###### Abstract
Based on the finite element calculation results, a formula for calculating the axial bearing capacity of a BLC-C composite wall was proposed. The problem of cracks at the junction of the main structure and the infill wall often occurs in reinforced concrete frame structures, reinforced concrete frame-shear wall structures, reinforced concrete shear wall structures, and steel structures. In a BLC-C composite wall structure, interface cracks between the BLC-C composite wall and the infill wall are also a problem and have been troubling owners and developers. Due to the significant difference in stiffness between a BLC-C composite wall and an infill wall, they cannot synergistically deform. In addition, the cohesive force of a BLC-C composite wall to an infill wall is weak, so interface cracks are likely to occur. An interface crack directly affects the esthetics of a building. The adverse effects on the senses of the owner cannot be ignored either. Moreover, a house is the private asset of an owner and the existence of interface cracks can easily cause economic disputes. Interface cracks cause owners to question the safety of the structure and even sue the developer, even though they do not have much of an effect on the bearing capacity of the structure. Therefore, it is necessary to further study the initial cracking of an interface. However, no related research is available on the interface cracks between a BLC-C composite wall and an infill wall although a large number of studies have been conducted on frames with infill walls. A method for calculating the lateral stiffness of masonry-infilled reinforced concrete frames with a central opening has been proposed [9]. The influence of an infill wall on the strength, stiffness, ductility, and dynamic characteristics of a reinforced concrete frame was experimentally investigated [10]. The interaction between an infill wall and a boundary frame was studied [11]. [PERSON] et al. [12] studied an infillized reinforced concrete frame under a lateral load and also investigated a numerical model of the out-of-plane response of a frame with infill walls [13]. [PERSON] and [PERSON] [14] conducted a pseudo-dynamic test on a two-story infilled reinforced concrete frame and explored the relationship between the crack type and hysteresis energy. The test results showed that an upper story with openings mainly produced diagonal cracks whereas a lower story without openings primarily produced bed joint shear cracks. [PERSON] et al. [15] applied the smeared crack continuum model and the cohesive crack interface model to establish a finite element model of reinforced concrete frames with masonry walls. The established model accurately simulated the load-displacement response, crack mode, and failure mechanism in a cyclic lateral loading test. As a new type of structure, the connection mode between a BLC-C composite wall and an infill wall is worthy of further study. At present, there are two main types of structural connections between a BLC-C composite wall and an infill wall that have been applied in practical engineering. As depicted in Figure 1, two HPB300 steel bars with a diameter of 6 mm are arranged every 500 mm along the wall height and the ends of the steel bars are welded to the BLC-C composite wall. The joint between the BLC-C composite wall and the infill wall is filled with 20 mm-thick cement mortar and sealed with a sealant. On both sides of the wall, welded wire fabrics coated with zinc are arranged and they are leveled and plastered with gypsum plaster. Figure 2 is different from Figure 1 in that the cement mortar is replaced with anti-crack mortar. The dry mix of anti-crack mortar comprises cement, fly ash, sand, rubber powder, fibers, cellulose ether, and an admixture. In this study, we aimed to investigate cracks in the interface between a BLC-C composite wall and an infill wall. An experiment was conducted on two infill wall specimens constrained by BLC-C composite walls on both sides under unidirectional horizontal loads.