asce 7-98. cl.no 6.5.8.2

huangyhg

asce 7-98. cl.no: 6.5.8.2
dear all,
in one of my project, i used etabs package for lateral analysis. this is a 15 storyed structure and i got a fundamental period of 2.2 sec. the dimension of building is 150' x 150' and 150 ft height. this is just a square building envelope.
as per code, this is classified as flexible bldg & i have come out with gust factor = 1.05.
i took mass source as 100% self weight, 100 %super imposed dead load, 25 % live load.
is the procedure right?
can i consider this building as a rigid structure & take gust factor as 0.85 with a view of height / min width < 4.0.
please provide your inputs.
thanks in advance