongly with I; adequate strength alone does not guarantee stiffness.

Calculation

Euler-Bernoulli EI·w″ = M(x) links moment to curvature; boundary conditions determine deflection.

Example

Doubling I approximately halves deflection for the same load case.

Sources and limits: Classical small-deflection, linear-elastic beam theory; shear deformation and self-weight are excluded.

Technical article

Beam deflection using Euler-Bernoulli theory in detail

Calculate reactions, moment, stress and deflection for basic beam load cases.

What does this quantity describe?

Mechanical calculators translate geometry and load into a response such as torque, stress, deflection, spring force or bearing life. The position of the load relative to the effective axis is often decisive.

Formula and variables

Euler-Bernoulli EI·w″ = M(x) links moment to curvature; boundary conditions determine deflection.

Choose the inputs correctly

Length, load and position, Young's modulus E, second moment I and section modulus W describe beam and load. E describes material stiffness, I section distribution and L load leverage. Deflection therefore grows strongly with L and falls strongly with I; adequate strength alone does not guarantee stiffness.

How to use the calculator

Select the load case and support type (e.g. a point load on a simply supported beam), then enter length, load and load position plus Young's modulus E and second moment of area I. The calculator returns reactions, moment, stress and deflection.

Worked example

Doubling I approximately halves deflection for the same load case.

Understand the result and units

E describes material stiffness, I section distribution and L load leverage. Deflection therefore grows strongly with L and falls strongly with I; adequate strength alone does not guarantee stiffness. The result shows the idealized component response for the selected load case. A small change in diameter, height, length or load can have a large effect because of power laws.

Length in millimetres or metres, load in N or kN, E in MPa or GPa, I in mm⁴, deflection in millimetres.

Typical applications

Estimating whether a beam or girder stays within an allowable deflection limit under a known load, or comparing different sections or supports for stiffness.

Assumptions, limits and common mistakes

Classical small-deflection, linear-elastic beam theory; shear deformation and self-weight are excluded.

Common mistake: Don't swap load case and actual support conditions arbitrarily – a fixed beam deflects noticeably less than a simply supported one under the same load and length, since curvature boundary conditions differ fundamentally. This model assumes small deflections; for very slender parts or large deflections the linear approximation becomes inaccurate.

Frequently asked questions

Why does a fixed support reduce deflection so much?

A fixed support additionally prevents rotation at the support, making the beam curve less over a larger portion of its length than with a pinned support.

What happens if I double the second moment of area?

Deflection falls to roughly half, since it is inversely proportional to I; stress and reactions are unaffected by this change.

Are shear deformation and self-weight included?

No, the model uses classical Euler-Bernoulli theory without shear deformation; for very short, thick beams or where self-weight matters, this must be added separately.

Sources, method and review

  • Classical small-deflection, linear-elastic beam theory; shear deformation and self-weight are excluded.

Our method, source hierarchy and automated checks are documented on the methodology page. Read the methodology

Responsible
NormCalc-Redaktion
Last updated
2026-09-04
Load cases

Supports, load and deflection

Four basic cases show how support and loading determine deflection. θmax is intentionally omitted.

Simply supported · point load

FLyₘₐₓ

Simply supported · distributed load

wLyₘₐₓ

Cantilever · end load (free end)

FLyₘₐₓ

Cantilever · distributed load

wLyₘₐₓ
Original schematic illustration · not to scale
Purpose

What the calculator is for

Length, load, elastic modulus, I, and W describe a prismatic beam. Typical applications include early stiffness estimates for beams, brackets, and machine frames.

Limits

What still needs checking

Euler-Bernoulli theory assumes small deformation, linear-elastic material, and a slender beam. Shear deformation, self-weight, and stability failure are excluded.