Maximum Load Calculation


Old 08-26-07, 01:44 PM
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Location: Minnesota
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Maximum Load Calculation


Can anyone help me calculate the maximum load for a specific deck design? I'm not sure if "maximum load" is the correct term- but I essentially want to find out how much weight my deck design can handle- both static and "live".

The deck is 12' x 24'.
12" diameter poured cement footings.
6x6 posts
4x10 beams, made by sandwiching 2, 2x10's together.
2x10 joists, spaced 16" on center.
5/4" thick decking.

There are 8 footings/posts, 4 on each side, running parallel to each other. The footings/posts are spaced 8 feet apart (4 on each side).

The beams are mounted on top of the posts, and the joists are on top of the beams, so this is a cantilevered design with the joists extending 2' over the beams on each side.

The deck is on a hill. On the low end, the posts are only about 8" tall. On the other end, they are about 36" tall.

Is there someone out there that knows the correct way to calculate loads for this design?

Please let me know if more info would help.

Thanks in advance.
Old 08-26-07, 05:02 PM
Join Date: Mar 2000
Location: Arlington, WA
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Before the load capacity can be determined, more info is needed.

You say the footings are 12" diameter, but how deep?

How are the 6X6 posts attached to the footings? (Why 6X6's if your beams are only doubled 2X10's??)

How are the beams attached to the posts?

Obviously, this is a freestanding deck -- how is it crossbraced?

What species of wood are the posts, beams, and joists?
Old 08-26-07, 07:29 PM
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What is it that you want to put on this deck?

Assuming that all the connections are correct and the deck is properly braced, it should be fine for normal use. Now, if you want to put a spa on it, that may be another story.

You are asking us to go backwards from our normal calculations. Normally, I know what the load requirements are and I size everything else from there.
Old 08-26-07, 07:50 PM
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I realize this may be a backwards question. Thanks for responding.

Jut want to be sure we would be OK with 25 or so people on the deck.

This is made of AC2 treated wood. The footings are 42" of concrete, flared to 24" at the bottom, w 4" of compacted gravel under each. Posts attached to the footings with metal post anchors. 6x6's attached to the beams with "adjustable" metal post caps, one on each side of the 4x beam. Yes, this is a free-standing deck. What is cross-bracing? I will be doing "blocking" down the middle between each joist. Each joist is attached to the beam with 2 rafter-ties (one at each beam). I also attached a 2x10 between the beams at each end to add a little stability.

So far, this deck feels more rock solid than any deck I've ever stood on.

Thanks again for the responses...
Old 08-27-07, 01:58 AM
Join Date: Jan 2007
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I am in the process of trying to build a deck and here are two resources available for download that I located. Book.pdf

This site has some very helpful information also.


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