Ct=0.085 for moment resistant space steel frames,
Ct=0.075 for moment resistant space concrete frames and for eccentrically braced steel frames and
Ct=0.050 for all other structures.
H is the height of the building, in m, from the foundation or from the top of a rigid basement (EN 1998-1 section 188.8.131.52.2).
We can use this approximation for buildings with heights up to 40m provided that they follow the regularity criteria that are described in table 4.1 (EN1998-1 section 184.108.40.206).