Participating Mass of Large-Scale Complex Dynamic Machine Foundation: Taking the National Facility for Earthquake Engineering Simulation (NFEES) as an Example

To satisfy the performance and technological requirements of large-scale dynamic machines, the foundation is evolving toward considerable size and complex structure. This makes it vibrate asynchronously, and the existing relevant guidelines and specifications that consider the foundation as a rigid body are no longer applicable. Initially, by referencing the concept of the participating mass of soil (the mass of surrounding soil that vibrates synchronously), the concept of participating mass of large-scale complex dynamic machine foundations is proposed. Subsequently, the theoretical and corresponding numerical solutions are given based on the elastic half-space theory and finite element analysis. Furthermore, referring to the prototype of the foundation of the NFEES in China, a refined finite model encompassing the surrounding soil, multilayer complex machine foundations is established. After validating the numerical model, the vibration response and the participating mass of the foundation are analyzed. Additionally, parameterized analyses are conducted by varying factors such as the overall and local stiffness of the foundation, the presence of piles at the bottom of the foundation, the integration of a large shaking table foundation and an underwater shaking table foundation. Results indicate that the foundation of the large shaking table demonstrates vibration synchronization during operation, and the participating rates exceed 80%. The piles at the bottom and the separation of the large shaking table foundation from the underwater shaking table foundation perform effectively to reduce the vibration response and enhance the synchronization of the foundation vibration. The vibration response calculated by the numerical model can be directly applied to assess whether the foundation design satisfies the vibration limit requirements, and the parameterized analyses can provide suggestions for the dynamic design and analysis of similarly large-scale complex dynamic machine foundations.