Western Red Cedar Glulam Specific Gravity

[cmbyrd77]

Does anyone know if the specific gravity of a Western Red Cedar Glulam is more than regular sawn Western Red Cedar? I am designing a canopy and the architects want to use Western Red Cedar. It has a 12'-10" cant. and I am having a heck of a time trying to get the connections to work. I find it very hard to believe that (3) 1" dia. bolts are only good for about 3 kips of shear perpendicular to grain. What is killing me is my Wet Service Factor. Thanks in advance for the help.

 

[msquared48]

Have you tried calling the engineering department at either Weyerhaeuser or Boise-Cascade?

Mike McCann
MMC Engineering

 

[dhengr]

Cmbyrd77:

Talk to a laminater, or a local cedar lumber distributor as to what grades and mechanical properties are available. Not just what any lumber yard can supply or the run of the mill materials from the NDS specs. For the connections, take a look at shear plates, split rings, or timber rivets, they offer much better shear values, whatever the lumber, than just plain bolts.

 

[woodman88]

If you looked at Doug-Fir (.5sg) vs Cedar (.36sg) you will only get about a 1.25 increase in the bolt allowable. If a 1.25 increase is what you need than add another bolt. If you need more than a 1.25 increase, you will need to look at other connections like dhengr states.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[Sawbux]

I think cedar glulam will be a specialty product - not generally available.

Cedar is pretty soft (SG=.36 as per above), so the bolt values for perp to grain will also be low.

You say you are using wet-use factor - is this beam exposed? without a roof over it? If it is covered, you should be able to use the normal loads.

Don't forget duration of load factors, if the loads you are resisting are snow or wind or? That will increase the allowable values. If possible use bearing type connections, saddles, etc. Architect may want to hide the connections?

Calling Engineering department at Weyerhaeuser probably not possible - I don't believe there is one any more! I used to work there years ago. The laminating business was shut down or sold also. They spun off Trus-Joist, but they don't do anything in cedar- I believe.

There was a laminator in Centralia, WA that did cedar - but I don't remeber their name or know if they are still in business.

Good luck!

 

[cmbyrd77]

Thank you all for your help. It looks like using split rings/shear plates is my only option. I do have another question. In the NDS is only shows a bolt diameter up to 7/8" with a 4" shear plate. The architects want the look of a bigger bolt and that is why I am using 1" bolts. Is there a penalty for using a bigger bolt? I wish NDS gave the equation they used to derive the allowables in Tables 12.2A and 12.2 B because I would just calc. it myself. I really probably would only need a 2 5/8" shear plate. Thanks in advance for the help.

 

[hokie66]

The bolt has to fit the hole in the shear plate.

 

[cmbyrd77]

Yeah, I kind figured that for the shear plate, but it looks like teh split ring would work, right?

 

[hokie66]

Yes.

 

[dhengr]

Cmbyrd77:

I think you should be able to use a larger size bolt with a split ring without any trouble, but for a shear plate you have to match the hole in the shear plate you are using. The dapping tool might have the correct size drill on it, but you should be able to redrill for the larger bolt for the split rings, where the bolts primarily clamp the joint together to make the split rings act properly. The split rings and shear plates take most of the load in wood to wood connections.

Alternatively, the Architect could have Tiffany’s make some bejeweled fake 1" nuts, bolts and washers to fit over the ones doing the real work. But, why not 4" bolts, that would mean four times even bester architecture. And, I’ll bet he’ll bitch about the cost of your GlueLams and connections because the job is over budget while he mulls over 14k gold or platinum.

 

[cmbyrd77]

HAHA! Man you hit the nail right on the head there. Thanks for all the help.

 

[Goodfellow]

We are glulam fabricators in Canada maybe we can help you with your project Goodfellow Inc 800-361-0625 ask for John

 

[cmbyrd77]

Thanks John. I will keep you in mind. It's a design/build job so I can be in the contractor's ear a little more. Just out of curiousity, what kind of cost increase is it to do custom glulam sizes. For example the architect is wanting 10x10 columns (not 9x9.25).

 

[Goodfellow]

Maybe around 35% we have to use one extra lamination plus we have to use 2 x 12 instead of 2 x 10 for lamstock

John