Weight of Threaded Rod

[bostonman]

I have a question about threaded rod.

1/2" stainless steel threaded rod (according to McMaster-Carr) lists 70,000psi. From my understanding, this is the point where the threaded rod will not return to original size after being stretched under a load - and possibly break.

Assuming we de-rate the value by half for safety (35,000psi), how do I know how much weight the rod can take since I only have the psi value?

[KrudyZ]

For the rod itself you would use the root (or minor) diameter of the thread to calculate your area.
For a 1/2-13 thread that is 0.417" resulting in an area of 0.136 sq in.
However, you also need to consider what this is threaded into.
Depending on how many threads are engaged and the mating material, the thread may fail (internal or external) and strip instead of the rod breaking.

[beanflying]

If it is for a load critical static job then I wouldn't be using threaded rod for a start. You would use 1/2" Bar and turn or cut the threads on the ends and maximise the diameter for the rest of the rod.

Also it matters if the threads are rolled or cut typically a rolled thread will have a slightly reduced diameter than that of a cut thread. So as per the above post you will need to reduce the effective area some more. Typically all thread is rolled for cost reasons.

The other thing is what S/Steel rod are you looking at as it also matters a lot. Stainless Steel consists of a very large range of mechanical, machining and chemical resistance properties. 304 for example is a lot different to say 410.

[SparkyFX]

I have a question about threaded rod.

1/2" stainless steel threaded rod (according to McMaster-Carr) lists 70,000psi. From my understanding, this is the point where the threaded rod will not return to original size after being stretched under a load - and possibly break.

Assuming we de-rate the value by half for safety (35,000psi), how do I know how much weight the rod can take since I only have the psi value?

PSI = pound per square inch = (smallest) cross sectional area in square inches of the rod x the 70 kpsi = weight in pound before tensile strength limit is reached
Or in other words, a 1 inch diameter rod could hold 70000 pound of (non-moving) weight (given it is attached without compromising diameter, etc. pp). For very long rods the weight of the rod itself needs to be considered.

This is of course all for forces along the axis of the rod, there are other things to consider for sideloading.

As derating happens on the side of the weigth or by upscaling the diameter of the rod, the tensile strength of the material is not affected by it.

[bostonman]

Basically I'm going with 3/8" stainless steal threaded rod through five wood shelves to suspend them.

I over estimate each shelf will be 100lbs max, so two rods supporting 500lbs with a nut under each shelf.

Per McMaster-Carr, ss rod is 70,000psi, but I don't know what that means in the amount of weight it can support.

[pardo-bsso]

Basically I'm going with 3/8" stainless steal threaded rod through five wood shelves to suspend them.

I over estimate each shelf will be 100lbs max, so two rods supporting 500lbs with a nut under each shelf.

Per McMaster-Carr, ss rod is 70,000psi, but I don't know what that means in the amount of weight it can support.

The cross-sectional area of your rod is:


$$ Area = \left( \frac{1}{4} \right) \cdot \pi \cdot (3/8 inches) ^ 2 == 0.11 square-inches $$

So:


$$ Weight = 70000 \left( \frac{pounds}{square-inches} \right) \cdot 0.11 square-inches = 7700 pounds $$


(it should be a bit lower in your case because the threading reduces the effective diameter and also one nut does not always engage a sufficient number of threads. But even so with what you stated it will be more than enough)

[CatalinaWOW]

This is a situation made to order for proof testing. 

You clearly don't understand the mechanics well enough to trust your calculations, though calculations provided by others here show large margins to your needs.  But the calculations done here don't include the strength of your anchor or any loads due to shock, misalignment or anything else and also seem to presume that the load is shared evenly among the four hangers (or is it only two and a ledger?)

But it is relatively easy to get rocks, bricks or maybe even books to add up to your load plus a safety margin.  Just be sure not to be under the shelves while testing.  If your load tests are successful you can feel good about having your mother, girlfriend or kid brother around when the shelves are in use.

[ebastler]

Are you going to actually suspend the rods and shelves? (From the ceiling? Or some overhead beam?) If so, the tensile strength of the rods is probably not your problem. How do you want to attach them, and to what supporting structure?

