Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: FW: CMU Site Wall using 2001CBC

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Nels,
 
I am no so sure about "conventional" walls not being flexible...
 
Calculate the natural period of vibration, using formula for cantilever beam in Timoshenko's "Vibration Problems in Engineering."  For 6" thick, 6'-10" wall reinforced/grouted @48" (#4@48") the formula yields: T=0.087 sec (using Icr and assumed: 5 km to Type B fault, R=2.9 =>q=0.271*W).  This wall is formally a flexible structure (T>0.06 sec).  Considering the likely rotation of minimal footings, the natural period of vibration may be even even greater.    
 
After Northidge and more recent earthquakes, I observed damage even to the DBS-compliant walls...  
 
On the related subject - did anybody ever check the so-called "Standard Details" issued by cities and counties?  My experience is that these details often are very non-conservative...  At the same time, jurisdictions are never willing to even hear about that.
 
Steve Gordin, SE
Irvine CA   
 
 
----- Original Message -----
Sent: Wednesday, August 04, 2004 6:23 PM
Subject: Re: FW: CMU Site Wall using 2001CBC

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
|
|
|
| ******* ****** ******* ******** ******* ******* ******* ***
| *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
| *
| *   This email was sent to you via Structural Engineers
| *   Association of Southern California (SEAOSC) server. To
| *   subscribe (no fee) or UnSubscribe, please go to:
| *
| *   http://www.seaint.org/sealist1.asp
| *
| *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
| *   send to the list is public domain and may be re-posted
| *   without your permission. Make sure you visit our web
| *   site at: http://www.seaint.org
| ******* ****** ****** ****** ******* ****** ****** ********



******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********