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37.5 lbs is a lot!!

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

I think you're kidding...right?

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. 

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. 

https://www.youtube.com/watch?v=CsKKDLKYsVU - https://www.youtube.com/watch?v=CsKKDLKYsVU

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.  

I'm good except you don't need to do the duration test portion, that data is available. Its like this for wood:

10 years 1.0

2 months 1.15

1 week: 1.25

10 minutes: 1.6

Impact 2.0

Meaning that wood can take 2x the impact load that it can a 10 year occupancy load. 

The 10 minute load is typically used for peak wind and earthquake loads for buildings but our rolling earthquake-mobiles get a lot more than 10 minutes of "earthquakes". Probably the 1 week duration would be more appropriate for us.  

So probably the best thing would be to apply the test loads for 10 minutes to each sample screw, average those loads, divide that by 1.6/1.25=1.28 and call that the max bump load rating. Since the bump loads are about 2gs that means that a factor of about 2.56 over the actual weight on the screw should probably be used. 

There is also the typical engineering factor of safety added on top of that. I just did a quick look for safety factor for wood fasteners and found 6x is typical for pullout loads and 1.6 to 2 for lateral loads because of variability, humidity, and aging, 

Using the 1.6 number I get an overall multiplier of 2.56 x 1.6 - 4.1, call it 4, or an allowable 1/4 of the average lateral test load at failure. 

The reason I prefer fasteners to adhesives is the long term failure risk of adhesives. They can be great right after you attach things but a few months later they can fail due to changes in temp and humidity. Fastener strength varies with environmental conditions too but not nearly as much and that is taken into account in the safety factor. 

If you want to use the adhesive method that's fine, I just personally have had those strips fail on me so I don't trust them in the long run. 

Personally, I think my method of a combination of a coarsely threaded short screw with a patch of 3M double sided extra strong foam tape will win the contest, but I have been wrong so many times in my life ......  Suffice it to say, I don't patronize our fine casinos here in Dayton, NV.  

If you're going to allow adhesives as part of the test then a year probably is about right and a you'd have to to test for all sorts of humidity and temp conditions, surface prep variation, etc. For solar modules, which are of course held together by adhesives, you do heat soak, thermal cycle and humidity freeze testing, really nasty. You need a test chamber and months of testing.

Love it!  I'm with OG.

For corroboration, We used a factor of safety of 4 for wood poles carrying transmission lines.  The poles were Southern yellow Pine, one of the strongest woods. 

Generally, bumps should be considered impact loads and doubled for equivalent weight. 

Please retest with your screw almost screwed all the way in and loaded parallel to the wood panel (90 deg/in shear).  I'll bet the result is about twice the 37 lbs you got. 

Then, your load rating should be that divided by 4 for safety and divided again by 2 for impact.  Let's guess and call it 10 lbs.  *I* would allow double that for 2 screws on the top row if they are at the same "elevation", but only allow half that for screws in an additional row (5 lbs/screw).  There is a shear strength and buckling load limit for the panel, so don't go hanging propane bottles on your walls.    I also wouldn't place the screws closer than about 4" apart, as the stresses from one overlap and add to the stress from the other.  Admittedly, 4" is a guestimate without further data. 

Shut up in the hot sun, my pod got hot enough for one of my Command Strips to come loose.  It was holding a picture.  The others stayed on without a load.  I'd expect they will all work fine, if the temps are controlled. 

+1. We engineers are often accused of being a conservative bunch, but generally our customers aren't happy with us when our designs fail. You might go a long time without a failure with lower safety factors, but statistics being what they are it could happen tomorrow.