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Re: Effects of the New Code on Wood structures - good or bad????? -Part 1[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Effects of the New Code on Wood structures - good or bad????? -Part 1
- From: Seaintonln(--nospam--at)aol.com
- Date: Thu, 22 Jul 1999 20:53:09 EDT
Mark, the answer is very simple - none of these provision were either applicable to wood framed construction with wood diaphragms until 1988 and none of them were either enforced or consider the "Standard of Practice" for wood framing until this code cycle. The actual reason is not known just why the provisions were not enforced prior to 1997 UBC but it is suspected that it was because there was no rational means to calculate the deflection of a flexible diaphragms (and there is only a multiplier suggested by APA at this time) and the provisions in the code could not be satisfied. Why all the ranting and raving as you put it? The code rationale is very straight forward if you are dealing with a simple geometric shaped building with a great deal of simplicity in the diaphragms and transfers of shear from floor to floor. This is typical of most commercial and industrial projects. It may even be somewhat easier considering a simple small residential structure that is fairly rectangular with few irregularities. Once you get into the design of a structure that is neither rectangular, with multiple levels offset from one another (such as split levels), roofs that frame upon one another or diaprhagms that cantilever and any other creative avenue that the architect dreams of, the design difficulties grow exponentially. Now if you reread all of my posts, you can begin to see the difficulty that this creates for almost all of us who specialize in wood. Most of us feel that the ends don't justify the means - there is not sufficient evidence to justify the change nor is there sufficient damage attributed to justify my rants (I don't rave about this code). I will review part two and respond. Dennis In a message dated 7/22/99 12:57:50 PM Pacific Daylight Time, Mark.Swingle(--nospam--at)dgs.ca.gov writes: << Since at least the 1967 version (that's as far back as I have looked), consideration of the following three items has been required for earthquake design (and wind design) in the UBC: 1) The relative stiffnesses of the various shear walls with respect to one another, 2) The relative stiffness of the diaphragm vs the shear walls in each line, and 3) The eccentricity between the center of application of the forces and the center of rigidity of the resisting elements. These three items have not changed, and these are the main issues that you imply have changed so drastically in the 97 UBC. >>
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