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- To: seaint(--nospam--at)seaint.org
- Subject: Re: Prescriptive Residential Construction Vs New Design Standards; Curee-Calt...
- From: ErnieNSE(--nospam--at)aol.com
- Date: Mon, 5 Oct 1998 00:32:07 EDT
I agree with Charles. The conventional framing provisions of the UBC is the best compromise we can get. We(structural engineers) have been constantly trying to improve these provisions to conform 100% to our standards and every code revision, there has been improvements. And we should continue doing so. I am one of those engineers willing to stick my neck out and take the risk of lawsuit if one of my room addition/remodel jobs fail because I leave existing framing as-is knowing it does not calc out. I just calc out the new framing system. Even if part of my new framing system does not calc out, if it conforms to the Conventional Framing Provisions, its OK with me. Most of my jobs are room additions. Somebody has to do the dirty, low paying jobs. Engineered buildings that calcs out assumes the ideal framing system. It does not take into consideration the other portions of the framing system that we assume do not resist any load. A conventional house basically is an indeterminate structure. But to be able to calc it out, we assume simple beam design of rafters, joist and beams assuming that the plywood sheathing and the drywall ceiling does not exist. To calc out kickers with purlins to roof rafters, we assume that we have isolated rafters, purlins, kickers,rafter ties and only the nails hold them together. We neglect the plywood sheathing distributing the load to the exterior wall top plates nailed to other ceiling joists with drywall. To calc out simple span hip beams, we neglect the kick- out resistance provided by the plywood sheathing distributing the load to the top plates that are lapped at the corner. And as Charles said, and I talked about it on my previous post, the interior braced wall transfer lateral load to the drywall ceiling to the ceiling joists to the rafter to the top plate, etc. Also, the top plates in bending distributes some of the lateral load to the interior walls that are not too far apart. All of these minor transfer mechanisms does not calc out but it sure does contribute something. These may be the reason old houses do not fall down. By the way, Dennis, ICBO has a book titled "Illustrated Guide to the Conventional Construction Provisions of the Uniform Building Code" It is for the 1994 UBC, about 193 pages, with a lot of illustrations and explanations. These might not be simple enough for all framers but a framing foreman would definitely understand it and will be able to guide his framers accordingly. We can use this book as a starting point, improving on it, and recommend to have it included as part of every building department's guidelines. I am personally more worried about the house being built per plan(assuming the plans are complete) than making sure the plans are based on exact calculations. I would put more emphasis on requiring structural observation on all houses than requiring all houses to calc out. Just my opinion. Ernie Natividad
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