Determination of soft story effects in reinforced concrete building using nonlinear analysis

The major part of the existing buildings in our country consists of mid-rise reinforced concrete buildings. It is a quite to use often ground floors in these buildings like shops, car parks, banks, hotel lobbies, warehouses. Ground floor heights are not the same for all floors of the building due to non-residential use. The soft story irregularity caused by the difference in floor heights weakens the ground floor compared to the upper floors and causes damage to the buildings under earthquake effect. In the scope of the present study, soft story irregularity was examined in 4, 6 and 8 storey buildings in order to represent the building stock in our country. A total of 12 types of models have been formed such as 4, 6 and 8 storey buildings modelled in 3D frame-system structures have reference buildings with a floor height of 2.8m each, and the first floor height of 3.5m, 4.5m ve 5.5m has been considered as soft storey buildings. In the analysis of the models, Non-Linear Elastic Time History Analysis Method as the dynamic analysis method was used in order to the aim of understanding real construction behavior by assigning joint with the SAP2000 program. In this analysis, 12 different types of buildings were evaluated in two directions as x and y directions with 64 earthquake acceleration records from different soil type, resulting in total 1536 analyses. As a result of the analysis carried out within the scope of the study, the comparison of various parameters including Base Shear Force, Roof Drift Ratio and Interstory Drift Ratio were performed in the building models with regular reference buildings and soft storey irregularities. The base shear force is inversely proportional to the floor height and the lowest base shear force is calculated in soft-story buildings according to the reference buildings. In soft-storey buildings, it is observed that 4-storey buildings are the most affected building group. It is known that the roof drift ratio increased as the number of stories increase, and the effect of roof drift ratio on the analysis varies with the change in the building period of soft story irregularity, although in general, the increase in the value of the 4 storey buildings is estimated to be more than 6 and 8 storey buildings. The results of the interstory drift ratio yielded similar results to the roof drift ratio. Among models; it is seen that the base shear force value is lower and the displacement demands are higher in the buildings with soft floor height 5.5m.