structural wood glue
structural wood glue
(OP)
My client needs to make a load bearing column out of maple that will be 3.5" x 3.5"
They can not get a 4x4 solid maple piece and so they are planning to make a "built-up" column.
They MIGHT go with 3.5" x 3.0" BUT... they don't want to use mechanical fasteners, they only want to use glue.
They have asked to use a structural glue (they are thinking Tightbond 2) along with as few fasteners as possible.
NDS indicate built up columns with nails and with bolts but nothing with screws. I'm a little concerned about nails in hardwood (although I don't know if that concern is justified)
Load is about 3000# (600 DL and 2400 LL)
Column height is 10 ft floor to ceiling.
There is no opportunity for bracing.
I'm interested in knowing if there is specific glue I can specify that will eliminate the need for mechanical fasteners.
Also interested in any insight about screws vs nails for hardwood. I'm thinking that either way (screws or nails) they will be pre-drilled.
For a 2) 2x4 column, NDS indicates 10d common wire nails at 6" o.c. alternating sides and staggered. If similar size finish nails could be used, maybe that would be acceptable but again, I'm not sure how softwood requirements apply to hardwood.
Ideas?
Thanks,
Steve
They can not get a 4x4 solid maple piece and so they are planning to make a "built-up" column.
They MIGHT go with 3.5" x 3.0" BUT... they don't want to use mechanical fasteners, they only want to use glue.
They have asked to use a structural glue (they are thinking Tightbond 2) along with as few fasteners as possible.
NDS indicate built up columns with nails and with bolts but nothing with screws. I'm a little concerned about nails in hardwood (although I don't know if that concern is justified)
Load is about 3000# (600 DL and 2400 LL)
Column height is 10 ft floor to ceiling.
There is no opportunity for bracing.
I'm interested in knowing if there is specific glue I can specify that will eliminate the need for mechanical fasteners.
Also interested in any insight about screws vs nails for hardwood. I'm thinking that either way (screws or nails) they will be pre-drilled.
For a 2) 2x4 column, NDS indicates 10d common wire nails at 6" o.c. alternating sides and staggered. If similar size finish nails could be used, maybe that would be acceptable but again, I'm not sure how softwood requirements apply to hardwood.
Ideas?
Thanks,
Steve





RE: structural wood glue
But I can tell you based on a LOT of woodworking experience that if the parts are properly prepared before the glue up is performed (pieces well milled, without twist or surface flaws) than the bond between them will be MUCH stronger with glue than it will with nails or screws. A laminated column will at minimum perform the same (possibly better) as a solid one-piece column would.
As far as glue selection, I would highly recommend Titebond III over Titebond II in an application like this- titebond 3 is slightly stronger than titebond II, about 10% or so. More importantly, Titebond III is Type-1 water resistant, while Titebond II is rated as Type-2.
RE: structural wood glue
Dik
RE: structural wood glue
Yeah, I can't figure a code compliant way for the GC to built it either.
They want to use #8 finish screws (like this http://www.homedepot.com/p/GRK-Fasteners-8-x-2-in-... ) .
I think that will be fine. Glue might not even be needed but NDS doesn't address using screws (only nails or bolts AND it is for softwoods only (I assume).
I'd feel much better with screws than nails in hardwood.
RE: structural wood glue
4x4 nominal = 3.5 x 3.5 = (3.5 x 1.5 inch (nominal board) + 3.5 x 3/4 (nominal center board) + 3.5 x 1.5 (nominal board) = 2 glued joints for a final 3.5 x 3.75 square column.
Glue them up, consider using 2-part structural epoxy (slow-set to allow make up and clampping), with the clamps about every 12 - 14 inches apart. (Getting that many clamps may be more expensive than the wood!)
AFTER the glue/epoxy has set, drill out dowel holes (1/2 inch dia) all the way through and insert the dowels to maintain the vertial loads across all three vertical members of the column. If you wish, add 3x tension elements (stainless steel through bolts) near the top, middle, and bottom, but they won't really be essential. You will need to glue wood covers over the bolts (use countersunk holes) to hide the bolt heads.
RE: structural wood glue
RE: structural wood glue
I need the plys to act compositely due to the l/d limit for wood
RE: structural wood glue
Developing composite action even with wood glue doesn't seem to be a problem to me.
RE: structural wood glue
Here's where I get bogged down:
#1 NDS doesn't address screws for a built up column and that is what they (and I) want to use.
#2 Code doesn't provide a clean way for me to say the GC can glue it up with this great stuff and it will be fine....
I just need to get happy with the lack of an ICC accepted strategy.
I will recommend Tightbond 3 but I can't go without the mechanical fasteners. Seems like a 1/4" dam. plug every 12" on each side might not be too bad.
Seriously though, thanks of the input.
RE: structural wood glue
The glue lines are less noticeable than other adhesives and are less likely to affect the finish. If clear finished, be careful with using any adhesives that may prevent finish from covering and will show up.
Dik
RE: structural wood glue
A through bolt creates the clamping force FROM the outside towards the interior joint of the glue holding the glued joint together. It is much stronger than the screwed joint. And "just as ugly"!
A dowel opposes the different linear compression forces down the column as they act on the three different glued members by resitsting those forces in shear across many compatible wood fibers. it is your best reinforcement with least likely chance of changing its forces over time as the wood shrinks and expands with temperature and humidity.
RE: structural wood glue
Good idea about the glue.
I have suggested they start with 5" boards and plane (or thickness sand) them down to the right width.
Thanks again
RE: structural wood glue
Your local building inspector should be in agreement, and, if not tell him you will take responsibility for the adhesive use (you are anyway, doesn't matter if he agrees).
Dik
RE: structural wood glue
Another option would be to use a standard lumber column and flue on a thin maple veneer for appearance only.
RE: structural wood glue
B.E.
You are judged not by what you know, but by what you can do.
RE: structural wood glue
Dik
RE: structural wood glue
Or one pint kits can be found at some hardware stores , Cascophen took over what Borden used to produce. They now produce CASCOPHEN® ADHESIVE SYSTEM G-1131 a two part Resorcinol glue, which has fair gap filling properties.
B.E.
You are judged not by what you know, but by what you can do.
RE: structural wood glue
I don't typically specify using adhesives because I deal mostly with residential work where good workmanship and quality control are lacking.
RE: structural wood glue
Please remember: we're not all guys!
RE: structural wood glue
Robert Hale, PE
RE: structural wood glue
Andreas
RE: structural wood glue
Dik
RE: structural wood glue
B.E.
You are judged not by what you know, but by what you can do.
RE: structural wood glue
Dik