Wood Moment Connection Using Simpson Straps (or Equivalent)
Wood Moment Connection Using Simpson Straps (or Equivalent)
(OP)
I'd like to query the gang here regarding whether or not you would consider the connections shown below to be valid moment connections. There are some engineers working withing my sphere of influence who do. My answers would be:
1st detail (upper): Not a chance. I think that stiffness concerns and P-delta effects neuter it.
2nd detail (lower): I guess, if all other issues could be resolved such as cross grain bending etc.
I would prefer to see discussion limited to the validity or invalidity of the moment connections themselves rather any other issues that may render the details crappy.
And yes, I am ashamed of myself for failing to number my details. Too lazy to make a second trip to the scanner. We have to type in employee / project / task codes now which makes scanning about as much fun as gouging out your own eyes out with a grapefruit spoon. But alas, I digress...

1st detail (upper): Not a chance. I think that stiffness concerns and P-delta effects neuter it.
2nd detail (lower): I guess, if all other issues could be resolved such as cross grain bending etc.
I would prefer to see discussion limited to the validity or invalidity of the moment connections themselves rather any other issues that may render the details crappy.
And yes, I am ashamed of myself for failing to number my details. Too lazy to make a second trip to the scanner. We have to type in employee / project / task codes now which makes scanning about as much fun as gouging out your own eyes out with a grapefruit spoon. But alas, I digress...

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: Wood Moment Connection Using Simpson Straps (or Equivalent)
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
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: Wood Moment Connection Using Simpson Straps (or Equivalent)
I digress slightly but partial vaults in gable end trusses have always caused me some pause. When the roof diaphragm is loaded longitudinally the double top plate of the wall at the gable end will be loaded in tension or compression. If this double top plate is discontinuous because of having to balloon frame under a partially vaulted gable end truss how is this supposed to work. My solution of course would be to strap the top plates together at the pitch breaks with a MSTC40 or something along those lines.
I've never tried detail 2 or seen it done. An application might be a half wall on a overlooking loft? Even if it calcs out and it has a couple of straps on each stud I'm guessing there will always be a slight gap between the wood members and the guard rail will always feel a bit shaky, giving the impression of weakness. A simple summation of moments shows that a 200lbs lateral load at 48" will exert a 2,743lbs moment couple with a 3.5" wall. This amount of force will cause some give in the fastener/wood interface and again the connection will probably not feel very firm, but again this could be a very subjective thing.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
I will say that i have done similar to #1 with heavy timber columns, step notched cut the splice, and sandwich with steel channels and bolts. I assume it acts similar but i am much more comfortable with those connections.
#1 in a gable end or great room wall has been proposed to me before. I have seen this repair (similar) provided to contractors before. I think it may not fall over from out-of-plane loads, but it will fail serviceability. I also think that it taxes the sheathing in ways that the sheathing wasn't intended.
#2 would not be my choice for this, i'd rafter make the connection where the post extends down to the bottom of the beam (like an exterior deck and Simpson DTT2Z clips)
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
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: Wood Moment Connection Using Simpson Straps (or Equivalent)
But at the same time, I've seen it done and it appears to work in practice (even if it doesn't calc out).
I also fail to see the difference between 1 and 2 from a strictly connection standpoint. If you're willing to consider the guard rail fixed at the base using 2 straps, why wouldn't the same detail work for a stud wall. In for a penny, in for a pound.
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
I guess the next question would be do you do it? I'll confess to having stamped a few of the guardrail details already.
The difference, in my opinion, is the impact of connection rotational stiffness. On the guard rail, the load is what it is and that's the end of it. With the wall to wall connection and meaningful axial load, connection flexibility will lead to amplified moments at the connection as a result of P-little-delta effects. Shanely would not be proud.
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: Wood Moment Connection Using Simpson Straps (or Equivalent)
Anytime I have come across situation 1, I make them cut in full height columns and turn the plate pack at the hinge into a wind beam spanning laterally.
I'd be curious what the test results from both of these details would come back at.
One thing that maybe makes me think the two details are likely similar in final performance. For detail 1, I'm providing those straps at every stud (it's also likely that the studs are at much tighter than standard spacing to work for deflection anyway. The guardrail is likely only done every 4 ft (depending on the guardrail design). The moment expected at each detail 1 would be say .6 k/ft service. The moment at each detail 2 would be upwards of 3 k/ft service. That's almost 5 times the moment going through the same detail.
There is in-plane stiffness that is tough to calculate but must exist for both drywall and wood sheathing (wood sheathing obviously much stiffer) otherwise they couldn't be used for lateral loads.
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
Mike McCann, PE, SE (WA)
RE: Wood Moment Connection Using Simpson Straps (or Equivalent)
Clever. I'll keep that in my back pocket for future use.
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: Wood Moment Connection Using Simpson Straps (or Equivalent)
I'd like to take credit for that idea, but alas it was passed down to me from someone much more experienced and intelligent than I. It works pretty slick.