Need a book? Engineering books recommendations...

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

RE: Shear Walls extending to Basement Level

[Subject Prev][Subject Next][Thread Prev][Thread Next]
James:

Basically, you and I are saying the same thing. The question really is....is
it practical to isolate the 1st floor diaphragm from the shear wall or to
tie it in rigidly and then handle these large cranking (or as you say
lateral forces often are reversed and increased) forces.

Jim K.

-----Original Message-----
From: james lane [mailto:engg101(--nospam--at)hotmail.com]
Sent: Monday, November 11, 2002 1:41 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Shear Walls extending to Basement Level


The first floor diaphragm rigidity is very stiff when connected to the
perimeter basement walls. You can run the shear wall down to the foundation
however your as a result of
doing so.

Consider how a braced frame would act in place of the shear wall and leave
out the brace from the 1st floor to the foundation. At the first floor
diaphragm all of the lateral load would transfer to perimeter basement walls
and just vertical loads would transfer through the end columns.

You can do the same with a shear wall but you still need to have the end
columns capable of taking the vertical tension and compression loads.

I came across this interesting load path back in my E.I.T. days when one of
my fellow engineers wanted to support the basement wall lateral soil
pressure through the ends of bar joists. I began looking at bar joist
overturning, bar joist axial loads, etc. Finally came to the conclusion that
the floor to wall connection should be concrete to concrete and be able to
take the building lateral load into the basement walls at the 1st floor.
Tried to run the bracing to the foundation however the forces reversed and
greatly increased from the 1st floor to the foundation. The cantilever
effect.

I have also seen engineers do a two dimensional analysis of this same
problem and take the bracing down to the foundation with no concern for the
basement walls. This is not the correct load path on account of the rigidity
of the floor being tied to the walls.

James






>From: "Jim Kestner" <jkestner(--nospam--at)somervilleinc.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: "'SEAINT'" <seaint(--nospam--at)seaint.org>
>Subject: Shear Walls extending to Basement Level
>Date: Mon, 11 Nov 2002 09:58:45 -0600
>
>Picture a shear wall extending to the basement level. It would seem that if
>the 1st floor diaphragm was tied into the shear wall with rebar (and that
>the diaphragm could transfer load to the perimeter foundation walls) that
>the shear wall would try to act as a cantilevered beam using the foundation
>in the basement and the 1st floor diaphragm as its supports. It would seem
>to me that this would potentially create a large cranking force on the 1st
>floor diaphragm that would be difficult to design for since the shear would
>be magnified.
>
>All my references show examples of shear walls going to grade level and not
>to the basement level.
>
>How is this condition normally handled? Is it practical to isolate the
>shear
>wall from the diaphragm at the 1st floor level so that all overturning and
>shear forces are transferred to the foundation at the basement level? It
>doesn't seem practical to stop the shear wall at the 1st floor level. The
>1st floor shear wall would have to be designed as a transfer beam and
>columns on either end would have to extend into the basement to transfer
>the
>up and down forces.
>
>How are these designed on high rises where there may be multiple basement
>levels to contend with?
>
>Jim K.
>
>
>
>
>
>
>******* ****** ******* ******** ******* ******* ******* ***
>*   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
>******* ****** ****** ****** ******* ****** ****** ********


_________________________________________________________________
Add photos to your messages with MSN 8. Get 2 months FREE*.
http://join.msn.com/?page=features/featuredemail


******* ****** ******* ******** ******* ******* ******* ***
*   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 
******* ****** ****** ****** ******* ****** ****** ********