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Re: Valley Rafters[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: Scott.M.Haan(--nospam--at)poa02.usace.army.mil, seaint(--nospam--at)seaint.org
- Subject: Re: Valley Rafters
- From: Rhkratzse(--nospam--at)aol.com
- Date: Tue, 13 Sep 2005 18:45:00 EDT
There's an interesting article in the current (9/05) "Structural Engineer" magazine (www.gostructural.com) that discusses an engineer's moral obligations to improve a damaged structure to a currently accepted level of safety, not just to the standard it was originally designed to. Although this article addresses steel moment frame failures in the 1994 Northridge earthquake I related it to my own practice of improving the earthquake safety of residences in the Bay Area.
The article is "Licensed not to kill, Evaluating your moral obligation" by Gary C. Hart, Ph.D., C.E. He argues that it's not good enough to just "fix" the broken welds, but that the joint should/must be upgraded to the current state of our knowledge.
I know--the immediate response is "I wasn't hired to do that" or There's no money to do that," etc. But he's just discussing the morals, not the legals.
In my practice I use the current code as the standard that I design to when I'm adding shear walls to existing structures, figuring that doing it "right" isn't that much more effort than a half-a** improvement. I feel that "if current code requirements are good enough for a new house, they're good enough for an existing house." Obviously this is not a complete upgrade--only an upgrade of the particular elements affected. You've got to stop somewhere, usually when the budget intervenes.
Ralph Hueston Kratz, S.E.
Richmond CA USA
In a message dated 9/13/05 3:30:31 PM, Scott.M.Haan(--nospam--at)poa02.usace.army.mil writes:
If I were you guys and found these conditions in Alaska – I would not recommend replacing as is. What you guys need is nice volcanic eruption on Mount Shasta or something and 3 or 4 inches of ash to help speed up gravity.
I have seen old building roofs that appear to be defying gravity. I have also seen a few roofs and floors partially collapse or be in the process there of. I think there is some law in physics that everything in the end will come to it’s most stable state.
From: S. Gordin [mailto:mailbox(--nospam--at)sgeconsulting.com]
Sent: Tuesday, September 13, 2005 10:03 AM
Subject: Re: Valley Rafters
When I first saw something like this, I had to call Dennis Wish to ask him if this was for real. It was. All roofs all over a huge apartment complex, may be, 20 years old. Some of the 2x4 rafters had cracked, most sagged under the weight of the concrete tile roof.
I came up with the repair details and specs, they paid me OK. However, they indicated that they were not going to do anything beyond the replacement of the broken rafters.
What could I do? Seriously (as they said), it had been there for 20 years, "nobody got hurt", and (as I know) there is no snow below 2,000 feet in Southern California...
Steve Gordin SE
----- Original Message -----
Sent: Tuesday, September 13, 2005 10:52 AM
Subject: Re: Valley Rafters
Another tidbit on Hips. After Northridge Earthquake I investigated several apartments and houses.
To my amazement On stick framed roofs I encountered several long span hips and valleys (+25') where the framer spliced 2x8 or 2x10 at midspan. An engineers dream of course. The splices were about 2-3 ft. long with a taper cut from top to bottom of member. 3-4 nails holding it together. These were clean cuts that went like a puzzle, some I had to look 3 times to make sure of what I was seeing.
As Nels stated earlier how do you justify this ?? Some had been there for over 40 years.
Yes, there was deflection but most people are unaware or cannot even see it.
Johnson & Nielsen Associates
Palm Springs, CA
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