Existing Glu-Lam Beam size question

[stevenspm]

I have a set of existing plans from a renovation done in '93. I do not have the original building design drawings. The renovation drawings indicate the main beams are 9 x 35-14 glu-lam beams. Field measurements on the beam confirm the size, but due to inaccessibility of the beam or the beam being painted there are no stamps visible. Has anyone come across a glu-lam beam of this size before? I am also wondering what grade to use, I have tried estimating the grade based on building being in Maryland and the roof load stated on the renovation drawings and what is coming working is a SP-SP 24F-V5. The beam has a span of 52.375' with a stated roof live load of 30psf (which I am putting as a snow load) with a tributary width of 17.708'. the problem I am having is that I do not know if SP-SP glu-lam beams are ones to use for that area or should I be using a different species for this glu-lam beam.
Thanks for your time

 

[dik]

The material is likely constructed from 22 laminations of 2x10 and planed to 9" wide. The SP likely indicates it is Spruce and the 24f is the flexural grade of the material (2400 psi); I don't have a clue about the V5 unless it is shear... and maybe 500 psi... There is nothing wrong with mixing grades... in these environs Doug Fir is common.

Dik

 

[boo1]

SP stands for Souther Pine (Loblolly Pine, Longleaf Pine, Shortleaf Pine, Slash Pine) pp16
Extreme Fiber in Bending 2400 psi tension, 1600 psi compression pp25 Table A1
5V stands for number lumber laminates in the outer zones that were visually graded.

AITC 117-2004

https://law.resource.org/pub/us/code/bsc.ca.gov/sibr/org.aitc.aitc_117-04.pdf

 

[stevenspm]

Dik,
Thanks for the response. From my understanding of glulam beams, the size I stated is not a common size for either Western species or Southern pine species of glu-lam beams. The grade I determined is for southern pine - southern pine with an fb of 2400psi (24F). The V5 I believe indicates the laminations are using visually graded lumber vs mechanically graded. The big issue I have is trying to figure out what grade to use so that I can determine if the beam will be acceptable with the new load I will be putting on it. As for species of lumber for glu-lam, I do not know what is common in Maryland.

 

[boo1]

Eastern US, SP (Souther Pine) is prevalent. Consider trying the building department and contractor, and see if they kept the truss sheets.

 

[dik]

boo is likely correct... with the SP and the V5 designation... southern pine is not common in these environs... the 24f is correct for flexure and they grade the lumber with the best characteristics and place it in the outer laminations...

Dik

 

[stevenspm]

Dik and boo1,
Thanks for the replies. We do have all the drawings available, but they do not include original building drawings just a facade renovation drawings from 1993.
I fear may have not asked my question correctly based on the replies you gave. What I am trying to find out is if the size of the beam was a standard size of glu-lam produced back before '93 and if so are the grades of glu-lams used today similar to those back then or was this beam a proprietary size which may or may not conform to American Wood Council/AITC grades.

 

[Ron]

Please note that allowable stress levels for southern pine and a few other species have been recently downgraded. If you have to comply with existing code, you might want to check this.

 

[EngineeringEric]

Contact Boise Cascade and get some literature from 1992/93. As for Ron's comment i disagree (sorry Ron, it is rare) you should evaluate what product is there, and that product's material properties did not get downgraded, they were made of better quality lumber then the current downgraded stuff. It would be similar as evaluating 1950 steel beam (A36) as new steel (A992).... just the inverse of capacity.

 

[Triangled]

Regarding species, generally, as noted above, the fabricator will utilize the lumber dominant in the region, simply because of economics. Southern Pine seems likely for your case. A telephone call to local laminators will increase your confidence. You may be lucky and find a laminator with an old-timer on staff who could tell you exactly what was common in the area at that time for that type of beam. The exception is complex glulam beams or structures such as radially reinforced or highly detailed architectural masterpieces. Since the effort input into the furnishing of beams for such jobs is quite a bit more than simple beams, laminators from across the country or Canada may have been competitively bidding or incorporated into the design and build process. In such a case you may have lumber from the West Coast, and then Doug Fir would be likely.

The size does not seem to me to be a standard size. But the fact that it isn't standard is not bad, it's just not helpful to you to determine the species. Whereas 5-1/8" width is standard for DF today, they can be obtained in 5" 5-18" 5-1/4" and 5-1/2". I have a research paper from the 60s in my file which tested 9" thick DF glulams, and this is definitely not a standard size today. Thickness of laminations can be a clue, but it also is not infallible. SYP lams are typically 1 3/8" (from memory on this one, perhaps it's 1 5/8") and DF is typically 1-1/2". But I recently inspected an older structure with 10 DF laminations in 9". As I understand it, the "5" in V5 does not refer to number of laminations but rather it is simply a number, but it refers to a specific combination regulated by AITC etcetera. The laminator building a beam to V5 combination must utilize specific grades of lumber varied through the depth of the beam to produce the design values advertised, such as "the outer 15% must be high tension capacity lumber ft = x, the next 15% must be such and such, the inner 40% must be such and such... etc". The "V" as noted above indicates Visually graded lumber.

A piece of wood from the beam can be sent to a lab for accurate species determination if desired. I believe the Univ of Wisconsin still offers this service, likely others too.

Glulams have been around a long time and if it's a standard beam in a standard building and not older than the 60s, I think AITC started around 1952ish) I'd be pretty comfortable assuming it corresponds to the AITC.

Good luck!

 

[Sawbux]

Southern pine needs to be planed again just before glue-up. The sap in the wood prevents glue adhesion unless it is on a freshly planed surface. That's why the lams are thinner in S. Pine. I wouldn't worry about a small variation in depth, the wood will shrink more than that in service anyway.
The 9" width was probably made from 2x10 lams, which are planed down to give an architectural side finish. I've seen 7" and 9" widths commonly called out in older glulam framing drawings.

 

[msquared48]

Well, it's probably a 9 X 35.75. See table from my 1958 Douglas-Fir Use Book. Also note the 1.625" laminations and the statement at the bottom of the table.

Mike McCann
MMC Engineering

 

[stevenspm]

Thanks for the replies, they have helped me get closer to the beam grade. Looking at the table Mike provided it looks like the beams are DF-DF glulam beams instead of SP-SP.

 

[msquared48]

Well, the tables were from the Douglas-Fir use book...

Mike McCann
MMC Engineering

 

[ThePioneer]

9 inches was a standard width for structural glued laminated timber prior to circa 1970. You indicated the beam was installed in 1993. Do you possibly mean 1963 or some other pre-1970 date? 8 3/4 inch is today's standard width and it has been since circa 1970.

Sided and molded dimensions vary depending upon when it was made. Also, virtually ANY size glued laminated timber can be manufactured as non-standard size.

And most likely "SP" indicates Southern Pine, NOT spruce.

1993 was not all that long ago. It should be simple to track down who manufactured it.

In your new work, allow any lumber species readily available. Southern Pine and Douglas fir/larch are two dominate softwood species utilized in glued laminated timber. Many other species are utilized as well. Specify the loading condition and building code to be met and let the supplier determine which species to furnish. The manufacturers of custom made glued laminated timber know how to design and make the stuff.