Fi = seismic force applied at level I.
C = seismic coefficient according to the article 1
η = constant defined by

Wi = weight assigned to level i according to the article 2
hi = height of level i measured from the base level.
N = total number of floors.

article 1  
The seismic coefficient C shall be evaluated by the following formula on the basis of classifications of foundation site, structural type and geographical location.

Where:
R = Reduction Factor to be multiplied to the maximum ground acceleration (a_max) in estimating the spatially averaged effective acceleration that occurs at the base of structure. For all cases, R = 0.80
a_max = maximum acceleration expected at the site, expressed as a fraction of gravity. This is obtained from the iso-acceleration maps, either directly or by a linear interpolation, reflecting the return period for which the structure shall be indicated in the article 3
FAD = Dynamic Amplification Factor depending upon natural vibration period of structure T, foundation site and structural type is related to the properties of ductility and damping as specified in table 1, no additional reductions under concepts being permitted.

article 2
 In determining the seismic load, the weight of each level shall be the permanent load plus a fraction of the temporary load assumed in the following way.
a) Warehouses :    ξ  =0.25
b) Buildings of general use :   ξ  =0.15
c) Roof floors, marquees and roofs :   ξ  =0
These values represent minimum fractions ; particular conditions leading to an increase of the fraction shall be considered necessary.

article 3
 It is possible to recommend the economic lifetime as related to the above classification. The following return periods in years, for which the structure shall be designed, are calculated by use of the formula accounting for its importance, its lifetime and its probability exceedance.

Group	Economic Lifetime (years)	Probability of Exceedance	Return Period (years)
A B C	100 50 30	0.20 0.40 0.45	500 100 50

During the construction process, these values for economic lifetime and probability of exceedance may be modified on the basis of proper justifications.