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Fw: [ETABS,SAFE,SAP] Property modifier of concrete sections in frequency calculations and p-delta effect

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Hi,
 
what do you think about following issue? Has anyone new solutions?
 
Thanks
Hossein Mardanlo
 
----- Original Message -----
Sent: Tuesday, June 19, 2007 10:20 PM
Subject: Re: [ETABS,SAFE,SAP] Property modifier of concrete sections in frequency calculations

> hosein_1353 <hosein.mardanloo@...> wrote:
> Hi,
>
> My question is what values of Property modifiers in calculation of
> natural frequncies of vibration must be assigned to concrete
columns,
> beams and walls based on ACI or UBC code?
>
> Thanks,
> Hossein Mardanlo
>
 
--- In ETABS2000@yahoogroups.com, imran rashid <ir319@...> wrote:
>
> Hossein,
>
> If your vibrations are resulting from earthquake or wind loads,
you can follow the commentary of section 10.11.1 of ACI 318-05 where
it is allowed to increase the property modifiers given in section
10.11.1 with a factor of 1.43 for serviceability checks of wind and
earthquake loads.
>
> If you are talking about vibrations due to machine loading on RC
components, it depends upon the member and severity of loading.
Generally you should see the degree of cracking in the member which
will help you to select the property reduction factor. I think for
RC structures, there will not be much effect generally.
>
> Vibrations are more important in composite slabs, concrete on
steel deck. For this case AISC design guide no 11 can be followed.
>
> Regards
> Imran Rashid
 
 
 
 
hosein_1353 <hosein.mardanloo@gmail.com> wrote:
Now suppose we are doing a spectrum analysis for a RC structure. To
consider cracking of sections we must use property modifiers given
in section 10.11.1, while for calculating periods of vibretions, we
must increase property modifiers with a 1.43 factor. So it seems the
software must be capable of considerring two sets of property
modifiers, one for p-delta analysis and one for period calculations.
But in the current versions only one set of property modifiers can
be introduced for software. Do you think we can find a solution to
overcome this limitation?

Thanks,
Hossein Mardanlo
 
--- In ETABS2000@yahoogroups.com, imran rashid <ir319@...> wrote:
I think presently there is no other alternative to run the program twice with different modifiers.
 
But I think we may reach to one modifiers both for design and serviceability with our judgement regarding cracking phenominon of the structure under lateral loads, but for every structure this might not be possible.
 
Regards
Imran Rashid


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