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Threaded Rod Buckling and Sagging

11/24/2015 5:11 AM

Dear Gents,

Please need to know the limits of buckling for threaded rod in tension and compression.

Thanks.

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#1

Re: threaded rod buckling and sagging

11/24/2015 5:57 AM

It probably won't buckle in tension.

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#3
In reply to #1

Re: threaded rod buckling and sagging

11/24/2015 7:09 AM

I also think that , but to which limit?

i have threaded rod safe in stresses in tension with dia. 10 mm and length 7 m.

Engineering sence for me , tell me it is not applicable.

please Advise me, or give me reference to read.

Thanks.

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#2

Re: threaded rod buckling and sagging

11/24/2015 6:55 AM

What do you think is "buckling" ? Only to be sure you get the right answer.

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#4

Re: threaded rod buckling and sagging

11/24/2015 9:06 AM

Composition of threaded rod and rod size determine strength properties and deformation limits.

Most manufacturers provide tables that contain this information.

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#26
In reply to #4

Re: threaded rod buckling and sagging

11/25/2015 9:29 AM

Beat me to it.

"When in doubt, ask the manufacturer."

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#36
In reply to #26

Re: threaded rod buckling and sagging

11/29/2015 6:03 AM

I doubt they would give a figure for a 7m long, 10mm dia rod in compression. It would be of no practical use.

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#5

Re: Threaded Rod Buckling and Sagging

11/24/2015 11:17 AM

42.

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#21
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Re: Threaded Rod Buckling and Sagging

11/25/2015 2:33 AM

LOL!!

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#29
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Re: Threaded Rod Buckling and Sagging

11/25/2015 1:40 PM

It's the only answer I know given the amount of information provided in the question.

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#6

Re: Threaded Rod Buckling and Sagging

11/24/2015 12:10 PM

no sizes, descriptions, material?.... and expect a reasonable answer.

You give us way too much credit.

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#7

Re: Threaded Rod Buckling and Sagging

11/24/2015 12:28 PM

For an unknown material, destructive testing is a solution...

https://www.youtube.com/watch?v=D8U4G5kcpcM

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#8

Re: Threaded Rod Buckling and Sagging

11/24/2015 1:00 PM

Threaded rod per se is used only for tension, not for compression.

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#9
In reply to #8

Re: Threaded Rod Buckling and Sagging

11/24/2015 1:03 PM

This comes to mind, The Hyatt in Kansas City

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#10
In reply to #9

Re: Threaded Rod Buckling and Sagging

11/24/2015 1:26 PM

Speaking of the Hyatt disaster, here's an excellent article about the (lack of) engineering ethics that resulted in complete system failure:

http://insights.globalspec.com/article/1408/disaster-in-kansas-city-a-lesson-in-an-engineer-s-responsibility

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#14
In reply to #10

Re: Threaded Rod Buckling and Sagging

11/24/2015 8:40 PM

Hats interesting, when i left a company where I was the engineering manager, they had me hire my replacement.

In my interview with the candidates, we talked (actually I lead them to discuss) about the various responsibilities, costing, profitability, ease of maintenance, design for manufacturing, etc,...

After discussing this, I asked a very direct question, and that was, if you had to name one item at the top, what would it be,... I receive answers all over the board. And I always replied, to the candidates answer with "Interesting". To see what their response was. Out of, I can't recall how,any I interviewed, only one asked my what I meant by, "interesting".

My reply was, " well, I never would have said that,"

The candidate then asked, what I would have said.

My response was "Product Safety".

For that (because he asked what I would have said) and other reasons, he was the one I hired as a replacement.

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#22
In reply to #8

Re: Threaded Rod Buckling and Sagging

11/25/2015 2:35 AM

GA

The first one to say it reading down from the top!! Well said!!

Using it in any other way, is simply wrong......

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#27
In reply to #8

Re: Threaded Rod Buckling and Sagging

11/25/2015 11:53 AM

Especially the 10m length in #3. For tension you need to know the yield stress of the material, calculate the x-sectional area and use a decent factor of safety based on dead and live loads.

You can get a lot of information out of AISC or CISC handbooks. (American or Canadian handbook of steel construction)

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#11

Re: Threaded Rod Buckling and Sagging

11/24/2015 1:59 PM
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#12

Re: Threaded Rod Buckling and Sagging

11/24/2015 4:46 PM

You state that it is 10mm diameter and 7m long ?

