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Ceiling Hung, Folding Sheet Storage Rack #4: Got the Storage Rack Ready to be Hung from the Ceiling

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Blog entry by Dirk Van Essendelft posted 10-29-2014 02:21 AM 1892 reads 0 times favorited 4 comments Add to Favorites Watch
« Part 3: Finished Lower Frame Part 4 of Ceiling Hung, Folding Sheet Storage Rack series Part 5: Got the Ceiling Connection on the Hinge Side Completed »

I have been waiting for parts to actually do the hanging, but over the last couple weeks, I got the frame ready and had time to get the video update put together. Check it out:

-- Blending Traditional Woodworking with 21st Century Tools http://www.21stCenturyWoodworking.com



4 comments so far

View Don Butler's profile

Don Butler

1086 posts in 2863 days


#1 posted 10-29-2014 12:36 PM

I considered hanging sheet goods from the ceiling of my very crowded shop. It’s 10 feet from floor to ceiling.

But two things caused me to reconsider.

1. Sheet goods are extremely heavy.
2. Wood does very well in compression, but often fails in tension.

Then I thought about sheet goods falling on me.

Don

-- No trees were damaged in posting this message, but thousands of electrons were seriously inconvenienced.

View Dirk Van Essendelft's profile

Dirk Van Essendelft

58 posts in 1362 days


#2 posted 10-29-2014 03:08 PM

Don,

Thank you for your comment. I too have had concerns about the weight above my head. That’s why I took some time to do the proper engineering of the jointed connections to the ceiling. I am taking several safety precautions:

1) I am over engineering every joint and ensuring that every jointed connection is rated to support not just the normal working load, but the entire weight of the fully loaded storage rack (650lbs) even though most joints only need to support between 82.5 and 162.5 lbs

2) I have designed the connections to the American Wood Council (AWC) standards. This is the governing body which sets the standards for wood truss and flooring design. The current standard is to design a doweled (bolt/nail) connection to 80% of the elastic limit of the wood. The elastic limit is the point where the wood will not permanently deform if placed under load (it will “bounce back” like a rubber band). Past this point, wood has a significant plastic deformation loading region before it ultimately fails. Experience has shown that the design load limit (80% of elastic limit) is about 6 times lower than the ultimate breaking strength of the wood.

3) As an example of the design limit, the support straps on the free swinging end are connected to the ceiling joist via 3, half inch bolts which sandwich the joist between two 1/4” steel plates. The bolts are put in single shear loading by the support strap and each one is able to support 263 lbs safely. The fact that the bolts use a sandwiched side plate significantly increases the load limit because it takes it out of a mere dowel load and into a compression plate load. However, I designed to the worst case. In reality, the joint is likely to support well over 1500 lbs before anything will fail and can support much more than that if the load is momentary. The jointed connection only needs to support 162.5lbs during normal operations. This is equivalent to 1 person standing on the floor above it.

4) The idea that wood does better in compression than tension is not really true. Yes, the ultimate strength of wood is better under compression. However, the elastic load limit is nearly identical in tension or compression and far lower than any failure mode. As a matter of fact, the loading tests to determine the safe limits are done by putting the wood under tension. If wood performed poorly under tension, it could not be used for trusses or floor joists. These structures, by their very nature demand that members are under compression along the top and tension along the bottom. If it is a beam, it must actually be equal and symmetrical about the mid-line. Wood has a surprisingly high tensile strength for its weight along the grain direction.

I have done the engineering to know that the support rack will not fall down, and I can sleep at night knowing that it is safe for myself, my wife, and my kids to walk under it.

-- Blending Traditional Woodworking with 21st Century Tools http://www.21stCenturyWoodworking.com

View ineedathis's profile

ineedathis

72 posts in 2127 days


#3 posted 10-30-2014 12:01 AM

I was very alarm to see a pregnant woman doing something dangerous,
I have seen many things go wrong with table saw to me and others,
I will thing twice next time before I do that if I was you,
Great job btw.

View Dirk Van Essendelft's profile

Dirk Van Essendelft

58 posts in 1362 days


#4 posted 10-30-2014 12:47 AM

Thanks for the concern. It was not really a dangerous cut to make though. Since the blade was embedded in a sacrificial fence to take off a very flimsy strip of material off the corner, there was really no chance of kickback. She was also 4 feet from the blade. I only needed her help to keep it pushed against the fence and lift the end onto my outfeed table that was covered up with the project.

I understand the concern though.

-- Blending Traditional Woodworking with 21st Century Tools http://www.21stCenturyWoodworking.com

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