How to specify response-spectrum scale?

The value for each force related design parameter of interest, including story drifts, support forces, and individual member forces for each mode of response shall be computed using the properties of each mode and the response spectra defined in either ASCE 7-05 Section 11.4.5 or 21.2 divided by the quantity R/I. The value for displacement and drift quantities shall be multiplied by the quantity Cd/I (ASCE 7-05 Section 12.9.2).

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