When designing vertical rod bracing system I would like to use F1554 grade 55 rod to achieve smaller diameters. But if I use a turnbuckle I am limited to the safe working load of that turnbuckle. Is there a higher capacity turnbuckle available?

You are correct that your capacity would be limited by the safe working load of the turnbuckle, but it would be limited to that regardless of the grade of steel used for the bracing rod. Let’s assume you are using mild steel, A307/A36 rods. The minimum yield strength of that material is 36,000 psi. Using a 1″-8 thread size as an example with a tensile stress area (the area at minor diameter of the threads) of 0.606 sq in, the math works out like this:

36,000psi yield x 0.606 sq in = 21,816lbs

If we move to F1554-55, that number is a bit higher:

55,000psi yield x 0.606 sq in = 33,330lbs.

The safe working load of a normal 1-8 x 6″ turnbuckle is listed as 10,000 lbs, well below both of the above numbers. This is due to the substantial safety factor used on turnbuckles and clevises of 5:1. Anchor rods and cross brace rods do not normally have such a large safety factor built in, so in effect, comparing turnbuckles to the brace rods is not an apples to apples comparison.

That said, to answer your question as to the availability of high strength turnbuckles (and clevises), yes they can be manufactured and heat treated to higher strength capacities. Forging specification ASTM A668 has several grades, ranging from the non-heat-treated Class A (clevises) to the annealed or normalized Class C (turnbuckles) to the quench and tempered Class F. Additionally, and more economically, sleeve nuts made to ASTM A563 grade DH are easily manufactured and have a strength well in excess of the higher class turnbuckles.

See the below note from our turnbuckle and sleeve nut supplier:

“From a thread strength standpoint, the nut area of carbon steel turnbuckle bodies forged to ASTM A668 Class C is roughly equivalent to an ASTM A563 Grade C heavy hex nut. For applications where high strength rods are specified and ASTM A563 Grade DH or ASTM A194 Grade 2H nuts would normally be used, sleeve nuts should be considered in place of turnbuckles. Sleeve nuts can be manufactured to meet all of the strength requirements of the ASTM nut specifications and will allow the full strength of the rod to be exploited.”

So there are a few options available to help you design your bracing system in the best way possible. Portland Bolt is happy to provide you with the information and let you determine the best course of action for your situation. We can then work with our turnbuckle/clevis and sleeve nut supplier to provide you the proper hardware for your situation.

Note: Portland Bolt manufactures the rods that are a component of various tie rod assemblies. Although we do not manufacture turnbuckles, clevises, or sleeve nuts, we supply them as part of a complete assembly.

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10 comments

    I am designing a steel canopy supported by tie rods to the building exterior wall. Most architects like to see tie rod for tension resistance (i.e. deal + live loads). However, when we design the canopy with wind uplift load, these tie rods become compression members. Can a turnbuckle be capable of taking compression load? I show in u-tube an experiment of testing turnbuckle in compression, it appears to me that the rod fails in buckling action while the turnbuckle remains in good condition. Do you have any information for turnbuckle in compression load?

    @Ban- I am sorry, but we do not have any information regarding the compression loads of turnbuckles. I will email you the name of someone you might contact.

    @Mark- I will need a bit more information in order to answer any questions you have. I will send you an email for clarification.

    Dane,
    I am designing a Structural Reaction Test Frame, which must be anchored to an in place, reinforced slab. The Slab has #8 Structural Clevises, but the plans do not indicate the steel used. The building was constructed in 1962. To ensure the large loads that will be transferred to the slab, I would like to assume the safest possible strength for the steel. What is the lowest grade of steel used for structural clevises?

    @Conner – I consulted the AISC manual from 1970, it lists a safe working load for a #8 clevis of 135kips, although the safety factor calculations they used then were different than today. As far as I know, structural clevises were made then as they are now, from medium carbon steel like AISI 1035. If you want to be very conservative in your estimations, you could assume they would be made from nothing worse than A36/1018 steel.

    Dane,
    Are custom tap sizes readily available in both clevises and turnbuckles? Essentially, can a larger clevis/turnbuckle be used with a smaller rod to address the allowable load difference or are custom tap sizes too cost prohibitive to fabricate?

    @James – Yes, sometimes custom tap sizes would be available, it would just depend of the specifics of your request. If your custom sizes are not feasible with our standard forgings, specials could be manufactured or machined. That would escalate the cost significantly, whether or not it is cost prohibitive would be up to you. One man’s prohibitive is another man’s reasonable. We’d be happy to take a look at your requirements if you’d like to send them to us.

    Dane,
    I noted 2 items here that made me a little curious:
    1) the inquiry was for F1554 rod for use as vertical bracing.This is an off-spec application and I’m sure that you have similar off-spec requests regularly but you didn’t enlighten the readers but identifying the (assumed ASTM) F1554 spec and the variance.
    2) for a building or other engineered application (must be if F1554 is used), the rod needs to be checked for the gross area at yield and net area in the threaded area at ultimate, each with reduction factors, which may actually be less than the value indicated. Also depending on how the rod is threaded may affect these results.

    On the other hand, thanks for the suggestion for sleeve nuts to replace turnbuckles!

    @Paul Ransom – Yes you are correct that this is a bit of an off-spec application, however there are no other fasteners specific standards that cover 50/55ksi fasteners. Many tines engineers will specify A572G50 tie rods, but that is a structural steel spec, and so is a bit off-spec as well. As for comment #2, the threading method shouldn’t make a difference (as long as both are done properly), the thread geometry will be the same whether it is cut or roll threaded, but you are correct that using reduction factors will reduce the allowable rod capacity. I chose not to address that since the safety factor may vary from application to application.

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