Strengths question
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Posted by: stud_wood25

02/21/2006, 17:55:11

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I was told that you can drill holes in the webbing of I-beams and it will not affect the strength of the beam and that the only purpose of the webbing is to hold the top and bottom of the beam together. Is this true?







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Re: Strengths question
Re: Strengths question -- stud_wood25 Post Reply Top of thread Forum
Posted by: ChrisMEngr

02/21/2006, 18:36:47

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For the most part what you say is true.

Any time you remove material from a structure you are going to weaken it. But in some cases, like the I-Beam, if you remove a little material from the middle of the flange, you wont loose much strength.

It has to do with the structural shape's section modulus.








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Re: Strengths question
Re: Re: Strengths question -- ChrisMEngr Post Reply Top of thread Forum
Posted by: swearingen

02/22/2006, 14:16:36

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The actual answer is: it depends. I'll give a few cases -

1. Horizontal beam, distributed load on top, hole in center of web at center of span = doesn't affect capacity much - no vertical shear in web here.
2. Horiz. beam, dist. load, hole in center of web near one end = could be a problem - web is distributing shear.
3. Horiz. beam, dist. load, hole in bottom flange at center of span = could be a problem - flanges taking full moment here.
4. Horiz. beam, dist. load, hole in bottom flange near one end = doesn't affect capacity much - flanges don't have much load here.
5. Column, tension load, hole anywhere = could be a problem - the hole reduces the amount of tension capacity almost proportionately.

The point is, it depends on your loading, the location of the hole, the size of the hole, the relative strength of the member to the load applied, and others. However, in general, if you have a beam with a distributed load on top that isn't loading the beam to its maximum, you can cut a small, round hole in the web at center span and not have any appreciable reduction in the beam's strength.








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