Which Bolt Type?

[BenHorris]

Hi,

Scenario 1:

I've got a beam supported by a hanger column, for which the connection is a column base plate and then 4 Bolts through the top flange of the beam below.

My question is related to whether it is best to use snug tight (S) or tension Bearing (TB) bolts for this connection.

My understanding is that the TB bolts will put a small amount of pre-load into the bolt, which is then relieved by the tension force applied under loading, until a point where the load applied exceeds the pre-load, when the load applied will be eating into the residual bolt tension capacity.

I'm wanting to use snug tight bolts, though I'm a little nervous that the bolts might loosen over time due to minor vibrations and movements. I've not got a situation where cyclic or vibration is really any issue, though I'm just worried I might be missing something.

Is this a scenario where TB bolts would be more appropriate? Or snug is OK?

Scenario 2:

If I have some packing plate (say up to 25mm) between the hanging column and the beam top flange (to allow for tolerance/deflections during construction) and I have a combined shear and tension load to resolve at the connection, would I need TB bolts to allow enough clamping force to transfer the shear and avoid any bolt bending? If so, then once the preload is fully relieved, will I have any issues?

Thanks in advance!

Ben.

 

[Ron]

Not sure what code you are working under, but in general if you have load reversals you should fully pre-tension the bolts.

 

[BenHorris]

Hi Ron,

It's to the Australian code.

No load reversal. The bolts will be in permanent tension, though also subject to shear.

Ben

 

[Lomarandil]

Depending on how beefy your ironworkers are, snug tight will produce a moderate to significant amount of bolt pretension by itself.

Without a code provision that drove you to pre-tension the bolts, I'd be ok with snug tight for scenario 1. For scenario 2, it would depend on the magnitude of shear that you're trying to take out in friction.

----
The name is a long story -- just call me Lo.

 

[PersonalProfile]

Scenario 1:

1. If a "pin" [i.e. shear] is otherwise acceptable, then S [as S provides limited preload - hence not incurred value effective, and will loosen], or
2. For any other application [i.e. "significant" capacity required, or loosening must be prevented], then use: TB, or TF [provides preload].

If the joint preload is exceeded, the connection has failed.
Refer following as a start:

http://www.boltscience.com/pages/basics2.htm

Scenario 2:

Refer scenario 1, and please review AS 4100 Cl 9.3.2.5.


For your safety, and the safety of others, please consider consulting a: competent, and qualified; engineer.