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Re: IDR

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You should do it both ways:

1.  Scale the dynamic analysis results by the factor of UBC base
shear/Dynamic base shear and do a Code level stress check.

2.  Calculate the Dynamic demand/capacity ratios of the members and
compare them to acceptable D/C factors for various level of earthquakes,
such as MCE, MPE etc. Tri-service manual has a list of acceptable D/C
factors that you can use for reference.

3.  If you have enough budget, you can also go a step further to do a
Push-over analysis to find out the inelastic responses of the structure,
to see if there is a collapse potential or not.


Good luck,
Tom Chiu, SE

Tom Long wrote:
> 
> We are designing a new 5 level airport in Manila, 188,000 m2.  The type
> of construction is concrete flat plate slab with drop panels.  We are
> using SAP2000 to analyze the structure.  After we perform the analysis
> and get the seismic forces from the response spectra analysis, should we
> apply an IDR to reduce the forces before we compare them with the
> capacity of the elements, or should we compare the d/c ratio to a
> acceptable factor for the type of structure.
> 
> Or in another case should we follow the UBC and just scale the results
> from the dynamic analysis.
> 
> Thank you
> 
> Best regards,
> Tom Long
> Asia
>