Nonductile reinforced concrete frames with masonry infill walls are a popular form ofrnconstruction in seismic regions worldwide. The typical multi-story construction in Ethiopiarncomprises reinforced concrete (RC) frames with HCB masonry infills. Unreinforcedrnmasonry infill wall panels may not contribute towards resisting gravity loads, but contributernsignificantly, in terms of enhanced stiffness and strength under earthquake (or wind) inducedrnlateral loading. However, in practice, the infill stiffness is commonly ignored in framernanalysis, resulting in an under-estimation of stiffness and natural frequency. Also, therninfill has energy dissipation characteristics that contribute to improved seismic resistance. Itrnis instructive to study the implications of the common practice of ignoring the infill stiffnessrnwith regard to performance under seismic loading. This research quantifies the effect ofrnthe presence and configuration of masonry infill walls on seismic collapse risk. Seismicrnanalysis of such buildings indicates that the fully-infilled frame has the lowest collapse riskrnand the bare frame is found to be the most vulnerable to earthquake-induced collapse.rnA typical existing office building located in severe seismic zones of Ethiopia (as perrnESEN1998) is identified. The office medium rise building is analyzed for earthquake forcernby considering three type of structural system. i.e. Bare Frame system ,partially-infilled andrnfully- Infilled Frame system. Effectiveness of masonry wall has been studied with the help ofrnfive different models. Infills were modeled using the equivalent strut approach. Nonlinearrnstatic analyses for lateral loads were performed by using standard package ETABS,2015rnsoftware. The comparison of these models for different earthquake response parameters likernbase shear vs roof displacement, Story displacement, Story shear, member forces and seismicrnperformance assessment are carried out. It is observed that the seismic demand in the barernframe is significantly large when infill stiffness is not considered, with larger displacements.rnThis effect, however, is not found to be significant in the infilled frame systems.The resultsrnare described in detail in this paper.rnKey words: Bare frame; Infilled frame; Equivalent Diagonal strut; infill; plastic Hinge