In design of precast concrete structures, frames are generally assumed to be two dimensional and analysed accordingly without taking into account participation of infill walls. However, it is well known that, the infill walls increase lateral stiffness and load carrying capacity of the frame structures. The objective of this study is to investigate the effects of infill masonry on structural behavior, performance and collapse mechanism of precast concrete structures. The diagonal strut model is adopted for modeling masonry infill. Load deformation relationship and collapse mechanism and of bare and infilled precast concrete structures are evaluated comparatively and results are given in figures.