Upper limit of fundamental period

[KenStructural]

The approximate fundamental period as per UBC should not be greater than 1.3Ta for seismic zone 4 and 1.4Ta for seismic zone 1,2,3,. and also "The restriction in SEAOC­ 88 that the base shear calculated using the rational period shall not be less than 80% of the value obtained by using the em­pirical period corresponds to a factor of 1.4 (Cole et al. 1992)". Is these simply means that the restriction in SEAOC88 is applicable only to seismic zone 4?.

Also, the factor 1.3 and 1.4 of UBC 97 is different to IBC where these factors changed to Cu which has a corresponding value depending on design spectral response acceleration SD1, my question is, is SEAOC88 restriction is also applicable to IBC.