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RE: seaint Digest for 18 Jul 2011-Cantilever Wall Forces

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Thank you all for responding.  Actually I meant to reference ASCE 7,
Table 15.4-2, but I see that there is a difference of opinion of what
table to use.  I would argue for the use of 15.4-2 because the wall is
cantilevered from the ground and is not permanently attached to a
building, as required by Ch 13, and because of the description:
...reinforced concrete distributed mass cantilever structures ...  It
seems odd that such a common structural system has no clearly defined
description in our available design references.

I will review the NEHRP Provisions as suggested by Mr. Sprague and
thanks again for the input.

Steve Widmayer, PE

-----Original Message-----
From: admin [mailto:admin(--nospam--at)seausa.org] 
Sent: Tuesday, July 19, 2011 12:00 AM
To: Steve Widmayer
Subject: seaint Digest for 18 Jul 2011


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                       seaint Digest for 18 Jul 2011

Topics covered in this issue include:

   1: Cantilever Wall Forces-ASCE 7-05=2C Ch 15<BR>Date: Wed=2C 13 Jul
2=
             by swidmayer(--nospam--at)willdan.com
   2: changes to a constant problem
             by "David Merrick, Structural Engineer, Merrick Group"
<mrkgp.se(--nospam--at)gmail.com>
   3: RE: changes to a constant problem
             by "Conrad Harrison" <sch.tectonic(--nospam--at)bigpond.com>



------------------------------------------------------------------------
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1                                Message:0001
1
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From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: Cantilever Wall Forces-ASCE 7-05, Ch 15

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Steve=2C
=20
There was discussion in the code development process whether a
cantilever w=
all such as you describe was a non-building structure or a
non-structural c=
omponent.  Regardless=2C Table 15.4-1 is titled "Seismic Coefficients
for N=
onbuilding Structures Similar to Buildings".  A cantilever wall is not
what=
 I would categorize as similar to buildings.  So the bottom line is that
Ta=
ble 15.4-1 does not apply.  One could argue that you could use Table
15.4-2=
 "Seismic Coefficients for Nonbuilding Structures Not Similar to
Buildings"=
.  But that is not what was intended for a cantilever wall. =20
=20
We tried to avoid duplication in the ASCE 7.  It was decided that a
cantile=
ver wall should be listed as a nonstructural component.  As such there
is a=
n Rp value and an ap value contained in Section 13.5.  You should be
refere=
ncing Table 13.5-1 and you should be calculating the Fp value to design
the=
 wall.  I would suggest an Rp of 2.5 and an ap of 1.0 using ASCE 7=2C
Secti=
on 13.3.1 to calculate the seismic design force. =20
=20
Further discussion is contained in the NEHRP=2C Recommended Provisions
for =
Seismic Regulations for New Buildings and Other Structures (FEMA 450)=2C
Pa=
rt 2: Commentary=2C Section 6.3. =20

Regards=2C Harold Sprague
=20




Subject: Cantilever Wall Forces-ASCE 7-05=2C Ch 15
Date: Wed=2C 13 Jul 2011 09:47:20 -0700
From: swidmayer(--nospam--at)willdan.com
To: seaint(--nospam--at)seaint.org








I=92m trying to clarify the base shear requirement for a cantilever wall
(c=
oncrete or masonry) using the =93Nonbuilding Structures=94 section of
ASCE =
07.  Table 15.4-1 does not describe a cantilever wall as a Structure
Type. =
 I assume that I would use this table to get the R value and that I
wouldn=
=92t use Sec. 12.11 (Structural Walls and their Anchorage)=2C Ch. 13
(Nonst=
ructural Components/Architectural Components).  If I=92m going to use
Table=
 15.4-1=2C what is the correct R & Omega values for a cantilever wall?
Tha=
nks.
=20
Steve Widmayer=2C PE
=20
  		 	   		  =