This sounds very impractical. It sounds almost impossible to install unless it is a cable, in which case you would need to look up the safe working load in the manufacturers catalogue.

It does sound like you need to talk over the whole problem with someone with experience. I think therefore your best bet is to find that person and present the entire problem to them. There is probably more to this than we can answer here given the little information that has been so far put forward.

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#15
In reply to #12

Re: Threaded Rod Buckling and Sagging

11/24/2015 8:41 PM

Maybe to hang have ducting.

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#28
In reply to #12

Re: Threaded Rod Buckling and Sagging

11/25/2015 11:57 AM

Can be used as sag rods in steel construction, but 10mm is rather small for this use at 7m length.

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#13

Re: Threaded Rod Buckling and Sagging

11/24/2015 5:15 PM

I don't know, but whatever you do, do not slide down it without thick trousers and gloves.

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#16
In reply to #13

Re: Threaded Rod Buckling and Sagging

11/24/2015 8:42 PM

How about doing it commando?

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#17

Re: Threaded Rod Buckling and Sagging

11/24/2015 10:39 PM

Depending upon your application , what you want are shear yields and compressive load yields , each will change according to the material , and the diameter of the threaded rod . For example , a threaded rod may be held in tension , fixed at both ends , and so a tension failure would be at maximum yield , or proof yield . Each material has a different yield , either in PSI or a Metric equivalent . Say 4130 chrome moly steel may have a proof yield in excess of what you want , in pure tension , for a threaded rod of , say , diameter 0.50 inches , proof yield may be as high as thousands of pounds , depending on
if the rod is in pure tension , or not . This is what you need to find out . Unthreaded has a higher load capacity , you may want to take a shank , no threads , and cut threads into it for a certain distance . A machinist who works with tension bearing rod can tell you how much thread you need to bear a certain amount of stress in tension .

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#20
In reply to #17

Re: Threaded Rod Buckling and Sagging

11/24/2015 11:20 PM

1. Why would a sane person ever put a 10mm diameter, 7m long piece of threaded rod in compression?

2. Unthreaded rod?

3. Threads are well defined and should not be cut, but rolled, if maximum performance is desired.

The OP has given no indication they are able to understand any information provided, since their question gives no indication of fundamental knowledge of materials, or mechanical engineering in general.

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#23
In reply to #20

Re: Threaded Rod Buckling and Sagging

11/25/2015 2:43 AM

I have to agree with you on all three points!!

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#30
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Re: Threaded Rod Buckling and Sagging

11/25/2015 2:30 PM

Yes, but point 1 is all that needs to be said.

You couldn't put 5 pounds of compression on a 0.4" diameter 22' long rod before it deformed.

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#31
In reply to #30

Re: Threaded Rod Buckling and Sagging

11/25/2015 3:58 PM

For an even better laugh: BRAKING CALCULATION FOR GO KART

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#33
In reply to #31

Re: Threaded Rod Buckling and Sagging

11/25/2015 6:35 PM

He is evidently using trees as brakes.

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#34
In reply to #31

Re: Threaded Rod Buckling and Sagging

11/26/2015 4:21 AM

When you were as young as this guy I doubt that you would have done it better. I do not consider that this attitude is the one we should have. He took equations from books and those are correct but he still does not know how to think "engineering". Such guys deserve support in comparison with those who ask with the goal to avoid own work.

We should be CONSTRUCTIVE and not DESTRUCTIVE. I know that such an opinion about Lyn's comment will lead to a lot of nasty remarks but I do not mind.

I say what I think and think what I say, this is my basic principle.

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#35
In reply to #34

Re: Threaded Rod Buckling and Sagging

11/26/2015 9:59 AM

I agree that we should all speak frankly, as you have done.

No one should take offense when others speak the truth.

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#38
In reply to #30

Re: Threaded Rod Buckling and Sagging

12/04/2015 3:22 AM

<...0.4" diameter 22' long rod...> That's not a rod; it's a cable.

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#18

Re: Threaded Rod Buckling and Sagging

11/24/2015 10:49 PM

Roark's Formulas for Stress and Strain , Chapter 7 , deal with Tension , Compression , Shear and Combined Stress .McGraw Hill ISBN # 0-07-072542-X . Here you may find correlating numbers to your application. Probably the toughest would use cold rolled high alloy steel , in pure tension . I assume you are after a steel tension member . Compression means a crush force , and if you are afraid of bending a threaded piece that is any length at all , you should be careful . Even strong alloy steel , like a threaded rod , if it's compressed , will eventually buckle under load . The PSI rating may not help you , this is a manufacturer's code , and is developed by stressing a member in context , like between two surfaces which are pulling apart , or shearing a bolt , as you would if you wanted to attach two metal pieces together , which held say , a hull together , and tended to pull in different directions ( in shear ).

