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Old 10-12-2011, 06:44 PM   #1
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concrete pad for a concentrated point load?


Hey guys.. I am installing a LVL beam for a ridge..I was told the two columns that will support the 10,000 lbs roof load need to have the correct sizing of the concrete pad under the columns...I will be installing these columns in the 2x6 exterior wall on each end of the great room..(new construction). This is a slab on grade pour that will have 12"x12" thickened edge footings.. How much more concrete is required for this point load? And will I need to extend it to the outside of the structures? So as if the column would be centered in the ctr of the pad? Was thinking I might be able to thicken up the footing to 2'x2'x12"thick and keep it to the interior side of the footing.. but to be honest I want it to be correctly done.. so any help is appreciated.

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Old 10-12-2011, 09:02 PM   #2
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concrete pad for a concentrated point load?


I assume the LVL beam was designed by an engineer or architect. Presumably the house framing was designed by an architect. You need to talk to them about the required support for the LVL. I don't know how you know the load is 10,000 lbs, presumably you were either given that number by the designer or you computed it, but that is a substantial load, and of course requires a substantial footing, which CANNOT be designed by an internet chat group such as this. The design of the footer will depend on a variety of conditions that can only be determined in the field, such as soil type, groundwater table, design of the slab, type of post to be used etc.

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Old 10-13-2011, 01:08 PM   #3
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concrete pad for a concentrated point load?


Daniel is right, you need to hire an engineer for this. This isn't a hard calculation to do, and the engineer will likely make assumptions on the soil type to save design costs (My local city allows us to forgo soil tests as long as we assume minimum values for the soil. The downside to this is that the foundation ends up over designed but this doesn't add much construction costs on small projects.).

Even if you wanted to do the calculation yourself, most building departments (at least here in California) don't consider point loads as falling under the "Conventional Light-Frame Construction" portion of the CBC, and an engineer stamp would then be required to submit the plans.
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Old 10-13-2011, 09:08 PM   #4
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concrete pad for a concentrated point load?


Quote:
Originally Posted by Daniel Holzman View Post
I assume the LVL beam was designed by an engineer or architect. Presumably the house framing was designed by an architect. You need to talk to them about the required support for the LVL. I don't know how you know the load is 10,000 lbs, presumably you were either given that number by the designer or you computed it, but that is a substantial load, and of course requires a substantial footing, which CANNOT be designed by an internet chat group such as this. The design of the footer will depend on a variety of conditions that can only be determined in the field, such as soil type, groundwater table, design of the slab, type of post to be used etc.
Yep.......

Quote:
Originally Posted by loftezy View Post
Daniel is right, you need to hire an engineer for this. This isn't a hard calculation to do, and the engineer will likely make assumptions on the soil type to save design costs (My local city allows us to forgo soil tests as long as we assume minimum values for the soil. The downside to this is that the foundation ends up over designed but this doesn't add much construction costs on small projects.).

Even if you wanted to do the calculation yourself, most building departments (at least here in California) don't consider point loads as falling under the "Conventional Light-Frame Construction" portion of the CBC, and an engineer stamp would then be required to submit the plans.
And yep....

This is one area where 'backyard guesstimating' should not be used.

To give you a relative idea.....I built a 2-story garage....which has a 7x16 PSL beam across the middle....below that beam on each side is a 3'x3'x12" pad in addition to the footing....which is 24" deep and 16" wide....for pics see the link in my signature.

What you need can only be determined by a qualified engineer who will also take into account your soil......What works in E Texas may not work in California or NC.....conversly...what works in Florida may not work in California...

I'm the classic "do it cheap" DIY guy....but this is one area you can't go cheap.

Remember, once concrete is down....it's not like you can lift if up and add a bit more...changes get expensive.
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