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[SEAOC] Re: [SEAOC] Re: [SEAOC] Re: [SEAOC] Re: [SEAOC] Re: [SEAOC] ASD vs. LRFD Survey Summary[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: David Owens <dtowens(--nospam--at)cogent.net>
- Subject: [SEAOC] Re: [SEAOC] Re: [SEAOC] Re: [SEAOC] Re: [SEAOC] Re: [SEAOC] ASD vs. LRFD Survey Summary
- From: Julie Mark Cohen <jmcohen(--nospam--at)emf.net>
- Date: Wed, 12 Jun 1996 20:31:34 -0700 (PDT)
- Cc: seaoc(--nospam--at)power.net
On Wed, 12 Jun 1996, David Owens wrote: > At 10:30 AM 6/12/96 -0700, Julie Mark Cohen wrote: > >On Wed, 12 Jun 1996, David Owens wrote: > > > >> At 09:16 AM 6/12/96 -0600, Christopher Wright wrote: > >> >>fine. The most common reason given for switching to LRFD is that it results > >> >>in slimmer, more efficient designs. > >> > > >> As in Tacoma Narrows, perhaps? > > > >The Tacoma Narrows Bridge collapse was a design and systems-oriented > >problem. Torsion can be limited somewhat by increasing member sizes, > >but can by understanding overall geometry and behavioral response. > > > Dear Julie Mark- > > What do you mean-exactly-by a systems-oriented problem? They had to add > trusses-and did it to most of the bridges in America. > Heh, GUYS, This is the 19th or 20th time that someone messed up with my name! I have used my full legal name since kindergarten eons ago and have had NO problems with it until this mailing list. For the record, my first name is Julie and I am female. My middle name is a family name, something that was very commonly used in the U.S. for females when I was born. Add trusses? You answered your own question! If someone tries to build something that is not thought out ahead of time -- in 3-D in a systems manner -- then it responds badly to dynamic loading that will inevitably tear it apart. The Golden Gate bridge is another example in which "pony trusses" were added. As for buildings, please look at my article "The Northridge Warning: Has 3-D Design Been Lost?" that was published in the Dec. 1994 issue of ASCE's Civil Engineering magazine. This should offer a clear concise outline of what is historically meant by the various terms. What I am _very_ troubled about is that I seem to be one of very few who has a *design* background using systems-oriented methodologies. In plain simple English -- this stuff goes back to the late 19th century, but the words had not been formalized at that time. Almost every time that I have seen structural drawings for a new mid- or high-rise building, I see framing that was slapped together as a collection of 2-D vertical and horizontal frames. (again, see my article). It is only when I look at framing from those who worked directly with the likes of the late Fazlur Khan do I see anything that even begins to resemble the 3-D framing systems about which I learned as an undergraduate architecture student. For buildings, structure should be indicative of architectural function. Our human bodies reasonably well follow this analogy. How many structural engineers would give a human one leg to support vertical and lateral loads and the other leg to only support vertical loads? Optimization, not minization. Symmetry. Regularity. Continuity. Redundancy. THEY DO NOT COST MORE than minimization -- which gives building owners big problems in the long-term. There are many studies on such things, some published widely. The first studies are decades old!!! This comprehensive thinking, when carried out rationally, ensures lobal safety. This started to fade into oblivion after WWII when structural engineers started to "economize." After the launch of Sputnik in 1957, there are numerous articles about structural engineeers economizing, while other engineers were innovating. In the 1990s, most structural engineers cannot differentiate between the two. They were not taught much in the way of history of their field (again see my article), whereas my undergraduate background in the parent profession of architecture included much work on the history of building technology (which I have continued to pursue on my own since my undergrad degrees). Hope this helps a bit. Julie > > ... > > ------------------------------------ | Dr. Julie Mark Cohen, P.E., | | Director and Principal | | Cladding Research Institute | | 6 Commodore Drive, Suite 330 | | Emeryville, CA 94608-1620 | | Tel (510) 654-7917 | | FAX (510) 4500-CRI | ------------------------------------ ...
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