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Design Procedure for Increasing the Strength of a Standard Steel I-beam

written by: Suvo • edited by: Lamar Stonecypher • updated: 1/24/2010

This article will discuss a method of I-beam design by which you can modify a standard size steel I-beam so that the I beam strength will increase with minimal extra cost.

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    Steel I-beams are available in different standard sizes. You normally don’t modify its form or shape before using; you just select the correct size steel I-beam and use it for your structure.

    But, in this article we will discuss a beam design method for increasing I-beam strength by modifying its shape or form.

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    A Bit of Basics

    If you cut steel I-beam and see its cross section it will look somewhat like below:

    Typical I beam Cross Section 

    The overall nomenclature of the beam is also shown in the above picture.

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    Steps for Modifying the Beam

    1. Cut the web area of the beam in a zigzag way through out its length, like shown in the picture below:

    I Beam Side View 

    The above picture is showing the side view of the I-beam and the red line indicating the line you have to cut (slit) the beam. So, you will get two pieces of the beam after cutting it.

    2. Now, you have to weld at the crests of the two pieces. After the welding is done it will look like below:

    I Beam Side View Welded 

    Please observe that the overall height of the beam is increased after you weld it.

    3. Cut the extra projected portions of both the halves of the beam and give it a good looking form like below:

    I Beam Side View Cut 

    4. The modified I-beam is ready for your structural use now.

    5. You might be wondering, how you will get additional strength from this modified beam, to answer your query let’s go to the basic beam deflection equation:

    f/(d/2)=M/ I………………….eqn.1

    Where,

    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.

    Now, as you have already observed that in the process of cutting and welding the I-beam, the overall height of the beam has been increased and, as the height of the beam increased, the area moment of inertia of the beam is also increased. Thus, from the eqn.1 you can draw the conclusion that the developed bending stress value (f) will decrease with increasing height of the beam, or in other words, the strength of the beam will increase.

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    Conclusion

    As already discussed,the standard steel I beam strength can be increased by the method discussed in this article, but cutting a I beam is not a normal practice and the modified I beam strength depends a lot on the workmanship related to the cutting and welding.So, it is heighly recommended that during the steel I beam design you perform all the related tests as well the FEA so that the I beam does not fail for your application.