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<DIV dir=3Dltr>Steve=2C<BR>&nbsp=3B<BR>There was&nbsp=3Bdiscussion in
the c=
ode development&nbsp=3Bprocess whether a cantilever wall such as you
descri=
be was a non-building structure or a non-structural component.&nbsp=3B
Rega=
rdless=2C Table 15.4-1 is titled "Seismic Coefficients for Nonbuilding
Stru=
ctures Similar to Buildings".&nbsp=3B A cantilever wall is not what I
would=
 categorize as similar to buildings.&nbsp=3B So the bottom line is that
Tab=
le 15.4-1 does not apply.&nbsp=3B One could argue that you could use
Table =
15.4-2 "Seismic Coefficients for Nonbuilding Structures Not Similar to
Buil=
dings".&nbsp=3B But that is not what was intended for a cantilever
wall.&nb=
sp=3B <BR>&nbsp=3B<BR>We tried to avoid duplication in the ASCE
7.&nbsp=3B =
It was decided that a cantilever wall should be listed as a
nonstructural c=
omponent.&nbsp=3B As such there is an Rp value and an ap value contained
in=
 Section 13.5.&nbsp=3B You should be referencing Table 13.5-1 and you
shoul=
d be calculating the Fp value to design the wall.&nbsp=3B I would
suggest a=
n Rp of 2.5 and an ap of 1.0 using ASCE 7=2C Section 13.3.1 to calculate
th=
e seismic design force.&nbsp=3B <BR>&nbsp=3B<BR>Further discussion is
conta=
ined in the NEHRP=2C Recommended Provisions for Seismic Regulations for
New=
 Buildings and Other Structures&nbsp=3B(FEMA 450)=2C Part 2:
Commentary=2C =
Section 6.3.&nbsp=3B <BR><BR>Regards=2C Harold Sprague<BR>&nbsp=3B<BR>
<DIV>

<HR id=3DstopSpelling>
Subject: Cantilever Wall Forces-ASCE 7-05=2C Ch 15<BR>Date: Wed=2C 13
Jul 2=
011 09:47:20 -0700<BR>From: swidmayer(--nospam--at)willdan.com<BR>To:
seaint(--nospam--at)seaint.org<=
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<P class=3DecxMsoNormal><FONT face=3DArial><SPAN style=3D"FONT-FAMILY:
Aria=
l=3B FONT-SIZE: 10pt">I=92m trying to clarify the base shear requirement
fo=
r a cantilever wall (concrete or masonry) using the =93Nonbuilding
Structur=
es=94 section of ASCE 07.&nbsp=3B Table 15.4-1 does not describe a
cantilev=
er wall as a Structure Type.&nbsp=3B I assume that I would use this
table t=
o get the R value and that I wouldn=92t use Sec. 12.11 (Structural Walls
an=
d their Anchorage)=2C Ch. 13 (Nonstructural Components/Architectural
Compon=
ents).&nbsp=3B If I=92m going to use Table 15.4-1=2C what is the correct
R =
&amp=3B Omega values for a cantilever wall?&nbsp=3B
Thanks.</SPAN></FONT></=
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<P class=3DecxMsoNormal><FONT face=3DArial><SPAN style=3D"FONT-FAMILY:
Aria=
l=3B FONT-SIZE: 10pt">Steve Widmayer</SPAN></FONT><FONT
face=3DArial><SPAN =
style=3D"FONT-FAMILY: Arial=3B FONT-SIZE: 10pt">=2C PE</SPAN></FONT></P>
<P class=3DecxMsoNormal><FONT face=3DArial><SPAN style=3D"FONT-FAMILY:
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style=
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------------------------------------------------------------------------
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2                                Message:0002
2
------------------------------------------------------------------------
--
From: "David Merrick, Structural Engineer, Merrick Group"
<mrkgp.se(--nospam--at)gmail.com>
To: SEAINT <seaint(--nospam--at)seaint.org>
Subject: changes to a constant problem

Feeling COMPETENT that increasing design code, changing jurisdiction or 
changing certification will fix a constant rate of failure.

The following bog is from a very close college.

http://danquo.blogspot.com/

Here are some excerpts from its first entry.

to err is human and all of us will eventually fail at any task no matter

how careful, skilled or knowledgeable we are.

failure rate for different classes of civil engineering structure is 
between 1 and 5 percent...the constant at fault is the human factor.

Self-serving bias can prevent humans learning from their mistakes.

It is comic to think about it but half of us are below average in any 
skill category but when asked, the majority will assess themselves as 
above average.

It is disturbingly common to find that the less competent a person is at

a task, the higher the esteem in which they hold their own competence.

The catch 22 of engineering is that if you think you know what you are 
doing, you probably don't while if you doubt you own skill, you may 
actually be quite good at what you are doing.

David Merrick, SE

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3                                Message:0003
3
------------------------------------------------------------------------
--
From: "Conrad Harrison" <sch.tectonic(--nospam--at)bigpond.com>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: changes to a constant problem

David, 

Thanks for the link, 


http://danquo.blogspot.com/


looks like an interesting blog to follow, with other posts on causes of
failures and such.


regards
Conrad



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*   This email was sent to you via Structural Engineers 
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*   send to the list is public domain and may be re-posted 
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*   site at: http://www.seaint.org 
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