slip critical connections
slip critical connections
(OP)
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.






RE: slip critical connections
BA
RE: slip critical connections
Outside of strict engineering necessity, there are cases where the EOR may not want to spend additional time and effort to approve the change, issue revised drawings, and take additional liability for something that only saves the builder money. If the builder is offering a credit, you might find the conversation goes more smoothly, but I can't remember ever having that happen.
AISC has had some discussion about this, for example at this link.
RE: slip critical connections
Dik
RE: slip critical connections
RE: slip critical connections
RE: slip critical connections
added (from my drawing notes):
SLIP CRITICAL CONNECTIONS SHALL BE USED FOR ALL DIAGONAL CROSS BRACING, ALL BEAM SPLICES WITH BOTH DESIGN SHEAR AND MOMENT STIPULATED, AND ALL BEAM TO COL CONNS LOCATED AT EXTERIOR WALLS
SLIP CRITICAL CONNECTIONS SHALL BE USED FOR ALL CRANE AND HOIST SUPPORTS AND RELATED BRACING ELEMENTS
SLIP CRITICAL TYPE CONNS ARE TO BE DESIGNED FOR THE ABSOLUTE VALUE OF THE DIFFERENCE BTN MAX AND MIN LOAD
Dik
RE: slip critical connections
RE: slip critical connections
RE: slip critical connections
RE: slip critical connections
That said, the drawings say what they say and the EOR is under no obligation to make any changes unless a material benefit to the owner can be tabled. This is the same reason that so may firms still spec connection shear forces as % uniform load capacity. Specifying precise load requirements may save somebody money but it's not the EOR and it's rarely the owner.
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: slip critical connections
RE: slip critical connections
Thank you guys for all your comments. I appreciate it very much!
RE: slip critical connections
How about if you ask the EOR if you can detail the connections as SC, but design them as bearing bolts – and point out that this is what AISC permits in the Seismic Specification? This way you get the economy of the bearing bolts and the EOR gets their SC bolted connections.
RE: slip critical connections
"We always request slip critical bolts, because they're easy to inspect and they should become standard on all steel jobs. The shop drawings already show slip critical bolts, the calculations should match what is shown on the shop drawings"
RE: slip critical connections
It sounds like the engineer may be referring to TC bolts in the response, but mistakenly calling them "slip critical bolts". Requiring pre-tension in high strength fasteners is a very different thing than requiring slip critical connections and I would hope the EOR would understand that.
RE: slip critical connections
RE: slip critical connections
RE: slip critical connections
Dik
RE: slip critical connections
RE: slip critical connections
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!
RE: slip critical connections
RE: slip critical connections
RE: slip critical connections
"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."
RE: slip critical connections
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