In the seismic analysis of a framed building with masonry infill walls, it is necessary to model the effect of the walls on the lateral stiffness, strength and ductility of the building. The equivalent strut method is a convenient method for modelling the walls. Out of the two approaches of equivalent strut method, the one based on elastic analysis is suitable for linear methods of seismic analysis such as equivalent static and response spectrum methods. The approach based on ultimate load is suitable for nonlinear methods of seismic analysis such as pushover analysis. The present study proposes a nonlinear axial load versus deformation behaviour for the equivalent strut to be used in conjunction with a pushover analysis.