There have been numerous numerical and experimental studies conducted to investigate the performance of a moment frame with reduced beam section (RBS). However, most of the numerical studies have not been carried out using realistic material properties and constitutive model that can more accurately represent the material response. Strain rate dependent material properties and parameters for mixed-mode hardening model for two heats of steel have been considered. One heat has the yield strength close to the minimum yield strength of CAN/CSA G40.20/21 350W steel and the other has the yield strength close to the probable yield strength of 385 MPa for grade 350W steel. Non-linear dynamic analyses on four-storey moderately ductile and limited ductility moment resisting frames with RBS for a suite of scaled ground motions have been carried out to investigate effects of material properties strain rate dependency on the response of the frame.