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In urban areas, residential buildings are often located at small distances from each other. The mutual influence of these buildings, depending on the distance between them, under the effect of earthquake vibrations, is of great importance, which has been less studied and investigated. Normally, the soil-structure interaction is considered when only one structure is present on the soil, although the structure-soil-structure interaction takes place when at least two structures are placed on the soil. In case, in addition to the discussed structure and soil layer, another adjacent structure is added to the system, the response of the soil layer will be affected by the presence of both structures and the response of each of the structures will also be affected by the response of the soil layer and its adjacent structure, and therefore the soil and Each of the two adjacent structures will have a mutual effect on the response, which is known as structure-soil-structure interaction. In other words, in this interaction, the vibration energy of a structure affects its neighboring structures through the soil environment and can change its structural response. The presence of the adjacent structure can increase or decrease the dynamic response of the structure and the amount of damage depending on the dynamic characteristics of the soil and the structure and the frequency content of the incoming earthquake. When an earthquake occurs, its waves pass through the soil layers and reach the foundations of both structures. These waves cause deformations in the foundations and structural elements. Therefore, a shear force and an overturning moment are created in the foundation of the structure, which results in the deformation of the foundation and the structure. After that, the vibrations of the structure are transferred to the soil, until this part, the responses and behaviors in these systems (structure, soil and foundation) are similar to the conventional soil-structure interaction; But there is a slight difference in the transmission of these waves from the structure to the soil, which causes the structure-soil-structure interaction. In this research, the structure-soil-adjacent structure interaction has been investigated for building structures based on soil prone to liquefaction. For this purpose, similar buildings of fifteen concrete storey at different distances from each other, along with the continuous environment of the soil bed with different mechanical  properties and the application of the  advanced elasto-plastic constitutive model under the effect of the earthquake acceleration history applied at the bedrock level, have been analyzed. In order to validate the results, the amount of settlement of the structure under static load was investigated and using the results of two laboratory models, the structure-soil-structure interaction analysis process and the soil constitutive model were validated. Based on the obtained results, the structure-soil-structure interaction in the general state increases the lateral displacement of the structure compared to the case with a rigid bed. The interaction effects are different depending on the number and distance of the structures. Also, the results show that the effects of  structure-soil-structure interaction depend on the position and thickness of the soil layer prone to liquefaction, so that with the increase in the thickness of the liquefaction layer, more exess of pore water is produced and finally, the deformations created in the soil and the structure are more intense.

Many attemps have been made to model the mechanical behavior of soil materials. The assumption that predicting soil plastic behavior in some engineering problems don’t present a significant relation with construction time, has led to the neglect of the time effect in many constitutive models in geotechnical engineering. However, damage due to settlement or instability of excavations and many other such problems are caused by time dependent plasticity behavior of soil. Also in some phenomena such as explosion, earthquake or consolidation, the issue of time is inherently raised. Therefore, it is important to install a time dependent constitutive model in finite element codes that can properly predict the time dependent behavior of structures in geotechnical engineering. In this study, an elastoplastic-viscoplastic constitutive model via UMAT subroutine was installed in the ABAQUS finite element code. By considering the nonlinear elastoplastic-viscoplastic behavior with mixed (kinematic and isotropic) hardening mechanisms, this model removes most of the limitations of the constitutive models already installed in the ABAQUS code. The results of validation under laboratory paths such as creep, relaxation and rate effect indicate the high capacity and capability of the model in predicting the time - dependent behavior of soil.