slip critical connections 4

[Heldbaum]

Hello folks. I have a question, is there any way to justify slip-critical connections for typical steel frame in residential building? I prepared calculations for all connections in the building (shear and moment connections) treating them as normal bearing connections but EoR rejected the calculations saying all of them shall be slip-critical. And yes, I found this information in his notes but I am just wondering what is the reason for those connections..? It's a 6 story, 25'x100' steel frame with sloped roof..Thank you for any thoughts.

 

[cliff234]

RWW0002 - I think you are correct about the EOR thinking that TC bolts are the same as SC bolted connections. And many engineers don't realize that just because the tips of TC bolts are twisted off, that the connection was properly tightened and that all of the bolts achieved their required pre-tension.

And then there's this.... years ago someone told me that he went to a job site and saw that the tips of the TC bolts were burned off. I don't think the use of torches is listed as an approved method for pre-tensioning TC bolts in the AISC Specification!

 

[Leftwow]

I've used slip critical connections once, on a structure that help up a crane. I understand why some engineers are requiring slip critical connections to make sure adequate bolt tension is required but every book I've read says slip critical is only used in extreme cases of load reversal.

 

[Heldbaum]

That's what I thought too Leftwow..

 

[Shu Jiang PEng SE]

AISC 360-10 section J1.10 specifies cases where slip critical bolts are required:

"Joints with pretensioned bolts or welds shall be used for the following connections:
(1) Column splices in all multi-story structures over 125 ft (38 m) in height
(2) Connections of all beams and girders to columns and any other beams and girders
on which the bracing of columns is dependent in structures over 125 ft (38
m) in height
(3) In all structures carrying cranes of over 5 ton (50 kN) capacity: roof truss splices
and connections of trusses to columns; column splices; column bracing; knee
braces; and crane supports
(4) Connections for the support of machinery and other live loads that produce
impact or reversal of load
Snug-tightened joints or joints with ASTM A307 bolts shall be permitted except
where otherwise specified."

 

[dik]

RWWOOD:
Maybe not clear in my reply... but, I've encountered some engineers, including older ones, that spec slip critical all the time... I use snug tight all the time, except generally, for bracing and moment connections for plastic design. For plastic moment connections, I provide the actual design moments and shears.

Shu Jaing:
I've added note #4 to my drawing notes, thanks...

Dik