This paper studies mainly the relationship between the fundamental translational periods of vibration, in tall reinforced concrete building (more than ten floors) located in Antofagasta, Chile, for both conditions, cracked and uncracked. For thatpurpose, the fundamental translational periods of vibration and also the roof displacement were calculated using the modal spectral analysis proposed in the Chilean seismic code NCh433 Of.96 Mod.2009/D.S.61, considering the gross section (uncracked condition). Afterward, the flexural stiffness of structural walls was modified applying reduction factors to the moment of inertia to consider the cracked condition. These reduction factors were taken from different recommendations given by the scientific community to take into account cracking in structural walls. Results for the different models were comparedamong them and with what is specified in the DS 61 with respect to periods and roof displacement. Finally, it is concluded that, in general, the ratio between periods for the cracked and uncracked are less than 1.5; except for the model E (Doepker). Similarly, the roof displacements are smaller than that specified by the formula included in the DS 61.