PORCH DECK DIAPHGRAGM

[JRSE]

I have a 16' x 20' deck with 2x6 lumber flat supported on joists that are supported on beams. A wood frame is at one end and concrete shear walls are at the other. Glass panel railing is at the perimeter of the porch and large wind pressures result (V=105 mph). How are the lateral pressures distributed to the supporting MWFRS system (frame and walls)? As discussed flat 2x6 lumber with spaces in between are not recognized by the codes; therefore is horizontal bracing (similar to metal buildings) utilized to distribute the loads. In an online paper rotation of the flat lumber during a lateral event introduces local moments at the nailing and results in ripping apart the top of the supporting members. Any advice would be appreciated. I have seen in photograph via Simpson an entity installed a let-in brace on the underside of the joists and in the field I have seen flat metal strapping attached to the bottom of the boards. I assume for small porches that engineers are treating the deck system as a rigid body, similar to a trellis, and just simply distribute the loads to the vertical lateral force resisting system.

Thank you.

JRSE

 

[msquared48]

You can use diagonal blocking with metal strapping over or under the blocking to resist the lateral forces. Have to anchor the ends of the deck too to take the induced T/C forces.

Or you can use the knee braces if allowed in your area.


Mike McCann, PE, SE (WA)

 

[wannabeSE]

How big of spaces are between the boards? I have not done much wood design. But, have you looked at the NDS SDPWS for 2x6 diaphragms?

http://www.awc.org/pdf/codes-standards/publications/sdpws/AWC-SDPWS2015-ViewOnly-1411.pdf

 

[Tmoose]

Seems like the "let in" bracing would compromise the joists, at least toward mid-span.

Or studs, for that matter.

http://www.homedepot.com/catalog/productImages/1000/83/83da5827-bfdf-4e01-9373-cdf974983a83_1000.jpg