Abstract：When the elastic fulcrum method is used to calculate the retaining structure, the elastic support stiffness of the supporting structure is needed. However, due to the particularity of prefabricated prestressed fish-belly steel support system, there is no convenient and effective formula to calculate the system stiffness. In this paper, the concept of equivalent average stiffness of fish-belly beam is introduced. The simplified expressions of stiffness of the support system before and after prestressing are derived, and verified by finite element software. Meanwhile, with the actual foundation pit project of Diamond Mansion in Xiamen taken as an example, the high-precision numerical results of three-dimensional finite element simulation are compared with the field monitoring data and the theoretically derived results. On the one hand, the finite element results are generally consistent with the field monitoring data, indicating that the finite element method is capable of accurately simulating the actual development law of the foundation pit. On the other hand, the stiffness of the support system obtained by the finite element analysis is almost the same as that of the theoretical derivation, implying that the simplified stiffness formula of support system deduced in this work is more accurate, which can be applied or referred by relevant designers.
