My guess- no interior plywood shear walls, gypsum shear walls were not yet constructed. Only that short length of exterior plywood shear wall was effective.
Also - layout of adjacent buildings increased wind pressure.
The only piece of visible sheathing which would have tended to prevent the collapse appears not to have been nailed to the studs except at the top. If you stop the video just as the collapse begins, that sheathing seems to retain its shape as it moves relative to the bottom of studs.
"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976
Notice that it was at least designed to fall away from the street, so as not to interrupt traffic flow. That’s a real soft first story and a sad story too. Probably designed and built by the local kindling wood broker.
In some of the wood structures I have done, it's like pulling teeth to get the contractor to install the required shear wall hold downs, drag strut connections, and sill plate anchors. With some of the stuff I have seen, it wouldn't surprise me if this played into it along with the lack of shear wall fastening also.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
In the area where this occurred (Raleigh, NC), I don't think any builder has ever heard of a drag strut. They are pretty adamant about stability plans now and doing a sheathing inspections - it just was not finished to that point. The winds that day were pretty strong with a Tornado dropping down nearby.
It appears to me that the building across the street is the same design and orientation. I would be curious to see if any signs of lateral displacement are evident there.
I don't know much about how a wood shear wall is suppose to fail but I agree with BA in the fact that the sheathing appears to retain it's original shape during the failure, almost like it wasn't nailed properly. It is interesting that the water barrier (green paper flying around) is not installed on the walls except for the gable end. I wonder if they were going to install the nails in the sheathing after the framing was complete?
ExcelEngineering:
I know it’s kinda old fashioned, but we used to start building at the foundation, and working our way up in the building, nailing and bracing per the final design, as we went. Thus, at first, you would/might be over-braced. Except in this case, with the open structure/bldg., full height too, the wind forces would likely be greater than would be the case once the bldg. was fully enclosed. I guess these old methods just don’t work any longer, what with the newest expedited and green building methods. My goodness, building a three or four story wood framed bldg. is different than building a 15'x20'x8' high chicken coup, and someone involved should know that difference, and be designing for and managing it. And, this should maybe be being done before the final nailing inspection. Maybe their sheathing inspections are being done at the wrong time or not often enough. I’ll bet there was almost no OSB or shear wall construction in place in that first story, except a few exterior pieces, one of which BA noted was not nailed. And, that looks like quick and dirty hanging and forgetting to nail. Once it’s fit and hung with three or four nails to hold it in place, and nobody is thinking or paying attention, you can walk away and assume the nailing specialists will catch it. Construction is getting scarier by the year, when no one is expected to know that they are doing, and no one is expected to pay attention to the details. Once you’ve run the computer on er, all’s well, so let er rip.
I would say the ply sheathing was nailed, but the building deflected so suddenly and so much that the ply nailing both bent and withdrew from the studs immediately. Of course the ply panels retained their shape, because the panels took the path of least resistance and that was to pull away from the studs.
