Advice request from mechanical engineers

[ROUSTABOUT]

Here in oilfield country, local supply houses have grade 10 all thread.

 

[mikester]

Can someone please explain why this chart is different from my expectation? Is hanger rod different from all thread? Did I come as close to fouling up as the ME said? Thanks in advance for your replies.

Maybe the chart is different than your expectations because you need to reassess your paradigms

There are reasons why we have Professional Engineers and it isn't to do with job protection...

 

[Streetcar]

Maybe someone knowledgeable in mechanical engineering can explain a situation to me. I used some 1/2" all thread on a project and was told that the maximum tensile load I could allow for is 550 poundsper all thread. This was based on the information in a chart that I later found on engineering toolbox.com

Threaded Rods - Loads in Imperial Units

Weight rating of threaded hanger rods.

www.engineeringtoolbox.com

As it was explained to me, since the allowable load on a 1/2" threaded rod is 1100 pounds per inch (according to the chart) and I was using a nut that was about 1/2" thick then I was only able to put a 550 pound load on that all thread.
When the chart was presented to me the note at the bottom was cropped out, that note states "The maximum loads in the table above are based on allowable tensile stress of 12 kpsi - reduced by 25% to 9 kpsi allowable stress." My understanding is that all thread is based on 60kpsi material. For background what I did with the all thread and nuts is this: I rolled a 1200 pound transformer into extremely tight quarters on a dolly then used the all threads (2) that were attached to an overhead beam as a screw jack to lift the transformer off the dolly and then lower it down in place. The task was performed successfully and no strain or imminent failure was noted.
Can someone please explain why this chart is different from my expectation? Is hanger rod different from all thread? Did I come as close to fouling up as the ME said? Thanks in advance for your replies.

Your question is structural and not mechanical
the all thread has safety factors for the load to assure the rod is not damaged or fails by fatigue.
without the proper equipment you can not measure strain on the all thread
as others noted there are different grades of steel
with your procedure you cut into safety factor, not close to failure

 

[jb1390]

Maybe someone knowledgeable in mechanical engineering can explain a situation to me. I used some 1/2" all thread on a project and was told that the maximum tensile load I could allow for is 550 poundsper all thread. This was based on the information in a chart that I later found on engineering toolbox.com

Threaded Rods - Loads in Imperial Units

Weight rating of threaded hanger rods.

www.engineeringtoolbox.com

As it was explained to me, since the allowable load on a 1/2" threaded rod is 1100 pounds per inch (according to the chart) and I was using a nut that was about 1/2" thick then I was only able to put a 550 pound load on that all thread.
When the chart was presented to me the note at the bottom was cropped out, that note states "The maximum loads in the table above are based on allowable tensile stress of 12 kpsi - reduced by 25% to 9 kpsi allowable stress." My understanding is that all thread is based on 60kpsi material. For background what I did with the all thread and nuts is this: I rolled a 1200 pound transformer into extremely tight quarters on a dolly then used the all threads (2) that were attached to an overhead beam as a screw jack to lift the transformer off the dolly and then lower it down in place. The task was performed successfully and no strain or imminent failure was noted.
Can someone please explain why this chart is different from my expectation? Is hanger rod different from all thread? Did I come as close to fouling up as the ME said? Thanks in advance for your replies.

I'm not completely sure I understand the question. The chart you are showing lists allowable capacities when using threaded rod as a hanger, and contain significant safety factors compared to what would actually fail. Given various vibrations, dynamic load, material variations, etc, safety factors are common to ensure that you don't design something right on the edge of failure.

I'm not sure where the 550 pound number is coming from, or the 1100 pounds per inch - I will say that as a rule of thumb, 3 threads or so of similar strength material is required to ensure that the main rod is what is limiting, not the threads. So, a thin nut will tear threads before you would break the rod. The same is true if you are using a softer material. It takes more threads of aluminum to achieve the same strength than it does in steel. So if using a thin nut or softer material nut, you would need to reduce holding capacity compared to what the rod itself is capable of holding.

But assuming you are using a standard thickness nut of similar grade to the rod, the chart indicates to me that a half inch diameter threaded rod is rated to hold 1100 pounds. No multiplier. This aligns with my calc - cross sectional area of 1/2-13 is .136 square inches, multiplied by 9 ksi is 1230 pounds. They rounded down on area in the chart even lower.

