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Re: FW: CMU Site Wall using 2001CBC

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Bill,

I believe that the free-standing walls that fell down in the Northridge
earthquake were typically unreinforced concrete block fences, and there were
many of them that fell -- at least that was my observation.

A freestanding wall responding to an earthquake responds only to ground
shaking at its base, un-amplified by the response of the building.  I
believe that the intent of the equation is that hx = 0, and that is a
reasonable value for a conventional freestanding wall, or fence. Steve
Gordon pointed out the exception, which would not be a conventional wall.

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net

----- Original Message -----
From: <BCainse(--nospam--at)aol.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, August 04, 2004 5:28 PM
Subject: Re: FW: CMU Site Wall using 2001CBC


| Molly-
| The Fp = 4.0 CaIpWp since hr has no meaning in the context of equation
32-2 (i.e., there is no "roof").  Thus what hx is becomes moot). A
freestanding wall is akin to a cantilevered column supporting a roof
structure (often referred to as a "lollipop on a stick").
|
| These structures have not performed well in earthquakes. I recall there
being a large number of such walls falling down in the Northridge EQ.  Also,
there was a strong directionality to failures (i.e., freestanding walls in
one direction fell down, walls perpendicular to that direction didn't).
Thus, if you are in a near fault area of a Type A fault with default soil
(soil profile, Sd)the Fp=4.0 x 1.5 x 0.44 x 1.0 x Wp = 2.64 Wp (LRFD value)
or 2.64 x Wp/1.4 (ASD level) = 1.88 Wp.  I wouldn't want to bet that my wall
was aligned with the less violent direction.  :<(.
|
| Remember also to consider load combinations per Section 1612. Section
1630.1.1 defines Eh = Fp for an element or component.
|
| Regards,
| Bill Cain, SE
| Berkeley CA
|
|
|
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