Wood Roof Truss Failure
Wood Roof Truss Failure
(OP)
All,
There were strong winds and possibly a tornado that come through my area last night and pulled the south half of the roof off one building (see attached photo) and the entire roof off another building. There are 11 buildings in this area. All are of very similar if not identical construction - all buildings were built at the same time using the same architect, structural engineer, and same details. The structural detail at truss bearing is as expected; cmu bond beam, 2x top plate, and wood truss. However, there is no attachment from the truss to the 2x top plate shown or called out, and when I went out to look at it the only evidence of attachment were a couple of toenails sticking out of the 2x top plate where the truss had once been.
These buildings were built in 1991. One question is; at that time, was it standard to just toenail trusses to the top plate and not use some sort of Simpson clip? Another question is; why didn't the other buildings roofs fail if they were of identical construction?
Thanks!
There were strong winds and possibly a tornado that come through my area last night and pulled the south half of the roof off one building (see attached photo) and the entire roof off another building. There are 11 buildings in this area. All are of very similar if not identical construction - all buildings were built at the same time using the same architect, structural engineer, and same details. The structural detail at truss bearing is as expected; cmu bond beam, 2x top plate, and wood truss. However, there is no attachment from the truss to the 2x top plate shown or called out, and when I went out to look at it the only evidence of attachment were a couple of toenails sticking out of the 2x top plate where the truss had once been.
These buildings were built in 1991. One question is; at that time, was it standard to just toenail trusses to the top plate and not use some sort of Simpson clip? Another question is; why didn't the other buildings roofs fail if they were of identical construction?
Thanks!






RE: Wood Roof Truss Failure
As for the fickleness of the failure, wind is a very fickle lady.
Oh, and it would be a very good time to recommend a retrofit of the trusses that did not fail with some end clips, wouldn't you say?
Mike McCann, PE, SE (WA)
RE: Wood Roof Truss Failure
RE: Wood Roof Truss Failure
Tornados are very fickle is the way they act, they may be several thousand feet wide, or they can hit small areas, trees, buildings and the like, and leave paper plates on a picnic table not far removed from the damaged area. You can also get very discrete down drafts or wind shear action from those storms. Usually, three toenails was fairly common carpenter practice, typical house building practice, two from one side of the truss down into the top pl. and one from the other side. As for different buildings..., same Arch., same Engr., same details, but maybe not the very same carpentry crew on every bldg., every roof, thus different details in the actual construction. You’ve heard it..., “that’s how my Grandpa taught me to do it, that’s the way we’ve always done it and never had a failure yet (until now).” We would not have detailed that connection if we were content with std. carpentry practice. And, 25 years ago Simpson and USP did not have nearly the sales staffs or sales pitches, or the members on the ICC code committees that they have today. High wind loads at bldg. corners, under eaves, and uplifts, particularly at leading edges, are a fact, and they are shown to exist in your photo. You can start unzipping a roof like that at a corner, one truss at a time, then the next, and next, etc. You have high upward pressures on the eave soffit and rake soffit at the corner, and the suction pressure (uplift) on the roof plane right at the corner, all working on that truss bearing detail on the gable end truss and the first interior truss, and then all hell breaks loose. This is at Camp Ripley, right? I’m down in St. Paul.
RE: Wood Roof Truss Failure
Mike McCann, PE, SE (WA)
RE: Wood Roof Truss Failure
TTFN (ta ta for now)
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RE: Wood Roof Truss Failure
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RE: Wood Roof Truss Failure
RE: Wood Roof Truss Failure
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RE: Wood Roof Truss Failure
Oldestguy: not sure on the specifics of the radio tower. I will post another interesting photo showing two communication towers next to a building just off the left side of the previous photo.
dhengr: your location guess is correct.
RE: Wood Roof Truss Failure
RE: Wood Roof Truss Failure