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# Uniform distributed load at the edge of the top flange on an I-Beam

## Uniform distributed load at the edge of the top flange on an I-Beam

(OP)
Dear all,

There is a uniform distributed load along an I-beam at the edge of the flange, please refer the attachment.

http://files.engineering.com/getfile.aspx?folder=6...

How do I design such an I-beam to resist the line-load?

I would like to know how to determine moment, bearing and shearing resistance at the edge of the top flange on an I-Beam.
I know there are couple of possible failure modes, such as web buckling, which failure mode governs the design?

### RE: Uniform distributed load at the edge of the top flange on an I-Beam

Please clarify your sketch or problem. Is that attempting to show a load applied to a top flange edge only?

Is the situation similar to a torsional load applied to the outside edge of the lip of a ledger support?

Jim

### RE: Uniform distributed load at the edge of the top flange on an I-Beam

Where are the reactions to the torsional moment?

BA

### RE: Uniform distributed load at the edge of the top flange on an I-Beam

If you are analyzing this by classical method, draw a free body diagram of all forces and moments, indicating all boundary conditions. Knowing the centroid or neutral axis of your geometry, you can simply solve the problem classically. Also bear in mind, you mind have secondary deformation effects like warping of your cross section which you may require more complex classical approach if you are to accurately predict the stresses in the structure.

### RE: Uniform distributed load at the edge of the top flange on an I-Beam

For a load of that magnitude applied at an angle, a closed section would be your best choice. Wide flange sections are very inefficient in torsion, and also in bending about the weak axis.

### RE: Uniform distributed load at the edge of the top flange on an I-Beam

You started by showing a vertical line load. Now you are showing a sloping concentrated load but have not indicated the slope. It seems that the torsion is quite low judging by the geometry shown but I agree with hokie. The wide flange is not a good shape to resist minor axis bending or torsion.

Is this structure real or imaginary?

BA

### RE: Uniform distributed load at the edge of the top flange on an I-Beam

(OP)
I am sorry about the confusion, I was trying to keep the problem simple.
I agree with both of you, but we gotta work with what we have. Is there a simple calculation to determine the size of the I beam?

Thanks.

### RE: Uniform distributed load at the edge of the top flange on an I-Beam

"Is there a simple calculation to determine the size of the I-beam?"

You've provided no information. What is the span? What are the boundary conditions? What are your serviceability requirements?

### RE: Uniform distributed load at the edge of the top flange on an I-Beam

Yes - superposition.

Split the problem into 2 separate ones -one with the distributed load acting in line with the web, and calculate usual direct stresses at beam extreme top/bott fibre with M/S.

Second half of the problem is a beam subjected to only the torsion component (torsion per unit length). Use torsion beam equations to determine the maximum applied torsion (similar to shear force diagram), and assume this is resisted by only the beam flanges in horizontal bending. This is another M/S calculation but only use the flange area to calculate S. This gives you a second component of direct stress that you add to the first.

Compare the sum of these stresses with an allowable, making sure that your allowable includes reductions for lateral/torsional buckling if applicable.

Maybe not THAT simple, but this is the usually accepted method.

tg

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