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.