lateral for decks

[tricalcim]

What are you folks using for lateral bracing for raised wood decks attatched to the house (via ledger board and joists) on one side, and supported by columns on the opposite side. I suppose I could design a steel column w/ moment connections, but I'm not really seeing that in conventional light weight wood constructed homes. Or, are some assuming All lateral reaction can be transfered to the ledger. Any thought are appreciated. thanks.........

 

[SperlingPE]

How are the columns attached and what type of foundation?
1. Use columns as cantilever posts
2. Knee brace columns to provide stiffness.
The side attached to the ledger board should go into house foundation through the sheathing.
I think the load for a deck would be fairly low (no area due to no walls). However, I have not had the opportunity to investigate this situation and wonder about some of the things I see on houses and apartment buildings in my area.

 

[FalsePrecision]

Generally, decks are designed as cantilevered horizontal diaphragms for lateral. Unless it is an unusual situation (we need to exercise good judgement), the outboard edge columns or posts are not counted on for lateral support, and kneebraces are unsightly.
The bottom line, the forces are transfered to the ledger board, and you can use Simpson straps connecting the end joists back to the main floor structure for your chord forces.

 

[tricalcim]

Yes, loads are low and cantilevered horiz diaphrams are what I'm generally seeing. Thanks to both of you for your input.

It would seem that there may be some benefit from a fully "blocked" deck diaphram, I'm thinking greater diaphram rigidity
(although I don't plan to detail it this way because the cost vs benefit does not merrit).

any final thoughts??

 

[UcfSE]

If you didn't want to design your decking itself as a diaphragm you could use horiztonal x-braces under the deck surface. Everything else would be the same, straps for chords forces and such.

 

[FalsePrecision]

Because of lack of damping (no partitions) and low dead load, decks are bouncy - makes people nervous, especially when high off ground. I generally recommend floor joists or trusses at 16" o/c max, and 7/8" T & G plywood/OSB minimum deck floor sheathing. 1-1/8" T & G or gypcrete fill is much better. Blocking prolly doesn't add much bang for the buck.

 

[shepherd]

Assume horizontal diaphragm cantilevered off house. Provide decking at 45 degree angle to joist. Gives you a much stiffer diaphragm. Columns on outboard end need only be designed for gravity.