Or are the shelves resting on the floor, with the threaded rods acting against a pushing (compressing) force? If so, the tensile strength is not the quantity you should be looking at. If the rods get strained laterally (by something or someone bumping into them), they can buckle under loads well below the tensile strength limit. That said, your rods will probably still be generously dimensioned for the task.

[calzap]

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).   It's not simple:  what material will the nuts be?  what thread will be used? what's the thread engagement?  will washers be used? etc.

My suggestion is overbuild it and safely test it as suggested by CatalinaWOW.  If it's going to support people or hang over people, use a plan from a qualified engineer.

Mike in California

[Ground_Loop]

You’re fine with the rods. They will not fail supporting a few shelves. Your limiting factor is how the rods are attached overhead.

[Someone]

You clearly don't understand the mechanics well enough to trust your calculations, though calculations provided by others here show large margins to your needs.  But the calculations done here don't include the strength of your anchor or any loads due to shock, misalignment or anything else and also seem to presume that the load is shared evenly among the four hangers.

I'll disagree about the value of the calculations presented so far, as they aren't even taking into account "rule of thumb" factors for the obvious (and still not mentioned) realities. This is non-trivial and just listing the half dozen or so confounding realities that need to be considered won't help as someone who can't see those immediately likely lacks the skills to calculate them adequately.

Mechanical engineering, actually quite hard to do properly.
Mechanical trades use codified tables/rules of thumb, but still require significant training to use them appropriately.

[bostonman]

The calculations provided above is a slap in the face. I made it too complicated and didn't see that 'PSI' is as simple as: lbs / in^2

When multiplied by the area of the rod (0.11 in^2 in this case), the in^2 cancel and you're left with lbs. Sometimes I over think things so much that I confuse myself.

To answer the questions everyone has. I went over this design with the mechanical engineers at work (I'm on the electronics side) to the point that one created a computer model to simulate bowing and stuff.

So the design is as follows: all the wood is slightly over 1" thick (I think about 1 and 3/16" - but labeled as 1.5"). The bookcase will have five shelves with sides (and a dado for each shelf) and open back. It will be about 45" wide, 12" spacing between shelves, and 11.25" deep.

Two threaded rods will go through each shelf with a washer underneath each shelf. From the computer model, the best is location for the rods is somewhere around 8" from each side (I have it noted somewhere - but going with 8" for purposes of discussion). So one threaded rod on each side, both being an equal 8" from the sides.

As for suspending, the threaded rods will go through the ceiling and into the attic where a 4" x 4" will be laid across about five joists. These joists are located on the load baring wall, so all the weight is transferred down to the basement steel posts. Most likely I'll put two or four screws into the wall just to keep the bookcase from pulling away from the wall (or shacking).

Hardware will be 70,000 psi stainless steel threaded rod, standard nuts, oversized washers under each shelf, and some aluminum plates (I have some spare pieces of aluminum) for washers on the 4x4.

I oversized everything. All the books I currently own weigh approximately 250lbs and doubt I'll add the same size large textbooks in the future (or even add another 100 or so books to make an additional 250lbs). In any case, I'm stating that the total weight (minus wood weight) will be 500lbs. Without looking at notes, I think 5/16" threaded rod is good for 2300lbs, so two will hold 4600lbs.

This 2300lbs is using 30,000psi as a safety margin (i.e. yield?).

[Someone]

As for suspending, the threaded rods will go through the ceiling and into the attic where a 4" x 4" will be laid across about five joists. These joists are located on the load baring wall, so all the weight is transferred down to the basement steel posts. Most likely I'll put two or four screws into the wall just to keep the bookcase from pulling away from the wall (or shacking).

Hardware will be 70,000 psi stainless steel threaded rod, standard nuts, oversized washers under each shelf, and some aluminum plates (I have some spare pieces of aluminum) for washers on the 4x4.

I oversized everything. All the books I currently own weigh approximately 250lbs and doubt I'll add the same size large textbooks in the future (or even add another 100 or so books to make an additional 250lbs). In any case, I'm stating that the total weight (minus wood weight) will be 500lbs. Without looking at notes, I think 5/16" threaded rod is good for 2300lbs, so two will hold 4600lbs.

This 2300lbs is using 30,000psi as a safety margin (i.e. yield?).

