## Interpretation of ASCE 12.9.1 - Modal Response Parameters

## Interpretation of ASCE 12.9.1 - Modal Response Parameters

(OP)

## Quote (ASCE 7-05 12.9.2)

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 of response shall be computed using the properties of each mode and response spectra defined in either Section 11.4.5 or 21.1 divided by the quantity R/I. The value for displacement and drift quantities shall be multiplied by the quantity Cd/I.

I want to clarify my understanding of this, as I am performing a response spectrum analysis. Using gravity = 9806 and R = 5, Cd = 5, I = 1 in ETABS scaling factor, which of the following options is correct.

1)

For member forces: 9806/(5/1) = 1961

Deformations/drifts: 9806 x (5/1) = 49030

**OR**

2)

For member forces: 9806/(5/1) = 1961

Deformations/drifts: 1961 x (5/1) = 9806

I feel like it should be option 2, as this would be the developed force assuming the structure remains elastic and we do not account for the allowance of plastic energy dissipation.

## RE: Interpretation of ASCE 12.9.1 - Modal Response Parameters

## RE: Interpretation of ASCE 12.9.1 - Modal Response Parameters

## RE: Interpretation of ASCE 12.9.1 - Modal Response Parameters

## RE: Interpretation of ASCE 12.9.1 - Modal Response Parameters

## RE: Interpretation of ASCE 12.9.1 - Modal Response Parameters

## RE: Interpretation of ASCE 12.9.1 - Modal Response Parameters

edit: I think maybe you're confused about 'g'? It's not a force, it's an acceleration.

## RE: Interpretation of ASCE 12.9.1 - Modal Response Parameters

## RE: Interpretation of ASCE 12.9.1 - Modal Response Parameters