Seismic Performance of RC Frame Structures with Masonry Infill Walls Strengthened by Mortar Surface Layers

Although infill masonry walls in frame structures are classified as non-structural components, they can still resist a portion of seismic forces during earthquakes. Historical earthquake damage indicates that infill masonry walls in frame structures often act as the first seismic defense line and fail first, thereby mitigating or delaying damage to the main frame to a certain extent. Such damage cases are frequently observed. Therefore, it is necessary to investigate the enhancement of the seismic performance of the main structure contributed by infill masonry walls, and further to study the effect of infill-wall retrofitting on the seismic behavior of frame structures. The mortar surface reinforcement method, owing to its convenient construction and low cost, is one of the commonly used techniques for enhancing the seismic performance of masonry walls. This paper conducts finite element analysis on a frame structure located in a seismic fortification zone of intensity 8. The seismic performance of a bare frame, a frame with infill masonry walls, and frames with mortar surface reinforcement applied to infill walls at different locations are compared. Parameters including inter-story drift ratio, floor seismic forces, column shear forces, and load–displacement responses under various earthquake actions are analyzed. The results demonstrate that, for the numerical model employing an idealized interface assumption, the presence of infill walls significantly reduces the inter-story drift and column shear forces of the frame structure. Compared with the unretrofitted model, the seismic bearing capacity of the frame structure with mortar-reinforced infill walls increases by 18.57–36.19%. Among the different retrofitting schemes, the case with vertical and horizontal reinforcement applied to half of the wall area each achieves similar inter-story drift control as other schemes, while simultaneously reducing the floor seismic forces and the shear forces carried by frame columns. Thus, partial reinforcement of infill walls is recommended in structural retrofitting design, accompanied by experimental validation to quantitatively assess the retrofitting efficacy whenever possible. The findings of this study can serve as a reference for improving the seismic bearing capacity of frame structures through the mortar surface reinforcement method applied to infill masonry walls.