عنوان مقاله [English]
Irregularity in structures is one of the most important factors in past earthquakes. Among different types of irregularity, we can refer to the one caused by split levels (in floors or foundation). In a duplex or in usual buildings, the foundation may be executed at two height levels. If the split level of two foundations is great and they cannot be linked with a slope less than 15, they should be linked with the help of three horizontal, vertical and diagonal, or other, approved details. According to different regulations, the ties of foundations without a split level are usually planned for a percentage of the maximum of the axial force of the columns of two sides of the tie. In this research, the same pattern has been used to study the force changes in bars of the tie (horizontal, vertical and diagonal) during lateral loading. Fourteen models with details of a duplex foundation in ANSYS software have been analyzed under non-linear analysis. In order to study the changes of the force of tie planning, the structures are investigated and four details at each split level, as well as changes in the structural behavior of each detail, are studied, considering the changes in the split level of the foundation. In this article, the distribution of tension, cracking, and its process during loading, as well as types of crack, their position, and the time and place of the formation of plastic joints in each detail foundation with split levels, are pointed out. The results of analysis show that the forces of tie planning and the rate of cracking in wedged details are much less than other details. Of course, only executing horizontal or vertical ties does not have so much effect on the decrease in cracking or the planning forces of ties, so, it is required that a perfect brickwork is done inside the wedge to provide sufficient rigidity for the vertical tie of wedged details. Increasing the split in the level enhances the possibility of early breaking of the foundation with the split level. Therefore, it is possible for the foundation to get dismantled before its superstructure.This issue can be of great significance in the analysis of a super structure, considering the interaction of soil and structure and, also, the presupposition of consolidating the super structure during ground movement.