Weight of Threaded Rod - Page 1
Forum section: electronics / projects

author: bostonman
author_rank: Super Contributor
timestamp: March 11, 2020, 03:26:08 am
content: 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?

author: KrudyZ
author_rank: Frequent Contributor
timestamp: March 11, 2020, 03:36:02 am
content: 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.

author: beanflying
author_rank: Super Contributor
timestamp: March 11, 2020, 05:16:01 am
content: 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.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: March 11, 2020, 06:45:26 am
content: Quote from: bostonman on March 11, 2020, 03:26:08 amPSI = poundpersquare inch = (smallest) cross sectional area in square inches of the rod x the 70 kpsi = weight in pound before tensile strength limit is reachedOr 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.

author: bostonman
author_rank: Super Contributor
timestamp: March 11, 2020, 06:44:51 pm
content: 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.

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: March 11, 2020, 08:01:04 pm
content: Quote from: bostonman on March 11, 2020, 06:44:51 pmThe 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)

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 11, 2020, 10:14:38 pm
content: 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.

author: ebastler
author_rank: Super Contributor
timestamp: March 11, 2020, 10:37:31 pm
content: Are you going to actuallysuspendthe 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.

author: calzap
author_rank: Frequent Contributor
timestamp: March 11, 2020, 11:56:41 pm
content: 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

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: March 12, 2020, 12:02:21 am
content: You’re fine with the rods. They will not fail supporting a few shelves. Your limiting factor is how the rods are attached overhead.

author: Someone
author_rank: Super Contributor
timestamp: March 12, 2020, 01:39:24 am
content: Quote from: CatalinaWOW on March 11, 2020, 10:14:38 pmI'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.

author: bostonman
author_rank: Super Contributor
timestamp: March 12, 2020, 02:03:19 am
content: 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^2When 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?).

author: Someone
author_rank: Super Contributor
timestamp: March 12, 2020, 04:51:27 am
content: Quote from: bostonman on March 12, 2020, 02:03:19 amYour 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.

author: bostonman
author_rank: Super Contributor
timestamp: March 12, 2020, 12:26:34 pm
content: QuoteI 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?

author: langwadt
author_rank: Super Contributor
timestamp: March 12, 2020, 01:12:37 pm
content: Quote from: calzap on March 11, 2020, 11:56:41 pmin that case it none of that failed, it was the box sections that connected the rods that were not build correctly

author: calzap
author_rank: Frequent Contributor
timestamp: March 12, 2020, 03:49:54 pm
content: Quote from: langwadt on March 12, 2020, 01:12:37 pmYup, 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

author: skylar
author_rank: Contributor
timestamp: March 12, 2020, 09:35:01 pm
content: Quote from: calzap on March 12, 2020, 03:49:54 pmThreads 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 pm5/16" 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.

author: Gregg
author_rank: Super Contributor
timestamp: March 12, 2020, 10:16:07 pm
content: 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.

author: langwadt
author_rank: Super Contributor
timestamp: March 12, 2020, 10:43:00 pm
content: Quote from: calzap on March 12, 2020, 03:49:54 pmthe 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

author: bostonman
author_rank: Super Contributor
timestamp: March 13, 2020, 02:40:41 am
content: QuoteThanks 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'?

author: calzap
author_rank: Frequent Contributor
timestamp: March 13, 2020, 02:56:42 am
content: Quote from: Gregg on March 12, 2020, 10:16:07 pmYes 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

author: coppercone2
author_rank: Super Contributor
timestamp: March 13, 2020, 04:25:17 am
content: 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.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 13, 2020, 05:10:10 am
content: Quote from: bostonman on March 11, 2020, 03:26:08 ameee yucks !!!P = 70,000psi = 483MPad = 3/8" = 0.95 cmm = weight (kg)g = gravity 10m/s^2A = pi.(d/2)^2 = 7.1e-5 m^2P = m.g / Am = P.A / g= 482MPa x 7.1e-5 m^2 / 10=3441 kg50% safety (like in aviation) = 1700 kg4x 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.

author: bostonman
author_rank: Super Contributor
timestamp: March 14, 2020, 01:45:46 pm
content: QuoteNot 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?).

author: coppercone2
author_rank: Super Contributor
timestamp: March 14, 2020, 02:27:38 pm
content: I don't understand from your post if the thing is hanging or standingif 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?)

author: bostonman
author_rank: Super Contributor
timestamp: March 14, 2020, 02:31:01 pm
content: QuoteThe bookcase is hanging, the threaded rods go through the ceiling, and through a 4x4 laid across the attic joists with nuts (maybe I'll use coupling nuts to catch more threads).You were implying I was suspending it to the A frame (or at least I thought you were), so I was correcting you.

author: coppercone2
author_rank: Super Contributor
timestamp: March 14, 2020, 03:58:44 pm
content: I thought you were building a shelf hanging from the top of the attic in the attic

author: bostonman
author_rank: Super Contributor
timestamp: March 14, 2020, 04:12:48 pm
content: No.The bookcase will be on the wall in the computer room suspended by the rods going through the ceiling and into the attic - this is a 3D image of what it will look like.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 14, 2020, 04:45:04 pm
content: i certainly wont make a bookshelf like that. its so non-portable and installation/removal is more difficult.. any decent house floor, concrete wall or studs can support 500lbs just fine. ymmv.

