# Progressive Collapse Performance of Prefabricated Step-Terrace Frame Structures in Mountain Cities
## 1 Introduction
[14] provided a risk assessment support tool for the purpose of retrofitting and creating potential design strategies for RC buildings; to model structures, the concentrated plasticity model, which considers the hysteretic deterioration of structural elements, was assumed at both ends of the elastic beam-column element. The proportion of mountainous terrain in China is nearly 2/3, and the application of step-terrace structures in mountain cities is growing more and more extensive. The foundation embedment of structures in mountain cities of different heights causes the uneven distribution of structural stiffness in the horizontal and vertical directions, and the horizontal force is transmitted to the foundation through different ground ends, which is the fundamental reason why the stress and deformation characteristics of structures in mountain cities are different from those of conventional structures [15; 16]. There are two types of vertical irregularities listed in the code for the step-terrace frame structures: irregular lateral stiffness and a sudden change in floor bearing capacity, which are congenital and difficult to adjust for. The general conclusions of the research on step-terrace structures are as follows: the damage to the structure mainly occurs in the upper grounding stories, and the damage to the upper ground column, the upper grounding stories, and the adjacent stories is the most serious, followed by the dropped stories and the dropped columns of the story. The weak story of a step-terrace structure is the upper ground and its adjacent story [17; 18]. The mechanical performance of PC structures subjected to significant deformations is complicated due to the diverse forms of joint connections, and it is obviously different from that of cast-in-place concrete structures. For the dry connection, a joint stress system is typically established by connecting multiple connection members to structural stress members such as beams and columns; the internal force transfer mode is more variable and the failure mechanism is more complex [19]. [PERSON] et al. reported several collapse mechanisms associated with half-joint connections, including corbel connections, in building structures which are influenced by function of the detailing and reinforcement [20]. Most studies indicate that the overall stability of PC structures, especially dry-connected PC structures, is not as good as that of cast-in-place frame structures, so the research conclusions on the performance of cast-in-place frame structures may not be applicable to PC structures [21]. At present, there is little literature addressing the progressive collapse performance of prefabricated structures in mountain cities, and it is necessary to conduct a series of studies to clarify their collapse mechanism. This paper investigates a typical dry-connected prefabricated joint with bolt steel plate connection. Employing a member removal methodology, the progressive collapse performances of prefabricated step-terrace frame structure models in mountain cities with different number of dropped stories and dropped spans are studied under different failure conditions.