## 1 Introduction  
A masonry-infilled frame is a reinforced concrete or steel frame structure filled with masonry walls, which is commonly used as the exterior walls or partitions of a building. In the past, masonry infills were considered nonstructural components as they do not carry gravity load, and their structural contribution was ignored. However, experiences from past earthquakes indicated that these components have a great influence on the seismic performance of the whole structure. Since the masonry infills restrain the deformation of the frame, they increase the strength and rigidity of the whole structure and reduce the deformation capacity [1, 2]. For the evaluation of seismic performance, the accurate prediction of strength, stiffness, and deformation capacity is important. In most studies, the strength of the masonry-infilled frame is calculated as the sum of the strength of the frame and the strength of the masonry infills [3, 4]. In the analysis results using the equivalent compression strut, which is the most common modeling approach for masonry-infilled frame buildings, the lateral strength of the structure is almost the same as the sum of the strength of the frame and the strength of the compression struts. The strength of the masonry infill varies with the failure mode. When subjected to lateral loads, the failure modes of the masonry infill are classified into three types: bed joint sliding (BJS) failure, diagonal tensile (DT) failure, and corner compression (CC) failure. Many researchers have proposed strength equations associated with one of these failure modes [5, 6, 7, 8, 9]. In most equations, the shear strength of the masonry is the most important material property. Various experimental studies have reported that the behavior of the infill wall is affected not only by its own strength and aspect ratio but also by the stiffness and strength of the surrounding frame [2; 9; 10; 11]. [PERSON] [12] proposed an analytical procedure to determine the strength of a masonry wall surrounded by a strong frame considering the interaction between the masonry and the frame. Some of the masonry strength equations consider the influence of the stiffness or strength of surrounding frames [7; 13], acknowledging that there is an interaction between the masonry infills and the surrounding frame. This also indicates that the behavior of the frame can be affected by the strength and stiffness of the infill wall [14; 15; 16; 17; 18; 19; 20; 21]. [PERSON] [14] reported that the maximum strength of the masonry-filled frame depends more on the failure of the RC frame than the masonry wall, and the failure mode of the RC frame varies with the length of the contact zone between the infill wall and the frame. Noting that the reactions from the masonry wall increase the shear demand of the columns, [PERSON] et al. [16] and [PERSON] et al. [17] proposed methods to prevent or delay the shear failure of columns. However, the relationship between the strength of the structure and failure mode was not investigated. In fact, in many experimental studies, the failure mode of the frames in a masonry-infilled frame was different from that of the bare frame, even when the material strength and dimensions of columns and beams were the same. However, studies investigating the influence of masonry infill on failure mode and accordingly quantifying the change in strength or deformation capacity of the frame are limited. Some researchers [18] attempted the use of artificial neural network analyses to predict the maximum strength and inter-story drift of masonry-infilled frame buildings, which are inherently inadequate to describe the interaction between the masonry wall and surrounding frame. Masonry infill walls are generally installed after the construction of the frame (columns and beams) is complete. When construction precision is low, grouting of the vertical and horizontal joints between the masonry units can be flawed.