strength of threaded rod?

S'mise

Senior Member
Location
Michigan
An electrical question although I'm not using it for electrical purposes.

What is the shear strength of standard galv threaded rod 5/8"?
Searching the web results in a wide range of answers.

​​​​​​Shear strength is said to be 60% of tensile strength.

Is there a reference that you trust?

​​​​​​In other words, If a 5/8 threaded rod is inserted into a wall, how much downward force can it bear (close to wall) before shearing off?
 

gar

Senior Member
190910-0638 EDT

I did not do any great amount of checking, and did not look at an old textbook. But you can expect a lot of different answers. One major factor is what is the assumed safety factor.

The kind of steel, processing, and heat treatment are major factors, and where it was made.

One interesting site is http://www.barnhillbolt.com/specs/Ep...wShearPerf.htm . But the site does not directly specify assumptions. It does compare 1018, ordinary low carbon CRS, 4140 a very good heat treatable alloy, and stainless.

If you assume 50,000 PSI for tensile strength, 0.3 sq-in reduced by some factor to get minor diameter, possibly 0.2 sq-in, then tensile is about 10,000 #. So 3000 # from the above site may not be too bad of a figure.

Just for comparison the tensile loading on a typical automotive pinion is about 25,000 to 35,000 #. These run with nil failure rate under some sever conditions.

.
 

kwired

Electron manager
Location
NE Nebraska
Temporary bracing in wood frame construction - what fasteners should one trust more, especially something that is to hold while you are working on the structure?

With lateral forces softer metal nails bend, but generally don't break. Hardened screws break quite often. But the screws are stronger when it comes to linear forces, plus engaged threads help hold more.

There is give and take here depending on what the goals are and composition of metal and heat treatments change those results.
 
Standard threaded rod is not very strong. Probably roughly equivalent to a grade 2 bolt, ~ 60KSI. You can get higher grades from a place like mcmaster carr. I remember looking into this in the past, and my recollection is that for steels you can figure shear strength is about 50% of tensile strength which isnt too far off from your figure. There is this thing called "maximum shear theory" that says that I think.
 

S'mise

Senior Member
Location
Michigan
Thanks for your advice but much of this confuses me.
Lets assume worst case and its soft crs threaded rod.
Barnhillbolt says tensile 2940 which is about 1500 shear?
Then, itwreadhead say 5870 tensile.
Why twice as much?
 
Thanks for your advice but much of this confuses me.
Lets assume worst case and its soft crs threaded rod.
Barnhillbolt says tensile 2940 which is about 1500 shear?
Then, itwreadhead say 5870 tensile.
Why twice as much?
Those red heads could be a higher grade steel. High grade steel is three times as strong as low grade. Grade 2 bolt is 60ksi, grade 8 is 150ksi - huge difference.
 

oldsparky52

Senior Member
Thanks for your advice but much of this confuses me.
Lets assume worst case and its soft crs threaded rod.
Barnhillbolt says tensile 2940 which is about 1500 shear?
Then, itwreadhead say 5870 tensile.
Why twice as much?
Barnhillbolt is allowable shear loads and itwreadhead is Average Ultimate Tension and Shear Loads, note 1 says the static loading should not exceed 25% capacity or the allowable load of the anchor rod. 5870 * .25 = 1,468.
 

oldsparky52

Senior Member
I don't know what you are engineering, but you might be surprised at how reasonable a 30 minute sit down with a structural engineer can be. It's worth making a phone call if people are involved or could get hurt from what you are doing.

Then again, maybe I'm just paranoid.
 

S'mise

Senior Member
Location
Michigan
Those red heads could be a higher grade steel. High grade steel is three times as strong as low grade. Grade 2 bolt is 60ksi, grade 8 is 150ksi - huge difference.
Both should be the same under column SAE1018/A307.
To Kwired's point, isn't it better for bending of softer metals as opposed to a harder grade/strength that would be more likely to snap off?

For instance stainless steel is very hard but breaks much easier than softener steel.
 
Both should be the same under column SAE1018/A307.
To Kwired's point, isn't it better for bending of softer metals as opposed to a harder grade/strength that would be more likely to snap off?

For instance stainless steel is very hard but breaks much easier than softener steel.
There is a common myth that, say, a grade 5 bolt is better than a grade 8 bolt because grades 8's are brittle. This is not true. A grade 5 will have exceeded yield and failed before the grade 8 even enters the plastic region.

Another thing to to consider about bolted joints is that bolts generally do not see much shear due to the tremendous friction between the shearing parts.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Another thing to to consider about bolted joints is that bolts generally do not see much shear due to the tremendous friction between the shearing parts.
This is correct. When you see the large splices in steel beams holding up interstate overpasses, it's the friction between the splice plates and the beams that provides the strength of the joints, which comes from the bolts' tensile strength, not shear strength.
 

S'mise

Senior Member
Location
Michigan
There is a common myth that, say, a grade 5 bolt is better than a grade 8 bolt because grades 8's are brittle. This is not true. A grade 5 will have exceeded yield and failed before the grade 8 even enters the plastic region.

Another thing to to consider about bolted joints is that bolts generally do not see much shear due to the tremendous friction between the shearing parts.
That's a greateat point. Can I assume threaded rod shear is essentially the same? That is, the weak point in either being the narrowest part of the thread?

Is tensile strength higher in a bolt since the head of a bolt would be stronger than a nut?
 

Carultch

Senior Member
Location
Massachusetts
That's a greateat point. Can I assume threaded rod shear is essentially the same? That is, the weak point in either being the narrowest part of the thread?

Is tensile strength higher in a bolt since the head of a bolt would be stronger than a nut?
There are formulas for "stress area of a bolt", and you can find online calculators that implement them. It is a function of nominal diameter and thread pitch. It is not necessarily equal to the minor diameter's area at the root of the threads, because of the way stress flows around the irregularities of the threads.

The nut is sized to have a thickness & thread engagement deep enough so that the bolt body ruptures before the threads strip. The head of a bolt is inherently stronger than the engagement of the nut, because it is rigidly cast as part of the bolt.
 

wwhitney

Senior Member
Location
Berkeley, CA
There is a common myth that, say, a grade 5 bolt is better than a grade 8 bolt because grades 8's are brittle. This is not true. A grade 5 will have exceeded yield and failed before the grade 8 even enters the plastic region.
But it depends on what the demand on the bolt is. If it is to resist a bounded force, then what you say is true. If, on the other hand, there is a displacement demand on the bolt (i.e. a very large force at 0 displacement that reduces as the displacement increases), then the grade 5 bolt may survive by yielding, while the grade 8 bolt may not have enough yield capacity and undergo brittle failure.

Cheers, Wayne
 

S'mise

Senior Member
Location
Michigan
No one asked what material the bolt was going through. Steel, wood, concrete, steel to wood, steel to concrete, wood to concrete.
No bolts.
5/8 threaded rod going through vertical wood timbers (10ft span) with flat washers and nuts on either side holding 2x10 horizontal planks on each side of them.

Trying to get a ballpark idea of the downward force it can withstand before shearing.

I assume If load is placed in center the rod can safely hold 2936lbs (1468 x 2).

....Or, perhaps x4 as there's 4 contact points.
 
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