Wood Deck Joist Sizing for Decks IRC TABLE R507.6 vs Hand Calc 1

[Everroux]

Attached is my hand calcs for a wood deck joist which matches the calcs in the program Enercalc. However, both state the beam does not pass bending code check by almost 50% when the IRC TABLE R507.6 says it should be acceptable. Is this another issue similar to deck ledger bolt spacing such that the table is based on more specific test data for decks?

 

[Everroux]

Forgot to attach my hand calcs

 

[jayrod12]

I believe the IRC is expecting full compression flange support in their calcs. I can't confirm that since I practice north of the border, but I know that our residential code here does the same thing. So the question is, your joist is 16 feet long and you're checking it for only a single piece of blocking at mid-length. Do you not have any decking or sheathing on the joists that could be considered to brace the top flange of the joists?

 

[Celt83]

looks like you've taken Lu = 8ft, I believe the IRC tables are built assuming the decking provides full bracing to the compression face of the joist.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[Everroux]

Got it!

I made two changes:
1. Changed support to be every 1 ft
2. Cm=1 based on Fb=800<=1150 per footnote on Cm table
Passes!

Thank you

 

[Celt83]

also note IRC takes the joist span to center of the hanger seat as well.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer