slip critical bolts in slotted holes LONGER than LSH

[mikeCTE]

i need to design a brace for a contractor so that he can adjust the length of the brace by up to 12". to simplify construction and fabrication costs, i am thinking of using a double angle with a single hole for a bolt at each end. this hole would be a STD sized hole. for the plates that the angles attach to, i would like to use a 6" long slotted hole at each end of the brace to provide the necessary range.

AISC only talks about long slotted holes, but nothing longer that i can see. are there no provisions for this because it's not allowed, or do the resistance factors for LSH apply to extra long slotted holes?

thanks

 

[JStephen]

I suspect the issue is that AISC covers construction details normally used, and if that's not one, it won't be addressed one way or the other. That may not prevent you from using it for your application, however.

Without any additional information, I would assume that design information for a long-slotted hole was not necessarily applicable to a much longer slot. My thinking is that even with a long-slotted hole, the bolt and washer is going to be overlapping material on the sides and at least one end, whereas with a longer slot, it could be overlapping material on just the sides.

For an adjustable brace on a construction site, there's no guarantee that the assembly would be done in a controlled manner, either.

 

[mikeCTE]

thanks.

subsequent research indicates that any length slot is allowed, but the engineer needs to use judgment on the appropriate resistance factors. essentially, the friction of a slip critical bolt in a standard hole, oversized hole, or slotted hole is the same in all cases. the reason the resistance factors are different for the various hole conditions is to acct for the event where friction is exceeded and the bolt impacts the material and goes into bearing.

for my case, the contractor is going to use a different method now, but in the future, i will know.