As far as how you used the rod, seems fine to me. If doing this continually you might find that the threads on 1/2" rod will potentially gall or wear faster than rod that is larger. Lubrication and frequency of usage would help determine that. A nut that engages more threads would also reduce the pressure on the threads and help them last longer. For lot of cycles at high stress, there are better designed threads (ACME as example), that are more difficult to make but better suited for that task. For one time use, obviously what you did worked.

 

[Deleted member 216442]

Maybe someone knowledgeable in mechanical engineering can explain a situation to me. I used some 1/2" all thread on a project and was told that the maximum tensile load I could allow for is 550 poundsper all thread. This was based on the information in a chart that I later found on engineering toolbox.com

Threaded Rods - Loads in Imperial Units

Weight rating of threaded hanger rods.

www.engineeringtoolbox.com

As it was explained to me, since the allowable load on a 1/2" threaded rod is 1100 pounds per inch (according to the chart) and I was using a nut that was about 1/2" thick then I was only able to put a 550 pound load on that all thread.
When the chart was presented to me the note at the bottom was cropped out, that note states "The maximum loads in the table above are based on allowable tensile stress of 12 kpsi - reduced by 25% to 9 kpsi allowable stress." My understanding is that all thread is based on 60kpsi material. For background what I did with the all thread and nuts is this: I rolled a 1200 pound transformer into extremely tight quarters on a dolly then used the all threads (2) that were attached to an overhead beam as a screw jack to lift the transformer off the dolly and then lower it down in place. The task was performed successfully and no strain or imminent failure was noted.
Can someone please explain why this chart is different from my expectation? Is hanger rod different from all thread? Did I come as close to fouling up as the ME said? Thanks in advance for your replies.

I realize this thread is old. I'll respond late. The published allowable load for each allthread is not "1100 pounds per inch." It is 1100 pounds. It is based upon a maximum allowable tensile stress of 9000 psi. It is calculated as Max Load =1100lb/0.13in**2= 8461psi which is approximately 9000 when rounded. That is their allowable stress calculation to avoid tensile failure in the rod. It has nothing to do with the shear stress in the threads between the nut and rod when the nut takes the rod's axial load and transmits it to the hangar. Your 1100 pounds per inch comment suggests you may be thinking about preventing failure in the threads. If you lifted 1200 lbs. using 2 rods, the tensile stress in each of your rods was 1200lb./(2)(0.13in**2)=4615psi. Quite safe as far as tensile stress in each rod. Mild steel will yield at around 30,000psi and allthread will likely have better material properties. So if you tried to lift about 6 or 7 times as heavy an object you might approach the yield strength of the rods. Agree with previous commentor regarding not using thin nuts with few engaged threads but that's not what is being offered in the chart.

 

[ArlyA]

Understanding stress is what helps DIY people to make less mistakes.

 

[LD1]

Its just a generic chart with no identifiers for type, strenght, or grade of thread rod.

I take it quite simply as 5:1 safety factor for overhead suspended items. Puts 60ksi steel at a 12ksi limit.

Further reduced by 25%.....because thats about the reduction of yield strength vs tensile strength.

Put it in other words......60ksi tensil steel is probably ~45ksi yield strength. 45ksi with a 5:1 safety factor puts you at the 9ksi they used.....then thats simply 9000 pounds per square inch. use Pi x R squared

The fact that you lifted 1200# with TWO rods....puts you at about 600# per rod.....whereas the yield strength of the rod is alot closer to 6000lbs. So yea....no surprise it worked without a hitch

 

[mwayne]

Thanks for the replies. I communicated with the mechanical engineer through an in between and the in between has never been able to get a response to my question. The question is, Why are those numbers so different from my expectation? After the fact I found this from Home Depot's web site:
The 3500 lb. load is more in line with what I would expect from 1/2" all thread. Link to the website here:

Superstrut 1/2 in. x 10 ft. Galvanized Threaded Electrical Support Rod (Strut Fitting) ZR1048 - The Home Depot

The Superstrut Threaded Electrical Support Rod is designed to suspend Superstrut metal framing channel from ceilings. The rod features an electro-galvanized finish and has a 3,500 lbs. load capacity. Each piece is 10 ft. L with a 1/2 in. Dia.

www.homedepot.com

 

[ArlyA]

The structures of steel within it is quite interesting to me. For example, hot rolled has less strength than cold.

 

[CADplans]

Do you have a drawing, sketch or photo of how this rod would be used?
If the rod extends only 2X the diameter, then there is no worry about buckling.

So, how the rod is used is a major input as to what it can do.