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# Deflection calculation of D Fir-L Decking for specified concentrated load

## Deflection calculation of D Fir-L Decking for specified concentrated load

(OP)
I am trying to calculate the deflection of D Fir-L decking using the specified concentrated load (NBCC 2010 4.1.5.9) for a serviceability limit of span/240. I tried using equation based on plate theory (Timoshenko) to calculate the deflection but my calculated span is nowhere near the ones provided in CWC's Wood design manual. Please see the attached.

D Fir-L properties according to CSA O86-14:
Grade = Commercial; E = 11000 MPa; thickness = 36 and 38 mm; Poisson's ratio (assumed) = 0.1; NBCC 2010 - concentrated load (roof) 1.3 KN on 200 x 200 mm; Deflection limit = span/240

I would appreciate if anybody can shed some light. Thanks.

### RE: Deflection calculation of D Fir-L Decking for specified concentrated load

I believe their maximum limits are based on strength and not serviceability. at least as far as I can back calculate. If you are trying to meet the serviceability requirements you won't for the point load at their maximum spans.

If you notice in the decking selection tables the star that directs you to the your posted note only applies next to the maximum factored loads and not for the maximum specified loads.

### RE: Deflection calculation of D Fir-L Decking for specified concentrated load

(OP)
Thanks a lot, jayrod12! I appreciate your time. It is also mentioned in the WDM. I missed that critical piece of information.

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