design of beams

Old 04-19-02, 06:59 PM
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Question design of beams

I am building a new deck, with a good design from Home Depot. My brother the engineer sketched out a style of beam resembling that of a vaulted ceiling in a church.
My design currently requires 5 6x6 posts supporting a 22' 2x10 (doubled). Has anyone seen an arch supporting a deck instead of the typical vertical posts? His sketch shows 6 2x6's forming one side of the arch, bent in a steam box and sitting on either a 6x6 block fastened to the outside beam, or sitting in a notch cut into the outside beam (perhaps 2' off the ground)

The laminate 2x6's could be bolted togethor at regular intevals. The deck is 11x22 and is 94" off the ground is sitting on a concretea bank.
Is this a feasible design, is it safe? We will be doing load calculations but would like realistic opinions on this proposal...

Thank you

Old 04-20-02, 02:34 PM
Join Date: Mar 2000
Location: Arlington, WA
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Let me comment on Home Depot's design first.

Why use 6X6 posts to support a beam that is double 2X10's? You are going to have problems attaching the beam to those posts. A double 2X is only 3" thick. What is the point of a 6X6 post? Why not use a properly supported 4X6 for the beam, and use 4X4 or 4X6 posts? This will allow you to use Simpson post-to-beam connectors to tie the posts to the beam, and will be stonger.

Your brother's idea? WHY?? This is going to be a very labor intensive method of achieving a post and beam arrangement that is no stronger than using the 4X posts and beams I mentioned above that are properly tied together. And, he's going to waste a lot of material that you are paying for. If it were decorative, that may be one thing. But this is going to be buried under a deck, where nobody but the neighborhood cats will see it. What's the point?
Old 04-21-02, 06:32 AM
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Hi Lefty, Thank you for your reply. For the benefit of other reading this. The 6x6 posts are building code for structure with a height between 6' and 8'. The idea would be to have two 2x10's sandwiched on the other 4 inches of the 6x6, and then have the last 2 inches of the joist sit on the post.

Perhaps some more background on the deck. The deck will be 8 feet in the air with a concrete pad underneath, and the idea was to use this area as a patio. It was envisioned that the arches would provide a different look to the support. The design calls for 5 6x6 posts to support the deck (the overall length of the deck is 22'. It was hoped that the arches would support the 22' without posts in the middle (essentially replacing the 3 posts in the middle, improving the view.

Old 04-21-02, 08:42 AM
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Your vaulted design in interesting. It will be very labor intensive though. Do you think the arched beams are your best option? How about stealing ideas from post and beam construction and useing straight pieces to support your vault? I can't explain it well but look at a barn, cathedral, or gazebo and you should see what I mean.
Old 04-22-02, 05:19 PM
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If your brother is good mechanical/structural engineer and has verified the design using a good FEA software package, the arched (prestressed) beam is a cool idea. Look at some of the aluminum flatbeds on the road today. they hold as much as a steel flatbed.

However, your building department will have a problem with it. Most likely they will require a structural engineer with P.E. license to sign off on the design.

Good luck. It you build it, you could probably get it into a magizine.

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