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I'm having difficulty with an assignment.

Briefly, the question relates to asimply supported I beamcontaining a UDL and a point load. I've calculated the maximum bending moment resulting from these loads (neglecting beam mass) to be5625kNm. I must select a universal beam from grade 43 steel (yield =275 MN/m) that can support this loading scenario.^{2}

Long story short, using this material the required elastic section modulus (20454.55cm^{3}) is just too high for any standard beams. I've been told I cannot change the material, loading or fixing scenerio and that I have to 'find a way around' the problem.

Approach 1

I was considering using the UTS for grade 43 steel (430 MN/m^2) which would solve the problem, but that surely doesn't lend itself well to sound engineering practice.

Approach 2

The other thing I found is that on http://www.corusconstruction.com/en..._beams_structural_steel/use_of_bs5950_part_1/ moment capacity for a simply supported beam is the lesser of

Mc = py.Sx

and

Mc = 1.2 py.Zx

Where Py is material yield strength, Sx is plastic section modulus and Zx is elastic section modulus. I have read BS 5950 and it seems to back this up.

Approach 3

Could I stack two I beams on top of each other? How would this affect the second moment of area (would it be double, or .. just over double of one beam)?

I am confident I could produce answers which make sense (to me) but I obviously need to produce answers that have resulted from sound engineering process. Which approach should I use? Or maybe none of the above!?

Any help would be appreciated.

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# Beam selection where moment capacity is exceeded

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