Per ASTM F3125 Annex section 2.1.1, the rotational capacity test is defined as a test, “intended to evaluate the presence of a lubricant, the efficiency of lubricant and the compatibility of assemblies.” In a 1970 study referenced by the Research Council on Structural Connections (RCSC), it was shown that galvanizing increases the friction between the bolt and nut threads as well as the variability of the torque-induced pretension. A lower required torque value and more consistent results are obtained when lubricated nuts are used as part of the bolt assembly. Rotational capacity testing must show that the galvanized lubricated nut may be rotated from the snug tight condition well in excess of the rotation required for pretensioned installation without stripping. In layman’s terms, the test is required to show that the nut will not gall on the bolt and that the assembly will develop the pretension load desired.
Since this test requires that each material lot of bolt and nut be tested individually, contractors will typically administer this test on the job site. However, Portland Bolt performs this test in our facility prior to shipping.
This video is a quick example of a few steps required when performing a ROCAP test.
Procedure
1. Standard A325 Rotational Capacity Procedure
The bolt, nut, washer assembly shall be assembled in to a steel joint so that 3-5 threads are located between the bearing surfaces of the bolt head and nut. The assembly shall be tightened to no less than 10% of the specified proof load. After initial tightening, the nut position shall be marked relative to the bolt and the specified rotation shall be applied. The specified rotation shall be as follows:
- 2/3 rotation (240deg), for bolt lengths that are 4 times the diameter or less.
- 1 rotation (360deg), for bolt lengths that are over 4 times diameter but no more than 8x.
- 1-1/6 rotation (420deg), for bolt lengths that are greater than 8 times diameter.
- For lengths over 12 times the diameter, the test is not applicable.
After the tightening rotation has been applied, the assembly shall be taken apart and examined for compliance. The assembly fails to pass if any of the following occur:
- Inability to install the assembly to the nut rotation specified.
- Inability to remove the nut after installing the the specified rotation
- Shear failure of the threads as determined by visual examination following removal.
- Torsional or tension failure of the bolt. Elongation of the bolt, between the nut and bolt head is to be expected and should not be classified as a failure.
2. Department of Transportation (DOT)/AASHTO Rotational Capacity Procedure
- 2/3 rotation (240deg), for bolt lengths that are 4 times the diameter or less.
- 1 rotation (360deg), for bolt lengths that are over 4 times diameter but no more than 8x.
- 1-1/3 rotation (480deg), for bolt lengths that are greater than 8 times diameter.
After the tightening rotation has been applied, the assembly shall be taken apart and examined for compliance. The assembly fails to pass if any of the following occur:
- Exceeding the maximum allowable torque in the torque/tension comparison.
- Failure to achieve the required rotation.
- Failure to achieve the required tension at the required rotation.
- Thread failure. The nut shall turn, with your fingers, on the bolt threads to the position it was in during the test. If you cannot turn the nut with your fingers it is considered thread failure.
- Torsional or tension failure of the bolt. Elongation of the bolt, between the nut and bolt head is to be expected and should not be classified as a failure.
Examples
- Bridge Rotational Capacity
- Standard
- Federal Highway Administration
Referencing Specifications
- Procedures for Performing Rotational Capacity Test – United States Department of Transportation
- ASTM A325 10.2 – Testing
- ASTM Work Item WK15535 Test Methods for Rotational Capacity Testing of Plain or Coated Bolt, Nut and Washer Assemblies
This Rotational Capacity test can be applied to galvanized bolts of other grades different from A325? how about grade 5 or grade 8 bolts? the difference in head dimensions from heavy hex fasteners is something that variate the minimun tension, max torque values from this test?
@Ricardo- A test can be performed on any grade you like, but the parameters and procedures would need to be modified to suit the grade being tested. The details of which we would leave up to the requestor.
What about metric size bolts testing. Can we test M20 dia bolts with 3/4″ plates and bush.
@Waqas- apologies, but we are not familiar with the specifics of testing metric fasteners and so are unsure of the answer to your question. Apologies.
what is the percentage required for testing from each lot of assemblies ? for
example if i am making 400pcs how many assemblies need to be sent out for testing ?
@Les- The test sample quantity varies based on the number of bolts in the lot, and is not a linear value. For 400pcs, you’d need to test three assemblies.