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I'm removing a load bearing wall and the structural engineer recommended a W8x15 steel I-beam. It would save me a lot of effort if I could use a 6" beam instead. So I'm trying to calculate the deflection of the W8x15 beam and then find a W6x?? beam with similar deflection.

I've found the specs for various wide flange beams here, but I can't find a max deflection equation that uses the elastic section modulus provided in the specs.

So, can someone point me in the right direction?

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    Not an engineer, but if I read that chart correctly a W6-25 should be equally or more robust. You should talk to your engineer. – UnhandledExcepSean Jun 13 at 14:49
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    I suppose there was a reason you hired, and presumably paid, and engineer for his recommendation. Generally an engineer will specify the minimal-sized components to support the loads. So you now want to save money by using something smaller than what the engineer specified. That doesn't sound wise to me. Why don't you go back to your engineer and see if a W6 could be used instead of a W8? – jwh20 Jun 13 at 14:50
  • Not sure what you are doing .Or how far a span you want open. Could you live with one center post. Or not a option . And if you go to the W-6 , do you loose ,head room. They do have a blind header. were the beam goes post to post. And the framing hangs on that,giving you a flush ceiling look and you do not see beam. Works on 2nd floor. with of beam goes into attic. – user101687 Jun 13 at 15:14
  • What is the span? – Lee Sam Jun 13 at 15:26
  • The span is 16 feet. The reasons as to why I would prefer 6" over 8" gets complicated, but cost is not the reason. – Joe Mac Jun 13 at 15:33
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I think I figured it out. I was thrown off by the Elastic Section Modulus.

Anyway, the deflection is calculated using the following parameters:

W = load

L = length

E = Young's Modulus

I = moment of inertia

And the equation for max deflection is:

a

I'm trying to find a beam with the same maxdef or smaller. I can ignore W and L because they are the same regardless of I-beam. Young's Modulus E is a property of the steel used, so it is also the same regardless of I-beam and can be ignored (this is what I misunderstood). This means, the only variable I have to worry about is I. I can see in the equation that I is part of the denominator, so if I increases, deflection decreases. So I just need a W6 beam with a larger I than what the W8x15 beam has.

Final answer: The only W6 beam with a greater I than the W8x15 beam is the W6x25,

  • So this was a homework question? O_o – noybman Jun 14 at 2:44
  • No, the beam arrives on Thursday. – Joe Mac Jun 17 at 13:36

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