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Re: Effective Section - ACI 318

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Dear Dr. Chandrasakeran:
I don't know how the values specified in the ACI code. probably the ACI can answer this
question(ACI committee 318 and liasion member of other committees such as 435, 421,....etc)    but
the values of Ig, I believe, were based on the research published in numerous  technical journals
including  the ACI journal. For example:
The flate plates and slabs and beams were based on the long term deflections while columns and
walls were based on the lateral loadings.
It is very difficult to cite any references because numerous references have been published.
I have over 200 papers  on flate plates and flat slabs related to the short and long term
deflections and over 400 papers on beams simply supported and continuous. Are you looking for a
particular 
reference(s)?
Himat
>>> for_prof_arc(--nospam--at)hotmail.com 9/1/2003 10:06:58 PM >>>
Dear Friends,

I would be thankful if some of you could explain the background to the
clause of ACI as quoted below:

The specifications of ACI 318 RM - 02 for moment of
inertia of members are
------------------------------------------
beams    0.35 Ig (gross moment of inertia)
columns  0.70 Ig
walls uncracked 0.70 Ig    cracked  0.35 Ig
Flat slabs and flat plates   0.25 Ig
--------------------------------------------
Is it based on analytical/experimental research or is it empirical ? Could
you suggest any References for me
to become more familiar with this topic ?

I have some experience of system identification studies -
trying to fit analytical model to match experimental results.
In particular for a RCC framed structure (TG framed foundation) we carried
out extensive experiments after the structure was built and operated under
actual loads.
The structure was analysed as a space frame as well as by using 3D solid
finite elements. The gross section of the concrete was used with static
modulus of elasticity.
The best fit was obtained when using an effective factor of 0.65. In one
sense, ACI 316 gave us confidence that the effective factor should be less
than unity but it was not possible to assign different factors for beams and
columns
to confirm ACI values. 3D analysis could predict frequencies and mode shapes
near the operating range of frequency (50 Hz) and space frame analysis could
not do so.

Thanks.
A R Chandrasekaran

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