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Clause # 4.3.4 of Draft IS: 800

 
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SKSNL at ltecd.ltindia...
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PostPosted: Fri Oct 10, 2003 7:21 am    Post subject: Clause # 4.3.4 of Draft IS: 800 Reply with quote

The subject clause calls for incorporation of base stiffness in to
analytical model. The stipulations under serial no a) and b) warrants:

1) Modeling of pedestal below the column base.
2) Pedestals are to be assigned with stiffness relative to the column
stiffness, depending on attachment.
3) Earlier draft included modeling of pedestal bottom end, which
probably is omitted because it related to foundation.

I understand that these might have got a research background. But I
anticipate a problem due to these stipulations.

i) In a large and complex 3-D model, with varying elevation of beams
and ties along two orthogonal directions, column stiffness calculation
will be a very time consuming and laborious task.
ii) Design will proceed in an iterative manner, to qualify each and
every member. Every time one column size is changed, the base stiffness
is to be recalculated.
iii) Boundary conditions are not specified in code and no reference is
indicated, as to how the pedestal end will be idealized. So, even if the
column base stiffness is accurately modeled, but boundary conditions are
not appropriate, then the purpose of such elaborate exercise will be
defeated. It will only increase the burden of design engineers.

As illustrated under serial no. i) and ii) above, I feel these
stipulations will impose a great deal of complexity in day to day design
work.

I might have felt so because of my strong prejudice about traditional
support idealization, i.e. fixed base or pinned base. But I did not find
such clause of base stiffness in couple of International codes, I have
worked with. I was wondering whether, they recognize the practical
difficulty in doing base stiffness modeling.


I request for Participants' / Design Engineers' view on practicability
of this codal provision.


Respectfully,

Subhamoy Kar

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