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deflection of wood members

deflection of wood members

deflection of wood members

(OP)
The IRC sets deflection limits for wood members under live loads. Are there any limits for immediate dead load deflection and creep?

RE: deflection of wood members

Generally you only look at long term deflection for dead load (i.e including creep).

 

RE: deflection of wood members

Check the NDS - it has formulas for predicting creep

RE: deflection of wood members

There are limits for both live and dead loads for wood members.  

The normal values I use for Residences are L/360 for live loads only, and L/240 for dead plus live.  In other structures, those are reduced to L/240 and L/180 respectively.  Some are as low as L/180 and L/120.  

When you have tile or ceramic flooring, you may want to consider the live load deflection at L/600 or L/1000, with the dead plus live load at 2/3 (or 1.5X depending how you view it) of those values.

For cambers, I normally spec 1.5X the dead load deflection.   

Mike McCann
MMC Engineering

RE: deflection of wood members

(OP)
Do I hold to L/240 deflection criteria including the effects of creep on sustained loads?  

RE: deflection of wood members

If you feel it structurally significant to add the calculated creep deflection to the dead load deflection, then yes, hold to the L/240.  The results are certainly conservative if the creep does not occur.  No worries.

Mike McCann
MMC Engineering

RE: deflection of wood members

Include creep load for dead load definately also for live load if this live load could be long term(e.g. storage).

 

RE: deflection of wood members

"if the creep does not occur"
I would say it's highly unlikely that creep won't occur with timber beams.
Australian codes assume 100% creep for seasoned timber, 200% if it's green.

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