This study investigates the effect of modelling the infill walls as a strut element on the building behaviour of a 5-story reinforced concrete frame building with and without modelling infill walls as a strut element. The study was conducted using finite element analysis. Five different building heights (15 m, 16.5 m, 17.5 m, 18.5 m, and 19.5 m) were considered as changing in the first story height. The results showed that the modelling of infill walls as strut element significantly increased the stiffness of the building, reducing the time period of building, and increasing the base shear force. The increase in stiffness was more clear in model with height 19.5 m model, also the modelling of infill walls as strut element were more effective in reducing the lateral displacement of the building at the higher floors.The results of this study suggests that the modelling infill walls as strut element can be effectively used to improve the seismic performance of reinforced concrete frame buildings, also provides valuable information for the design of infill walls and the effect of modelling the infill walls in calculating the soft story and torsion irregularities according to the Turkish earthquake code 2018 (TEC18) (Turkish Earthquake Code Mart, 2018).