Residential Deck Engineering Seismic

[rollinw]

I am designing a 10x36 covered residential deck attached to the end of a 36' wide house with 4x4 knee braces at the 8' tall posts in an area with high seismicity.

The plan reviewer here requested a seismic load calculation for the 36' long line and I'm curious what R factor is appropriate? From other posts/examples I've seen, it seems most have used the R factor for the overall structure the decks are attached to, and the ACSE 7-05 (code we are using) doesn't really seem to have an appropriate R factor choice for a knee brace situation...

 

[XR250]

Geez, diaphragm deflection calcs for a residential deck?

 

[rollinw]

Well the house is in seismic zone D2, so the plan checker doesn't believe there is enough ductility in a brace type system.

 

[jayrod12]

correct me if I'm wrong, but the lack of ductility just means you have to use higher seismic loads. Can your system handle the increased loads from a less ductile system?

 

[rollinw]

Yep handles easily. Used a reduced R value (1.5) to reflect this, plenty of redundancy.

 

[KootK]

Most of our floor and roof decks are considered low-ductility systems (save the new stuff on big box roofs). It's hard to imagine why a residential deck deserves special treatment in that regard.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.