huangyhg

wood blocking under steel columns in freezer structure
i am trying to find an alternative to the oak wood blocking or poly bocking that we use between the baseplates of steel columns and concrete footings as a thermal break in food freezer structures. these two methods have become long lead time items or too expensive.
jae (visitor)3 feb 00 13:42
we have used oak blocks on most of our facilities. however, if your base plate gets much larger than 12" square, the wood blocks must be "manufactured" by glueing together the block into a larger size. we have tried a polyurethane foam product produced by general plastics manufacturing co. (tacoma, wa 253-473-5000) called last-a-foam r-9330 but our client found it to be fairly expensive. we currently have resolved to use oak blocks, but limit our base plate size to 13" square, with a 12" square wood block. the larger plate size is used simply to provide edge distance for the anchor bolts, not for bearing.
is there a need for the column/foundation oak block separation if the freezer has a sub-floor heating system between the freezer slab and the top of footing?
the wood blocking takes the place of the insulation that has to be omitted under the column base plate. we continue to use this detail even if it is heated. if you don't separate the column and footing, the cold will transmit through the column and into the unheated footing and freeze the soil around the footing. the question has always been about the anchor bolts. they can't be separated from the footing, so we just accept the small amount of transfer from the bolts.
our columns are installed nas the mud slab in place over these footings as well but we have no wood block at the column/footing interface. do you have suggestions to counteract this thermal transfer without digging up the mud slab and trying to install these blocks. that would also require column/footing modification, too. we may choose to just wrap the column with insulation from the mud slab up to maybe 10 feet above the floor. suggesstions?? thanks.
the insulation on the column will only work if you take it to the roof and provide a heat source. you still run the risk of sweating on the column.
if the heating system is not in place yet, see if additional heating can be provided over the footing. talk with the heating system designer about this. you don't want to provide too much heat. also, be sure to provide a good separation between the column and floor slab. 1/2" insulation min. this is to help prevent sweating and freezing of water on the floor slab.
my suggestion, remove 2" of the top surface of the footing under the base plate and place the blocking there. second option would be the additional heating i talked about above.
hope this helps.
thanks.
by the way, how would you calculate the heave force? i assume the column area transmits the cold into the footing and then into the ground. what is the area influenced by that one column trnsmiyying that cold into the ground? it seems there would be some limit to the amount of cold that can be transmitted. it wouldn't seem likely for that column to freeze soil 15 feet away.
we had an underfloor vent system fail over the years and it caused freezing of the subgrade down about 21 feet. cold is cold and it will migrate as long as the freezer above is kept frozen.
alumpkinfff">:
you are correct: there is a limit to the amount of freezing that can occur. some of the critical variables include the btu rating of the freezer, the "average" ground temperature, the soil types(s) and profile, the soil moisture contents, depth to "the" groundwater table, and foundation type(s) / depths / geometry. that question is far too complicated to answer on this forum; you need to retain the services of a geotechnical engineer with relevant experience to answer that question (after s/he performs a proper field exploration and lab testing program, of course.)
and freezing to depths/distances in excess of 21 feet doesn't sound excessive to me. i've seen far stranger things happen...

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