Moment resistant slip critical connection

[jgrady]

Hi, wondering if anyone can help clarify the proper way to analyze this type of connection.

Say you have a bolted connection resisting moment which is putting a tension force on the bolts. Bolts further away from the connection centroid see a higher tensile force than those closer to the centroid or bolts in the compression side of the centroid.

The connection is also subject to shear force and must be a slip critical connection.

So you analyze the bolt furthest from the centroid of the connection to make sure it can handle the combined shear and tension load.

Now you have to check to make sure the connection is slip critical...this is where I have trouble.
Do you check the bolt furthest from the centroid of the the connection again?
Specification for structural joints in the steel manual has a blurb on pg36 saying

>For most applications, the assumption that the slip resistance at each fastener is equal and additive with that at the other fasteners is based on the fact that all locations must develop the slip force before a total joint slip can occur.

Does this mean you only need to check the bolt seeing the lowest shear/tension force? And if that one passes then the connection is slip critical? This is not what I would have thought but I am looking to see if anyone can point me in the right direction.

Thank you very much for your time.

 

[ahypek]

Can you post a sketch of the connection? I'm picturing an end-plate type of connection right now but would like to confirm before I expand. If it is an end-plate connection, you should keep an eye out for prying action.

 

[jgrady]

Please see sketch attached. I suppose this would apply to an end-plate connection as well however.

So intuitively, I would usually perform all checks on one of the front two bolts. However that blurb is telling me that unless the slip capacity is reached for every bolt then the connection is slip resistant? So as long as any 1 of the bolts is below slip capacity the connection is OK?

 

[canwesteng]

I don't think slip critical connections are suitable to resist moment. If fatigue is a concern, a properly detailed welded connection is probably more approriate for your situation. In general, for moment connections I would try to use end plate connections if load reversal is an issue.

The "slip capacity" is not per bolt; your slip capacity increases with more bolts as the clamping force between the plies increases. It is the capacity of friction between the plies. Maybe you could determine the shear stress at which slip occurs and not exceed that.

 

[azcats]

http://msc.aisc.org/globalassets/modern-steel/archives/2016/01/steelwise.pdf

"In a bolted joint with
pretension, some of the applied tension will overcome the
pretension in the bolt. Because the compression between
the faying surfaces is reduced, the friction force that resists
shear is also reduced. For this reason, the shear strength
of bolts in slip-critical connections is reduced when there
is tension present, per the procedure in AISC Specification
Section J3.9. "

 

[jgrady]

@canwesteng >The "slip capacity" is not per bolt; your slip capacity increases with more bolts as the clamping force between the plies increases.

You should be able to analyze it either way. Section J3.8 calculates the slip resistance per bolt. More bolts = less shear force per bolt.

@azcats

This the section of the SCM I am using. My confusion comes from pg 36 of the Specification for structural joints(which uses the same equations) saying that all bolts must develop the slip force for total joint slip to occur.

jgrady