Mechanical Engineering

# How do I calculate point load failure for various distances?

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If I know that a 10-foot pipe supported at both ends fails when a point load of 100 pounds is applied at the mid-point, how do I calculate the weight limit at other points along the pipe or how a change in the length affects the limit?

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You might start by calculating the bending stress for the known case with the load at the middle. Unfortunately, all you know is that this stress is too much. The pipe might also fail with a 90 lb load, but you have no way to know. Consequently, you only know a value too high, but you need the maximum load that does not cause failure.

If somehow you come up with a max load that avoids failure, then you can define a failure maximum stress. Then you could calculate the bending stress for the load at an alternate position and compare that to the known max safe value.

DrD

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It's somewhere between 90 and 100.  The test added 10 lbs weights until it failed.   For my purposes, I would start with 90 lbs (which does not cause failure).  Knowing that, is there a way to calculate other points along the beam?

@DrD and thank you for the reply!

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Many handbooks will provide the formulas for the moment at any point for one or two loads applied at any point(s). Knowing the moment M at any point, Stress = Mc/I. Set up a spreadsheet if you are searching for some sweet spot combination of max load vs location. I assume when 10 lb was added to the 90 the beam collapsed. Not knowing any more about the situation at hand I will stop here. If this a real world application vs a lab demonstration for a class there is much more to consider.Good luck.

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