Your 3/8" design was undersized even for unreasonably slim safety margins, 5/16" is going in the wrong direction. Looking at the rod diameter alone is like planning to tow a 747 with a Cessna because the tow rope is technically adequate.

Just the point loads you plan on the joists are enough to need more detail about the existing structure and its design.

[bostonman]

Your 3/8" design was undersized even for unreasonably slim safety margins, 5/16" is going in the wrong direction.

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?

[langwadt]

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). 

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

[calzap]

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). 

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

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]

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.

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.

Your 3/8" design was undersized even for unreasonably slim safety margins, 5/16" is going in the wrong direction.

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?

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]

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). 

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

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.

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]

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.

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'?

[calzap]

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.

Yes indeed, stainless threads can gall and bind ... very tightly ... and when and where it's hard to fix.  A few years ago at my ranch, we needed to extend the pipe that takes water out of a canal into the canal itself.  Previously, it ended in a well to the side of the canal, but there were silting problems there.  There was a big strainer to be fastened to the end of the pipe using large stainless bolts and nuts.  See the first picture.  We were doing this at the end of the offseason when the canal was dry, but knew the water could be turned-on at any time. It was a Thursday afternoon when we were installing the stainless bolts and nuts to replace the temporary zinc-plated ones.

Sure enough, the bottom bolt/nut galled and froze tight when part way on.  Decided to wait until Monday morning to cut it because would have no replacement bolts and nuts until then.  And there were more important things to do like installing the support brace for the upstream shield.  Figured irrigation district wouldn't turn on the water on a weekend ... but they did.  See the second picture.  Using an electric reciprocating saw was out of the question.  Waded in with a handheld hack saw, but soon gave up.  Decided the other bolts would suffice until next offseason.  The other bolts did the job.  Bad bolt and nut were replaced in the next offseason.   Water intake has worked flawlessly for more than 10 years.

Mike in California

[coppercone2]

consider putting a floor in and using normal shelves. if you suspend from an attic beam consider the effects of snow load and wind load and deformation of the roof and damage that can be caused by falling trees ETC. This might make analysis further complicated.

Then you can use threaded rod as a spacer and put pipe sections between the pieces so the thread does not get compressed. (to avoid flanges).

Also, I wonder if it could lead to a expensive roof leak if its weighed down in a section. I would not mess with the roof. + fire department likes to cut them open if there is a fire, having a shelf suspended from it may cause problems, especially if they are working from a roof ladder arrangement rather then a truck.

Also, bolts near the roof will experience greater thermal cycling.

[Mechatrommer]

...psi...

eee yucks !!!

P = 70,000psi = 483MPa
d = 3/8" = 0.95 cm
m = weight (kg)
g = gravity 10m/s^2

A = pi.(d/2)^2 = 7.1e-5 m^2
P = m.g / A
m = P.A / g

= 482MPa x 7.1e-5 m^2 / 10
=3441 kg

50% safety (like in aviation) = 1700 kg
4x rod can support 6800 kg evenly distributed.

whats next? torsion/shear/compressive/tensile stress analysis on the supporting rig.. so home will not collapse. ymmv.

[bostonman]

Also, I wonder if it could lead to a expensive roof leak if its weighed down in a section. I would not mess with the roof. + fire department likes to cut them open if there is a fire, having a shelf suspended from it may cause problems, especially if they are working from a roof ladder arrangement rather then a truck.

Not sure if I'm confusing my terminology. Attic joists as in the beams that go across the attic that the ceiling mounts to and you walk across when you're in the attic. I think you're referring to the beams () that are part of the A frame and what supports the roof.

I plan to lay the 4x4 across the attic joists, and agree, I'd be crazy to mess with the A frame (i.e. roof beams ?).

[coppercone2]

I don't understand from your post if the thing is hanging or standing

if you have it hanging you NEED the strength of the rod, if its sitting its only aesthetic decision (you can slip pipe over it). (the idea being that flanged pipe is more expensive, but it would make threaded rod unnecessary)... but slipping pipe over threaded rod thats under tension might be pretty cheap, and look better, be easier to clean, polish, paint, etc. Especially if you make a tiny counterbore for the pipe to sit snugly in (1mm?)