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Pretensioning a threaded bolted connection

Pretensioning a threaded bolted connection

Pretensioning a threaded bolted connection

I am designing a bolted connection for a steel assembly, where the A490 bolts are required to be pretensioned per RCSC due to the loading condition. My issue is that the bolt connects an outer plate with a thru hole to a threaded plate since there is no access on the other side of the threaded plate to use a hex nut. I can find no guidance in RCSC for this type of connection. All I know to do is check the shear stress of the 50 ksi plate inside threads. Can I assume the full length of thread engagement for my shear plane? Also, very importantly, how do I perform skidmore testing for a connection like this? Any guidance would be much appreciated.

I do not have any flexibility to change the connection design at this stage - I am only looking for advise on how to analyze it and perform skidmore testing.

RE: Pretensioning a threaded bolted connection

Let me preface this by saying that these are just my thoughts and I am certainly not an expert with the situation described.

1. Skidmore testing - the purpose of this test is to verify that the installation technique is installing the bolts to the proper pretension. Typically, one of the major factors that affects this is coating on the nut and/or bolt in the actual installation conditions. As you won't be using a true nut, it seems to me the most proper thing would be to fabricate a "nut" with the same plate that your bolted connection is using and use that for the skidmore testing.

2. There may well be some issues with getting the proper pretension without stripping the tapped plate as a typical nut (A563DH) is quenched and tempered (maybe not?). I would say you will probably get full thread engagement though as the plate threads will yield locally and deform to bear on the bolt threads.

RE: Pretensioning a threaded bolted connection

Thank you dauwerda. I was thinking the same about fabricating a plate of the same material to fit the Skidmore. I just didn't know if this was standard practice for a situation like this. I was very surprised that there was no guidance in RCSC or anywhere else that I could find that addresses this.

I determined the shear area of the threads and calculated the shear stress based on the pretension load for an A490 bolt of this size, and found it to pass based on an allowable of 0.4Fy.

RE: Pretensioning a threaded bolted connection

Bad idea IMO. Threading plate not the same as using a nut and this situation is outside the RCSC recommendations.

Can you use a one sided connector like Hollo Bolt?


RE: Pretensioning a threaded bolted connection

As follow up, is this bolt going to be loaded in shear only? I would be more willing (comfortable) to use this type of connection in a shear condition as opposed to a tension condition.

However, there has been some research and qualification for tapped HSS utilizing a process called flowdrilling. The difference being that by flowdrilling, the material that was in the hole is displaced to create a localized thicker section of wall that is then tapped. Assuming your tapped plate is plenty thick though, I imagine it would be comparable without the flowdrilling part that is required for thin-walled HSS. Cidect Design guide 9 covers this to some extent, see exerpt below:

RE: Pretensioning a threaded bolted connection

If connection design alternatives are allowed, maybe provide a sketch and we could advise? A490s are damn strong bolts, so you're obviously not working with toothpicks.

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