Comparing American and Canadian Floor joist spans 3

[woodman1967]

This is more of a curiosity thing than anything else.
When you compare the 2015 IRC and the Canadian NBC 2015 span tables a 2"x10" floor joist @ 16" OC spans 15'-5" (IRC) but only 13'-8" (4.17m) in the Canadian tables.
While I know the calculation process is different in Canada as compared to the US but shouldn't they both give a span that is relatively similar?
Canada has recently added vibration limit state, does the US have this as well? Would this be the difference? I've included the IRC and NBC span charts for 2"x10" SPF#2.

 

[phamENG]

I'm guessing it's vibration. US codes are still silent on that issue. I've been planning on incorporating either the Canadian method or another academic method for estimating vibration into my standard calcs for wood floors. Haven't completely implemented it as SOP yet, though.

 

[LuK13]

My guess would also be vibration.

IRC code minimum floors in a house can be bouncy. And I would never put tile on an IRC code minimum floor.

Before I finished getting my degree I worked for a custom home builder. He would always ask for the floor framing to be sized for 24" OC spans and then install the floor framing at 16" OC to insure he would never have a call back for a bouncy floor or cracked tile. It felt like driving a nail with a sledge hammer, but he never got a call back for a floor.

 

[ChorasDen]

Have some experience on this topic, while design methods do differ superficially (Limit States Design vs Allowable Stress Design), the big difference is as others have stated, vibration control. I think the Canadian method is far superior to the US method in regards to floor performance, but that's not saying much, as the US does not have a method...

 

[Tmoose]

I found this Canadian publication from 1985 . NRCC 24813.

https://nrc-publications.canada.ca/eng/view/accepted/?id=17a563a7-911a-4955-8c5f-8511a7e16cf0

I guess The designer needs to know if the occupants are more likely to Polka or Frug. page 621 table 2

Now to wade thru the NBC.

 

[woodman1967]

Thanks everyone, I appreciate your time.

 

[Kroc057]

Most have identified vibration as the driving difference, but when I did a comparison between the two methods I found differences mainly occured because the NBC tables use limit states design, while the IRC uses allowable stress design to achieve their respective spans. Make sure you are also comparing the same species and grade of lumber. No.1/No.2 s-p-f from Canada does not have the same design properties as Southern Pine or s-p-f(s) in the USA. Keep in mind that the NBC tables are based on the most conservative case for reinforcing for vibration. You can use the vibration equation in the appendix of the NBC, and specify better detailing like gluing and 3/4" sheathing to achieve longer spans than included in the NBC tables. Alternatively, buy the cwc Canadian span book, which provides spans for all the vibration reinforcing options described in the NBC appendix equation and also spells out the assumptions used to develop the tables. For a true apples to apples comparison you could get the cwc US span book which includes allowable spans for Canadian species but is developed following the same methods as the IRC or use the AWC span calculator available for free on their website.

 

[Canuck65]

Woodman, I just checked a 2x10 SPF No.1/2 floor joist in the WoodWorks software under the Canadian Code. I input a 15'-4" length. The joist passed in bending (74%), shear (26%) and deflection (97%LL). It failed in vibration (110%). The maximum joist span for vibration seems to be in the 13'-8" range.

 

[skeletron]

Are these from the Part 9 tables (NBCC)? If so, just be careful about what load is being applied in your comparison. The CWC Engineering Guide for Wood Frame Construction discusses this on Pg. A-8.

Also the wood species between NDS and NBC can vary a bit and I don't think there is a direct equivalent. So material properties may be at play here.