point loads on concrete patio

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Old 08-23-10, 07:27 PM
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point loads on concrete patio

I plan to build a pergola over my existing concrete patio. I would like to support it on 4 X 4 posts anchored to the patio. Does anyone know how much load the 4" concrete can hold, or how to compute it?
 
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Old 08-23-10, 07:58 PM
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Welcome to the forums! Patios don't offer the stability and strength of a nominal footer. They will crack with the weight and aren't code compliant for structures. Drilling holes for the fasteners will further compromise the strength. How big is your patio and how big will your pergola be?
 
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Old 08-25-10, 10:48 AM
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The patio is 14 X 14, I would like the pergola to cover this area.
 
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Old 08-25-10, 07:36 PM
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You can possibly spread out the vertical weight by building a base for the pergola all the way around and then standing your posts on the base. Leave out the base at the entrance, and I think you would be OK.
 
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Old 08-25-10, 08:47 PM
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bkinnipomo,

Don't anchor your posts directly to the slab. If the posts don't punch through the concrete, they will at least crack it.

The best option is to cut the slab where the posts will be and put footing in that the posts will attach to. If you are concerned about the "look" of the cuts, get creative and add some 'columns' at the bottom of the post that will cover the cuts. A 2' square column that goes up about 3', finish the 4 sides with rock or brick, and cap it to the post. I've done them and had planters at the top of the column just to finish them off. Just plan ahead so that you don't have 'earth-to-wood contact' in the planter.
 
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