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marwayne View Drop Down
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Direct Link To This Post Topic: Experiment
    Posted: 01 Aug 2020 at 7:30pm
Many people ask how they can attach things to the walls, so this is my experiment. I took a piece of wall panel, drilled a 1/16" pilot hole and put in a coarse thread drywall screw to find out how many pounds of pull it would it take to pull it out. the scale the pounds just as the screw started to pull out. It took about 37.5 pounds.

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fwunder View Drop Down
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Direct Link To This Post Posted: 01 Aug 2020 at 8:00pm
37.5 lbs is a lot!!

Could easily hang this 35 lb. striper! Probably not over a speed bump, though.


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offgrid View Drop Down
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Direct Link To This Post Posted: 02 Aug 2020 at 7:10am
Testing this is great and on the right track but a few comments.

In the case of hanging stuff I think you want to do a shear (lateral) load test not an axial load test. Most likely the attachment is stronger that way but it’s thin material so it’s worth testing to see. How far from the wall you apply the load makes a difference because it’s a little lever, so pick something typical for something hanging on a wall, maybe 1/4 or 1/2 inch?

Also since wood is a variable material you typically get a load variation in test results so you need to do multiple tests and look for the average and standard deviation. Generally speaking that is about 5-10 tests. If the variation in the first 5 tests is less than say 10% then thats good enough. Do the test slowly as wood unlike metal can take a lot more load for short periods than long ones.

I can dig out my Wood Products Handbook and see but IIRC for single fasteners a safety factor of about 2 is specified for short duration loads like bump loads in an rpod. Since those loads are about 2g I think an overall 4x safety factor would be safe. That would be around10 lbs per screw for the pullout test but I think it will end up being more than that for a shear load.
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JR View Drop Down
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Direct Link To This Post Posted: 02 Aug 2020 at 7:26am
Good test and everything that was learned so to extrapolate the findings if I use 2 drywall screws in the wall does that mean that I can hang something that has a weight of 75 pounds (4 screws 150 lbs) before the screws start to fail (pull out of the wall)?? 
Jay

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Direct Link To This Post Posted: 02 Aug 2020 at 8:10am
Every once in a while I read something here and think "oh, my! 'the guys' are going to have a field day with this." It usually has to do with tow vehicles and weight limits. 

I think you're kidding...right?LOL
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Direct Link To This Post Posted: 02 Aug 2020 at 8:20am
Originally posted by JR

Good test and everything that was learned so to extrapolate the findings if I use 2 drywall screws in the wall does that mean that I can hang something that has a weight of 75 pounds (4 screws 150 lbs) before the screws start to fail (pull out of the wall)?? 

No, it doesn't work that way. Its close to 2x for 2 fasteners but after that it stars to drop off because some fasteners (usually the outer ones in a row) take more load, and you reach a point where the inner ones aren't doing much. Also, see me previous post re load testing and safety factors. 
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Direct Link To This Post Posted: 02 Aug 2020 at 8:28am
Originally posted by EchoGale

Every once in a while I read something here and think "oh, my! 'the guys' are going to have a field day with this." It usually has to do with tow vehicles and weight limits. 

I think you're kidding...right?LOL

Sometimes by taking things to extreme limits you can identify where the assumptions have gone wrong. Practical engineering is fun, everybody gets to learn some stuff they didn't know before. Much better to do it with stuff hanging on walls of an rpod than say finding out the hard way because of a bridge collapse. Star

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lostagain View Drop Down
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Direct Link To This Post Posted: 02 Aug 2020 at 9:04am
I think that an experiment should be set up using a section of wall from an rPod in which each method mentioned by members is tested to see which is strongest.  The test could use 3 applications of lateral force:  one sudden, one for a sustained period of time, and one that simulates repeated applications of lateral force as in bouncing down the road, with, as OG suggests, 5 actual load tests for each fastening method to compute averages.

To make it interesting, the members of the board could place bets on which method s/he feels will win with the money pooled.  The winner(s) would be those who selected the strongest fastening method would win the pot.  Big smile
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Direct Link To This Post Posted: 02 Aug 2020 at 9:08am
I'm in for the betting!
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podwerkz View Drop Down
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Direct Link To This Post Posted: 02 Aug 2020 at 9:16am
Never mind all that, was the fish fry good?

Cool
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