author: ebastler
author_rank: Super Contributor
timestamp: March 14, 2020, 05:44:37 pm
content: Quote from: bostonman on March 14, 2020, 04:12:48 pmOops -- hold on. All the time I was assuming that you were planning forlongrods which go all the way down to the bottom of the shelf, through each of the shelf boards, providing direct support for each board. The way you show it, the top board of the shelf (or its frame, if you want to call it that) will have to carry the full weight, and it will see a significant bending force, not just a push/pull.What material and dimensions are you planning for that top baord? (Sorry if you already wrote about this and I didn't pick it up; my "rods threaded through all the shelves" mental picture might have been in the way.)

author: calzap
author_rank: Frequent Contributor
timestamp: March 14, 2020, 06:26:00 pm
content: The bottom shelf is close to the floor. Why not extend the sides down, support it from the floor, and forget the rods? It would be less work and more portable. Good idea to have a couple of anti-tilt brackets from bookcase to wall.Mike

author: bostonman
author_rank: Super Contributor
timestamp: March 14, 2020, 07:24:40 pm
content: The picture is an error. The rods would go through all the shelves.As for wby suspended? I’m just trying to keep things off the floor, make it more open.

author: Gregg
author_rank: Super Contributor
timestamp: March 14, 2020, 09:14:21 pm
content: Masonite or tempered hardboard is thin stiff pressed wood fiber material available in 1/8” 3/16” and ¼” sold in any big box home improvement store. It is available in one smooth side or both sides smooth and is easily painted. It is good for things like shelf backs and drawer bottoms.McMaster sells B7 zinc chromate plated medium strength (120K psi or about equivalent to grade 5 or 6 bolts)https://www.mcmaster.com/99086a192To keep the part of the rod in the attic from corroding, just coat it with some grease (or fluid film if you want the best protection). WD40 is too thin and short lived for this application. A light coat of grease covered with some heatshrink for where the rod goes through the 4x4 may be a good idea because the wood will tend to keep moisture in contact with the rod.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 15, 2020, 12:58:09 am
content: So much angst over what appears to me to be a more than adequate approach.Just a couple of comments:The conversion to a metric calculation may be of use to those who have no access to traditional English units, but is an example of where the purity of metric actually complicates the calculation. While the metric version eliminates confusion between pounds mass and pounds force, in this simple non-accelerated system there is no difference, hence no confusion. As pointed out in several prior posts the answer is a the simple product of area times tensile strength in traditional units.I don't really think a proof test is necessary, but you have seen the variety of opinions here. Getting a solid theoretical answer will be more difficult than getting empirical results.You haven't mentioned any interface to the wall. I would recommend some form of attachment to eliminate any possibility of a rattle or bang from either air currents or vibration from passing traffic. Such an attachment greatly complicates the theoretical analysis, but the need has often been demonstrated in practice. There are ways to make said attachment theoretically sound (applies a load to the book case without supporting any vertical loads), but only one is worth considering in practice, which is placing the ceiling end of the threaded rod slightly closer to the wall than the penetrations of the shelves. The problem with this approach is that I am not aware of any really good way to determine how much closer you need to be. You can do the geometry to see how much side load is generated, but the data for how much is enough will be non-existent.Or you can do what most tradesmen would do and put a couple of wall anchors in and screw it to the wall. The reality is that these anchors will deform as needed under the vertical loads and it will work.

author: coppercone2
author_rank: Super Contributor
timestamp: March 16, 2020, 02:55:29 am
content: i would just put a normal shelf there and modify it so its screwed to the floor with some molding so you can vacuum around it, its going to be better lol. I assume you want the vacuum cleaner to go around it nicely. IMO its ridiculous to try to save that space.Or just screw it to the ceiling and route molding around it on a small face plate if it must float.You get more use out of it anyway, because there is no threaded rod in the middle of the top shelf blocking stuff?? Thats going to be annoying to clean anyway... flat surface wipes down nicely and you can poke your hand in there without going around threaded rods.. and its way cheaper then stainless hardwareI think this thread has so much discussion in it because it does not make sense to make it and it does not look that great IMOoscillating tool + miter block + hand saw can do this really cheap with a few feet of molding without the craziness, you can make a angle block to press an oscillating tool into to make a angle cut in the molding without removing the entire piece if you please, you can probably even cut the pieces at an angle with the saw provided in home depot before you buy them if you bring the saw block to the store if you wanna save on a saw... or just cut a prism out of the shelf so it fits around the molding (possibly using a rasp if you want it snug tight against the molding).So the top corner of the shelf would be / rather then |.. if you want it perfect you can buy a contour gauge for 5$ , if you don't want to do trim carpentry work with molding

author: SkyMaster
author_rank: Frequent Contributor
timestamp: March 16, 2020, 04:26:49 am
content: Quote from: bostonman on March 14, 2020, 07:24:40 pmAre you planning to use a total of four threaded rods, one near each shelves corners?You could use 7/8" diameter threaded rods, especially if the rods are visible; this would give a "sturdier" look.I designed and built several bookcases, all my bookcases are made of solid wood, with center dividers to prevent the shelves from sagging.All my bookcases are floor standing, but I salute your approach to design a bookcase hanged from the ceiling.

author: bostonman
author_rank: Super Contributor
timestamp: March 16, 2020, 12:34:05 pm
content: I'm using two rods (one on each side), centered front to back, and about 8" from each side.A computer model showed that using the wood type (Poplar), thickness, weight, etc... the location of the rods (I think it was 8", but I'll need to check) will cause the shelves to sag very little with a full 100lbs on each shelf (which is unlikely since I only have about 250lbs of books).QuoteThanks, some people really like this idea and thought my creativity is great. Many of them want pictures of it's complete.

author: coppercone2
author_rank: Super Contributor
timestamp: March 17, 2020, 12:02:52 am
content: it reminds me of a HVAC or something hanging off of factory ceiling beams