Hurricane Ties and Top Plate Rollover

[phamENG]

Attached is a technical bulletin put out by Simpson about the proper installation for hurricane ties. I agree with it, in principle, 100%. Very clear and continuous load path = good. In practice, however, I'm curious if anyone has ever seen this type of rollover failure. When you hook up a series of hydraulic pistons to a wall and pull - it will certainly roll over. Wind doesn't exactly work like a series of hydraulic pistons, though, so I'm not empirically convinced that it'll happen quite the way their claiming.

I do think there are conditions where it could happen, and so I'll detail it as Simpson shows it, but I like to know just how conservative things are. Any thoughts? Thanks.

 

[WARose]

I'm not sure I've heard of a failure from it.....but like anything else: you have to follow the load path.

The thing I would question about that pic is why there (appears to be) no direct connection between the top plate and the studs below (either nailed, toe nailed, or some Simpson product)? I've almost never transferred the uplift through the plywood/gyp board that way.

 

[hokie66]

When a house gets blown apart in a hurricane, you don't know what failed first. The only way to know these things is full scale testing.

The technical note is undoubtedly correct. Perhaps Simpson knows of their connectors being used incorrectly. At the least, if the sheathing is used to resist the uplift, the ties should be on the same side.

 

[jayrod12]

I haven't seen a full fledged failure like their picture, but I always detail them on the outside where the sheathing is. I've seen a few garages with no finishes on the interior have the top plate slightly separated from the studs indicating that type of failure, but not to the extreme.

Generally the connection from stud to plate is just a couple of nails through the plate while it's laying on the ground, not much there for uplift resistance.

 

[Huevo]

This isn't just a Simpson thing. I believe this was mentioned in the 2008 SDPWS in text but the 2015 SDPWS has a figure (C3.4) dedicated to this condition.

 

[phamENG]

WARose - I think it's just hard to see, but it's a pull-out failure in the nails fastening the plate to the stud end-grain.

hokie66 - You certainly bring up a good point. The failure investigations I've done haven't included a pile of rubble, so I may have had a flawed expectation going into this. Perhaps the better question is, can anyone point to a roof failure that had them used incorrectly? (You should still be able to see which side it was fastened to, even if it is scattered around on the ground).

Like I said, I agree with the TB - I just want to understand the practical and observed implications.

 

[NorthCivil]

I'm not from a high wind area, in my area, getting into this would be a bit overkill.

Lots of little things help this detail that are hard to quantify. the end nails from the top plate to the stud, toe nails, the gypsum on the interior.

You engineers out in hurricane country though, i'm sure this would be standard practice

 

[SlideRuleEra]

You should still be able to see which side it was fastened to, even if it is scattered around on the ground.

As Hokie says, it's rarely that simple after a hurricane. If a house keeps it's roof (or at least some it's roof framing) there is nothing to see.

If the roof sheathing stays on long enough for a top plate roll failure, the entire roof is quickly "gone", often followed by the remainder of the house.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[hokie66]

A lot of full scale house testing for wind loading has been done at James Cook University in Townsville. This research has affected Australian practice, but I am not sure if it has gone further afield.

https://www.jcu.edu.au/cyclone-testing-station/research/full-scale-house-testing

I think similar testing has been done at Texas Tech.