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How to Select a Correctly Sized Steel I Beam

written by: Suvo • edited by: Lamar Stonecypher • updated: 8/23/2013

Selecting the correctly sizez steel I beam is very important for your structural design. Gain more understanding of the selection procedure for a steel I beam for given load specifications.

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    A steel I beam typically has the following important features or dimensions. (Please refer to the picture below):

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    I Beam 

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    I-Beam Terminology

    • Flange thickness: Top and bottom horizontal plate-like sections of an I-beam are called flangen. The thickness of the flanges is called the flange thickness.
    • Flange width: The width of the flanges is called flange width.
    • Beam depth: The height between the top and bottom surface of the steel I beam is called beam depth.
    • Web thickness: The vertical section of steel I beam is called web, and the thickness of the web is called web thickness.
    • Fillet radius: The curved portion, where the transition between the web and flange happens is called a fillet. The radius of the fillet is called the fillet radius.
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    Steps for Selecting a Correctly Sized I Beam

    The overall procedure of selecting the correct size of the I beam is based upon basic mechanical design calculations as follows:

    • The first input you need is the steel I beam load specifications or loading details on the steel I beam.
    • Draw bending moment diagram for the given loads and you will find the value of maximum bending moments (say M) that the steel I beam is expected to experience.
    • Find out the area moment of inertia (say I) of the selected steel I beam.
    • Get the beam depth (say d) of the selected steel I beam.
    • Now use the following formulae for calculating stress developed (f) in the beam:

    f/(d/2)=M/ I

    f is the bending stress

    M - the moment at the neutral axis

    y - the perpendicular distance to the neutral axis

    I - the area moment of inertia about the neutral axis x

    • Compare the calculated value of the bending stress with the yield stress of the steel in order to check the safety factor of your design.
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    Correctly sized I beam selection is the first step toward correct structural design. The procedure explained above is based upon static I beam load specifications. In the cases where dynamic loads are involved, you need to use FEA tools like ANSYS, Pro Mechanica, etc.

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    See also

    • How to design a valve spring: The valve springs are a critical component for any engine’s performance. This article will talk about how to design a valve spring.