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Further Reading: Ubc-1997-Volume 2 (Wind Seismic Considerations).pdf

Ahmed, It is explained very clearly in UBC 97. You need to consider pertinent clauses together. See excerpts below. 1631.5.4 Reduction of Elastic Response Parameters for design. Elastic Response Parameters may be reduced for purposes of design in accordance with the following items, with the limitation that in no case shall the Elastic Response Parameters be reduced such that the corresponding design base shear is less than the Elastic Response Base Shear divided by the value of R. 1. For all regular structures where the ground motion representation complies with Section 1631.2, Item 1, Elastic Response Parameters may be reduced such that the corresponding design base shear is not less than 90 percent of the base shear determined in accordance with Section 1630.2. 2. For all regular structures where the ground motion representation complies with Section 1631.2, Item 2, Elastic Response Parameters may be reduced such that the corresponding design base shear is not less than 80 percent of the base shear determined in accordance with Section 1630.2. 3. For all irregular structures, regardless of the ground motion representation, Elastic Response Parameters may be reduced such that the corresponding design base shear is not less than 100 percent of the base shear determined in accordance with Section 1630.2. The corresponding reduced design seismic forces shall be used for design in accordance with Section 1612. Section 1631.5.4 refers to 1630.2, which is your Static Force Procedure. Please see the following topic to understand how to setup your model for Response Spectrum and do the scaling. Thanks.

Yes. When following procedures of UBC Section 1631.2, R value is not to be used

Your base shear used for dynamic analysis can't be less than 85% of static. This would not affect your R. See responses above. Thanks.