Glulam Post Base Moment Connection

[XR250]

There have been several threads about this but I would like to get some additional information. I have a free-standing carport that was designed using flagpoled tube steel columns. Now the Architect wants to switch to glulam columns and beams. The service base moment is 4.5 ft-k. Seems like my options are a shoe, a knife plate or burying the treated column in concrete. I prefer to bury it just from an ease of construction standpoint but, of course, there are debates about rot. My problem with a shoe is getting the column to fit it tightly. Potential knife plate issues seem to be getting the contractor to drill a proper hole in the wood for the bolts. I am worried about looseness that might cause the carport to shake. Do glulam suppliers have bases that can be used for this with pre-drilled columns?

What has been y'all's experience with this issue?

Thanks!

 

[XR250]

Just talked to a local glulam supplier. They said to either bury the column in concrete (they claim it will not rot) or they can provide an engineered shoe.

 

[CANPRO]

XR250, I have never actually designed a connection like this, but my first thought was to do something like the attached sketch. 4 individual side plates and then you can through bolt or lag screw to the post. I think its easier to get a tight fit this way, and it gives the water a way to escape if it gets into the connection.

As for burying in the concrete - it may not rot, but if a car damages a post to the point it needs to be replaced, its going to be difficult if it is embedded in concrete.

http://files.engineering.com/getfil...b7-b339-7819bedee070&file=base_connection.pdf

 

[dik]

Even pressure treated stuff rots in concrete... just a matter of time. If the concrete is embedded in soil, then it's a never ending source of moisture. Best to use a steel shoe assembly that puts the post out of the ground and maybe use 'glulam rivets' to secure the side plates for moment resistance.

Dik

 

[XR250]

Thanks CANPRO. I like that detail.

 

[XR250]

@dik - heard of glulam rivets but never really paid attention to them. Seems like a good choice.

 

[dik]

OP:
They are extremely good fasteners and I'm surprised more people haven't been using them... been using them for 20 years or more... They are easy to design for... often use a little executable program I wrote in Delphi about 20 years back to handle shear and moment... No viruses, or malware... but is executable. Usual cautions about using software intelligently. Program is 'self-explanatory' and unitless...

Dik

 

[MotorCity]

I would be ok burying the column in concrete if it was coated w/ mastic or something similar. I'd continue it a few inches above grade.

 

[chicopee]

Directed at dik- is your .exe program compatible with MS window 7, 32/64 bit?

 

[Shotzie]

@chicopee

It runs on mine. I have Windows 7 64 bit.

 

[dik]

Runs on Win 7 and 8.1 64 bit and pro... don't have Win 10 installed in the house... and likely won't. I've used it hundreds of times and never had a glitch... it's pretty simple one of several 'knock offs' that I wrote for simple tasks...

Dik

 

[XR250]

Thanks dik. i'll check it out. I still have XP running so I assume it will run.

 

[Sawbux]

Many pole barn builders commonly use treated laminated columns. I've seen detail with wood pretreated before gluing up. Sometimes they just treat the part that's embedded when the building has wall siding. Typical size is 3 lams, making up a 6x6 approx. column size.

 

[XR250]

The glulams i was looking at are treated prior to gluing

 

[dik]

Most pole barns in these locales do not concrete the posts in... they are packed in with free draining aggregate. Concrete is 'bad news'.

Dik

 

[KootK]

I'm quite curious about the outcome of this. Can you share the detail recommended by the glulam guys? Also, how does the process work? Do they describe the connection to you at the design stage or do you have to wait and see what shows up in the glulam shops?

Having struggled with this on many occasions, I'd basically given up hope that such a connection was possible (bi-directional moment with potential shrinkage issues). While it's a very week form of proof, I'd kind of taken the fact that Simpson offers no such connector as evidence of it not really being possible/practical. Everybody wants there to be such a thing. So badly, in fact, that Simpson has seen fit to put that "don't use this for moment dummy" warning on all of their post base products. There's got to be something keeping them from developing a response to what is clearly a significant market demand.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

Simpson has released a moment capable post base for 4x4 and 6x6 in the states
see here

 

[XR250]

Simpson has released a moment capable post base for 4x4 and 6x6 in the states

The moment capacity of that is pretty minimal - 1960 ft-lbs in cracked concrete - prolly only suitable for fences and maybe decks. Would have to run the stiffness calc to see how flimsy they are.

Update:
The owner has decided they want chunky 10"x10" I-beams and columns - so W10x49 or HP10x42 moment frame it is. Made this pretty easy.

 

[jayrod12]

True, but it's better than nothing.

Nice of the owner to make your job easy.

 

[Wallache]

Simpson now offers a moment post base, the MPBZ and has stiffness and max moments shown.

The Perma-column company has a metal bracket attached to a precast base that apparently creates a fixed connection for pole barn type framing. I haven't dug through all of their test reports to see how true that is, though.