Electronics > Projects, Designs, and Technical Stuff
Weight of Threaded Rod
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calzap:

--- Quote from: langwadt on March 12, 2020, 01:12:37 pm ---
--- Quote from: calzap on March 11, 2020, 11:56:41 pm ---Tensile strength of rod material is only a starting point.  If you think about it, the holding strength of a rod threaded into a nut or sleeve is dependent on the number of threads engaged and the shear strength of threads from core of the rod and from shell of the  nut.  It was failure to fully account for this that led to the infamous Hyatt Regency Hotel disaster in Kansas City in 1981 (google it). 

--- End quote ---

in that case it none of that failed, it was the box sections that connected the rods that were not build correctly

--- End quote ---
Yup, you're right in that the box beams splitting at the welds pressing on the nuts was the proximate cause of the disaster.  And thanks for mentioning it.  Your reply caused me to look more carefully at the reports.

However, it was fear of thread damage and failure that caused the ad hoc redesign.  The redesign caused increased pressure on the beams, rods and nuts.   I'm not aware that any threads failed, but haven't seen the detailed damage assessment.  If washers had been used between the nuts and beams, disaster might have been avoided.

And the box beam structure and welds should have been properly specified and inspected.  If that had been done, it would not have mattered which way they were installed.  Having two adequate sides and two inadequate sides depending on orientation ... no, no ... don't do it that way.  Even if the beams had been installed with an unwelded side against the nut, the welds, which would now be on the sides of the box, might have cracked with the increased load of the redesign.  Then the two edges of the U-beams that formed the box could slip pass each other or crumple.  The added force due to downward movement could cause beam, rod or nut failure.

Biggest failure though was not doing a proper engineering study on the redesign.

Mike in California

skylar:

--- Quote from: calzap on March 12, 2020, 03:49:54 pm ---I'm not aware that any threads failed, but haven't seen the detailed damage assessment.  If washers had been used between the nuts and beams, disaster might have been avoided.

--- End quote ---

Threads didn't fail but ordinary washers wouldn't have helped, load plates would have been a marginal improvement until a few more people stepped onto the walkways.

As you have said, definitely was a misunderstanding of the pulley problem (or a related logical conundrum, more accurately), not a material strength or welding problem at the root cause.


--- Quote from: bostonman on March 12, 2020, 12:26:34 pm ---
--- Quote ---Your 3/8" design was undersized even for unreasonably slim safety margins, 5/16" is going in the wrong direction.
--- End quote ---

I meant that even 5/16" is more than enough and I'm probably going with 3/8".

What do you mean 3/8" is undersized, but then you stated the rod can pull a 747?

--- End quote ---

5/16" or 3/8" will be fine, a single 5/6" grade 5 bolt will support your average vehicle (4450 lbs), don't use grade 2 or unrated hardware (check your nuts too, not just the threaded rod). As others have said its all about anchoring and you have a suitable plan in place there. Locktite or jam nuts to keep everything from spinning and making the load distribution uneven on each shelf would be a decent idea but not a likely issue, locktite or jam nuts on the last threaded connection on each end of each rod is a must as you can't keep an eye on the nuts in the attic. You've over speced this to have a fair margin.

Edited for poor phrasing.
Gregg:
I have no doubt that two 3/8 inch threaded stainless rods will do the job installed as you described.  Some type of fastening to the wall like you stated will keep the load on the rods from weakening at any point they may want to bend if the shelf sways.
A few things to consider: Stainless nuts on stainless threaded rod can gall and bind; plated steel or brass nuts may be a better choice. Threaded rod has relatively sharp threads all around that can cause damage to anything that is put against them; you may want to consider covering them with plastic or stainless tubing.  If you do cover them, it may save a bunch of money to use steel threaded rod grade 5 or better; stay away from the grade 2 or lower junk that most hardware stores stock. 
The shelves are going to want to sag in the middle.  Installing a back of even something thin like 1/8 inch tempered Masonite will do wonders to help keeping them straight.  A lip on the back of each shelf would help if a back isn’t going to work for you.
langwadt:

--- Quote from: calzap on March 12, 2020, 03:49:54 pm ---
--- Quote from: langwadt on March 12, 2020, 01:12:37 pm ---
--- Quote from: calzap on March 11, 2020, 11:56:41 pm ---Tensile strength of rod material is only a starting point.  If you think about it, the holding strength of a rod threaded into a nut or sleeve is dependent on the number of threads engaged and the shear strength of threads from core of the rod and from shell of the  nut.  It was failure to fully account for this that led to the infamous Hyatt Regency Hotel disaster in Kansas City in 1981 (google it). 

--- End quote ---

in that case it none of that failed, it was the box sections that connected the rods that were not build correctly

--- End quote ---
Yup, you're right in that the box beams splitting at the welds pressing on the nuts was the proximate cause of the disaster.  And thanks for mentioning it.  Your reply caused me to look more carefully at the reports.

However, it was fear of thread damage and failure that caused the ad hoc redesign.  The redesign caused increased pressure on the beams, rods and nuts.   I'm not aware that any threads failed, but haven't seen the detailed damage assessment.  If washers had been used between the nuts and beams, disaster might have been avoided.

And the box beam structure and welds should have been properly specified and inspected.  If that had been done, it would not have mattered which way they were installed.  Having two adequate sides and two inadequate sides depending on orientation ... no, no ... don't do it that way.  Even if the beams had been installed with an unwelded side against the nut, the welds, which would now be on the sides of the box, might have cracked with the increased load of the redesign.  Then the two edges of the U-beams that formed the box could slip pass each other or crumple.  The added force due to downward movement could cause beam, rod or nut failure.

Biggest failure though was not doing a proper engineering study on the redesign.

--- End quote ---

the original design was crazy and seemingly by someone who never tried to assemble anything. imagine trying to feed a number of four story long  threaded rods through beams with out damaging the thread and then screwing on nuts all the way from the bottom end 

bostonman:

--- Quote ---A few things to consider: Stainless nuts on stainless threaded rod can gall and bind; plated steel or brass nuts may be a better choice. Threaded rod has relatively sharp threads all around that can cause damage to anything that is put against them; you may want to consider covering them with plastic or stainless tubing.  If you do cover them, it may save a bunch of money to use steel threaded rod grade 5 or better; stay away from the grade 2 or lower junk that most hardware stores stock.
The shelves are going to want to sag in the middle.  Installing a back of even something thin like 1/8 inch tempered Masonite will do wonders to help keeping them straight.  A lip on the back of each shelf would help if a back isn’t going to work for you.
--- End quote ---

Thanks for the help. Since a section will be in the attic, I was going with stainless to avoid any corrosion over time due to moisture that may occur. I imagine I could go with zinc plated, but always fear a scratch (either from nuts being threaded onto it or dings) will cause corrosion in that area. Also, I didn't see any different grade threaded rod on McMaster-Carr, but maybe I wasn't looking hard enough.

What is 'tempered Masonite'?
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