Design Response Spectrum and Reduction factor R - IBC2006/ASCE7-2005

[antiwheel]

Hi guys,

I have a question about the design response Spectrum of IBC2006/ASCE7-2005.

In ASCE7-2005, Section 11.4.5, the design response spectrum is developed based on Sd,Ss,S1,T, etc. In this spectrum, the reduction factor R is not included which means the design response spectrum does not consider the structure's ductility and all members and joints are working under "elastic" range.
These S1,Sd and other parameters are used to develop either Equivalent Lateral force procedure or Model analysis(dynamic analysis)

So section 12.8, Equivalent Lateral Force procedure
These response spectra parameters are divided by R/I to include the ductility per structure's own characteristics. It decrease the seismic factor by R/I

In section 12.9, Model Response spectrum analysis, it also mentioned that the design parameters shall be divided by R/I these design parameters includes story drifts, support forces, and individual member forces.

I have a steel frame that one direction X braced frame and the other direction is moment frame. I need to run a dynamic analysis based on response spectrum method, which is Section 12.9 to decide the member sizes. I will take care of the connections design based on other sections later.

My question is,
shall I use the design response spectrum which does NOT consider the Reduction factor R
or
I should use the response spectrum that divided by R/I?


Thanks.

 

[JoshPlumSE]

You can use the elastice spectra (which doesn't account for I and R). But, if you do so, then you will scale down most of your results by multiplying by I/R.

Or, you can multiply your spectra by I/R and choose not to scale your results.

This is an elastic analysis, right? Either way, your final design results will be the same.