# Need a pair of forumlas to help me build a lifting platform

## Main Question or Discussion Point

I'm planning on building a platform for Olympic weightlifting. I'm trying to minimize the weight, so I'd like to be able to properly estimate the sturdiness.

The first one is for a piece of wood sitting on beams of some sort. I know that as the beams move father and farther apart, the board can support less and less weight inbetween the beams.

What is the formula for estimating the strength difference for the board for different spacings of the beams? I.e. If the board has a limit of 10 lbs with the beams x inches apart, what is the weight limit with the beams y inches apart?

The second question has to do with relating the strength to the thickness of a board. For a scenario like above, imagine that the distance of the beams are fixed, but the thickness of the board is not. What is the formula that lets me relate the strength to the thickness of an item?

Ex: If a board 1/2" thick can support 10 lbs, how much weight can a board 3/4" thick support?

In case you can't tell, I'm hoping to have a board sitting on beams, and I'm trying to estimate how thick to make the board and how far apart to have the beams. The thinner/farther apart, the lighter it will be.

Sorry to post this in two different places. I'm hoping that the reason I didn't get a response in the General Physics board is that it was the wrong place.

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rcgldr
Homework Helper
Something this important to the safety of the particiapants should involve someone like a civil engineeer. I don't know if stress/strain information is available for ordinary boards as opposed to beams designed to handle a load.

Not sure what you are trying to achieve but your boards will be at their strongest if your two supports (underneath) are placed 1/3 and 2/3 of the way along the boards, not at the ends.

Something this important to the safety of the particiapants should involve someone like a civil engineeer. I don't know if stress/strain information is available for ordinary boards as opposed to beams designed to handle a load.
It will be used just by me at my home.

Not sure what you are trying to achieve but your boards will be at their strongest if your two supports (underneath) are placed 1/3 and 2/3 of the way along the boards, not at the ends.
To give more details, my platform will be 4' x 4', and will be raised off the ground by pieces of wood. The number of pieces and spacing is one thing I was trying to decide on. The platform will be raised so that I can put layers of carpet next to either side of the platform to drop the weight on, reducing noise and damage to the concrete below.

My platform's estimates were getting above 70 lbs, which would be difficult to move around daily.

I think I have solved my problem and found how to get the weight down. However, I still am curious just from a mathematical/physics standpoint how to relate the strength of two similar objects of varying thickness and how adjusting the spacing effects the maximum load. I majored in math a few years ago, so you can understand my general curiosity for this.

Most structures are limited by excessive deflection not ultimate failure (breaking).