effect of shear wall cracking on soft storey phenomenon

according to the iranian code of practice for seismic resistant design of buildings, soft storey phenomenon happens in a storey when the lateral stiffness of the storey is lower than 70% of the stiffness of the upper storey, or if it is lower than 80% of the average stiffness of the three upper stories. in the combined structural systems containing moment frames and shear walls, it is possible that the shear walls of the lower stories crack however, this cracking may not occur in the upper stories. the main objective of this research is to investigate the possibility of having soft storey phenomenon in the storey, which is bellow the uncracked walls. if the tension stresses of shear walls obtained from ultimate load combinations exceed the rupture modulus of concrete, the walls are assumed to be cracked. for calculating the tension stresses of shear walls in different conditions, 10 concrete structures containing 15 stories were studied. each of the structures was investigated according to the obligations of iranian, canadian, and american concrete building codes. five different compressive strengths of 30, 40, 50, 60, and 70 mpa were assumed for the concrete of the structures. in other words, 150 computerized analyses were conducted in this research. in each analysis, 5 load combinations were imposed to the models. it means, the tension stresses of the shear walls in each storey, were calculated 750 times. the average wall to total stiffness ratios of the buildings were from 0.49 to 0.95, which was quite a wide range. the final conclusion was that the soft storey phenomenon did not happen in any of the structures investigated in this research.