You basically want to replicate your bolting procedure just like you were bolting a connection. The Skidmore just proves that you are in fact tensioning the bolt,washer, and nut combination to the correct tension by using your bolting procedure. Testing several bolt assemblies(min of 3) from each lot is also required to verify the bolts, ie. TC bolts should be wringing the splines off at or above the min. tension given in the RCSC tables. I'll try and give more specific instructions at a later time. I'm very busy at the moment and will try to give a better reply soon if no one else replies before then,
John Wright
Check out this, it will be a help to you, if you could get your hands on a copy.
http://www.steelstructures.com/SBH/SBH%20general.htm
Hi,
Not a procedure, but here's how the Skidmore works. The device is a hydraulic load cell. Tightening the bolt creates pressure in the unit. The inter-changeable bushing in the back of the Skidmore sits in a piston. Between the piston and the body of the unit is hydraulic fluid which is compressed by the tension in the bolt. This hydraulic pressure is then read on a dial gage, scaled to read in terms of bolt tension in thousands of pounds (kips), rather than psi of hydraulic pressure. Because of the slight movement of the piston, the unit underestimates the actual tension that would be put into a bolt for a given rotation. Some of the rotation is taken up by piston movement. In the structure, the steel does not compress and all rotation is used to tighten the bolt. Bolt calibrators should be checked at least annually for accuracy.
Did you purchase your own Skidmore or just rent one for the audit? An M (most common) or an MS (for short structural bolts) model? Having managed a calibration company in the past, I have calibrated, serviced, rebuilt, etc. more of these than you can throw bolts at. Please see a link to the Skidmore website: ( http://www.skidmore-wilhelm.com/products/m_110_2.asp ). John Wilhelm is a very nice gentleman and I am sure would be happy to assist any way he could.
I know this is a welding forum, but many here probably use Skidmores. May I respectfully make a couple of suggestions:
1) Be sure the calibration facilty you use actually puts the Skidmore in a test frame and applies the forces to the whole assembly. There were a few calibration companies we "competed" with who would take the gauge off and put it on a pressure test bench or dead weight tester. NOT a valid way to calibrate/verify a Skidmore. Gets you close, but no cigar. We had various test frames that could exert forces to over 2,000,000 lbf, so 100,000 lbf was no problem.
2) Depending upon how well the Skidmore will be cared for in your facility, buy an extra pressure gauge and an extra seal kit. Sooner or later you will need them and that will always be when you can least afford to be down. Spend the money to have the extra gauge placed on the Skidmore when it is being serviced and have it calibrated and put it on your shelf. The seals are relatively easy to replace by a competent maintenence man. Just fill with hydraulic oil and bleed the air out of the system.
The advise above for use of the Skidmore is sound.
Skidmores are simple and complicated at the same time. This isn't meant to be a smart alec reply, once you get through it you will know what I mean.
Basically, for "turn-of nut" tightening you select 2 fastener assemblies and install them one at a time in the Skidmore exactly as they will be installelld in production. (tightening the nut? tightening the bolt?)
Tighten to snug tight (~10% of the MBT)
Mark the nut and face plate
Turn the nut the additional amount from turn of nut tables
Verify the tension registered on the Skidmore is at least the minimum required.
That is very much oversimplified and there are many other things that need to be addressed. I would suggest reviewing again the RCSC section 16.4 in the 3rd edition of the 'Manual of Steel Construction'. You should be able to get what you need out of that. Also look at the bolting requirements for the various state DOTs, and AASHTO, and also info from Skidmore-Wilhelm. Some states have written out some pretty good procedures within their Standard Specs.
But if the steps are still unclear, I would suggest contacting SSTC for their Structural Bolting course. That course is well put together, is done as self-study, and is a good way to document training. It also helps you to understand why the various steps are important.
During the audit, you (or someone from your company) will be required to demonstrate how to perform a pre-installation verification check. You do not normally have to have procedures for more than the "turn-of-nut" tightening method if that is all you do in practice. However if your procedures address DTI's, calibrated wrench tightening, TC bolts, or etc, you will be required to demonstrate those installation procedures. In other words, make sure your procedures address what you actually do, but the more you add, the more you will be audited on. It is perfectly OK to state in your procedures that methods you don't normally use will be addressed on a job specific basis when the contract requires.
Hope that helps.
Chet Guilford
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