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AbelGus (Industrial)
23 Mar 06 22:06
I am working on a design using parallel chord roof trusses @ 7'-6" centers.  The trusses are alrady calculated and confirmed by the manufacturer.  I am looking for a table which will give allowable uniform load on a 4 X 4 (nominal)
spruce purlin.  Design spacing is 26" centers.  Purlins are supporting a corrugated metal roof panel and 45 psf snow load.  Total load on each purlin is 815 pounds assuming 5 psf dead load.  Connectors for wind uplift etc. are already considered - just trying to confirm spacing is OK.

Thanks

Abelgus
boo1 (Mechanical)
27 Mar 06 12:08
Treat it as a beam.  Design for bending, deflection and shear.  Check your dead load again and consider the wind loading. See this example for beams:
http://jan.ucc.nau.edu/~dsl/egr437/class/woodbeams/design/example.html
AbelGus (Industrial)
27 Mar 06 13:22
Thanks for the link and the tips.  They were very helpful.

Abelgus
boo1 (Mechanical)
27 Mar 06 15:39
The beams you selected will not work.  Both delfection and bending are way above allowable.  Need to look at bearing loading to.  You need to consider having someone (professional) help you design the system.
AbelGus (Industrial)
28 Mar 06 15:38
I agree, thanks again.  Before turning it over to an engineer I was attempting to get the structure in the ball park, for budgeting.  I pulled the allowable uniform load from a National Forest Products Association Table @ 801#, but as you say there is more to look at.  I do intend to run each purlin over two spans.  I would prefer to keep the 4 X 4 profile and change the spacing to permit this (unless it becomes ridiculous).

abelgus

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