deep grout beds under steel columns
i've got a couple columns located within a slab depression, and the revised base plate elevation didn't get picked up on shops... which leaves about 7" between bottom of base plate and top of bearing surface. column loads are on the order of 400-450k, shear/moment are not concerns at this location (other than incidentals during erection), and anchor bolts have sufficient length to be set high.
refabricating the steel would cause significant delays, and forming/reinforcing a 5" long pedestal seems a bit much. other than putting some pea gravel in the grout mix, are there other significant problems with just simply grouting this space solid, maintaining 45 degrees out from the base plate?
there can be. most grouts for base plates are not intended for such a large gap. the grout would probably break or buldge out. you might be able to confine it by providing plates on all side of the base plate and a few additional anchors. i would contact the manufacturer to be used and consult with them on this, or provide additional steel to get you where you need to be. most of the ones i have seen recommend contacting them if the grout is to be placed thicker than 3 to 4 inches. that much load is too much to play with.
can you have to contractor place additional base plates so that you can get the required grout thickness down? i wouldn't think they would need to be welded for gravity loads and would be more like full-size shims.
rudely (sorry
) answering a question with a question:
so how on earth are you going to deal with the anchor rods?
the anchor rods were spec'd with 18" embedment plus 2" grout, and for the loads we're seeing here we can easily live with only 13"... and the bearing surface isn't cast yet so we can just set them high.
adding additional thickness of plate should work, and the fabrication should be pretty quick on those... we've got about 3 weeks until the first steel goes up, so that should be more than enough time to get a few more plates done. a quick call to the grout manufacturer sounds like a good idea as well, even if the base mix won't do this, it stands to reason they might have another mix that would. thanks for the quick response!
how about casting a 4" pedestal in the top of the footing? this would work better than grout and could be unreinforced at thet height.
"forming/reinforcing a 5" long pedestal seems a bit much."
i don't think it is too much, and it is the contractor's mistake isn't it?
a single tie around the anchor bolts, formwork and you're ready to pour. easier than packing in 7" of grout i would think.
what about shear transfer at the base plate?
a plain concrete pedestal 5" thick should pose no problem for the loading. this would be to reduce the cost a bit, otherwise 7" of grout would be ok. the grout is generally tougher than concrete. if the bpl is large enough, you might consider levelling plates because the grout is so thick - doesn't form a concave surface.
dik
dbuzz-
i believe he said in the op that this was a gravity only column (or at least that shears and moments were not a concern at this location).
have the contractor contact sika or the like and formulate a plan to fix his mistake. i would think sika has a grout strong enough which can be placed to the thickness you require.
since i have run into this little problem a time or two...my first was to have the steel fabricator lengthen the column, either at the shop or in the field. no one is happy except the inspector and, basically, he's the guy to keep happy, imo! i have, against my better instincts, used anchor bolt extensions (both welded and sleeved) along with a poured in place add on to the pier along with proper grouting.
keep in mind, jmorrison, that there never seems to be enough time to do it correctly, but always enough time to do it over!
rod
2009-09-08, 04:41 PM
deep grout beds under steel columns
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