Joist Loaded on “Wide” Face

Question

Joist Loaded on “Wide” Face

Woody1515 (Structural)

(OP)

19 Nov 20 02:19

Hi everyone,

I have a situation where a contractor wants to use a 2X8 on the flat for a header over a new opening in an existing concrete wall. I am calculating the moment resistance of this 2X8 on the flat, and I am not sure what specified strength to use (in Canada, so using CSA 086). Table 6.3.1A is for structural joists, which is what I would normally use for a joist loaded “normally”. Should I still be using the same specified strength for the joist on the flat? I see that for Table 6.1.3C (beam and stringer grades), there are reduction factors for beams loaded on the wide face. These reduction factors are not mentioned in Table 6.3.1A.

Thanks!

jimstructures (Structural) · Answer 1 · 2020-11-19 05:26:29

Woody1515,

Is this 2x8 actually seeing any load or is more like a buck frame around a door or window opening???

Is it acting as a lintel over a masonry opening? What kind of load is it actually carrying?

Is it carrying any more loading than that which is not supported by arching action?

A sketch or elevation view would be helpful.

Jim

Agent666 (Structural) · Answer 2 · 2020-11-19 09:06:59

I'd imagine for sawn (natural) timber that the same strength properties apply irrespective of the direction of bending.

Manufactured wood products like glulam or LVL often have different characteristic strengths for bending on the flat.

jayrod12 (Structural) · Answer 3 · 2020-11-19 15:31:01

Tabel 6.3.1A is joist and plank. this would be considered plank orientation. so you can use the numbers from that table directly.

But, In this application will it be in direct contact with concrete? If so, you'll want to use PT lumber. And I believe 2x8 PT lumber is incised, so you need to take that reduction into account.

All in all, I think that's a terrible idea. Put in a real lintel. a couple of 2x4 will be infinitely stronger than a single 2x8 on flat.

Woody1515 (Structural) · Answer 4 · 2020-11-27 01:42:54

Thanks everyone. I went ahead and designed a lintel instead, I’m not sure how I missed the joist and plank values.

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Joist Loaded on “Wide” Face