ASTM A325 9

[lesdurham]

I AM TRYING TO FIND A REFERENCE CHART FOR THE TORQUE SETTINGS REQUIRED TO INDUCE A TENSILE STRESS OF 70% OF YIELD STRENGTH OF A325 BOLTS. THE STRESS NEEDS TO BE IN kips

 

[TVP]

There is a lot of information on this site regarding fasteners, torque, etc. Check out this thread:

thread288-21503

Also, you can perform an ADVANCED SEARCH using keywords like torque and fastener for more information.

 

[Rjeffery]

RCSC Specifications for Structural Joints (11/13/85) states: "This specification does not recognize standard torques determined from tables or from formulas which are assumed to relate torque to tension."

As the condition of the individual bolt/nut/washer set changes the torque required to acheve the required tension changes. The only way to determine that value for the lot of A325 bolts is to use a Skidmore/Wilhelm, and take the average torque developed to meet the required tension.

 

[Kenneth]

Intrigued by Rjeffery’s reference above (See Qshake’s, Ron’s and evelrod’s comments at thread507-26703 as they relate to A325 bolt applications in particular, and my January 20, 2002 post at thread31-14960 on what I see as an over-reliance on “nut factor” type of data and/or "torque tables" for establishing installation torques for “critical” joints in general. Note: The first link provided in that post has since moved to

http://www.fastenal.com/documents/Miscellaneous/FastenalTechnicalReferenceGuide.pdf),

I tracked down the current (June 23, 2000) revision of RCSC’s “Specification for Structural Joints Using ASTM A325 or A490 Bolts (see

http://www.boltcouncil.org/download/RCSC Specification 6-23-2000.pdf).

It carries forward much of the language and requirements (see shaded “commentary” starting on page 50 of the document) noted by Rjeffery in the now-superceded ’85 document.

Thanks for the reference Rjeffery, this is definitely a “keeper”. I always enjoy it when I find (in this case, more like “am handed”) a “non-aerospace” document that I can use to shame less “enlightened” “aerospace” co-workers with, as in: “See, not even the civil engineering guys would do that..." (No flames please. The last really was intended to be a good-natured -- and completely undeserved -- jibe. “You guys” really do impress me.)

 

[CoryPad]

I would like to provide an automotive perspective for this thread. Automotive companies routinely use 3 procedures for setting torque specifications. These include:

1) use a standard value from a table for noncritical applications (example: M6 screw to attach wiring clips to vehicle structure)

2) use calculation for a non-safety-critical, but structural application (example: M10 screw to attach powertrain mounts to vehicle structure)

3) use testing for safety-critical applications (example: M12 nut to attach steering arm to upright)

Automotive companies have spent considerable time developing materials and coatings specifications for fasteners. For example, friction coefficient is tightly controlled, so using calculations like those from VDI 2230 Systematic Calculation of Bolted Joints (see the thread posted by TVP above) can be used with confidence.

I concur with previous comments that tables and calculations cannot be used for critical attachments if there is no knowledge about the important joint variables. However, calculations are very accurate is the variables are known. These include:

joint geometry
joint material properties
fastener geometry
fastener material properties
friction coefficients
input forces
input torque variation

 

[Rjeffery]

If the application is in a staticly loaded structure and IDEAL conditions were maintained, torque to tension conversion would be a reasonable and cost effective way to ensure tension at 70% yield strength. BUT, most ironworkers don't understand (or don't care) why keeping the fastners clean and dry is so important. they just want to stuff the hole, go and blow. the phrase I hear over and over is "I can't see that from MY house!" and it makes my ears burn.

The last job I was sent to inspect has me face to face with the iron worker foreman who told me that I didn't need to look at any thing because he had personaly 'torqued' all the 3/4 inch bolts to 490 ft/lbs 'just like it said on the bolt head...'

OBTW turn of the nut was specified and there was a pile of sheared bolts in the dumpster!

I also found 35 shoulder bound bolts!

Torque should never be specified for buildings.

I can see the need for uniform tension on a head or oil pan in the automotive field and that is achieved by specifing a standard torque value. But most mechanics (marine, aerospace, rail or automotive) are fastidious.

 

[Kenneth]

As someone who works and lives in those buildings, thank you!

 

[Rjeffery]

And for your kind words, thank you, Kenneth.

 

[THEHERR]

Les,
Torque is not a reliable means of achieving tension load in bolt assemblies. According to the RCSC, you can get as much as +/-40% variation from one bolt assembly to the next using torque as your installation criterion. See if you can get a copy of the Research Council on Structural Connections manual - Specification for Structural Joints using ASTM A325 or A490 Bolts -

http://www.boltcouncil.org.

This will give you much useful information. Check out load indicating washers or ultrasonics, depending on what you want to spend.

 

[Kenneth]

THEHERR,

The direct link to that document (which was referenced by Rjeffery in this thread) is included in my Dec 9, 2002 post above ...