I’m shoring up an old house and have placed collar ties across the “A” frame members in the roof. The collar ties are 2×10 and placed on both sides of the “A” frame members and then filled in between the 2 collar ties. I now will run a column from the bottoms of those new collar ties down to the ground where they will sit on top of cement pads (12 inch sono tubes 3 feet into ground). My question is I was thinking of stacking 3 2x8s with a 1/2 plywood spacer between the 2x8s so I wind up with a actual size column of 7.5 in X 5.5 inch… these columns will run about 16 feet in length from the bottoms of the collar ties down to the concrete. And when I stack the 2x8s, I would scatter the joints. Does this sound like the correct way to do this? Thanks for your help.
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I depends on a heck of a lot of variables.
Starting with what the structure is to begin with, what goal you are trying to accomplish, and proceding to what sorts of loads the structrue will be expected to bear, and how big it is
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I'm no structural (or any other kind of) engineer, but why can't you use full length (16') 2x8's so the collar ties rest on them as sort of the outer layers of the sandwich (the outer 2x8's would be in the same plane as the collar ties and the infilling 2x8's (with spacers, as needed) acting like a tenon going up between the colar ties and you could lag or even through bolt through the collar ties and through this "tenon"). I would worry about butt joints where shorter boards are put together to make the longer post "kicking out" if they were the outer layers, but as inner "filling" it seems like they will be restrained by the outer two full-length boards. The inner boards could even be cut on and angle and run up to touch the rafters and be held there with gussets of plywood.
But like Piffin said, depends on loads and so on as to what you should be doing.