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Moment Connections

Moment Connections

Moment Connections

(OP)
Dumb question....no references around me presently....

Am I correct to assumed that endplate moment connections should have fully tensioned bolts?  

RE: Moment Connections

I think pretensioned bolts are required for all high strength bolting installations.

RE: Moment Connections

High strength bolts are not all required to be pretensioned.  A490 bolts under tension are required to be pretensioned.  All others are permitted to be installed snug-tight, including A325 bolts under tension.

RE: Moment Connections

(OP)
nutte-
I was under the impression that ALL bolts in tension connections must be fully pretensioned.  

RE: Moment Connections

Section J3.1 in the 2005 AISC Specification says A325 bolts under tension (and absent of fatigue loads) can be snug-tight.

RE: Moment Connections

I would not use a non tensioned bolt for a moment connection unless you are happy for it to deflect more like a partially fixed connection than a fully fixed one.

Use pretensioned bolts.

RE: Moment Connections

(OP)
CSD- I concur. This frame is cyclically/dynamically loaded..furthering the importance I'd say.  

RE: Moment Connections

If it's cyclically loaded, AISC does require that an A325 bolt is pretensioned.

RE: Moment Connections

nutte,

Throw away the code book for a minute and use that grey matter between your ears.

The analysis program will assume that this fully fixed connection will remain at 90 degrees even when everything else deflects. Now if you do not have a pretensioned bolt then how can the connection even remotely resemble this fixed state? As soon as you apply load to a snug tight bolt the plates will start to separate thus altering the connection angle.

RE: Moment Connections

Arguing about philosophical points is fine, but we also have the benefit of research to check how we think these things actually work. In the case of the extended end plate moment connection, we know that these have been tested with both snug tight and pretensioned bolts.  We also know that procedures have been developed using this information to design these connections as fully restrained.  Back to the gray matter, this doesn't surprise me.  A snug tight bolt still develops a fair amount of pretension.  We're not talking about finger tight bolts.

I mentioned the code to provide a reference from the authorities on the subject.  Obviously a long-winded explanation wasn't my goal.

RE: Moment Connections

Right On, Nutte!

RE: Moment Connections

Using the Canadian Code, CSA S16-01 all high strength bolts must be pre-tensioned when subject to tensile loading.  

BA

RE: Moment Connections

Unless there is cyclical loading A325 bolts can be snug tight.

I don't use that. For all x-bracing and connections (typically end plated) stipulating both a shear and a moment, I use slip critical...

Dik

RE: Moment Connections

End plate moment connection has a combined shear and tension on the bolts.   Per RCSC 4.2 A325 and A490 bolts with combined shear and tension must be pretensioned, regardless of fatigue.  Slip-critical is not required but pretension is required.   

http://www.FerrellEngineering.com

RE: Moment Connections

Sorry I miss stated, RCSC.  A490 bolts only require pretension for combined shear and tension.  This is a change in the 2009 Spec.   

http://www.FerrellEngineering.com

RE: Moment Connections

Sorry again.  I should look first before I comment.  The 2004 RCSC Spec reads the same as the 2009.  So I am double mistaken.  I will do better next-time, maybe.


Pretension required for A490 bolts in combined shear and tension, regardless of fatigue.  A325 bolts can be snug-tight.   

http://www.FerrellEngineering.com

RE: Moment Connections

I only use a slip critical conn where it is specifically required such as seismic or cyclic loading as it is far more expensive than pretensioning.

RE: Moment Connections

We always pretension A325 bolts in end plate moment connections but do not require slip critical (i.e. inspection of the pretensioning)

 

RE: Moment Connections

nutte,

I would be interested to see that research as what you are saying to me is very counterintuitive.

Sorry if I came across a bit confrontational, I just get a bit edgy when people start automatically going code says.... e.t.c. are we engineers or code lawyers?

Also, you would be surprised at how different the codes of different countries can be on what you would think are well known topics. I have come across situations where two codes are mutually exclusive (i.e you cannot design something that meets both).

RE: Moment Connections

What stops a "snug tight" nut from working loose in service?

RE: Moment Connections

(OP)
Snug tight bolts don't work loose. They still have significant preload.
I guess, its the same thing that keeps your car/truck wheels from falling off!

RE: Moment Connections

JAE
Without inspection, how do you know you are getting pretensioned bolts?  I agree that Slip-Critical is not necessary.  But, inspection should be required for all pretensioned bolts, if not all bolting in general (IMHO).  Most iron workers do not know the specifics of slip resistance and faying surfaces.  The process for installing slip-critical and/or pretensioned bolts is the same.  And the method of installation should be inspected.   

http://www.FerrellEngineering.com

RE: Moment Connections

connectegr - by AISC definition - pretensioned bolts mean "do everything you'd do for slip critical but without inspection".  That was the definition a couple of years ago.  Not sure if they've changed it recently.

 

RE: Moment Connections

JAE
Per RCSC and AISC, the only difference between slip-critical and pretensioned is the required surface preparation for slip critical.  Both require inspection per RCSC 9.2, dependent on the method of installation selected.   

http://www.FerrellEngineering.com

RE: Moment Connections

You can use load indicating washers to aid in inspection.

RE: Moment Connections

JAE - I would disagree.  "Slip critical" refers to more than just the bolt.  It also deals with the faying surface of the material being joined.  "Pretensioned bolt" has nothing to do with the faying surface.

RE: Moment Connections

connectegr - I stand corrected - It USED to be that a pretensioned connection was simply a slip critical connection without inspection (see either the silver or green AISC manual specification).

You are correct,I think, that the current spec just looks at the faying surface.

nutte - thanks - I meant to say connection, not bolt.

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