plazma cut holes @ conn. plates?

[jeffcurrey]

Sirs,
What a great website!
My question is regarding AISC specs on holes designed for connection plates using HS bolts. Is it primarily a dimensional requirement? If so, what about the slight taper created by in the kerf of the cut? We are interested in burning these plates vs. layout/punching due to the ease of manufacture.

Thank you in advance,

Jeff

 

[Qshake]

AASHTO, our design specifications for highway structures here in the US has edge distances specifically set for whether or not a plate was burned or punched (sheared). I have to believe that AISC also has these requirements. If not check out AASHTO for the requirements.

 

[RHK]

In Australia, oversize flame-cut holes are the norm for thick base plates, but rarely used elsewhere. I have used them in end flange plates for tubular tower bolted joints where the bolts are subject to tension loads with minimal shear.

I would be very cautious about using flame-cut holes in bridgeworks, because the rough, hard profile of the flame-cut surface would be susceptable to fatigue.

Also, before you commit to flame-cut or plasma-cut holes, check the economics. It probably takes more time and energy to produce the initial pierce than to cut the profile of a small hole. I know with flame-cutting, the direct cost per pierce is about $1, which is about the same as the cost of drilling through 20mm plate.
Russell Keays

 

[evelrod]

I can't speak to the rest of the world, but here in the Los Angeles area there is NO acceptable method of flame cutting holes for HS bolts.(Point of fact, the area inspectors frown on ANY flame cut holes!) On some occasions, usually smaller beams, ie. thinner plates, flame cutting undersize holes and finish reaming to size has been acceptable (Usually at the inspectors disgression???). Care must be taken with this approach as eggshaped or octogonal shaped holes will be rejected(then they must be welded up and redrilled). On thicker material (base plates, etc. ) weld washers can be used, but most anchor bolts are NOT HS. Holes that are slightly missaligned may be reamed to the next oversize in almost all applications with no problem aside from cost. The extreme would be (it IS often used)FP weld up the holes and redrill them!


Q---I am surprised that , considering your background with JFB that you wouldn't be " totally anti flame cut holes"! I have 'chopped' a few in my time, but I doubt it would be legal today.


Rod

 

[Qshake]

Well your right ROD, I do frown on such things in the field - only because it is normally "forgotten" to ream out the rough edges and maybe even place a large bolt if required.

In the shop its a different story, especially for very thick plates that can't be easily punched. In the shop at least there are more eyes looking over the workers - or so I've been told

 

[evelrod]

The problem with flame cutting in the field, John, is the quality of the "burner"! In many cases where I have had to do repairs on 'flame cut' holes (everything else flame cut , too) the word "butcher" came to mind first off. There is sufficient testing and certification process for welders and the like, but NO testing or certification of "burners" that I know of aside frome the testing they receive at 'punk' school. I consider myself (they call me Mr. Burner) a cut above average as are my boys and my son-in-law simply because we took the time to learn. It is NOT all that easy to do in the field. I always carried my 'tip' in my pocket for my use ONLY! Still, here on the left (shaky) coast, drilling is the prescribed method for making holes, even in thick baseplates. 'Whitney punch' for little stuff and 'Hogan' drill for big. The shops around here have VERY large rotary broaches for BIG holes.

Rod

 

[jeffcurrey]

Thanks for the input. What we commonly do on our machinery is draw the part in dfx format with the holes sized to accomadate typical clearances. These dfx files are loaded into a CAM program and cut. There is a negligable kerf in gauge material but in base plates it is pronounced. All of these holes though are round because of the lead-in/lead-out cuts provided by the software. So (without having the actual AISC spec in front of me) I can surmise that plazma cut holes as a part of manufacturing, not field retro-fit, are permisable. On baseplates we should probably undersize the holes for reaming though drilling may be more cost effective for the end result.

 

[Qshake]

Rod, tremendous information on the drilling process. I've been witness to many hogan drilling operations myself. I guess I was wrongly placing the making of hole with the cutting of a thick plate. It didn't occur to me about the larger drills - Keep up the good work Rod!