Actual dimensions (cross-section) of lagging boards. 1

[jdrumgool]

AASHTO and FHWA tables regarding lagging design for soldier pile excavation support walls specify lagging board thickness as "rough cut lumber." Is there a standard that identifies the actual dimensions for rough cut lumber? My understanding is rough cut is 1/8" inch larger than the standard (NDS) dressed size. This issue is under debate now as some on my project believe rough cut lumber to mean nominal size equals actual size. Who is correct?

 

[SlideRuleEra]

You are correct... but there is a "loophole". Rough cut lumber is "not less than" 1/8 inch larger than dressed size - so nominal size would meet that criteria.

Lumber sizes are established by a voluntary standard issued by the "American Lumber Standard Committee, Inc." Here is a link to download the (free) .pdf version of "American Softwood Standard PS 20". Concerning your question, see Paragraph 5.1 on page 5.

http://www.alsc.org/untreated_ps20_mod.htm

http://www.SlideRuleEra.net

 

[DRC1]

Lagging is generally rough cut. It is intended to be milled at some point and therefor is not cut to any great prescion. A 3" board will be about 3" thick rough and 2 1/2 dressed both sides. The actual stress distribution across the lagging is debated. Arching at the soldier piles reduces the effects of lateral load on the boards. Although it is possible to calculate the load from one of the methods, most designers rely on experience and thus designs are generally conservative.
My point is that you don't need to be too fussy with the actual thickness

 

[PEinc]

On the east coast, a 3" lagging board is approximately 2 3/4" thick. I have seen them vary from 2 1/2" to a full 3" within a delivery. Mostly they are 2 3/4". A 4" board would be about 3 3/4" plus or minus 1/4".

Some lagging suppliers try to deliver 3" boards that are mostly 2 1/2" thick. This is a rip off.

I am unaware of any literature that describes a standard for lagging board thinkness. Over many years, this problem has surfaced over and over agin. In fact, I am currently arguing board thickness with a highway consultant. If anyone has a good reference, I'd like to see it. I'll also check out SlideRuleEra's link above. Thanks.