Has anyone seen a gravity failure in a 1-2 family house? I’ve inspected many underdesigned wood stair beams, ridge beams, rafters, connections, etc and have never actually seen a collapse in 9 years. Yeah, nobody is supposed to use a 2x4 as a roof rafter, or use that wrong load transfer, but the thing has been sitting there solidly for 60 years. On the other hand, I’ve seen plenty of failed steel/concrete beams in garages and large apartments.
I’ve only seen two residential failures from a structural vantage… lots of fires, though. One was a partial collapse due to overloading caused by a ‘hoarder’, and the other was due to structural inadequacy.
There was a third that was caused by overloading of a masonry foundation wall (it was completely pushed in) caused by oversaturated soils.
Dik
It says something that you’ve only seen two cases in your experience. What was the structural inadequacy?
And the masonry foundation wall is pretty upsetting; I haven’t seen that yet. But I guess I have another 50 years to go!
With the first, the load was excessive with areas loaded to over 150 psf and in the second case, the member was inadequate by a factor in excess of 2.
The masonry wall collapse was due to the building being constructed into a sloped hill and there were several weeks of rainfall that saturated the soil. For the latter case the insurance company would not allow the claim.
Fortunately with all my reports, I stipulate that I’m working for the client, but, my report would essentially be the same no matter who had retained me, also include that the owner can retain their own engineer, and that the owner request a copy of the report. This is verbally stated to the owner before I start my investigation and the above information is included in the report that the owner has been advised.
I’ve seen a lot ‘freakier stuff’. If safe, I often took my grandchildren to collapses and fire damaged structures. I often had them on the ‘stick’ when I was running level shots or helping me with measurements. They were actually well paid for their assistance in addition to the experience.
Dik
I was around a lot of small scale residential early in my career and have never seen a gravity failure. When things got wrong with residential, its usually related to building envelope.
I’ve been inside of many residential buildings where major girder hangers were either missing or just toe nailed into place. Still no failures.
I have - several times. Most were started by another cause such as water deterioration or insect damage, but the members would likely have been fine if they were properly sized to begin with.
I’ve also seen an entire floor collapsed because it was added on like an interior porch. The floor joists didn’t bear on the walls, they were nailed on with a ledger. Craziness.
I did a report on an upper floor collapse about 20 years back… it was wood framed construction. A beam failed and the attached joists came down with it. It was a century building and the business had started storing their files on the upper floor… the cause of the collapse was overloading. Failure initiated at the framing for an old and abandoned stair opening. No hangers at the time of construction. All framing was mortised and tenoned. First time ever encountered.
Dik
@KootK Yeah, I feel that way. I’ve seen several stairs framed with a single joist, but they’re still fine.
@SLTA A professor told me that structural failures are usually caused by two things going wrong. So in your cases, it was underdesign plus damage. But strangely, I’ve seen water damaged joists that have held up over decades, if not a century. Maybe the water damage was recent.
@dik Thanks for sharing the experience. Thankfully overloading is rare.
MSL:
Just found an old photo showing the mortise and tennon… I’ve used them for building furniture… but not for floor framing.
Dik
BWAHAHAHA
Sorry… that is funny. Overloading is super common, and we’re just lucky that materials are usually way better at handling it than we think they “should” be!
I’ve seen entire roofs being held together by a few shingle nails that happened to hit the rafters. I’ve seen concrete block foundation walls bowing in 4 inches over 8 feet. I’ve seen roof trusses sagging inches and pulling apart at the plates. And yet, they were standing. But for how long?
@SLTA Overloading is pretty rare. I’m a young engineer and not experienced but I’ve been to at least 100 job sites and I’ve seen overloading only twice. Most of the time, nothing came close to the design live load or snow load.
I agree with you though. There is some terrible work out there, and I have to thank ASD for having safety factors. Yesterday I made a report on a tiny member (single 3x3x1/4 angle) being overloaded by 50 times the theoretical bending load, but somehow it’s still holding, probably by tension and catenary action, and the tiny tack welds are enough.
A couple of years ago, when I attended Umass, a floor fell in at a party because it was overloaded. Looked like (from photos) all of the joist hangers to a beam failed, and a full section of floor dropped.
Not your typical residential loading. Im sure when you get a bunch if college jids jumping up and down, you exceed residential loads wuite quite quickly
Welcome… pull up a barmaid, and join the party…
Dik
Too many spilled drinks on the joist hangers causing them to get (over)loaded.
Welcome to the party…
Mike:
That’s like watering the lawn with beer, so it comes up half cut…
Dik