Analysis to Existing Residential Wood Deck, above grade

[csg-1201]

Looking for thoughts:

Older designs have ledgers at the exterior of the building and wood pilings on the most exterior edge and sides of decks.
Joists span perpendicular to the ledger (obviously) and the beams straddle the posts on the other sides.
It does not appear to me that the straddled single ply beams are designed so they act as box beams, nor as a built up beam or multi-ply, and I am not sure how justify repairing like for like, especially with the increased live load from 40 to 60psf
It seems as though the in place loads would bear on the one interior beam until it is overloaded, then based on need, the exterior beam on the other side of the post would pick up the rest.. Does anyone have a sound engineering principal that permits the use of straddled beams as a "same" for a 2 ply?
current and replacement design has hangers for joists on inside face of the first beam.
Thanks for your thoughts

 

[jayrod12]

Wait, so the "beam" is 2 separate plys, one on each face of the posts, and the joists are flush framed into the interior ply only?

If that's correct, then you would not consider it a 2 ply beam. It would be a one ply. Sorry to tell the owner that upgrades are required to the beams.

I've seen decks framed similar where the joists pass over both plys. I've let that one go in those instances where a bit of deflection of the inner ply would allow loading of the outer ply. but I still design them as two discrete plys supporting 1/2 the load each.

 

[XR250]

I consider each to be taking 1/2 the load - unless the inner ply was infinitely stiff and the outer play was made of spaghetti. The connection of the beams to posts is usually the bigger issue. Sometimes cleats are needed below the beams to supplement the bolted connection.

 

[HouseBoy]

".... the exterior beam on the other side of the post would pick up the rest...."
If the joists are flush framed with hangers into the interior ply, how would the load get over to the ply (that is on the other side of the post)?

Perhaps some substantial blocking between the two plys would help get some of the load over to the "outer" ply but I would expect (much) more than half the load would be supported by the "inner" ply (the one that the joists are fastened to).

 

[XR250]

Ahh, did not catch that it was flush framed - makes sense. Thought it was dropped like it would normally be framed in this situation. WTF? Who builds shit like this?
Yea, I would only consider the interior ply.