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RE: Steel Column Tolerances

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Charlie is right on, and I also applaud the detailer for identifying the
issue as a potential problem. 

And shame on the erector for refusing to do any survey. It may cost a little
but anyway........sometimes it is very important to understand exactly what
you have, and goes a long way toward flagging erection or fabrication errors
before they are locked in or buried in concrete. There are some very savvy
GC and CM guys out there that write survey activities into the scope for
their steel or concrete subcontractors; it does not need to be a PLS or PE
stamped survey, but two ironworkers or two carpenters with a laser level can
spot elevations on 15,000 sf of deck in an afternoon. I am now a believer
because we found a 1-1/2 inch bust in fabricated column length splice to
splice at 4 columns on a line in one tier of a 7 story building(of course
they were repetitive) that otherwise would have been unnoticed until in the
middle of a pour. The early flag that came out of the survey allowed an
informed decision to be made as to what was to be done to address the
condition. Transfer girders or trusses should always be monitored during
erection. In high-rise construction it is essential to be checking
elevations because there are often over lengths specified in heavily loaded
columns to allow for differential shortening; if that gets screwed up the
costs can be catastrophic. In short, if you even think you might have a
situation where you could have a problem with elevations and tolerances for
a project, you should review this with the CM/GC to see if it can be bought
in his scope somewhere, or require it as a submittal from either the steel
subcontractor or the concrete subcontractor. They will bitch, but if you
have a strong feeling about the potential, you should ask for this. However,
I would not make it a standard for a "typical" steel frame building; the
subs are obligated to meet tolerances and maybe that is sufficient; I am
talking about complicated conditions where there are a lot of "links in the
chain" where something screwy with elevations would really be an issue.

Actually, the 1/8 inch beam depth tolerance should disappear in the
accumulated tolerances for the frame itself, and finally the slab pour.

On the other hand, if you are down (or up) 1/8 inch at the support, where
will you be out at the end of the cantilever? Is it set with intentional
camber? These issues may impact the need for shims. If they are not
considered to be important issues, then it all probably disappears in the
slab pour.

Ok, I'll get off the soap box.

Cheers.




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