American Journal of Civil Engineering 2018; 6(1): 24-33 http://www.sciencepublishinggroup.com/j/ajce doi: 10.11648/j.ajce.20180601.15 ISSN: 2330-8729 (Print); ISSN: 2330-8737 (Online) Seismic Performance of Reinforced Concrete Buildings with Masonry Infill Girma Zewdie Tsige * , Adil Zekaria Department of Civil Engineering, Addis Ababa Institute of Technology, Addis Ababa, Ethiopia Email address: * Corresponding author To cite this article: Girma Zewdie Tsige, Adil Zekaria. Seismic Performance of Reinforced Concrete Buildings with Masonry Infill. American Journal of Civil Engineering. Vol. 6, No. 1, 2018, pp. 24-33. doi: 10.11648/j.ajce.20180601.15 Received: September 24, 2017; Accepted: October 23, 2017; Published: January 2, 2018 Abstract: Unreinforced masonry Infills modify the behavior of framed structures under lateral loads; however, in practice, the infill stiffness is commonly ignored in frame analysis, resulting in an under-estimation of stiffness and natural frequency. The structural effect of hollow concrete block infill is generally not considered in the design of columns as well as other structural components of RC frame structures. The hollow concrete block walls have significant in-plane stiffness contributing to the stiffness of the frame against lateral load. The scope of present work was to study seismic performance of reinforced concrete buildings with masonry infill in medium rise building. The office medium rise building is analyzed for earthquake force by considering three type of structural system. i.e. Bare Frame system, partially-infilled and fully- Infilled frame system. Effectiveness of masonry wall has been studied with the help of five different models. Infills were modeled using the equivalent strut approach. Nonlinear static analyses for lateral loads were performed by using standard package ETABS, 2015 software. The comparison of these models for different earthquake response parameters like base shear vs roof displacement, Story displacement, Story shear and member forces are carried out. It is observed that the seismic demand in the bare frame is significantly large when infill stiffness is not considered, with larger displacements. This effect, however, is not found to be significant in the infilled frame systems. The results are described in detail in this paper. Keywords: Bare Frame, Infilled Frame, Equivalent Diagonal Strut, Infill, Plastic Hinge 1. Introduction Infill have been generally considered as non-structural elements, although there are codes such as the Eurocode-8 that include rather detailed procedures for designing infilled R/C frames, presence of infill has been ignored in most of the current seismic codes except their weight. However, even though they are considered non-structural elements the presence of infill in the reinforced concrete frames can substantially change the seismic response of buildings in certain cases producing undesirable effects (tensional effects, dangerous collapse mechanisms, soft story, variations in the vibration period, etc.) or favorable effects of increasing the seismic resistance capacity of the building. The present practice of structural analysis is also to treat the masonry infill as non- structural element and the analysis as well as design is carried out by only using the mass but neglecting the strength and stiffness contribution of infill. Therefore, the entire lateral load is assumed to be resisted by the frame only. Contrary to common practice, the presence of masonry infill influence the over- all behavior of structures when subjected to lateral forces. When masonry infill are considered to interact with their surrounding frames, the lateral stiffness and the lateral load capacity of the structure largely increase. The recent advent of structural design for a particular level of earthquake performance, such as immediate post-earthquake occupancy, (termed performance based earthquake engineering), has resulted in guidelines such as ATC-40 (1996) [14], FEMA-273 (1996) [26] and FEMA-356 (2000) [13] and standards such as ASCE-41 (2006), among others. The different types of analyses described in these documents, pushover analysis comes forward because of its optimal accuracy, efficiency and ease of use. The infill may be integral or non-integral depending on the