Building Period Based on a Shearwall System

[bkgd]

My question is for a dyanmic design using etabs i have dynamic period of 4.5 s with 70% mass participation. If I use the alternate equation for building fundamental period for a shear wall buildings it gives me a period of 2.7 secconds and with a 1.4 factor that allows me to base my base shear coefficient on a period T=1.4 x 2.7= 3.78 seconds. Alternatively if I use the other fundemental equation for period which is T=Ctx(hn)^3/4 then i get a period that is 1.23 seconds or with the upper limit of 1.4 it comes in at 1.72 which is significantly different than 3.78 seconds.

Two quesitons:

1. From what i have seen in ASCE 7-02 the alteranate peroid equations is allowed...commnets?

2. It appears that the alternate period equation is only for planer shearwalls and not walls that have flanges,T's or form a tube,ect, is the use of this equations accpetable if the walls are anything but planer?


thanks for the input