child-friendly column base connection

huangyhg

child-friendly column base connection
i have an unusual situation where i have to connect a steel structure to the lid of an existing cip concrete sistern, and the column base connection needs to be "child-friendly".
i am using tube columns (friendly), but the column base will be exposed. i have tried to look at expansion anchors that would have a countersunk head, such as a phillips flat head, but they only come in 3/8" maximum diameter, and that seems pretty small for a structural column. i have ts7x7 columns, and the maximum uplift load is 10.8 kips, with 2.7 kips of base shear.
does anybody know of a larger diameter fastener available with a countersunk head, or is there another way of skinning the cat? also, it would be nice not to have to use four bolts, because the columns are very close to the edge of the lid, and edge distances become an issue.
hilti makes one of their more significant anchors with a countersunk head... can't re  
skin the cat by encasing the bp in chamfered concrete?
put a circular concrete encasement over the first 3-4' of the column?
some kind of sheet metal cap like we see on light pole foundations, except without sharp corners?
bolt down the baseplate, with anchors located inside the tube, and then site weld column to it.
you could use an internally threaded rod (made by several anchor companies) with adhesive anchors.  then put in whatever type of screw you would like.
my thinking is similar to aspix where there is a base plate with a tube section insert, maybe 6" high that will fit inside the 7x7 and welded to the plate.  that assembly is after set bolted or epoxy bolted to the concrete cistern with one bolt, then the new column is placed over the smaller tube section and field welded to the baseplate.  after this final welding, the corners of the base plate could be field chamfered.
mike mccann
mmc engineering
thanks for the responses.
there are two problems with field welding. first, since the structure is outdoors, everything is hot-dip galvanized. second, this job is in st johns, us virgin islands, and i don't know what the field welding capabilities are, but welding galvanized steel is not good.
i wish i could simply encase the base plate some how, but the columns are very close to the outside wall of the cistern, making it physically impossible to use a round encasement.
not sure i understand packerfan's idea. what do you mean by "type of screw"? if i had a 7x7 base plate with holes in it and internal nuts, you could screw in allthread rods, and lower into epoxy grouted holes. however, the column wouldn't be too stable under construction (osha req'mts).
how about wrapping the whole thing in some sort of soft plastic protective cover, like they use at daycare centers?
this is not a job for engineers, just one requiring common sense.  there's nothing child-friendly about concrete, last time i checked...
or, you could google playground supplies and hardware - you'd be amazed how many products are out there.
tg
build with normal construction techniques and then encase the base in grout.
just in case this might still be usefull, hilti's hsl-3 heavy anchor comes in a "-sk" version which has a flush head... thus calling up a 16mm diameter version would be "m16 hilti hsl-3-sk"
hopefully you're not in us, or if you are, hopefully the kwik bolt ii comes in a similar flush-headed version.
cheers,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...