Calculate reactions, shear, bending moment, stress, and maximum deflection for four basic load cases.
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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.
Load cases
Supports, load and deflection
Four basic cases show how support and loading determine deflection. θmax is intentionally omitted.
Simply supported · point load
Simply supported · distributed load
Cantilever · end load (free end)
Cantilever · distributed load
Original schematic illustration · not to scalePurpose
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.
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