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# Two-stage analysis

## Two-stage analysis

(OP)
I have some general questions about determining seismic loads for situations that aren't described in ASCE 7-10. Any insight or information would be greatly appreciated:

1. When attempting to qualify a two-stage analysis (ASCE 7-10, Sect. 12.2.3.2) for a 2-story building that has one SFRS stacked on top of another:
a. When using Eqn. 12.8-7 to determine the fundamental period, which value for Ct & x are used if you have a SRCMF at the top level and a concrete shear wall at the base?
b. Is there a way to combine the fundamental period of varying lateral force resisting systems? ASCE 7-10 Sect. 12.2.3.1 indicates what to do for the design coefficients when the systems are stacked, but not how to determine the fundamental period.
c. Additionally, how do you determine the fundamental period of the upper level only?

2. Are there design equations that can be used to approximate the stiffness of light gauge shear wall systems? I understand that stiffness can be determined by dividing the story shear by the total story drift, but how can that be done if have not yet determined your seismic forces?

### RE: Two-stage analysis

Wouldn’t you also treat them as two separate structures for the purposes of determining the period(s)? You design the top one as stand alone building and then transfer the seismic base shear to the lower one as additional seismic effect on the “stand alone one story structure”.

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