deflection of wood members

[jgajary]

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

 

[csd72]

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

 

[MiketheEngineer]

Check the NDS - it has formulas for predicting creep

 

[msquared48]

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

 

[jgajary]

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

 

[msquared48]

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

 

[csd72]

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

 

[apsix]

"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.