Gap in slip-critical connection allowed?

[ABA102]

Hi,

In our project with huge steel structure trusses, upon inspection I have noticed a small in between flange of joint connection which is a slip-critical connection.
Is there an allowable gap to a slip-critical joint. Please state what code.

 

[klaus.]

hello
maybe a picture or sketch would be helpful to understand
If there is a gap...how can there be friction ???

 

[CARunderscore]

Based on my understanding of what the OP is saying, the connection has no faying surface, and by definition cannot be considered to function as a slip-critical connection.

Moreover, I don't think the connection even falls under AISC's definition of a bolted connection." See Specification for Structural Joints Using High-Strength Bolts Section 3.1:

"Compressible materials shall not be placed within the grip of the bolt."

I think that air would fall under the category of "compressible materials."

 

[12345abc6ttyui67]

I suppose the alternative is OP means that there is a gap between the two ends of a beam at a splice location, which is designed as a slip critical / friction joint. In this case I suppose it wouldn't matter if there was a gap between the beams at the splice, so long at the splice plates were still functioning with friction on the faying surfaces.

 

[azcats]

The commentary in Section 8.2 of the RCSC Specification may address the question. Not sure if you have a thick, stiff connection or if something else is really out of whack.

In some joints in thick material, it may not be possible to reach
continuous contact throughout the faying surface area, as is commonly achieved
in joints of thinner plates. This is not detrimental to the performance of the
joint. If the specified pretension is present in all bolts of the completed joint, the
clamping force, which is equal to the total of the pretensions in all bolts, will be
transferred at the locations that are in contact and the joint will be fully effective
in resisting slip through friction.

 

[ABA102]

Hi klaus,

Please refer to photo attached on is the gap in between the shim plate and the flange.

 

[CARunderscore]

Ah, that kind of flange.

Then you might be okay if there is still contact on the opposite side of the connection. Do you think that gap is due to construction tolerances, or due to a moment?

 

[SlideRuleEra]

That is a pipe flange with a raised face.
From the above link: "The purpose of a raised face flange is to concentrate more pressure on a smaller gasket area and thereby increase the pressure containment capability of the joint."

Diameter of the raised face shown as Dimension "G" on this illustration:

As long as the gap is uniform around the circumference of the flange and the joint does not leak, should be ok.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[azcats]

Love to see the detail of that connection.

I'm not convinced that it is a raised face flange.

My guess is that there was so much weld from the pipe to the flange plate that it warped the plate and the bolts couldn't close the opening. Is that gap uniform all the way around? Do the flange plates make contact deeper within the joint?

 

[ABA102]

@CARunderscore
The gap is due to erection and this gap is noticed around half of the flange area.
And I would to know if there's any code allowing such gap. I can say the gap is approx. 1mm.

 

[ABA102]

@SlideRuleEra
The flange is not with a raised face. The flange is flat and there is a shim plate in between the pipes flanges.
And the small gap is in between shim plate and the flange of one of the connecting pipe.

 

[SlideRuleEra]

...small gap is in between shim plate and the flange of one of the connecting pipe.

The pipe must be only a structural member. I assumed it was transporting a liquid or gas, also... sorry.

IMHO, with a gap the joint cannot be slip critical. I would not search for some code "loophole" to allow acceptance.

Perhaps if a proper tapered filler piece is used, the problem can be corrected:

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Tmoose]

"The flange is not with a raised face. The flange is flat and there is a shim plate in between the pipes flanges.
And the small gap is in between shim plate and the flange of one of the connecting pipe. "
" ........... the gap is approx. 1mm."

Please Describe the shim plate with words and a picture.
I AsSsuMe/b] the shim plate is round, with an Outside Diameter almost as large as the flange OD, and through holes for the bolts, similar to this -

https://encrypted-tbn0.gstatic.com/...vbPnHo16MJU_bDpR_FerHrlyDzzObR8LBz38TPrIViNPt

In the off chance this wild unfounded assumption is correct I'd say there should be no gap anywhere any bolted flange joint expected to be slip critical.

If the shim plate has no bolt clearance holes, and the OD is significantly smaller than [ the bolt circle diameter) minus one bolt diameter], then there must be a gap equal to the shim plate thickness all the way around the flange outside the shim plate, but again no gap anywhere between the flange/shim/flange if the bolted flange joint expected to be slip critical'

Is your cardboard probe butted up against the shim plate outside diameter?
Would a 0.002"/.05mm feeler gage slip in the full width of the flange, past the shim plate, at several locations around that bolted joint ?

 

[steel neil]

Hi, interesting structure, sure is huge! I cant see why this is a slip critical connection? is the
connection in tension or compression?

 

[klaus.]

I don't think this need to be slip critical connection...
I tis an standard steel construction connection....not a pipe with liquid
I assume the bolts are prestressed but this is all...

 

[ABA102]

@Tmoose

Apologies to my delay response.
Yes, almost similar to that plate but the one I am referring is full shim plate no hole in the middle.
Actually, that piece of cardboard on the picture I attached, can be fully inserted in the gap which I can say the gap is half of the shim plate/flange area.

 

[ABA102]

@steel neil

It's actually the steel truss structure of roofing of a stadium.
The connection I am referring to is subjected to tension.

 

[structSU10]

If there is only tension there, no shear, as long as the bolts are pre-tensioned properly, there should be no issue. I would guess you want the bolts to have enough pre-tension such that the bolts don't stretch once the load is applied.