Deck design: attaching beams to existing posts

I have an existing third floor deck (10'x40'). It is supported by a 6"x12" beam resting on 18' tall 8"x8" posts.
My question: I want to install a second floor deck, underneath the existing deck, by tying into the existing posts. Which is the best way? One contractor recommended notching into the existing posts and inserting 4x12 beams. This seems like more work and also means cutting halfway into the post and weakening it. Another contractor said to tie into the post with custom made hardware or maybe a Simpson connector. This method seems simpler, but will the ties support the weight of a deck and people?
I haven't seen either method in any of the how-to books. They always show the beam resting on top of the post.
Thanks, Karamo
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In a previous post karamo wrote...

Simpson makes several connectors that might do the job. You could also add a bearing block bolted to the post that the new beam will rest on. If you use this method be sure to add some straps or other ties to keep the beam on the bearing block.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Easy to answer. The best way is the one that will be approved by the building inspector. I cannot imagine the problems if you were to notch the post and the building inspector refused to approve the deck.
I agree that notching the post may not be best, at least cutting them half way. There is a lot of different deck hardware at www.mcfeeleys.com They may have what you need.
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8X8 what? 10' on center??
You could always design in shoulder supports. Then ask the inspector if notching would suffice.
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You'll will probably need a building permit for this project. Check with your local building inspection department. To get the permit, you will need detailed drawings with structural calculations. Existing posts might need reinforcing, depending on the additional load of the new deck. You may need additional bracing members for the posts, since they are very tall. In other words, you should have it designed by a structural engineer. You are dealing with heavy loads and tall posts and don't want to see it collapse the next time you have a rowdy party.
Goodluck, Keybored Architect

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