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# Response Spectrum Analysis

• To: seaint(--nospam--at)seaint.org
• Subject: Response Spectrum Analysis
• From: "Anantha Narayan C.K." <anant_27(--nospam--at)yahoo.com>
• Date: Tue, 26 Sep 2006 13:47:45 +0100 (BST)

Greetings,
I am using ETABS to do a Response Spectrum Analysis for a parking garage. I have never done an RSA on ETABS before and hence, want to make sure
that I am doing things the way they are supposed to be.

1. I have done an ELF analysis on the building and have the base shears from it. I have used an R value of 6 for my system (combination of shear walls
and braced frames)
2. For the response spectrum analysis, I am using the IBC 2003 curves generated by ETABS with Ss = 1.71 g and S1=0.68g. When I use the curve to set up
my response spectrum cases, there is a scale factor term on the program. For the first run, I would scale the accelerations in "g" to the corresponding units "k-in" or "k-ft" using the factor 386.1 or 32.2. Is this correct?
3. The generated response spectrum is an elastic response spectrum and the base shears are for an elastic response. In the end, would I divide the base shear by my R value to get the inelastic response or use a scale factor of 386.1 / 6 or 32.2/6 to get the inelastic response?
4. Or should I use 0.85 Base shear (elf) / Base shear (modal) for the scale factor?
I would appreciate a response for carrying out a RSA analysis in ETABS.

Thanks
Anantha

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ANANTHA NARAYAN, E.I.
Structural Engineer
Bliss and Nyitray Inc.
Miami, FL - 33134

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