Vertical Acceleration - Modal Analysis

[slickdeals]

Folks,
I have a question pertaining to the vertical accelerations per UBC 97.

In Section 1631.2 - 5, it states that vertical accelerations can be defined by scaling the horizontal accelerations by 2/3.

In Section 1630.1.1, a Ev factor is used to include the vertical effects.

My question is thus:

I have performed a modal analysis and need to scale my base shears to 90% of the static base shear.

Can this be done in any one of the options I list below?

Option 1. Compute E using equation 30-1 including the effects of vertical acceleration. Scale the response spectrum results to 90% of the above computed value in both directions and not use Section 1631.2-5

Option 2. Compute E using Equation 30-1 but without the vertical effects. Scale the response spectrum to the static values in X and Y direction, and use a 2/3 factor on these scale factors for vertical excitation. ETABS for example has a UZ excitation component. I am plugging the 2/3 horizontal value into this input box for each direction separately.

Please let me know if this approach is right.

Thanks