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RE: OSHA 4-bolt column anchorage

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            Mark Remmetter asked, “A related question regarding precast columns.  Assuming they are properly attached to the foundation per the precasters connection detail (4 anchor rods), should these columns be braced off at the top prior to the erection of the rest of the precast framing or is it left up to the erector to make this decision?  Seems like the flagpole condition (even if it is temporary) might be a little unstable even with the base anchorage.”

 

            Mark,

                        Before seismic design was required on the east coast, we built a number of one-story buildings that have 24” square precast concrete columns that are the lateral-load resisting system. The weakest link of these are probably the 1” diameter bent anchor rods. The interaction diagrams I’ve done with 36 ksi ARs and 5,000 psi grout show plenty of capacity compared to ASCE 37-02 winds for set but unloaded columns. I’ve done four interactions, the ARs and grout, the pier steel and concrete, the baseplate studs and precast concrete and the column steel and concrete. The ARs and grout provide the least capacity. Moment transfer diagrams from one set of steel to another define the minimum moment capacity points.

Grout that is only 2,000 psi (just past initial set) still provides substantial overcapacity for the column. The ARs and shims hold the column while the grout is curing, or a push-pull shore to hold the column steady may be used.

 

            And Harold Sprague is correct (as usual): I wrote OSHA Subpart M (precast erection) and meant to write Subpart R (steel erection).

 

            Jim Getaz

            Precast Concrete Engineer