This document presents a comparative analysis of square shaped reinforced concrete frames with and without masonry infill using response spectrum analysis. Masonry infill walls are commonly used to fill gaps in RC frames but are often ignored in design. The study models an 8-story RC building in ETABS and replaces the masonry infill with an equivalent diagonal strut. Response spectrum analysis is performed for different relative stiffness levels by reducing the strut width by 5-50%. Parameters like time period, base shear, storey displacement and stiffness are compared. Results show infill increases stiffness and strength but displacement increases as strut width decreases. Infill frames generally perform better seismically than bare frames by reducing displacements and increasing stiffness