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Big Beam LVL or Glu Lam load capacity to support a gymnast

Engineering Asked on July 21, 2021

I need help knowing if I am selecting the correct wood beam.

The load will be all near the center and a 250 pound man will be doing pull ups on it. I would estimate a 1,000 pound dynamic load to be safe.

I am looking at a 3.5in x 12 in x 20ft Big Beam (LP makes it, it’s an LVL). It will only be supported at the ends.

How can I calculate the correct beam size? Thanks.

One Answer

If you can approximate it as isotropic material, then you can use Euler beam theory to find the stress and compare it to the yield stress:

$ sigma = My/I$

  • $ sigma $ = normal stress

  • $ y $ = distance from neutral plane (midplane of symmetric section beam). Maximum stress occurs at the outside edge so use $y=h/2$ where $h$ is the height of the beam (12 in).

  • $ I $ = 2nd moment of area of the section about the axis perpendicular to y and also in the plane of the section. For a rectangular section, $I=b h^3/12$. $b$ is the width of the beam. For other shapes like I-beam, see Google.

  • $ M $ is the bending moment. For a simply-supported beam (is it simply supported?) with point load at the center, the bending moment at the center (where it's maximum), is $ M = FL/4 $. $F$=load (1000 lb_f) and $L$ = length (20 ft).

Beware that there might be other failure modes too.

Answered by user1318499 on July 21, 2021

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