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Concrete Pier and Column Support

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StructEngineer11

StructEngineer11

Structural
Apr 4, 2016
11
I have been tasked with designing concrete piers that will support existing wood columns, and I was wondering if anyone could offer any helpful tips as far as how I should approach the design from the beginning. The wood columns currently stand on top of a concrete slab, but due to water/other liquids on the slab, the columns have started to rot a good bit. Thus, the bottom 3-4 feet of the columns will be cut off, and the columns will be placed on new piers that will project from the top of the existing slab.

Any tips as far as how to design the concrete pier? How to design the connection from the column to the pier? I was told that the column will be placed on a steel base plate, sandwiched between two steel angles, with a couple of bolts going laterally through the column and two angles, and 4 anchor bolts going through the angles and base plate into the concrete pier. See attached image.

Any help would be appreciated. Thanks!
 
 http://files.engineering.com/getfile.aspx?folder=16afb3d9-1fd8-47a5-9251-a4771f1d0940&file=Wood_column_atop_concrete_pier.jpg
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For the pier to post, this is something already fabricated for use -


For the concrete piers, you will need to exceed the post size by 2 to 3" on each side. The pier will also need to be developed into the existing slab to take some overturning moment from the shear load at the base of the wood post (which the existing slab is no doubt NOT designed for).

I'm thinking an all steel bracket that moment connects to the post will make more sense. Use a 6x6 tube steel to socket (and screw later) over the wood post and then slip that down and screw over a 5x5 tube that has a base plate bolted to the concrete. The fabrication cost will be significant, but field labor should be a lot less than concrete. It will keep your loads on the slab the same and the steel extension will keep a tight envelope.
 
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wood_post_repair_gekahy.jpg
 
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So there won't be a new footing here? The new pier will just sit on the slab? It's a slab on grade, right?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
 
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Thanks so much for the responses. Yes, I believe it is a slab on grade... Roughly 14" thick from the information I have.
 
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You may also look at temporary support before you cut the wood column.
Also you will need to hilti epoxy the rebar of new concrete pier to existing slab.
 
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