Wood Column Splicing
Wood Column Splicing
(OP)
Hello all,
I've searched the forum and haven't found the answer to my question (I may not have looked hard enough but I did use the search function).
I have a job where we are using 4 ply 2x8 columns that are sunk 6 feet into the ground and extend to 19' above ground giving a total column length of 25 feet. Obviously they cannot get 25 foot laminations.
Does anyone have any references to designing a column for combined loading when none of the laminations are the full length? I scoured the NDS (And the Canadian equivalent as this is being built in Canada) and some other references that were posted in the forum for other questions that were similar to this one.
I have a old job in our office that was done by an engineer over 15 years ago. He has that in the spliced region (1/4*L before the first lamination splice to 1/4*L after the last lamination splice with no lamination splices lining up with each other) the allowable bending stress is 0.42 times the allowable of the unspliced region.
I cannot find where he would've gotten that number. The engineer no longer works at this office and I'm sure would no longer remember where that number came from.
Any help would be appreciated.
I've searched the forum and haven't found the answer to my question (I may not have looked hard enough but I did use the search function).
I have a job where we are using 4 ply 2x8 columns that are sunk 6 feet into the ground and extend to 19' above ground giving a total column length of 25 feet. Obviously they cannot get 25 foot laminations.
Does anyone have any references to designing a column for combined loading when none of the laminations are the full length? I scoured the NDS (And the Canadian equivalent as this is being built in Canada) and some other references that were posted in the forum for other questions that were similar to this one.
I have a old job in our office that was done by an engineer over 15 years ago. He has that in the spliced region (1/4*L before the first lamination splice to 1/4*L after the last lamination splice with no lamination splices lining up with each other) the allowable bending stress is 0.42 times the allowable of the unspliced region.
I cannot find where he would've gotten that number. The engineer no longer works at this office and I'm sure would no longer remember where that number came from.
Any help would be appreciated.





RE: Wood Column Splicing
http://www.awc.org/pdf/WSDD/C3.pdf
RE: Wood Column Splicing
RE: Wood Column Splicing
Mike McCann
MMC Engineering
RE: Wood Column Splicing
ISC= Fbu*d*(0.0024 + A*d/L^2 - MoE/B)
I'm assuming the Fbu is unspliced allowable bending stress. but I don't know where this formula came from. Is it a standard structural analysis formula for interface shear between plies?
RE: Wood Column Splicing
The reason I say almost is I've determined the proper method for this post-frame building analysis is to assume there is a spring at the top of the column frame that has been calibrated to provide the an allowable shear resistance of around 100 plf. This makes the deflected shape look more realistic and very similar to a k=1.5 (Fixed bottom and semi-pinned top).
Since there is only slight lateral restraint at the top the positive moment seen by the column is very small magnitude and acts over a small area. The majority of the column is in negative bending.
I did find a US DoA Forestry Service Research paper on spliced nail-laminated posts that suggest a spliced post has strength that is equivalent to 48% of an unspliced post with all the same other characteristics. So that explains the 0.42 factor in my original post
RE: Wood Column Splicing
RE: Wood Column Splicing
Actually, there are suppliers for GlueLam columns. The butt joints are finger jointed, and the lower portions are pressure treated and then transition to untreated a few feet above grade.
Off the top of my head, three of the suppliers for the laminated columns are:
>> Timber Technologies, LLC
>> Rigidply Rafters, www.rigidply.com
>> Gruen-Wald Engineered Laminates, Inc., www.gruen-wald.com
And, I would bet that there are others, regionally. Most any laminator should be able to do it, although they may not want to mess around with small quantities. These laminated columns are promoted mostly for post-frame agricultural bldgs. and the like. The biggest issue is that they must be treated for structural use in continuous contact with the ground and moisture, to some distance above grade.
There are also a number of variations on the theme for precast conc. posts/piers which extend below frost and then terminate with some column connection hardware, 6" or a foot above grade. The biggest problem with these is that they be light enough so you can handle them, and still big enough in dia. so I can get some lateral soil resistance out of them, in the hole, and assuming well compacted backfill.
RE: Wood Column Splicing
There are done all the time as has been said in other places and so someone has had to have done this kind of design before.
RE: Wood Column Splicing
http://www.eng-tips.com/viewthread.cfm?qid=333686
Basically an elastic vector distribution method (using the moment and shear forces) See how it compares.
EIT
www.HowToEngineer.com
RE: Wood Column Splicing
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RE: Wood Column Splicing
RE: Wood Column Splicing
RE: Wood Column Splicing