Concentrated Load Distribution in Wood Floor Joists

[omoreno1]

I have a wood floor joist system with 2x joists and plywood decking. How would the 2000# concentrated business loading in ASCE 7-05 distribute to the floor joists? I have heard several arguments about the load sharing ability that the plywood decking allows especially at 16" and 12" o.c. spacings. My idea would be to distribute the load equally to three joists at 16" o.c. and 2 joist at 24" o.c. Are there any advantages of using the plywood sheathing in "two way" action to computationaly verify this assumption? I appreciate any ideas.

 

[msquared48]

The bridging requirement primarily accomplishes the load distribution between the joists. The plywood does have some effect though.

Mike McCann
McCann Engineering

 

[DaveAtkins]

As I recall, the 2000# concentrated load is to be spread across a 2.5' X 2.5' area, per the IBC. I wouldn't spread it anymore than that.

DaveAtkins

 

[omoreno1]

To clarify my question is to how many joists can I distribute the load to?

 

[Lion06]

Additionally, you have a repetitive member factor of (I believe) 1.33 in the allowable bending stress calc. If you were to then spread the load to take advantage of the load sharing of the load distribution of the closely spaced members you would be "double dipping".
Spread the load as DaveAtkins suggests and use the repetitive member factor. Don't spread it any thinner.

 

[ctcray]

We've usually handled it by taking 2000lbs/6.25 sf = 320psf over 2.5' length of the joist under consideration. It's not really a matter of "how many joists take the load," just a line load of 320plf over 2.5' for 12"oc or 427plf over 2.5' for 16"oc.

Also, the repetitive member increase is 1.15 (Cr) for joists spaced less than 24"oc.

 

[JAE]

...and don't add the uniform live load to the concentrated 2000 lb live load...they are applied separately.