needed, one number cruncher
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Posted by: Guido

12/20/2005, 16:02:56

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Would someone with some "hi-powered software" please help me generate a Moment of Inertia (I value) for a reinforced beam. My structural engineer dad passed away not long ago, and I really miss him at a time like this. Planning to reinforce the web of an S8x15 with 1/8" x 7" flats both sides and stagger weld 2" every 9"oc top/bottom both sides. So I ultimately look to generate a deflection number I can live with....maximizing my span. I don't have a clue how to calculate the I value of a composite beam like this. My question may just be too involved for a quick answer.....if so please tell me. Not being a trained engineer, and having enuf knowledge to be dangerous with the torch/welder.....I tend to get in over my head at times ;o) Suddenly grounded in humility, thanks in advance for any consideration you may offer.

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Re: needed, one number cruncher
Re: needed, one number cruncher -- Guido Post Reply Top of thread Forum
Posted by: swearingen

12/21/2005, 08:31:42

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If you already know the I of the S8x15 and if the flats are centered vertically on the S8, then you just add the I of the flats to the I of the S8 for the total. The I of the flats is 7.15 in^4. I would tighten up the weld stagger, though. A 9" unsupported length of 0.125" plate may not transfer the internal shear you need without locally buckling. I probably wouldn't go over 6" O.C. In fact, a 1" stitch every 4" would be even better.

One other thing: you can get much more help with deflection if you put plates on the top and bottom flanges. If you put the plates top and bottom and w = plate width, t = plate thickness, and d = depth of the S8, then the I of the plates that you would add to the beam would be:

I = (2*w*t^3)/3 + (w*t*d^2)/2 + w*t^2*d

Modified by swearingen at Wed, Dec 21, 2005, 08:37:56

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