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Dilemma

 
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Rudra Nevatia
...
...


Joined: 26 Jan 2003
Posts: 206
Location: Mumbai

PostPosted: Tue Dec 28, 2004 5:14 am    Post subject: Dilemma Reply with quote

Thank you Mr. Barua. As expected, the response came
from an old timer who would have gone through many
such discussions on ill-conditioning in the early
seventies.

As you rightly pointed out, the problem can be solved
by using higher precision math though I would not bet
on 16 bits. Pivot exchange strategy is perhaps another
way.

The point I would like to make is this: There is a
possibility of error when out of plane stiffness is
increased arbitrarily to model a rigid diaphragm. It
is better to use a master-slave model.

Regards,
Rudra Nevatia


--- ibarua@deguild.com wrote:

Quote:

Re.: Mr Nevatia's dilemma
--------------------

Ill-conditioned equations, which occur frequently in
real life, can be solved only by so-called 'exact'
or rigorous methods such as matrix inversion and not
by iterative methods. Even in matrix inversion, it
becomes necessary to use double precision. Our
computer programs noramally work in single
precision, that is, up to 8 significant places. If
double precision is declared for the variables
involved,then the calculations extend up to 16
significant places, precluding round-off errors so
common in ill-conditioned equations.

I thought that increase in the stiffnes of the
horizontal diaphragms, the slabs, will enhance
diaphragm action and help to transfer lateral forces
to the stiffer elements in the building, such as the
shear walls or the braced frames.

Indrajit Barua.


Message From  rudra_nevatia@yahoo.com
Subject: permissible limit
of
drift
Date: 27/12/04
Time: 20:46:24


---------------------------------------------------------
Quote:
--
I am confused.

I was taught that arbitrarily increasing
out-of-plane
stiffness of beams to account for diaphragm action
results in large off-diagonal elements in the
global
stiffness matrix and the resulting system of
equations
can be ill-coditioned giving wrong results from an
otherwise well behaved software.

But then this was thirty five years ago.

Rudra Nevatia

--- ishacon@vsnl.net wrote:
You may want to increase IY & IZ of beams to
account
for diaphragm action of slab.













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