How to Calculate Deflection of an I-Beam

Written by charlie higgins
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An I-beam is a type of beam commonly used in the construction of steel buildings and structures. Its cross-section forms the shape of an I, hence its name. The deflection of an I-beam is defined as how much it bends when a load is applied to it, measured from its original position to the lowest point. You can calculate the deflection of an I-beam using relatively simple equations.

Skill level:


  1. 1

    Gather the following information about your I-beam and its load:

    Q--Uniform Load (N/mm) F--Point Load (N) L--Length of Beam (mm) I--Moment of Inertia (mm4) E--Modulus of Elasticity (N/mm2)) Y--Perpendicular distance from neutral axis (mm)

    The latter three values are inherent properties of the I-beam which vary depending on its size. Find the corresponding values of your I-beam in the table listed in the resources section.

  2. 2

    Substitute your values into one of the following equations. If your beam has a distributed load, use ? = (5 q L4) / (E I 384). If your beam has a point load, use ? = (F L3 )/( E I 48), where ? is the amount of deflection.

  3. 3

    Solve the appropriate equation using your values. The final figure is the maximum deflection of your I-beam.

Tips and warnings

  • Head to for a quick online calculator. Simply enter your values and hit the “Calculate” button.

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