Journal of Rehabilitation in Civil Engineering 11-4 (2023) 122-137 How to cite this article: Hosseini Gelekolai, S. M., & Tabeshpour, M. R. (2023). Soft Story Design of Reinforced Concrete Structures with Masonry Infill Walls. Journal of Rehabilitation in Civil Engineering, 11(4), 122-137. https://doi.org/10.22075/jrce.2023.30956.1868 Journal homepage: https://civiljournal.semnan.ac.ir/ Soft Story Design of Reinforced Concrete Structures with Masonry Infill walls Seyed Mojtaba Hosseini Gelekolai 1 , Mohammad Reza Tabeshpour 2* 1. Department of Civil Engineering, Sharif University of Technology, Tehran, Iran 2. School of Mechanical Engineering, Sharif University of Technology, Tehran, Iran Corresponding author: tabeshpour@sharif.edu ARTICLE INFO ABSTRACT Article history: Received: 15 May 2023 Revised: 02 July 2023 Accepted: 07 July 2023 Based on the seismic design codes to prevent soft-story failure, columns of a soft story must be designed for amplified loads due to the discontinuity of braces or shear walls in that story. Because of the masonry infill walls discontinuity, Soft story failure has been reported in the recent earthquakes. Most national seismic design codes don't consider the effect of masonry infill walls for the design of the soft story. This paper aims to investigate the soft story failure and then present a simple formula for the design of soft-story in moment resisting frame structures. In this paper, the different arrangements of masonry infill walls are considered. Structural modeling was carried out based on reliable parameters and some national or international seismic design codes. By using nonlinear static analysis, a simple methodology is proposed and the main result is a simple formula that can be used for the engineering design of concrete moment resistant frames. Keywords: Soft story; Masonry infill wall; Seismic design; Concrete structures; Overstrength factor. 1. Introduction Masonry infill walls exist in several buildings but their role in the rehabilitation and retrofitting of the structures is neglected by most structural engineers. Research on the behavior of frames with masonry infill walls has been started in the 1950s. Several lateral loading tests have been done on the full-scale and prototype models including masonry infill walls. The material property of the frames was almost reinforced concrete or steel and infill materials consist of bricks, concrete blocks (reinforced or not), or reinforced concrete. The main effective parameters in the behavior and failure modes of the frames with masonry infill walls are strength, stiffness, hysteresis energy dissipation factor, the boundary condition of the infill, distributions of strain and stress inside masonry infill walls, applied load to the frame, existence of openings and the manner of construction [1]. There are two general methods for considering the effects