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Fw: Foundation design for seismic

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Alex:

I see your point, I think, but I still disagree.  One of the obstacles in
this case is that foundations are usually not accessible, so it would be
pretty difficult as well as time/money consuming to check the foundation of
a structure after an earthquake.

The way I see it, the foundation is part of the seismic resisting system,
since all forces must pass through the foundation structure to get to good
old terra firma.  My point was, why does it seem that the code stops
requiring rational seismic design right at the superstructure/foundation
interface.

As an example, you state that beams, columns and joints require attention,
with which I agree.  Rational seismic design would require that all
components be designed so that, relatively speaking, they all act together
to prevent undesireble yield/failure mechanisms.  These three elements
should be designed such that beam flexural yielding is likely to occur
BEFORE beam diagonal tension failure, column flex/shear yielding, or joint
shear yielding.

I guess I am asking: why is then that the code does not require a check for
maximum column axial load in order to preclude (or at least minimize) the
chances of a punching shear failure, which would be undesirable, just like
the other undesirable failure mechanisms?

Anyway, enough said.

T. Eric Gillham PE
GK2 Inc.
PO Box 3207  Agana, Guam  96932
Email - gk2(--nospam--at)kuentos.guam.net
Ph:  (671) 477-9224
Fax: (671) 477-3456


-----Original Message-----
From: Alex C. Nacionales <alexcnac(--nospam--at)easycom.net>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Saturday, May 22, 1999 6:13 AM
Subject: Re: Foundation design for seismic


>Eric,
>I agree with you that in some actual earthquakes, code level
>forces(axial,moments.shear) will be exceeded. The intent of the design is
>seismic resistance not "seismic proofing".But I maintain that beams,columns
>and their joints require more attention because these elements are the most
>damaged during past earthquakes.
>
>Your theory is OK. Its good if you can cite an example where a structure
was
>damaged or collapsed due to settlement of column caused by punching shear
>failure.
>
>Alex Nacionales
>Iloilo City, Philippines
>
>----- Original Message -----
>From: T. Eric Gillham PE <gk2(--nospam--at)kuentos.guam.net>
>To: seaoc list <seaint(--nospam--at)seaint.org>
>Sent: Friday, May 21, 1999 6:19 AM
>Subject: Fw: Foundation design for seismic
>
>
>> Alex:
>>
>> My point was that code level forces, such as .75(1.4D+1.7L+1.7E) are NOT
>the
>> axial loads that will be expected during the actual design earthquake, if
>> Rw=12 for calculating Vb.  The expected axial loads on exterior columns
>(not
>> interior, mind you) will be a function of the strength-deformation
>> characteristics of the structure, more specifically the maximum net shear
>> that the beams which frame into the column line can input.  Thus,
>1.4D+1.7L
>> will, in all likelihood, NOT control.
>>
>> T. Eric Gillham PE
>> GK2 Inc.
>> PO Box 3207  Agana, Guam  96932
>> Email - gk2(--nospam--at)kuentos.guam.net
>> Ph:  (671) 477-9224
>> Fax: (671) 477-3456
>
>
>
>