Stud alignment in mid-rise wood buildings
Stud alignment in mid-rise wood buildings
(OP)
How do other engineers handle stud alignment with floor trusses/joists in 3-5 story wood buildings? Since most of my wood buildings use floor trusses and the truss manufacturers typically use 2x4 ribbon boards, I usually spec that the studs must align with trusses and so forth throughout the wall stacks. The double top plate can usually span between studs for one floor load, but any more than one floor, they don't theoretically work. Any thoughts? I'd really be interested in hearing from any west coast engineers since apparently this doesn't seem to be too much of an issue with TJI joists they like to use out west.






RE: Stud alignment in mid-rise wood buildings
Don't know how deep you want/need to go with your analysis, but I assume some of your lower level rim joists could also be counted on to help span loads across multiple studs?
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
Easier for me to say right now: Give them a hearty laugh and tell them one of the two are a requirement unless they have a better idea. They can follow your ideas now, or they can follow them later when they are fixing cracked/failed members.
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
Your original response was mine exactly: a hearty laugh. I never had any pushback until recently (my last 2 wood buildings). I brought up the issue to Woodworks and they said when you get something that works, let us know (they mentioned they get this question a lot in the Atlantic or Midwest but not really out west). I assumed it was because of TJI joists and the TJ rim board, but this is speculation. They did mention they are going to try and write a white paper in the next year or so about the topic.
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
Just to throw a couple more wrenches in the gears of our designs...
Non-aligned std. studs are bad enough in this multi-fl. situation, now try to justify jambs at openings if they are not aligned vertically. You do need a continuous, and competent, load path all the way to the found., and you do need to pay attention to shrinkage variations, cross grain vs. parallel to the grain. Secondly, your 2x header under the double top pl. might not be as effective as you think or wish it to be. When the cross grain shrinkage takes place in that header, you are left with a smaller stud end section, due to the header cut-out, causing compression perpendicular to the grain on the top pls. to be a design problem. I think you might be right about the TJI’s and manufactured rim boards. The TJI’s may need web/bearing blocking, but mostly the rim boards don’t shrink vertically, so they act as a better beam to distribute concentrated loads, without settlement issues. We probably don’t give enough credit to rigid sheathing (maybe even sht. rk.) in its ability to help with this redistribution of concentrated loads. It just helps even out the top pl. deflection, or load distrib., to several adjacent studs. We just don’t know how to apportion all of these small redistributions which seem to make the whole system work. But, it does. One significant life saver is the large FoS which we apply the allowable wood stresses, because of its strength variability. Then, once in awhile we find a few pieces of wood acting together which actually approach ‘fully stressed,’ and we get to fix some sht.rk. cracking, etc.
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
I would add in that the contractor on one of the projects allowed his framer to cut holddown anchors because "they were in the way of the sill plate"
RE: Stud alignment in mid-rise wood buildings
Fox gets my point on the let-in header. I meant the 2x header shrinks in width and pulls down, away from the two top pls., which are now sitting on a smaller stud end in bearing. And, the top pl. now has to deflect before it starts loading the header. Although, the two top pls. will shrink cross-grain too, but more or less as a double thick unit. Be sure that they do a good job on those let-in cuts, so the top of the stud and the header are in the same plane under the top pls. The double top pls. are there for the bending strength btwn. studs, just what we’re talking about, and to provide longitudinal continuity down the length of the wall and at corners; staggered butt joints, spacing of these joints and lapped at the corners, etc. If I were using the let-in header on all the bearing walls (all walls in one direction, some consistency in plan orientation, for the framers) I might consider the header and only a single top pl. Stagger their joints for continuity and maybe some straps around the corners to what would likely be a double top pl. condition.
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
I'd like to push towards the rim board option but I don't know how you get any real positive attachment of the rim board to the trusses. I know a deeper ribbon has been discussed here before but I've been told by a truss manufacturer those are only used to align and prevent rotation of trusses. I'd hate to use it since I don't know how they would splice it.
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
EIT
www.HowToEngineer.com
RE: Stud alignment in mid-rise wood buildings
With floor trusses and a standard 2x4 ribbon board, trusses need to (or should) bear directly on a stud pack. The top plate can span between studs for one floor's load, but if they line up for multiple floors above and are off on one of the lower floors, then the top plate won't work for the build up of load. Rim board can be used to evenly distribute the loads from the walls above, but there is concern about proper installation at party walls. I was just curious how other engineers handle it. Making them align all the way up in tilt up wood walls requires thinking about truss locations ahead of time and that's something framers are not good at.
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
- right, right, I see now. Thank you. We have been aligning them, I just didn't realize it was an becoming an issue.
EIT
www.HowToEngineer.com
RE: Stud alignment in mid-rise wood buildings
You could you shear transfer clips from the rim board to the top plate. You could also use clips to attach the rim board to the trusses.
Does the rim board need to be fastened to the trusses for buckling resistance? If so, switch to an LVL.
RE: Stud alignment in mid-rise wood buildings
RE: Stud alignment in mid-rise wood buildings
So most contractors that have asked the question have received this response from me "You can align the studs as per note 188 on the plans or provide continuous blocking below all the mis-aligned studs as per note 189 on the plans. The choice is ultimately yours however from an economics standpoint I advise you adhere to note 188."
They've never called about it again. And oddly enough, continue to call the company for further projects so I must not be that difficult to deal with.
RE: Stud alignment in mid-rise wood buildings
1) mostly TJI
2) lots of pushback on stud alignment for non-panelized walls.
3) no robust solution to this problem.
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.
RE: Stud alignment in mid-rise wood buildings
Letting in headers is time consuming and may not solve the problem you think it does until the floor deforms. I would expect a 1/16" fit tolerance for typical carpenters. If you consider that and the differences between cross grain vs. lengthwise shrinkage I would expect a small gap between the header and top plate a few months after the building heat is turned on. If they are cutting the notches with a typical skil saw you may end up with one or two small circular slits extending past the inside notch corners.
Like Koot, we mostly use TJI's. Many like to use an extra bottom plate for screeding the sound barrier topping so we have been using Simpson SDS screws of late to attach walls to the rim boards. We do not like the extra plate, but it is practical, and you all know the wood market.
RE: Stud alignment in mid-rise wood buildings
EIT
www.HowToEngineer.com
RE: Stud alignment in mid-rise wood buildings