threaded rod allowable tensile stress

[gte447f]

I have seen 9000 psi used as an allowable tensile stress for threaded rod on several load tables from manufacturers, etc. Anyone know how this value was derived?

 

[Ron]

If you are using it for any critical structural application, get a mill certificate for the material. Threaded rod can come from anywhere and doesn't necessarily always comply with any particular standard.

 

[gte447f]

Ron, I agree that they can come from anywhere. I think that is the reason for the overly conservative 9000 psi allowable stress that is sometimes referenced. I found a reference in a footnote to a hilti product data sheet to MSS SP-58 which states 12000 psi for AISI 1010 steel. Hilti aplies a further 25% reduction to "allow for normal installation and service conditions".

 

[wannabeSE]

As you have already noticed, many of the pipe support manufactures seem to use 9 ksi for the allowable stress in threaded rods. Salmon and Johnson's Steel Structures Design and Behavior uses AISC 360-05 Section J.3 (bolted connections) to calculate the capacity of tension rods. When I want to justify more than 9 ksi for hanging equipment with A36 threaded rods, I treat it as a tension member (AISC 360 chapter D) and use the minor diameter of the threads to calculate the gross area.

 

[firai]

I can't find any references to AISI 1010 in MSS-SP-58, but section 4.7 in the document specifies the 25% reduction that Hilti applied as you pointed out.

Several different factors can contribute to safety factors much greater than typical structural specifications:
- MSS-SP-58 (and presumably whatever Hilti product you're looking at) was specifically developed for pipe hangers and supports. Safety factors for mechanical applications tend be grossly over-conservative to account for fatigue and other accidental loading conditions, and
- AISI 1010 doesn't specify any particular strength but only the composition. Unless tested or specified, the steel MAY have different properties/strength variabilities than A36 or A992.

Structural Design Engineer
New York, NY