Laminating a long beam for strength

Question

Very similar to this question I want to create a balance beam to span the narrow part of a swimming pool which is 16'. I'm thinking of a length of 18' to allow 1' on either side. My initial thoughts around this beam are to laminate together 3 sets of 6-foot 2x4s in this pattern:

Some questions about this:

• Is there a way to roughly-measure/estimate/guess how much weight this could bear in the middle?
• Will this even work or is there a better way to do this?
• It's going to get plenty of water splashed on it when used. Any considerations with respect to that?
• If I'm able to find longer 2x4s that are straight enough would 9' lengths in the same pattern work better?

Answer 1

I just looked at my building code span tables for Glue-Laminated beams (I work at a Architectural/Structural Engineering Firm in Ontario, Canada) and The best options for a 16' beam spanning 14' is 2 - 2x10s which can support 198lbs per linear foot or 3 - 2x10s which can support 298lbs. There is no number on 3 - 2x8s but 2 - 2x8s will only support 84lbs per linear foot at a 14' span.

These numbers represent a deflection of 1/360 of the length so over 14' that would be only 0.46"

Personally I would not use 2x4s. If you don't care to much about deflection you could likely get away with 3 - 2x6s but expect a deflection of 1-2"

Answer 2

EDIT: I reran the sagulator and found an error in my input (first sentence in italics is in error). The deflection is only 1/4". However, I believe the discussion of the dynamic nature of the loads and the behavior of the end points requiring a secure connection remain important considerations.

I just ran this through the Sagulator assuming 200lb total load and got a deflection of nearly 2". Statically, the wood can carry the load, but the problem is that your load is dynamic. Two or three kids could be jumping and shifting weight continuously. Your wood composite beam will probably not crack under their activities (you would need to use a waterproof type of glue to prevent its weakening as it gets soaked). The real problem is not vertical loads, but rather the fact that forces will come at many angles. As the beam sags under the weight it will have a tendency to bow and twist. Enough force in the right direction will cause the beam to rotate around its long access. This will result in the beam bouncing and rotating from the direct line across the pool perpendicular to the edges to something else. It is only a matter of time before it will shift one or both ends to the point it is not supported by the edge. There is great risk of someone getting hurt.
One solution to that is to properly secure the edges to the edge of the pool so that they cannot shift.

I would also consider that someone falling near the edge may land on the pool edge rather than the water. Cracked heads are no fun. I would make certain that at least the edges of the pool are properly padded and that the kids are wearing helmets.