What is the minimun percentage of bolts required on a 75 ton girder (1 1/4" bolts) at each end before we can turn the rig loose? I'm thinking 20%?
Assuming we're talking about properly designed connections using high strength bolts and no slip after releasing from crane the proceedure for a connection might look like 1)snug connection with erection bolts 2) fill 30% of the holes with drift pins. Add and pretension 20% bolts. Some might say this should be 25% pins and 25% bolts. 3) Tension the bolts. 4) Release from crane. If the girder cantilevers then the single connection probably needs 75% of the holes filled, half with drift pins and half with bolts before releasing. Caution - jobs should have a written plan that specifies erection procedures like this and other special circumstances.
AGAIN---from the REAL world. On a girder this size, before I would 'cut it loose', ALL the holes would have something in them. I would stuff as many bolts as would go and pin the rest(yes, there will sometimes be a hole or two that just won't line up, but that's rare on the big stuff). Then snug up all the bolts. Yes, folks, we use to hang iron on 'Beasley Bolts', but those days are , thankfully, long gone. It is only going to take, at most, a half hour extra to do it right.
Since I retired the rules for erection bolts (in the Los Angeles area) is up to 50% now. That means a minimum of 2 bolts per connection before you 'cut loose' even on the little beams.
Rod
PS---It is somewhat common for some contractors to bolt up 100% as they hang . I never liked that approach, but it IS rather common on small jobs.
