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- To: seaoc(--nospam--at)power.net
- Subject: [SEAOC] Re: [SEAOC] Conventional construction provisions
- From: Wish <wish(--nospam--at)cyberg8t.com>
- Date: Thu, 23 May 1996 10:52:48 -0700
RLFOLEY(--nospam--at)aol.com wrote: > > I have just read your letter regarding the 1994 UBC conventional construction > provisions. > While I haven't focused as much attention on the subject as you obviously > have, I would like to discuss this. I noticed that a couple of connections > have been added to the nailing schedule table. Sorry I dont have all the > code section references as I am home without my code as I am writing this, > but one is nailing from rafter blocking to top plate and the other is from > rim rafter to top plate. These connections may represent the shear transfer > from roof diaphram to shear wall you were concerned with. > I'm sure you are familiar also with the testing that was done last year as > UCI by Seb Ficcadente and others which sought to explain why, although a lack > of shear transfer nailing from roof to walls was routinely lacking, roofs > were not sliding off the walls. It seems the toenails from the rafters to > the top plates alone was capable of transfering loads at least as great as > the allowable shear capacity of an unblocked diaphram. > I don't feel that the conventional construction provisions themselves were to > blame for the damage we saw after Northridge as much as poor construction > practices, inspection, and lack of structural observation. > Keep the thread going. Thank you for your response. The code does call for nailing of rim joist and blocking to the plate. It does not, however, call for connection of the diaphragm to the blocking/rim joist. To make matters worse, there is no provisions for connection of the diaphragm to braced panel on the interior of the building. The code is clear about blocking at perimeter walls, but not so clear on connections at interior walls used to resist developed shear. I did read the two studies that you mentioned in the SEAOC Proceedures. Although I find this very probable, until it is voted and accepted as code governing, I would not place much merit in it. The one interesting case in point from the study was the placement of blocking outside of the plane of the wall - used typically as a stucco molding. The study concluded that the minimum nailing of the diaphram to the rafters was sufficient to transfer roof shear to the top plate of the wall - while the blocking reduced or eliminated rafter rotation. I think that this needs further clarification as to capacity of the diaphragm. If the diaphram capacity of minimal (ie, unblocked), I doubt that I would questions this. However, if the line of shear occures in a blocked panel zone or in the center of a diaphragm where the wall's demand may exceed the capacity of the diaphragm connection - a development (drag) must be designed and the results of this study do not necessarily reflect this. Simply put, basic number crunching of interior braced panels does not work when the panel is installed in a prescriptive manner - as I noted in my original letter. The purpose of my concern is the lack of construction quality found in both damaged wood structures and other buildings where the basic engineering principles are not understood by the builder. Ben Schmidt SE is currently working on SEAOC to author a change in the code allowable values for Gypsum and Stucco shear walls. Heavy damage was sustained during Northridge (and Loma Prieta) in Gypsum and Stucco walls due, primarily, for improper connection of the stucco lath to the studs and general poor performance of gypsum products. If Ben is successful, then this discussion is moot since changes in Stucco and Gypsum vaules will essentially negate conventional framing and nullify the section or force it into rewrite. Construction quality by framers in my area are very poor. Framing and shearwall installation, unless clearly detailed, is not understood by the framer and is therefore not properly done in the field. Inspectors, too, are not trained to spot these problems and so, are left unresolved. Finally, the question is not really collapse or failure. The real question is the cost of repair and how it affects the pockebook of the home owner and insurance company. With better control on construction, financial loss can be minimized. Is this not the responsibility of our professional community - above and beyond the protection of life. Sincerely Dennis Wish ...
- [SEAOC] Conventional construction provisions
- From: RLFOLEY
- [SEAOC] Conventional construction provisions
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