Moment Connections 2

[ToadJones]

Dumb question....no references around me presently....

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

 

[JedClampett]

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

 

[nutte]

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.

 

[ToadJones]

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

 

[nutte]

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

 

[csd72]

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.

 

[ToadJones]

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

 

[nutte]

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

 

[csd72]

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.

 

[nutte]

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.

 

[spats]

Right On, Nutte!

 

[BAretired]

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

BA

 

[dik]

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

 

[connectegr]

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

 

[connectegr]

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

 

[connectegr]

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

 

[SAIL3]

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.

 

[JAE]

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

 

[csd72]

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).

 

[leisure17]

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