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#19

Re: Threaded Rod Buckling and Sagging

11/24/2015 11:06 PM

Wiley Engineer's Desk Reference ISBN # 0-471-16827-0 lists Structural Steel , and will give you a reference , a starting point . A36 Carbon Steel has a Minimum Yield Stress of 36 ksi , Tensile Stress 58-80 ksi . Higher strength alloy , different shear numbers. A 325 is structural bolt steel , high carbon , high tensile yield . And an A 325 bolt maybe is the strongest type , not absolutely , but off the shelf , that I would recommend. Say take a bolt with a shank diameter of 5/8 inches , and a length of 7 inches , and arrive at a yield strength , making sure that you take into consideration how may inches ( or mm ) you need threaded , at your attachment point . For any given change in length of threaded portion , your yield will change . An unthreaded shank will hold more in tension than a threaded shank . An A 325 7/8 " shank bolt 10 inches long may be able to withstand a tensile load of 5,000 pounds , in pure tension.

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#24

Re: Threaded Rod Buckling and Sagging

11/25/2015 8:38 AM

Use the American Institute of Steel Construction (AISC) "Steel Manual"....either ASD or LFRD: the choice is yours.

You shouldn't be using thin rods in compression due to buckling. Only a moron would do this.

The net tensile area in the threaded region (say at end connections and intermediate turnbuckles) will govern in regard to Tensile Stress in Threaded Rods. Do NOT use the Gross cross-sectional area to properly size the rod.

A must: Design Tensile Stress < Allowable Tensile Stress.

SMH....

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#25

Re: Threaded Rod Buckling and Sagging

11/25/2015 9:27 AM

Limits of threaded rod:

In Tension - When it starts to stretch past its elasticity point, meaning that when the tension is released, the thread is longer than when it started.

In Compression - When it deforms past the point of elasticity, meaning that when the pressure is removed, it does not return to its previous straightness.

Limits of OP:

- Asks general open ended question with insufficient details to provide an intelligent answer.

- Expects anonymous group of online persons to take time out of their busy day to cater to his needs, for free.

- Is most likely WAY underqualified for the job assigned to.

You're welcome.

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#32

Re: Threaded Rod Buckling and Sagging

11/25/2015 4:43 PM

Between not much and a whole lot! When it turns into a pretzel, it was too much. -- JHF

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#37

Re: Threaded Rod Buckling and Sagging

11/29/2015 8:13 AM

I am still not sure if the notion of buckling is understood by you however looking at all the blabla you got I prefer to give you a QUANTITATIVE way to estimate how your question could be answered.

The thread M10x1.5 has an internal diameter of 8.325 mm and an equivalent diameter for loading dc= 8.593 mm. I presume the rod is made of steel with a Young modulus of 2E5 N/mm² and a yield limit if 150-200 N/mm².

The giration radius of the area (internal) is r=di/4= 2.08 mm,thus the slimness is λ=L/r=7E3/2.08=3363. If λ>160 the stability loss is in the elastic domain and the critical load is P*buck= π²*E*J/(Lf²) where J= π*di^4/64 = 235.8 mm^4

Because of the VERY high value for λ the Lf=L=7000 mm.

P*= 9.5 N = 2.135 lbs. Since in stability even small deviations from the straight line have important effects the usual safety coefficient is around 6 which means the rod should NOT be loaded in COMPRESSION with more than 0.3559 lbs = 1.58 N.

This for buckling, now for TRACTION. The are to be considered is Ac=π*dc²/4=57.99 mm². Thus the traction force limit at the yield limit of the steel used for the bar will be P*trac= 8699...11598 N = 1955.6...2607 lbs. safety coefficient depending on the load kind are between 3 and 10.

As you see the ratio between traction and compression limits is 640...2139!

Does it make clear why such bars can ONLY be used in traction?

I do not go into the discussion if a M10 should or not be used in such works this is clear when you look at the values. It can only be mentioned that for places where human beings are using the construction safety values turn around 10.

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