1x Structural Wood Members? 2

[medeek]

I am working on a project that would like to use 1x material (ie. 1x2, 1x3 and 1x4 boards) in a structural application where there is primarily tension and compression with some combined bending. Table 4A along with its adjustment factors is for dimensional lumber with a min. thickness of 2" nominal. Table 4E and corresponding adjustment factors are for decking. What would be the appropriate reference design values and adjustment factors to use in this application?

RISA 3D will not me do any checks for lumber this size, I'm hoping there is a work around.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[XR250]

I would probably just use numbers for equiv. 2x material and don't design it to the gnat's ass. Seems like the thicker members have lower design values in the NDS so maybe the thinner ones have higher values.

 

[racookpe1978]

The 1x2, 1x3 (have seen very little of that used except in trim and battens), and 1x4 is cut to 3/4 inch thick - half the thickness of a 2x4 or 2x2 nominal.

 

[JLNJ]

I'm not sure what the appropriate factors are, but you will want to be conservative since any flaw in such a narrow member could have a catastrophic effect.

 

[medeek]

@JLNG

I would tend to agree with that statement. Perhaps that is why the NDS restricts it mention of sawn lumber to 2x material. I agree also that this is not typical construction.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[mike20793]

I think it has more to do with the grading agencies. If you look at the rules for the different species, it's actually pretty tough to visually grade 1x material and most grading agencies won't even list the knot criteria for smaller than 2x material. There just isn't much room for product flaws so I think mills would rather not manufacture it if they can't make money doing it.

 

[OldBldgGuy]

I have just reviewed 2 hockey arenas built in the 1940s with wood trusses built up from 1x8 & 1x10 8' long pieces; 95' span & 114' span. Obviously it works, one has been bastardized but the other is in beautiful shape. As XR250 says, thinner pieces means better grade because there simply isn't room for the flaws, the pieces get rejected in manufacturing. Use the values for 2X material, figure it for your material built-up, & you should be able to work through it.

 

[medeek]

Mulling this over a bit more I'm noticing that the only factor that will really come into play that appears to be a function of the lumber size is the size factor (C_F). As the depth of the lumber increases the general trend is for a decrease in the size factor however as the thickness of the lumber decreases so does the factor (see Table 4A adjustment factors NDS Supplement 2012).

Given the way the 2",3" & 4" sizes are lumped together in the table and the same values for the different thicknesses at this depth the logical conclusion would be that the factor would be C_F = 1.5 for 1x2, 1x3, and 1x4 boards.

I sent an email off to AWC support and they suggested I contact the grading agencies with my question.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[focuseng]

It is not that the 1x doesn't have strength but that it is not reliably so and it is not tested or graded for such an application. The values published in NDS are not applicable to a 1x visual grade. The 1x boards are usually graded for aesthetic only without a consideration for strength and the grade stamps don't correlate to the strength grades. You can use them but I would apply a generous safety factor and know that any given board may not have any value at all. Boards used in decking applications (ex: 5/4 R.E.) are different again because they are graded with strength value in mind which has been tested. The key thing is to know the grade agency and if the board is graded to its standards for the application. I absolutely would not use Cf on a 1x board unless explicitly allowed due to in-grade testing.

______________
MAP

 

[allgoodnamestaken]

Everything smaller than a deck board or a fence post can be jointed, meaning you are unlikely to be able to use it for tension even were you allowed in code. I don't think I've seen anything smaller than 1x4 in unjointed members recently.

I don't think there are any smart savings to be had here. If you can satisfy it with a 1x4, you're probably better off using a 2x4. no.1 no.2 SPF and move on.

 

[medeek]

It seems that there is no consensus on the use of 1x members in structural applications. I spoke with the NLGA (National Lumber Grades Authority) yesterday and there is a grade labeled as "SRB" for 1x lumber however availability may be an issue. The AWC tech support did point out that footnote 2 of Table 4A does allow for stress rated boards when graded per the stress-rated board provisions. Somehow I missed this footnote.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[EngineeringEric]

Trusses are braced with 1X material often (or so i have seen)... so it works for that?

 

[RHTPE]

I would proceed carefully when using 1X lumber in a structural application.

I have been involved with a recent project using P/T 1X material. The quality of the logs that these 1Xs were cut from was horrific. Some portions of some of the 1x4 & 1x6s actually had the grain pattern of a burl. Far too many loose knots as well.

If you can selectively find reasonably clear & straight grained 1X boards, you may be fine. I just have a real problem with the quality found in my region.


Ralph
Structures Consulting
Northeast USA

 

[Ron]

Agree with RHTPE....wouldn't consider 1x as structural. Further, any grading anomaly is exacerbate in a 1x material as compared to 2x