Effect of irregularity on seismic design parameters of RC-infilled structures

A four-storey reinforced concrete (RC) building is seismically evaluated with the incorporation of different irregularities. Three model systems have been considered, i.e., model I: (RC-infilled regular frame in X and Y direction), model II: (RC-infilled plan irregular frame in X and Y direction), and model III: (RC infilled vertical + plan irregular frame in X and Y direction). Adaptive pushover analyses have been carried out to evaluate the seismic performance of the structure by using seismostruct software incorporating inelastic material behaviour for concrete, steel, and infill walls. Infill walls have been modelled as "double strut nonlinear cyclic models". The most up-to-date seismic design includes the nonlinearity in the structure through a response reduction factor (R). The ductility reduction factor and overstrength factor are the main components of the response reduction factor. These seismic design parameters were computed from the adaptive pushover analysis, and finally, the response reduction factor has been calculated for all models and compared with the value recommended by IS 1893 part-1 (2016). The result shows that the evaluated R-factors are higher than the value recommended by the BIS code. However, it is observed that R-values are higher than the corresponding values recommended in the BIS code when the irregularity present in the structures.