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RE: ASCE 7-05 Wind[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: ASCE 7-05 Wind
- From: "Scott Maxwell" <smaxwell(--nospam--at)umich.edu>
- Date: Wed, 21 Nov 2007 00:18:15 -0500
From: WISH DENNIS [mailto:dennis.wish(--nospam--at)verizon.net]
Sent: Tuesday, November 20, 2007 10:49 PM
Subject: Re: ASCE 7-05 WindDoug,I'm in the same boat. I believe in most cases the as long as you are working with a light framed structure that is an othogonal system (non-angular shear walls) you can have a system that can be broken into blocks which would eliminate the issue of limitations to rectangular based on how you define your system. There also seems to be the matter of what is considered "semi-rigid" or "semi-flexible" as being left to the discretion of the design engineer.In my opinion, if the issues are not clear then the same reality of what existed in the 97 UBC will be assumed applicable to the 2006 IBC. In other words, while SEAOC issued a recommendation for allowance of flexible analysis as the standard of practice, the letter of the code put us all at risk.The problem seems to be that those in high wind regions understand this section much more than those of use who may experience regions of high gusts but have little recorded history of damage due to wind compared with our state's history of seismic damage.I mentioned that SEAW (in a previous post) is supposedly being accepted as having released a publication that models most building designs for wind load conditions and various types of roofs. This was mentioned in the November 2007 Structure Magazine article on the Rapid-Solutions Methodology for wind design (article published on page 61 by Ed Huston, P.E., S.E.). There is supposedly more "tweaking" to do before publication in early 2008 occurs for SEAW Simplified methods but it seems that this will be more of the standard as it is evolving at the moment.For my own opinion, I think it is the wrong time to introduce complicated change in regions where wind damage has not been as prevalent on light-framed structures less than 65-feet and we should be presented with a simplified version due to the loss of profitability in a structural design due to the learning curve and the current recessionary slowdown.I'm not sure how other's feel about this (outside of the Hurricane regions most hit), but when you have the suggestion that strap-tie holddowns are failing due to improper installation or corrorsion in thousands of structures, our priorities are a bit messed up. We should be focusing on correcting an inherent industry problem that will affect thousands of light framed buildings constructed with the ecconomical strap tie holddowns rather than attempting to improve the complexity of the wind design methodology where the historic damage has lied with earthquake damaged structures.I'm sorry I can't be of more help to you, but I think we are in for a very dry period as we try to understand what the codewriters had in mind when evaluating a document or methodology that is inherently ambiguous or left to the descretion of the engineer of record (such as the consideration for semi-rigid structures).I only wish I was ten years older, then I could retire and forget about all of this :>) And during an election year yet - who would have thought ?>)Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant
----- Original Message ----
From: Doug Mayer <doug.mayer(--nospam--at)taylorteter.com>
Sent: Tuesday, November 20, 2007 6:36:32 PM
Subject: ASCE 7-05 Wind
I am making the transition to the new code (CBC 2007) and being confronted with the ASCE wind provisions. They seem astoundingly complex and I have a couple of questions that desperately need some answers.
First off, what is a “regular-shaped building”? ASCE defines this as “a building or other structure having no unusual geometrical irregularity in spatial form.” To me, this sounds like any non-rectangular structural is irregular. Is this true? This is very important because it leads into the next question of which analysis method to use. Both Method 1 and Method 2 require “the building or other structure…” to be “… a regular-shaped building or structure as defined in Section 6.2.” This would seem to indicate that you have to use Method 3 (wind tunnel testing!) for an non-rectangular building. I can’t believe that is the case, so I think the definition of a regular-shaped building is different than what it seems to be.
Any help would be greatly appreciated. Also, I apologize if I am asking questions that have already been asked.
Doug Mayer, SE
Visit our new website at www.taylorteter.com
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