How do the importance factors within ETABS relate?
Extended Question: There is an importance factor, within the Shear Wall Design Preferences form, which defaults to 1.0. How does this importance factor relate to the Wind and Seismic Load Generator importance factor? If I have 1.15 for the wind importance factor, should I increase the value listed in on the Shear Wall Design Preferences form?
Answer: The importance factor I, and the system Deflection Amplification factor Cd, specified within the ETABS Wall Pier / Spandrel Design Preferences form, are used for boundary-element design. These values are independent of Auto-generated Seismic Load specifications. I and Cd control design displacement du, which in turn controls the neutral-axis equation for shear-wall boundary elements.
This ETABS formulation is based on the requirements of ACI 318-05 Section 21.6.6. Additional details and an overview are given in the materials available through Help > Documentations and Tutorials > Shear wall design> ACI 318-05 > Wall Pier boundary Element.