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RE: SEAOC seismology opinion regarding 10/Lw factor for calculating rho[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: RE: SEAOC seismology opinion regarding 10/Lw factor for calculating rho
- From: Charles Greenlaw <cgreenlaw(--nospam--at)speedlink.com>
- Date: Tue, 23 Nov 1999 10:49:58 -0800
Thanks, Mark, for helping me to make my point. The distinction to be made with these proprietary shear panel substitutes is that each model, although fabricated of many pieces, is pre-approved by a code agency as a discrete structural, unitary element having listed allowable and/or strength values. One employs those values in one's design without further concern or inquiry into the internal construction of the item. That's the whole idea: to have convenient, out-of-the-catalog alternatives to conventionally engineered, jobsite-built shear walls. Further convenience and efficiency is found with height-to-length ratios typically narrower than now allowed in scratch-built wood shear walls. But the reduction in Lw that is so attractive in them runs afoul of the as-enacted Rho provisions (and still will, you say.) This dimensional snag comes in spite of the fact that these proprietary assemblages are explicitly tested and approved to be equal in performance to much wider conventional shear panels. That equivalence is spoiled if their actual dimension, or internal features of construction (like diagonal metal bracing) is allowed to take precedence for Rho purposes over the package approval already achieved. As has been revealed, the Seismology Committee that first foisted Rho into code never contemplated these everyday realities in residential-type engineering. The focus, fleetingly, was on industrial tilt-up walled buildings. The Committee still appears not to have an adequately competent grasp of their subject matter. A starting point for a third attempt might be to revisit the basic aims of Rho: redundancy and reliability. See if shear walls (of any sort) and their proprietary substitutes have any reliability ills that are remedied by any form of Lw-based methodology. What other approach might be better if any remaining need is in good faith proven? It is regrettable the extent to which code writing and code complying (and later legal recriminations over code) have become a nitpicky parlor game that entertains a few, but distracts and diverts most professionals from getting on with their tasks efficiently and professionally. As Arnhem was in retrospect a bridge too far, so is Rho for shear walls a code burden too far. Charles O. Greenlaw SE ------------------------------------- At 03:01 PM 11/22/99 -0800, you wrote: >I don't think it leaves an ambiguity regarding a diagonal brace since that is clearly covered under braces. Any diagonal brace counts as a brace. A chevron brace provided 2 braces. The length of the braced bay is of no significance, only the total number. Thus, a 4' long single brace proprietary frame would count as one brace. If it were a shear wall it would only count as 40% of a shear wall. > >Mark E. Deardorff > >> -----Original Message----- >> From: Charles Greenlaw [mailto:cgreenlaw(--nospam--at)speedlink.com] .... >> This proposal is appreciated and would appear to help in >> houses and other >> small buildings, etc., but leaves ambiguous what happens in a >> basically >> light-frame building where a proprietary steel diagonally >> braced frame is to >> be used in lieu of a wood shear wall, or some other non- "light frame" >> element like a Simpson Strong Wall or a steel moment column >> or moment frame >> is to be used.
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