Bearing and Slip Critical Connections.....
Bearing and Slip Critical Connections.....
(OP)
AISC says that if there is a significant stress reversal, the connection should be designed as slip critical. This is clear for connections that have wind uplift reversing gravity loads; however, should this also include lateral force reversals such as for shear walls? I have my thoughts on this, what are yours?






RE: Bearing and Slip Critical Connections.....
Not gonna lie. I didn't know that. What part of spec is that in?
I will say this. In my career, I have never specified a SC connection. I may be wrong to not have done it due to ignorance.
Also, the firm I used to be at, I don't know of anyone that ever spec'ed SC connections.
I'm ready for the njlutzwe roast if it is needed!
RE: Bearing and Slip Critical Connections.....
1. A brace member that can experience either tension or compression depending on the direction of lateral load on the building.
2. Flange plate moment connections that can experience load reversals depending on the direction of lateral load on the building.
RE: Bearing and Slip Critical Connections.....
https://www.dropbox.com/s/zdjoaed1kw7uw0i/Slip%20C...
RE: Bearing and Slip Critical Connections.....
RE: Bearing and Slip Critical Connections.....
I think the requirement for seismic is that they have a slip critical surface and the bolts be pre tensioned, but the connection isn't designed as slip critical. Don't quote me as I don't use AISC specs much and rarely do seismic design.
These are needed when under vibrating machinery that subjects the connection to load reversal (ie dynamic forces overcome dead load), or in oversized or slotted holes where slip would be a problem.
RE: Bearing and Slip Critical Connections.....
J3.1 also comments on it:
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RE: Bearing and Slip Critical Connections.....
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RE: Bearing and Slip Critical Connections.....
RE: Bearing and Slip Critical Connections.....
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RE: Bearing and Slip Critical Connections.....
I don't know that AISC says this. It's not in the FAQ sections you mentioned, or in the Specification sections noted by JAE. "Pretensioned bolts" does not mean "slip critical connection."
RE: Bearing and Slip Critical Connections.....
In some cases, slip resistance is required. The AISC and RCSC Specifications list cases where connections must be designated by the Structural Engineer of Record as slip-critical:
•Connections with oversized holes
•Connections with slotted holes when the direction of the slot is not perpendicular to the direction of the load, unless slip is the intended function of the joint.
•Connections subject to fatigue or significant load reversal.
•Connections in which welds and bolts share in transmitting shear loads at a common faying surface
RE: Bearing and Slip Critical Connections.....
RE: Bearing and Slip Critical Connections.....
Unfortunately, specifying an SC connection doesn't get you out of checking the bearing strength of the bolts. From AISC 13th edition, J3.8:
"High-strength bolts in slip-critical connections are permitted to be designed to prevent slip either as a serviceability limit state or at the required strength limit state. The connection must also be checked for shear strength in accordance with Sections J3.6 and J3.7 and bearing strength with Section J3.1 and J3.10."
(underline added by me)
RE: Bearing and Slip Critical Connections.....
RE: Bearing and Slip Critical Connections.....
Back to the original question, I don't think collectors, drag struts, shear walls, and other such elements necessarily need slip critical connections. Design wind load is an infrequent load. I believe the intent is that members that will have frequent live load reversals, like those supporting cranes or other types of machinery, should be designed as slip critical. If this were not the case, then every bolted vertical bracing connection would need slip critical bolts, and this is not the common practice.
RE: Bearing and Slip Critical Connections.....
RE: Bearing and Slip Critical Connections.....
RE: Bearing and Slip Critical Connections.....
RE: Bearing and Slip Critical Connections.....
Including collectors and drag struts? That's the big question for me as that takes you from a hand full of beams and braces to 1/3 of them.
From a cost perspective, SC connections in my area are a killer because of the costs associated with inspection/correction.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Bearing and Slip Critical Connections.....
RE: Bearing and Slip Critical Connections.....
Dik
RE: Bearing and Slip Critical Connections.....
One of the issues we deal with in construction is the lax procedural methods of "snug tight". Faying surfaces are to be brought into full contact! I see many times that unless there is greater specificity in the tensioning specification, this does not occur. ALL high strength bolts are to be tightened to a "snug tight" condition, at least. A non-specific requirement at best, other than the faying surface requirement.
I ran into a condition where TC bolts were used for numerous connections; however, they were not tensioned as required for TC bolts. The plans were vague and the fabricator could not provide shop drawings. An interesting condition at least. Why would a fabricator use bolts that cost 3x the normal bolt cost, yet not use them for their purpose? Further, TC bolts are very difficult to tighten to a snug tight condition without using a TC bolt tool (TC bolts do not have hex heads, so they are prevented from rotating during tightening with the spline engagement of the tensioning tool.) Does it make sense?