Seismic evaluation of set-back RC frames with and without masonry infill walls

This paper examines the impact of masonry infill walls on the seismic performance of reinforced concrete frames with setbacks in elevation. Several setback Reinforced Concrete Moment Resisting Frames (RCMRFs), both with and without Masonry Infill Walls (MIWs), are designed and subjected to nonlinear dynamic analysis. The nonlinear responses of the structures are assessed using acceptance criteria. Including masonry walls in the frame modeling for this research reduced the maximum drift by 40%, the maximum plastic rotation of columns by 55%, and the maximum plastic rotation of beams by 37%. These results indicate that masonry walls can significantly enhance the seismic performance of the setback concrete frames, as well as concrete beams and columns. In some of the studied irregular frames, the maximum drift values at the Life Safety (LS) level exceed the limit of 2% when the effects of infill walls are not considered. However, these values fall within the allowable range when the effects of the infill walls are included. Additionally, the plastic rotations of certain columns in irregular frames without masonry infill walls surpass the LS allowable limit of 0.016 radians. By accounting for the effects of the infill walls, these rotations are reduced to acceptable levels in nearly all columns. Furthermore, the results show that in the upper-story beams of most irregular frames, the plastic rotation values exceed the allowable limits, even when the effects of infill walls are considered. Consequently, the local life safety performance criteria for these beams are not met.