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- To: seaint(--nospam--at)seaint.org
- Subject: Height of Building/Shear Wall design
- From: Michael Hemstad <mhemstad(--nospam--at)mbjeng.com>
- Date: Tue, 27 Sep 2005 09:03:59 -0500
Let me answer your second question first.
Based on what I've been led to understand (and confirmed by your question), the New Zealand code is probably far better than either the seismic or the concrete expertise in the UBC97. In truth, the analogy that comes to my mind is of a doctor setting aside his medical texts and seeking advice on leeches and amulets.
Presumably, you have a project in California that requires you to follow UBC97. My advice, if you have the time and budget, would be to prepare a design using your own code, then verify that it meets the requirements of UBC. It should.
I'm afraid I'll be even less help on your first question. Obviously, there were some bad experiences with taller shear wall systems. My assumption is that rather than fix the problem (e.g. by improving ductility with capacity design), someone decided that our current state of knowledge was not adequate to address whatever shortcomings this system has. And, if you have to adhere to UBC97, I'm afraid you're stuck with that. Hopefully someone else can give you a more detailed and fact-based answer.
Mike Hemstad, P.E.
From: "Tim Shannon" <Tim(--nospam--at)nsw.meinhardt.com.au>
Subject: Height of Building/Shear Wall design
I am looking for a some advice on table 16-N of the 1997 UBC - as a New =
Zealand Engineer I am not really sure the background for some of the =
height limitations. =20
I have a "theoretical" building in a zone 4 region with a height of 260 =
feet from basement slab to roof. UBC97 table 16-N will allow a maximum =
height of the building to be 240 feet for a Concrete Shear-Wall _only_ =
system. Accordingly I would require a combined SMRF and Shear Wall =
system for over 240 feet - unless this height was not measured from the =
lower basement level. =20
Question 1 - If I have a rigid basement structure and shear walls only as =
the lateral resisting system above "ground" level the height from ground =
level to the roof is only 230 feet, so does this justify a shear wall _only_ =
system given it is under 230 feet measured from ground level?
Another question I have relates to Shear Design of Concrete shear walls - =
the UBC does not seem to consider in depth that shear walls will have =
Potential Plastic Hinge Zones at the wall base just like a "beam-column =
joint" might have in a ductile moment resisting frame at the column face =
- I cannot find any attempt to try and suppress undesirable "shear =
yielding" through capacity design in the instance of flexural yielding at =
the base of the shear wall. When I am designing the shear strength for a =
ductile wall in New Zealand I would always design shear capacity of =
ductile walls to overstrength according to capacity design principles with =
a much reduced shear strength contribution from the concrete - is this not =
required in the UBC, am I missing something? Or would I just follow the =
normal simple shear design rules in Section 1921 of the UBC97.
Any replies would be much appreciated.
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